Medical waste: any solid waste which is generated in the diagnosis, treatment (e.g. provision of medical services) or immunization of human beings or animals, in research pertaining thereto, or in the production or testing of biologicals (US-EPA).
Infectious agent: any organism (such as virus or bacteria) that is capable of being communicated by invasion or multiplication in body tissues and capable of causing disease or adverse health impacts in humans (US-EPA).
Infectious waste: waste that contains pathogens with sufficient virulence and quantity such that exposure to the wastes could result in infectious diseases.
However, currently there is no definitive quantitative analysis that can be used to determine whether or not a waste is infectious. The characteristic of infectious potential is therefore based on principles of disease transmission. The process of disease transmission can be conceptualize as a series of six links, with each link representing an essential step in the transfer of an infectious agent from one susceptible host to the next. If a break occurs in any of the links along the chain, the process of disease transmission is inhibited. The six links are as follows:
- The presence of a sufficient quantity of an infectious agent.
- The existence of a favourable environment for survival of infectious agents.
- A mode of escape for infectious agents.
- An infectious mode of transmission.
- An infectious route of entry.
- A susceptible host.
Four main transmission modes of infection (US Department of Health and Human Services):
- Direct transmission occurs when there is contact between an agent’s source and susceptible host. Direct transmission can occur through direct contact or droplet spray.
- Airborne transmission occurs when the etiologic agent is contained in or on relatively small particles that remain suspended in air for long periods of time.
- Vehicle-borne transmission occurs when an infectious agent is transported from its source to a susceptible host by contaminated materials or objects (indirect contact).
- Vector-borne transmission occurs when a vector, most commonly insect, carries the agent on or in its body, or the agent develops in the vector.
Types of Medical Waste
The rationale behind the definition of what constitutes medical waste is based on two sets of criteria:
1. The potential of the waste to transmit infection. These wastes, by virtue of their characteristics, are capable of preserving the chain of disease transmission. These wastes are universally handled as medical wastes, regardless of their source, because:
- The infectious potential of a waste cannot necessarily be determined by its appearance.
- The particular source of the item and/or its infectious nature may not be identifiable.
- It is impractical and infeasible to test each item for its pathogen content (i.e. type and quantity).
These types of medical waste fall into seven categories as follows:
- Sharps that have been used in animal or human patient care or treatment or in medical, research or industrial laboratories. Includes hypodermic needles, syringes, scalpel blades, blood specimen tubes, pasteur pipettes and broken glass that have been exposed to infectious agents.
- Cultures and stocks of infectious agents and associated biologicals. Includes specimen cultures from medical and pathological laboratories; cultures and stocks of infectious agents from research and industrial laboratories; waste from the production of biologicals; discarded live and attenuated vaccines; and culture dishes and devices used to transfer, inoculate and mix cultures.
- Bulk human blood and blood products. Liquid waste human blood, products of blood, items saturated and with the potential for dripping blood, serum, plasma and other blood components.
- Pathological wastes. Human tissues, organs, body parts and body fluids that are removed during surgery and post mortem procedures, with the exception of teeth, faeces, excreta and corpses and body parts intended for interment or cremation.
- Isolation wastes. Includes wastes contaminated with blood, excretions, exudate or secretions from sources isolated to protect others from highly communicable infectious disease which are identified as viruses.
- Animal waste. Contaminated animal carcasses, body parts, fluids and bedding of animals that have been afflicted with suspected zoonotic disease or purposely infected with agents infective to humans during research, in the production of biologicals or the in vivo testing of pharmaceuticals.
- Unused sharps. Hypodermic needles, suture needles, syringes, scalpel blades. This category is included because of the risk of the item having been used without the handlers’ knowledge and the added potential for illicit use if these items are disposed as solid waste. In addition, unused sharps have the potential to causing physical injury from improper handling.
2. Wastes which possess a risk to public health or the environment for reasons other than infectious potential. These wastes fall into three additional categories as follows:
- Low level radioactive waste. From administering radiopharmaceuticals and performing nuclear medicine procedures and radioimmunology procedures. These wastes, such as radioactive sharps, are not under the regulations of nuclear agency/commission.
- Antineoplastic (cytotoxic, cytostatic) drugs. Trace contaminated materials and contaminated human excreta that are not handled as hazardous waste.
- Small volume of chemical hazardous waste. These wastes are products of a process or operation involving the use of hazardous chemicals.
Items That Are Not Medical Waste
According to the principles of infectious disease transmission, minimally soiled items in contact with infectious agents are probably not capable of infectious disease transmission because the potentially infectious materials will be contained or confined in the waste materials. If the items become saturated with blood, excretions, exudate or secretions containing a sufficient number of infectious agents, however, they would then be similar to material in the cultures and stocks, bulk human blood and blood products and animal waste categories and capable of infectious disease transmission, provided an appropriate portal of entry is present in a susceptible host (US Department of Health and Human Services).
Generation of Medical Wastes
There are many sources of medical waste with a wide variation in the amount of waste produced by each type of generator. The range of potential generators includes:
- Hospitals: general medical and surgical, psychiatric, tuberculosis, other specialty (OB/GYN, eye, ENT, rehabilitation)
- Intermediate care facilities: nursing homes, in-patient care facilities for the developmentally disabled
- Clinics: chronic dialysis, free clinics, community, employee, surgical, urgent care, abortion, drug rehabilitation, health maintenance organization
- Physician offices: general and family practice, internal medicine, paediatrics, OB/GYN, ophthalmology, orthopaedic surgery, general surgery, dermatology, psychiatry, otorhinolaryngology, urological surgery, cardiovascular disease, neurology
- Dental offices
- Laboratories: medical, research, industrial, commercial diagnostic, biologics manufacturing, medicinal chemicals and botanical products, pharmaceutical preparations
- Funeral homes
- Blood banks
- Animal care: shelters, fur farms, breeders, experimentation units
- Emergency medical services: ambulance service
- Household/home health care: health care providers, self care
- Health units in industry, schools, correctional facilities, fire and rescue services
- Medical and nursing schools
- Illicit drug users
Ekstraksi superkiritis merupakan salah satu metode operasi ekstraksi dengan menggunakan solven berupa fluida superkritis, yaitu fluida yang kondisinya berada di atas temperatur dan tekanan kritis. Temperatur kritis adalah suhu tertinggi yang dapat mengubah fase gas suatu zat menjadi fase cair dengan cara menaikkan tekanan. Sedangkan tekanan kritis adalah tekanan tertinggi yang dapat mengubah fase cair suatu zat menjadi fase gas dengan cara menaikkan temperatur. Pada kondisi ini fluida memiliki sifat di antara cairan dan gas. Metode ini memiliki beberapa kelebihan, antara lain:
- Kekuatan solven dapat diatur sesuai keperluan dengan mengatur kondisi operasinya.
- Daya larut solven tinggi karena bersifat seperti cairan.
- Viskositas solven rendah karena bersifat seperti gas, sehingga koefisien perpindahan massanya tinggi.
- Pemisahan kembali solven dari ekstrak cukup cepat dan sempurna karena pada keadaan normal solven tersebut berupa gas, sehingga dengan penurunan tekanan solven otomatis akan keluar sebagai gas.
- Dapat menggunakan solven berupa fluida yang tidak merusak lingkungan dan tidak mudah terbakar.
- Difusi dalam padatan dapat berlangsung cepat.
- Temperatur operasi bisa rendah sekalipun tekanannya tinggi.
Salah satu fluida yang sering dipakai sebagai solven dalam ekstraksi superkritis adalah gas CO2, yang memiliki temperatur kritis 31,3 derajat Celcius dan tekanan kritis 74 atm. Dengan menggunakan CO2 sebagai solven, ekstraksi superkritis dapat dijalankan pada suhu rendah dan tekanan yang tidak terlalu tinggi. Keuntungan lain adalah kita tidak perlu membuat CO2 melainkan cukup menyaringnya dari udara sekitar.
Sebagai fluida superkritis, CO2 telah cukup banyak dimanfaatkan di bidang penelitian dan industri. Contohnya adalah dalam proses ekstraksi maupun de-ekstraksi senyawa-senyawa aktif dari tumbuhan untuk pengobatan atau senyawa-senyawa penting untuk industri makanan, misalnya ekstraksi minyak atsiri lemon, jahe, beta-carotene dari tumbuh-tumbuhan atau de-ekstraksi kafein pada kopi.
All waters, especially surface waters, contain both dissolved and suspended particles. Coagulation and flocculation processes are used to separate the suspended solids portion from the water.
The suspended particles vary considerably in source, composition charge, particle size, shape, and density. Correct application of coagulation and flocculation processes and selection of the coagulants depend upon understanding the interaction between these factors. The small particles are stabilized (kept in suspension) by the action of physical forces on the particles themselves. One of the forces playing a dominant role in stabilization results from the surface charge present on the particles. Most solids suspended in water possess a negative charge and, since they have the same type of surface charge, repel each other when they come close together. Therefore, they will remain in suspension rather than clump together and settle out of the water.
Coagulation and flocculation occur in successive steps intended to overcome the forces stabilizing the suspended particles, allowing particle collision and growth of flock. If step one is incomplete, the following step will be unsuccessful.
Coagulation is the first step that destabilizes the particle’s charges. Coagulants with charges opposite those of the suspended solids are added to the water to neutralize the negative charges on dispersed non-settle-able solids such as clay and colour-producing organic substances. Once the charge is neutralized, the small suspended particles are capable of sticking together. The slightly larger particles, formed through this process and called micro-flocks are not visible to the naked eye. The water surrounding the newly formed micro-flocks should be clear. If it is not, all the particles’ charges have not been neutralized, and coagulation has not been carried to completion. More coagulant may need to be added. A high-energy, rapid-mix to properly disperse the coagulant and promote particle collisions is needed to achieve good coagulation. Over-mixing does not affect coagulation, but insufficient mixing will leave this step incomplete. Coagulants should be added where sufficient mixing will occur. Proper contact time in the rapid-mix chamber is typically 1 to 3 minutes.
Following the first step of coagulation, a second process called flocculation occurs. Flocculation, a gentle mixing stage, increases the particle size from submicroscopic micro-flocks to visible suspended particles. The micro-flocks are brought into contact with each other through the process of slow mixing. Collisions of the micro-flock particles cause them to bond to produce larger, visible flocks called pinflocs The flock size continues to build through additional collisions and interaction with inorganic polymers formed by the coagulant or with organic polymers added. Macro-flocks are formed. High molecular weight polymers, called coagulant aids, may be added during this step to help bridge, bind, and strengthen the flock add weight, and increase settling rate. Once the flock has reached it optimum size and strength, the water is ready for the sedimentation process. Design contact times for flocculation range from 15 or 20 minutes to an hour or more.
Flocculation requires careful attention to the mixing velocity and amount of mix energy. To prevent the flock from tearing apart or shearing, the mixing velocity and energy input are usually tapered off as the size of the flock increases. Once flocks are torn apart, it is difficult to get them to reform to their optimum size and strength. The amount of operator control available in flocculation is highly dependent upon the type and design of the equipment.
Sedimentation basins are used in conventional plants. Direct-filtration plants skip the sedimentation stage and go directly to filtration. Detention times for sedimentation are in the range of 1 to 4 hours. Inlets are designed to distribute water evenly and at uniform velocities. Overflow rates should not exceed 20,000 gallons per day per foot of weir length. Velocity should not exceed 0.5 feet per minute. Sedimentation basins are used to settle out the flock before going to the filters. Some type of sludge collection device should be used to remove sludge from the bottom of the basin.
Conventional plant designs separate the coagulation stage from the flocculation stage. Normally this is followed by a sedimentation stage, after which filtration takes place. Plants designed for direct filtration route the water directly from flocculation to filtration. These systems typically have a higher raw-water quality. Conventional designs can incorporate adjustable mixing speeds in both the rapid-mix and slow-mix equipment. Multiple feed points for coagulants, polymers, flocculants, and other chemicals can be provided. There is generally adequate space to separate the feed points for incompatible chemicals. Conventional plant designs have conservative retention times and rise rates. This usually results in requirements for large process basins and a large amount of land for the plant site. On-site pilot plant evaluation of the proposed process, by a qualified engineer familiar with the source of the water, is advisable prior to selection and construction of the units.
Retention or detention time is the theoretical time in minutes that water spends in a process. It is calculated by dividing the liquid volume, in gallons, of a basin by the plant flow rate in gallons per minute. Actual detention time in a basin will be less than the theoretical detention time because of “dead areas” and short circuiting, which could be due to inadequate baffling.
Retention time = basin volume (gallons) : gpm flow
The rise rate is calculated by dividing the flow in gallons per minute by the net up-flow area of the basin in square feet.
Rise rate = gpm flow : surface area
Some designs incorporate coagulation, flocculation, and sedimentation within a single unit. These designs can be separated into up-flow solids contact units and sludge blanket units. Most solids contact designs use recirculation of previously formed floes to enhance flock formation and maximize usage of treatment chemicals. Sludge bed designs force the newly forming flocks to pass upward through a suspended bed of flock. In both styles of units, the cross-sectional surface of the basin increases from the bottom to top, causing the water flow to slow as it rises, and allowing the flock to settle out. The combination units generally use higher rise rates and shorter detention time than conventional treatment. Numerous manufacturers market proprietary units based on these design concepts. These units are more compact and require less land for plant site location. On-site pilot plant evaluation of the proposed process, by a qualified engineer familiar with the source water, is advisable prior to selection and construction of combined units.
The choice of coagulant chemical depends upon the nature of the suspended solid to be removed, the raw water conditions, the facility design, and the cost of the amount of chemical necessary to produce the desired result. Final selection of the coagulants should be made following thorough jar testing and plant scale evaluation. Considerations must be given to required effluent quality, effect upon down stream treatment process performance, cost, method and cost of sludge handling and disposal, and net overall cost at the dose required for effective treatment.
Inorganic coagulants such as aluminium and iron salts are the most commonly used. When added to the water, they furnish highly charged ions to neutralize the suspended particles. The inorganic hydroxides formed produce short polymer chains which enhance micro-flock formation. Inorganic coagulants usually offer the lowest price per pound, are widely available, and, when properly applied, are quite effective in removing most suspended solids. They are also capable of removing a portion of the organic precursors which may combine with chlorine to form disinfection by-products. They produce large volumes of flock which can entrap bacteria as they settle. However, they may alter the pH of the water since they consume alkalinity. When applied in a lime soda ash softening process, alum and iron salts generate demand for lime and soda ash. They require corrosion-resistant storage and feed equipment. The large volumes of settled flock must be disposed of in an environmentally acceptable manner.
Common coagulant chemicals used are alum, ferric sulfate, ferric chloride, ferrous sulfate, and sodium aluminate. The first four will lower the alkalinity and pH of the solution while the sodium aluminate will add alkalinity and raise the pH. The reactions of each are as follows:
Al2(SO4)3 + 3Ca(HCO3)2 –> 2Al(OH)3 + 3CaSO4 + 6CO2, with calcium carbonate presents in the water to be treated
Fe2(SO4)3 + 3Ca(HCO3)2 –> 2Fe(OH)3 + 3CaSO4 + 6CO2, with calcium bicarbonate presents in the water to be treated
2FeCl3 + 3Ca(HCO3)2 –> 2Fe(OH)3 + 3CaCl2 + 6CO2, with calcium bicarbonate presents in the water to be treated
FeSO4 + 3Ca(HCO3)2 –> Fe(OH)2 + CaSO4 + 2CO2, with calcium bicarbonate presents in the water to be treated
2Na2Al2O4 + Ca(HCO3)2 –> 8Al(OH)3 + 3Na2CO3 + 6H2O, with calcium bicarbonate presents in the water to be treated
Na2Al2O4 + CO2 –> 2Al(OH)3 + Na2CO3, with carbon dioxide presents in the water to be treated
Na2Al2O4 + MgCO3 –> MgAl2O4 + Na2CO3, with magnesium carbonate presents in the water to be treated
Polymers are becoming more widely used, especially as coagulant aids together with the regular inorganic coagulants. Anionic polymers are often used with metal coagulants. Low- to-medium weight cationic polymers may be used alone or in combination with the aluminium and iron type coagulants to attract the suspended solids and neutralize their surface charge. The manufacturer can produce a wide range of products that meet a variety of source-water conditions by controlling the amount and type of charge and relative molecular weight of the polymer. Polymers are effective over a wider pH range than inorganic coagulants. They can be applied at lower doses, and they do not consume alkalinity. They produce smaller volumes of more concentrated, rapidly settling flock The flock formed from use of a properly selected polymer will be more resistant to shear, resulting in less carry-over and a cleaner effluent. Polymers are generally several times more expensive in their price per pound than inorganic coagulants. Selection of the proper polymer for the application requires considerable jar testing under simulated plant conditions, followed by pilot or plant-scale trials. All polymers must be approved for potable water use by regulatory agencies.
Waste water treatment is designed to use the natural purification processes (self purification processes of streams and rivers) to the maximum level possible. It is also designed to complete these processes in a controlled environment rather than over many miles of a stream or river. Moreover, the treatment plant is also designed to remove other contaminants that are not normally subjected to natural processes, as well as treating the solids that are generated through the treatment unit steps. The typical waste water treatment plant is designed to achieve many different purposes:
- Protect public health.
- Protect public water supplies.
- Protect aquatic life.
- Preserve the best uses of the waters.
- Protect adjacent lands.
Waste water treatment is a series of steps. Each of the steps can be accomplished using one or more treatment processes or types of equipment. The major categories of treatment steps are:
- Preliminary treatment: Removes materials that could damage plant equipment or would occupy treatment capacity without being treated.
- Primary treatment: Removes settle-able and float-able solids (may not be present in all treatment plants).
- Secondary treatment: Removes BOD and dis-solved and colloidal suspended organic matter by biological action. Organics are converted to stable solids, carbon dioxide and more organisms.
- Advanced waste treatment: Uses physical, chemical, and biological processes to remove additional BOD, solids and nutrients (not present in all treatment plants).
- Disinfection: Removes micro-organisms to eliminate or reduce the possibility of disease when the flow is discharged.
- Sludge treatment: Stabilizes the solids removed from waste water during treatment, inactivates pathogenic organisms, and reduces the volume of the sludge by removing water.
Generation of Waste Water
Waste water is generated by five major sources:
- Human and animal wastes: Contains the solid and liquid discharges of humans and animals and is considered by many to be the most dangerous from a human health viewpoint. The primary health hazard is presented by the millions of bacteria, viruses, and other micro-organisms (some of which may be pathogenic) present in the waste stream.
- Household wastes: Consists of wastes, other than human and animal wastes, discharged from the home. Household wastes usually contain paper, household cleaners, detergents, trash, garbage, and other substances the home owner discharges into the sewer system.
- Industrial wastes: Includes industry specific materials that can be discharged from industrial processes into the collection system. Typically contains chemicals, dyes, acids, alkalis, grit, detergents, and highly toxic materials.
- Storm water run-off: Many collection systems are designed to carry both the wastes of the community and storm water run-off In this type of system when a storm event occurs, the waste stream can contain large amounts of sand, gravel, and other grit as well as excessive amounts of water.
- Groundwater infiltration: Groundwater will enter older improperly sealed collection systems through cracks or unsealed pipe joints. Not only can this add large amounts of water to waste water flows, but also additional grit.
Classification of Waste Water
Waste water can be classified according to the sources of flows:
- Domestic (sewage) waste water: Contains mainly human and animal wastes, household wastes, small amounts of groundwater infiltration and small amounts of industrial wastes.
- Sanitary waste water: Consists of domestic wastes and significant amounts of industrial wastes. In many cases, the industrial wastes can be treated without special precautions. However, in some cases, the industrial wastes will require special precautions or a pretreatment program to ensure the wastes do not cause compliance problems for the waste water treatment plant.
- Industrial waste water: Consists of industrial wastes only. Often the industry will determine that it is safer and more economical to treat its waste independent of domestic waste.
- Combined waste water: Consists of a combination of sanitary waste water and storm water run-off All the waste water and storm water of the community is transported through one system to the treatment plant.
- Storm water: Contains a separate collection system (no sanitary waste) that carries storm water run-off including street debris, road salt, and grit.
Waste Water Characteristics
Waste water contains many different substances that can be used to characterize it. The specific substances and amounts or concentrations of each will vary, depending on the source. It is difficult to precisely characterize waste water. Instead, waste water characterization is usually based on and applied to an average domestic waste water.
A. Physical Characteristics
- Colour: Fresh waste water is usually a light brownish-grey colour However, typical waste-water is grey and has a cloudy appearance. The colour of the waste water will change significantly if allowed to go septic (if travel time in the collection system increases). Typical septic waste water will have a black colour.
- Odour: Odours in domestic waste water usually are caused by gases produced by the decomposition of organic matter or by other substances added to the waste water. Fresh domestic waste-water has a musty odour. If the waste water is allowed to go septic, this odour will significantly change to a rotten egg odour associated with the production of hydrogen sulfide (H2S).
- Temperature: The temperature of waste water is commonly higher than that of the water sup-ply because of the addition of warm water from households and industrial plants. However, significant amounts of infiltration or storm water flow can cause major temperature fluctuations.
- Flow: The actual volume of waste water is commonly used as a physical characterization of waste water and is normally expressed in terms of gallons per person per day. Most treatment plants are designed using an expected flow of 100 to 200 gallons per person per day. This figure may have to be revised to reflect the degree of infiltration or storm flow the plant receives. Flow rates will vary throughout the day. This variation, which can be as much as 50 to 200% of the average daily flow is known as the diurnal flow variation (occurring in a day or daily).
B. Chemical Characteristics
- Alkalinity: This is a measure of the waste-water’s capability to neutralize acids. It is measured in terms of bicarbonate, carbonate, and hydroxide alkalinity. Alkalinity is essential to buffer (hold the neutral pH) of the waste water during the biological treatment processes.
- Biochemical oxygen demand: This is a measure of the amount of biodegradable matter in the waste water. Normally measured by a 5-d test conducted at 20 deg. C. The BOD5 domestic waste is normally in the range of 100 to 300 mg/L.
- Chemical oxygen demand: This is a measure of the amount of oxidized-able matter present in the sample. The COD is normally in the range of 200 to 500 mg/L. The presence of industrial wastes can increase this significantly.
- Dissolved gases: These are gases that are dissolved in waste water. The specific gases and normal concentrations are based upon the composition of the waste water. Typical domestic waste water contains oxygen in relatively low concentrations, carbon dioxide, and hydrogen sulfide (if septic conditions exist).
- Nitrogen compounds — The type and amount of nitrogen present will vary from the raw waste water to the treated effluent. Nitrogen fol-lows a cycle of oxidation and reduction. Most of the nitrogen in untreated waste water will be in the forms of organic nitrogen and ammonia nitrogen. Laboratory tests exist for determination of both of these forms. The sum of these two forms of nitrogen is also measured and is known as total kjeldahl nitrogen (TKN). Waste water will normally contain between 20 to 85 mg/L of nitrogen. Organic nitrogen will normally be in the range of 8 to 35 mg/L, and ammonia nitro-gen will be in the range of 12 to 50 mg/L.
- pH: This is a method of expressing the acid condition of the waste water. pH is expressed on a scale of 1 to 14. For proper treatment, waste-water pH should normally be in the range of 6.5 to 9.0 (ideally 6.5 to 8.0).
- Phosphorus: This element is essential to bio-logical activity and must be present in at least minimum quantities or secondary treatment processes will not perform. Excessive amounts can cause stream damage and excessive algal growth. Phosphorus will normally be in the range of 6 to 20 mg/L. The removal of phosphate compounds from detergents has had a significant impact on the amounts of phosphorus in waste water.
- Solids: Most pollutants found in waste water can be classified as solids. Waste water treatment is generally designed to remove solids or to convert solids to a form that is more stable or can be removed. Solids can be classified by their chemical composition (organic or inorganic) or by their physical characteristics (settle-able, float-able, and colloidal). Concentration of total solids in waste water is normally in the range of 350 to 1200 mg/L.
- Water: This is always the major constituent of waste water. In most cases water makes up 99.5 to 99.9% of the waste water. Even in the strongest waste water, the total amount of contamination present is less than 0.5% of the total and in average strength wastes it is usually less than 0.1%.
Solids can be classified as follows:
- Organic solids: Consists of carbon, hydrogen, oxygen, nitrogen and can be converted to carbon dioxide and water by ignition at 550 deg. C.
- Inorganic solids: Mineral solids that are unaffected by ignition.
- Suspended solids: These solids will not pass through a glass fibre filter pad. Can be further classified as Total suspended solids (TSS), volatile suspended solids, and fixed suspended solids. Can also be separated into three components based on settling characteristics: settle-able solids, float-able solids, and colloidal solids. Total suspended solids in waste water are normally in the range of 100 to 350 mg/L.
- Dissolved solids: These solids will pass through a glass fibre filter pad. Can also be classified as total dissolved solids (TDS), volatile dissolved solids, and fixed dissolved solids. TDS are normally in the range of 250 to 850 mg/L.
C. Biological Characteristics
After undergoing physical aspects of treatment (i.e., screening, grit removal, and sedimentation) in preliminary and primary treatment, waste water still contains some suspended solids and other solids that are dissolved in the water. In a natural stream, such substances are a source of food for protozoa, fungi, algae, and several varieties of bacteria. In secondary waste water treatment, these same microscopic organisms (which are one of the main reasons for treating waste water) are allowed to work as fast as they can to biologically convert the dissolved solids to suspended solids that will physically settle out at the end of secondary treatment.
Raw waste water influent typically contains millions of organisms. The majority of these organisms are non-pathogenic, but several pathogenic organisms may also be present. (These may include the organisms responsible for diseases such as typhoid, tetanus, hepatitis, dysentery, gastroenteritis, and others).
Many of the organisms found in waste water are microscopic (micro-organisms); they include algae, bacteria, protozoa (e.g., amoeba, flagellates, free-swimming ciliates, and stalked ciliates), rotifers and viruses.
Summary of typical domestic waste-water characteristics:
|Total nitrogen||20–85 mg/L|
|Total phosphorus||6–20 mg/L|
|Fecal coliform||500,000–3,000,000 MPN/100 mL|
Secara garis besar pengawetan bahan dapat dibagi dalam 3 golongan yaitu :
- Cara alami
- Cara biologis
- Cara kimiawi
1. PENGAWETAN SECARA ALAMI
Proses pengawetan secara alami meliputi pemanasan dan pendinginan.
2. PENGAWETAN SECARA BIOLOGIS
Proses pengawetan secara biologis misalnya dengan peragian (fermentasi).
a. Peragian (Fermentasi)
Merupakan proses perubahan karbohidrat menjadi alkohol. Zat-zat yang bekerja pada proses ini ialah enzim yang dibuat oleh sel-sel ragi. Lamanya proses peragian tergantung dari bahan yang akan diragikan.
Enzim adalah suatu katalisator biologis yang dihasilkan oleh sel-sel hidup dan dapat membantu mempercepat bermacam-macam reaksi biokimia. Enzim yang terdapat dalam makanan dapat berasal dari bahan mentahnya atau mikroorganisme yang terdapat pada makanan tersebut. Bahan makanan seperti daging, ikan susu, buah-buahan dan biji-bijian mengandung enzim tertentu secara normal ikut aktif bekerja di dalam bahan tersebut. Enzim dapat menyebabkan perubahan dalam bahan pangan. Perubahan itu dapat menguntungkan ini dapat dikembangkan semaksimal mungkin, tetapi yang merugikan harus dicegah. Perubahan yang terjadi dapat berupa rasa, warna, bentuk, kalori, dan sifat-sifat lainnya.
Didapat dari buah nanas, digunakan untuk mengempukkan daging. Aktivitasnya dipengaruhi oleh kematangan buah, konsentrasi pemakaian dan waktu penggunaan. Untuk memperoleh hasil yang maksimum sebaiknya digunakan buah yang muda. Semakin banyak nenas yang digunakan, semakin cepat proses bekerjanya.
Berupa getah pepaya, disadap dari buahnya yang berumur 2,5 – 3 bulan. Dapat digunakan untuk mengepukan daging, bahan penjernih pada industri minuman bir, industri tekstil, industri penyamakan kulit, industri pharmasi dan alat-alat kecantikan (kosmetik) dan lain-lain.
Enzim papain biasa diperdagangkan dalam bentuk serbuk putih kekuningan, halus, dan kadar airnya 8%. Enzim ini harus disimpan di bawah suhu 60 derajat Celsius. Pada 1 (satu) buah pepaya dapat dilakukan 5 kali sadapan. Tiap sadapan menghasilkan + 20 gram getah. Getah dapat diambil setiap 4 hari dengan jalan menggoreskan buah tersebut dengan pisau.
3. PENGAWETAN SECARA KIMIA
Menggunakan bahan-bahan kimia, seperti gula pasir, garam dapur, nitrat, nitrit, natrium benzoat, asam propionat, asam sitrat, garam sulfat, dan lain-lain.
Proses pengasapan juga termasuk cara kimia sebab bahan-bahan kimia dalam asap dimasukkan ke dalam makanan yang diawetkan. Apabila jumlah pemakainannya tepat, pengawetan dengan bahan-bahan kimia dalam makanan sangat praktis karena dapat menghambat berkembangbiaknya mikroorganisme seperti jamur atau kapang, bakteri, dan ragi.
a. Asam propionat (natrium propionat atau kalsium propionat)
Sering digunakan untuk mencegah tumbuhnya jamur atau kapang. Untuk bahan tepung terigu, dosis maksimum yang digunakan adalah 0,32 % atau 3,2 gram/kg bahan; sedngkan untuk bahan dari keju, dosis maksimum sebesar 0,3 % atau 3 gram/kg bahan.
b. Asam Sitrat (citric acid)
Merupakan senyawa intermediet dari asam organik yang berbentuk kristal atau serbuk putih. Asam sitrat ini maudah larut dalam air, spriritus, dan ethanol, tidak berbau, rasanya sangat asam, serta jika dipanaskan akan meleleh kemudian terurai yang selanjutnya terbakar sampai menjadi arang. Asam sitrat juga terdapat dalam sari buah-buahan seperti nenas, jeruk, lemon, markisa. Asam ini dipakai untuk meningkatkan rasa asam (mengatur tingkat keasaman) pada berbagai pengolahan minum, produk air susu, selai, jeli dan lain-lain. Asam sitrat berfungsi sebagai pengawet pada keju dan sirup, digunakan untuk mencegah proses kristalisasi dalam madu, gula-gula (termasuk fondant), dan juga untuk mencegah pemucatan berbagai makanan, misalnya buah-buahan kaleng dan ikan. Larutan asam sitrat yang encer dapat digunakan untuk mencegah pembentukan bintik-bintik hitam pada udang. Penggunaan maksimum dalam minuman adalah sebesar 3 gram/liter sari buah.
c. Benzoat (acidum benzoicum atau flores benzoes atau benzoic acid)
Benzoat biasa diperdagangkan adalah garam natrium benzoat, dengan ciri-ciri berbentuk serbuk atau kristal putih, halus, sedikit berbau, berasa payau, dan pada pemanasan yang tinggi akan meleleh lalu terbakar.
Merupakan larutan garam fosfat, berbentuk kristal, dan berwarna kekuning-kuningan. Bleng banyak mengandung unsur boron dan beberapa mineral lainnya. Penambahan bleng selain sebagai pengawet pada pengolahan bahan pangan terutama kerupuk, juga untuk mengembangkan dan mengenyalkan bahan, serta memberi aroma dan rasa yang khas. Penggunaannya sebagai pengawet maksimal sebanyak 20 gram per 25 kg bahan. Bleng dapat dicampur langsung dalam adonan setelah dilarutkan dalam air atau diendapkan terlebih dahulu kemudian cairannya dicampurkan dalam adonan.
e. Garam dapur (natrium klorida)
Garam dapur dalam keadaan murni tidak berwarna, tetapi kadang-kadang berwarna kuning kecoklatan yang berasal dari kotoran-kotoran yang ada didalamnya. Air laut mengandung + 3 % garam dapur.
Garam dapur sebagai penghambat pertumbuhan mikroba, sering digunakan untuk mengawetkan ikan dan juga bahan-bahan lain. Pengunaannya sebagai pengawet minimal sebanyak 20 % atau 2 ons/kg bahan.
f. Garam sulfat
Digunakan dalam makanan untuk mencegah timbulnya ragi, bakteri dan warna kecoklatan pada waktu pemasakan.
g. Gula pasir
Digunakan sebagai pengawet dan lebih efektif bila dipakai dengan tujuan menghambat pertumbuhan bakteri. Sebagai bahan pengawet, pengunaan gula pasir minimal 3% atau 30 gram/kg bahan.
Kaporit (Calsium hypochlorit atau hypochloris calsiucus atau chlor kalk atau kapur klor)
Merupakan campuran dari calsium hypochlorit, -chlorida da -oksida, berupa serbuk putih yang sering menggumpal hingga membentuk butiran. Biasanya mengandung 25~70 % chlor aktif dan baunya sangat khas. Kaporit yang mengandung klor ini digunakan untuk mensterilkan air minum dan kolam renang, serta mencuci ikan.
i. Natrium Metabisulfit
Natrium metabisulfit yang diperdagangkan berbentuk kristal. Pemakaiannya dalam pengolahan bahan pangan bertujuan untuk mencegah proses pencoklatan pada buah sebelum diolah, menghilangkan bau dan rasa getir terutama pada ubi kayu serta untuk mempertahankan warna agar tetap menarik. Natrium metabisulfit dapat dilarutkan bersama-sama bahan atau diasapkan.
Prinsip pengasapan tersebut adalah mengalirkan gas SO2 ke dalam bahan sebelum pengeringan. Pengasapan dilakukan selama + 15 menit. Maksimum penggunaannya sebanyak 2 gram/kg bahan. Natrium metabisulfit yang berlebihan akan hilang sewaktu pengeringan.
j. Nitrit dan Nitrat
Terdapat dalam bentuk garam kalium dan natrium nitrit. Natrium nitrit berbentuk butiran berwarna putih, sedangkan kalium nitrit berwarna putih atau kuning dan kelarutannya tinggi dalam air.
Nitrit dan nitrat dapat menghambat pertumbuhan bakteri pada daging dan ikan dalam waktu yang singkat. Sering digunakan pada danging yang telah dilayukan untuk mempertahankan warna merah daging.
Jumlah nitrit yang ditambahkan biasanya 0,1 % atau 1 gram/kg bahan yang diawetkan. Untuk nitrat 0,2 % atau 2 gram/kg bahan. Apabila lebih dari jumlah tersebut akan menyebabkan keracunan, oleh sebab itu pemakaian nitrit dan nitrat diatur dalam undang-undang. Untuk mengatasi keracunan tersebut maka pemakaian nitrit biasanya dicampur dengan nitrat dalam jumlah yang sama. Nitrat tersebut akan diubah menjadi nitrit sedikit demi sedikit sehingga jumlah nitrit di dalam daging tidak berlebihan.
Merupakan senyawa organik yang berbentuk kristal putih atau tak berwarna, rasanya asin dan sejuk. Sendawa mudah larut dalamair dan meleleh pada suhu 377 derajat Celsius. Ada tiga bentuk sendawa, yaitu kalium nitrat, kalsium nitrat dan natrium nitrat. Sendawa dapat dibuat dengan mereaksikan kalium khlorida dengan asam nitrat atau natrium nitrat. Dalamindustri biasa digunakan untuk membuat korek api, bahan peledak, pupuk, dan juga untuk pengawet abahn pangan. Penggunaannya maksimum sebanyak 0,1 % atau 1 gram/kg bahan.
Zat pewarna ditambahkan ke dalam bahan makanan seperti daging, sayuran, buah-buahan dan lain-lainnya untuk menarik selera dan keinginan konsumen. Bahan pewarna alam yang sering digunakan adalah kunyit, karamel dan pandan. Dibandingkan dengan pewarna alami, maka bahan pewarna sintetis mempunyai banyak kelebihan dalam hal keanekaragaman warnanya, baik keseragaman maupun kestabilan, serta penyimpanannya lebih mudah dan tahan lama. Misalnya carbon black yang sering digunakan untuk memberikan warna hitam, titanium oksida untuk memutihkan, dan lain-lain. Bahan pewarna alami warnanya jarang yang sesuai dengan yang dinginkan.
PROSES BEBAS KUMAN
Ada dua cara proses bebas kuman, yaitu sterilisasi dan pasteurisasi.
Adalah proses bebas kuman, virus, spora dan jamur. Keadaan steril ini dapat dicapai dengan cara alami maupun kimiawi.
a. Secara alami dapat dilakukan dengan:
- Memanaskan alat-alat dalam air mendidih pada suhu 100 derajat Celsius selama 15 menit, untuk mematikan kuman dan virus.
- Memanaskan alat-alat dalam air mendidih pada suhu 120 derajat Celsius selama 15 menit untuk mematikan spora dan jamur.
b. Secara kimiawi dapat dilakukan dengan menggunakan antiseptik dan desinfektan.
Merupakan zat yang dapat menghambat atau membunuh pertumbuhan jasad renik seperti bakteri, jamur dan lain-lain pada jaringan hidup. Ada beberapa bahan yang sering digunakan sebagai antiseptik, antara lain:
- Alkohol, efektif digunakan dengan kepekatan 50 – 70 %;untuk memecah protein yang ada dalam kuman penyakit sehingga pertumbuhannya terhambat.
- Asam dan alkali, penggunaannya sama dengan alkohol.
- Air raksa (Hg), arsen (As) dan perak (Ag), yang bekerja melalui sistem enzim pada kuman penyakit.
- Pengoksida, juga bekerja pada sistem enzim kuman penyakit. Terdiri dari iodium untuk desinfektan kulit dan chlor untuk desinfektan air minum.
- Zat warna, terutama analin dan akridin yang dipakai untuk mewarnai kuman penyakit sehingga mudah untuk menemukan jaringan mana dari kuman tersebut yang akan dihambat pertumbuhannya.
- Pengalkil, yang digunakan untuk memecah protein kuman sehingga aktifitasnya terhambat. Contohnya adalah formaldehid.
Merupakan bahan kimia yang digunakan untuk mencegah terjadinya infeksi atau pencemaran jasad renik seperti bakteri dan virus, juga untuk membunuh kuman penyakit lainnya. Jenis desinfektan yang biasa digunakan adalah chlor atau formaldehid. Jenis ini lebih efektif bila dicampur dengan air terutama dalampembuatan es. Untuk menjaga kualitas ikan penggunaan chlor sebanyak 0,05 % atau 0,5 gram/liter air sangat efektif.
Dilakukan dengan memanaskan tempat yang telah diisi makanan atau minuman dalam air mendidih pada suhu sekurang-kurangnya 63 derajat Celsius selama 30 menit, kemudian segera diangkat dan didinginkan hingga suhu maksimum 10 derajat Celsius. Dengan cara ini maka pertumbuhan bakteri dapat dihambat dengan cepat tanpa mempengaruhi rasa makanan dan minuman.
When they come in contact with each other, incompatible chemicals could react by releasing toxic or flammable gases, exploding or spontaneously igniting. Segregate and store chemicals by hazard class to minimize the risk of reactions between incompatible chemicals and label storage cabinets and cupboards with the hazard class of the stored materials. MSDSs should be available for all chemicals on site. Review them for information about incompatibilities. The following is a partial list of common incompatible chemicals that can react with each other.
Acids and Bases
Store strong acids and bases separately in enclosures made of corrosion-resistant materials.
Oxidizer are materials that yield oxygen readily to stimulate the combustion of organic matter. When oxidizer come in contact with flammable solvents, they can start or fuel fires.
Typical oxidizing agents found in laboratories include chromates and dichromates, halogens and halogenating agents, peroxides and organic peroxides, nitric acid and nitrates, chlorates and perchlorates, and permanganates and persulfates.
- Store oxidizer away from alkalis, azides, nitrites, organic compounds (including acetic acid), powdered metals and activated carbon.
- Avoid contact between oxidizer and common combustible materials such as paper, cloth and wood.
Water-reactive compounds include alkali earth metals such as lithium, potassium and sodium, sodium borohydride, calcium carbide and sodium peroxide. Solutions containing water, such as inorganic acids and alcohols, should be kept separated from these chemicals during storage and use.
- Store water-reactive compounds away from aqueous solutions, inorganic acids, base solutions and alcohols. Though many chemical storage systems recommend water-reactive solids be stored in the flammable storage cabinets, in many cases this would not be prudent since these cabinets often contain alcohols with 30 percent water.
- Keep a Class D fire extinguisher near storage and use areas for these compounds.
- Store these compounds in locations protected from automated sprinklers.
- Alkali metals should be stored in areas where they are free of moisture, contact with oxygen, and, in the case of lithium, nitrogen gas.
- Only the amount of water-reactive materials necessary to perform the work should be removed from storage. Spare materials should be returned to the appropriate storage container, and the container to its appropriate location.
- Storage containers should be labelled with their contents, hazardous properties and type of oil or gas used to inert the metal. Furthermore, these containers should be stored individually or in a manner that allows visual inspection for container integrity.
- Storage areas should be free of combustibles and of ignition sources.
- The portions of the building dedicated as storage area for alkali metals should not be equipped with automatic sprinklers. No other source of water (e.g., showers, sinks) should be in the immediate proximity of the metal.
- Storage areas should be prominently labelled to indicate the presence of alkali metals.
Potentially Explosive Chemicals
Several classes of chemicals may become explosive when they react with other compounds or may become unstable during storage. Seriously question whether you need these compounds in your facility. These include peroxidizable solvents, potentially explosive dinitro- and trinitro- organic compounds and elemental potassium.
Inorganic azide compounds, such as sodium azide, can react with metals and their salts to produce explosive metal azide crystals. For example, when azide solutions are poured down drains the dilute solution can react with lead solder and copper pipes to produce explosive lead or copper azide salts.
- If we must use azide solutions, replace metal pipes with PVC or other non-metal piping materials.
- If sodium azide solutions have been discharged to drains having metallic pipes or solder, we should assume our pipes may be contaminated with metal azide salts. Contact the authorized environmental institution for assistance in determining the proper disposal procedures.
Ethers and Other Peroxide-forming Chemicals
Certain ethers are more susceptible to peroxide formation than others. Peroxides are formed by oxygen that reacts with ethers: R-O-R is ether; R-O-O-R is peroxide. It is the oxygen-to-oxygen bond that makes ether unstable. Generally, the larger the alkyl group (R), the more readily the ether will form peroxides. Ethyl ether and isopropyl ether can react with air to form explosive peroxide crystals. Other solvents such as tetrahydrofuran and dioxane can also produce peroxides.
Peroxides can explode when subjected to heat, friction or shock. Do not disturb or open containers in which peroxides may have formed. A good rule of thumb is to dispose of any container holding a peroxide-forming compound one year after the date it was opened. Label these containers with the words “DATE OPENED” and add the date.
To prevent the formation of peroxides:
- Avoid using peroxide-forming solvents if possible.
- Purchase ether with butylhydroxy toluene (BHT) or ethanol added as an anti-oxidant.
- Label ether containers with the dates they are opened.
- Purchase ether in containers small enough to use all the solvent within six months.
- Check the MSDSs for our solvents to see if any are prone to creating peroxides.
Elemental potassium is a peroxide-former that is commonly used in school laboratories to demonstrate characteristics of period 1 earth metals. Potassium is a water-reactive earth metal that reacts with moisture in air to start the peroxidation process. This process can be observed by physical changes in the colour of the potassium sticks. Originally a dull silver colour potassium will oxidise and form white crystals on its surface. As these crystals progressively turn yellow, orange, red and purple, the peroxidation process is advancing and the compound is increasingly at risk of exploding when handled. [Blair, 2000]
Metal Picrates and Picric Acid
Metal picrate compounds and picric acid can become dangerously unstable as a dry powder. Picric acid can dry out and form explosive picrate crystals when exposed to air, especially when contaminated with even minute amounts of metals.
To prevent the formation of explosive picrate crystals:
- Always keep picric acid wet or in solution.
- Avoid contact between picric acid and metals. Metal picrate salts are prone to explode when subjected to friction or shock.
- Never purchase or store picric acid in containers with metal lids.
- Avoid flushing picric acid solutions down drains at concentrations above 0.01 percent.
- Dispose of more concentrated picric acid solutions as dangerous waste.
- Bouin’s Fixative contains picric acid and formaldehyde solution (formalin). Be sure to keep this fixative hydrated with water.
- If picric acid solutions have been discharged to drains with metallic pipes or soldered joints, assume the piping is contaminated with explosive metal picrate salts. Contact the authorized environmental institution for assistance in determining the proper disposal procedures.
Perchloric acid is highly corrosive and typically occurs as a 70 percent solution. When warmed above 150 degrees Fahrenheit, it is a powerful oxidizer. Perchloric acid can form explosive metal perchlorate crystals in combination with heavy metals. Any work with perchloric acid must be done in a specially-designed fume hood with a water wash down system designed to prevent the build-up of metal perchlorates in the duct work. If we have been performing perchloric acid digestions in a fume hood not specifically designed for perchloric acid, contact the authorized environmental institution for assistance in locating a contractor to evaluate the hood for perchlorate contamination.
- Spills and other emergencies: In the event of a perchloric acid spill, neutralize with soda-ash (sodium carbonate) or another appropriate neutralizing agent. Soak up the spill with an inorganic based absorbent. Do NOT use rags, paper towels, or sawdust and then put them aside to dry out, as such materials may spontaneously ignite. Likewise, spills on wood may present a fire hazard after the liquid dries.
- If we must use perchloric acid solutions, replace metal pipes with PVC or other non-metal piping materials.
- If perchloric acid solutions have been discharged to drains having metallic pipes or solder, we should assume that our pipes may be contaminated with metal azide salts. Contact the authorized environmental institution for assistance in determining the proper disposal procedures.
- Regularly inspect our containers of perchloric acid for discoloration. If the acid has turned a dark color and has crystals forming around the bottom of the bottle, there is a potential explosion hazard. Notify an emergency response agency and secure the area.
- White crystals around the cap are typically an ammonium salt, and small amounts may be washed off the bottle to the sewer using copious amounts of water.
Ammoniacal Silver Staining Solutions
Ammoniacal silver staining solutions are hazardous because they can form explosive silver salts. Whether disposed or deactivated, these wastes are counted against our generator status.
Safe use of these staining solutions includes the following procedures:
- Don’t allow silver nitrate to remain in ammonium solutions for more than two hours.
- Keep silver nitrate solutions separate from ammonium hydroxide solutions.
- Deactivate these waste solutions by diluting 15:1 with water. Then, while stirring frequently, slowly add 5 percent hydrochloric acid to the solution until the pH reaches 2.
- Add ice if the solution heats up.
- Silver chloride will precipitate out when the pH reaches 2.
- Filter out the precipitate and dispose as hazardous waste, adjust the pH of the solution to 6 to 7 with sodium bicarbonate, then discharge to the sanitary sewer.
A HW landfill shall have the following seven essential components:
- A liner system at the base and sides of the landfill, which prevents migration of leachate or gas to the surrounding soil.
- A lechate collection and treatment facility, which collects and extracts leachate from within and from the base of the landfill and then treats the leachate to meet standards, notified under E(P) Act 1986.
- A gas collection and treatment facility (optional), which collects and extracts gas from within and from the top of the landfill and then treats it or uses it for energy recovery.
- A final cover system at the top of the landfill, which enhances surface drainage, prevents infiltration of water and supports surface vegetation.
- A surface water drainage system, which collects and removes all surface run-off from the landfill site.
- An environmental monitoring system, which periodically collects and analyses air, surface water, soil-gas (option) and ground water samples around the landfill site.
- A closure and post-closure plan which lists the steps that must be taken to close and secure a landfill site once the filling operation has been completed and the activities for long-term monitoring, operation and maintenance of the completed landfill.
A landfill design life will comprise of an ‘active’ period and an ‘closure and post-closure’ period. The ‘active’ period shall be comprise of the period for which waste filling is in progress at the landfill and typically range from 10 to 25 years depending on the availability of land area. The ‘closure and post-closure’ period for which a landfill will be monitored and maintained shall be 30 years after the ‘active period’ is completed.
Waste Volume, Waste Compatibility and Landfill Capacity
The volume of waste to be placed in a landfill will be computed for the active period of the landfill taking into account:
- The current generation of waste per annum.
- The anticipated increase in rate of waste generation on the basis on the basis of past records.
A landfill comprise of separate ‘units’. In each unit, only compatible waste will be disposed.
The actual capacity of each landfill unit will be computed taking into account the volume occupied by the liner system and the cover material (daily/weekly (optional) intermediate and final cover) as well as the compacted density of the waste. In addition, the amount of settlement a waste undergo due to overburden stress and due to bio-degradation (if any) shall also be taken into account.
The total landfill area should be computed on the basis of the designed height of the landfill (usually between 5 to 20 m). Approximately 15 to 20% area more than the area required for land filling should be adopted to accommodate all infrastructure and support facilities as well as to allow the formation of a green belt around the landfill. This additional area shall be computed separately and may be as high as 30% of the total area in case of small to medium landfills. The total landfill area is computed on trial and error basis.
There is no standard method for classifying landfills by their capacity. However, the following nomenclature is often observed in literature:
- Small size landfill: less than 5 hectare area
- Medium size landfill: 5 to 20 hectare areas
- Large size landfill: greater than 20 hectare area
A landfill site will comprise of the area in which the waste will be filled as well as additional area for support facilities. The area in which waste is to be filled may comprise of separate landfill units with each unit, accommodating a group of compatible wastes. Within each unit work may proceed in phases with only a part of area under active operation. Such a layout must be prepared for all landfills. The following facilities must be located in the layout:
- Access roads
- Equipment shelters
- Weighing scales
- Office space
- Location of waste inspection facility (if used)
- Temporary waste storage and / or disposal site for stockpiling cover material and liner material
- Location of surface water drainage facilities
- Location of landfill leachate management facilities
- Location of gas management facilities (optional)
- Location of monitoring wells/environmental monitoring facilities
- Fencing and green belt along the peripheral boundary
- Emergency exit.
It is essential that for each landfill site, a layout be designed incorporating the above mentioned facilities.
Landfills may have different types of sections depending on the topography of the area. The landfills may take the following forms:
- Above ground landfills
- Below ground landfill
- Slope landfills
- Valley landfills (canyon landfills)
- A combination of the above
It is recommended that the landfill section be arrived at keeping in view the topography, depth to water table and availability of inner and cover material. Above ground landfills shall be preferred to below ground landfills, as leachate collection in the former is by gravity flow and does not require the use of pumps.
Slope landfills and valley landfills are normally adopted in hilly areas; above-ground landfills in flat undulating ground and below-ground landfills in low-lying areas, depressions or pits.
Before the main design of a landfill can be undertaken it is important to develop the operating methodology. A landfill is operated in phases because it allows the progressive use of the landfill area, such that at any given time a part of the site may have a final cover, a part being actively filled, a part being prepared to receive waste, and a part undisturbed. For each landfill unit, a phased operation plan will be drawn up.
The term ‘phase’ describes a sub-area of the landfill. A ‘phase’ consists of cells, lifts, daily / weekly (optional) or intermediate cover and capped within this period leaving a temporary unrestored sloping face. A ‘phase plan’ shall be drawn up for the active life of the landfill as soon as the landfill as soon as the landfill layout and section are finalized. It must be ensured that each phase reaches the final cover/intermediate cover level at the end of its construction period and that it is capped before the onset of monsoons.
During the monsoon months the waste may stockpiled in a temporary holding areas (covered with roof). During this period and the landfill may be kept capped with the final cover/intermediate cover and land-filling operations suspended to reduce infiltration of rain water into the landfill. However, if the incoming waste quantity is too large for temporary stockpiling or the monsoon period lasts for a long period, special phases may have to be designed with high leachate handling capacity and special operating procedures adopted.
Estimation of Leachate Quantity
Leachate is generated on account of the infiltration of water into landfills and its prelocation through waste as well as by the squeezing of the waste due to self weigh. The quantity of leachate generated in a landfill is strongly dependent on weather and operational practices. The amount of rain falling on the landfill, to a large extent, controls the leachate quantity generated. Precipitation depends on geographical location.
Significant quantity of leachate is produced from the ‘active’ phases of a landfill under operation. The leachate quantity from those portions of a landfill which have received a final cover is minimal. For designing, computer simulated models (e.g. HELP) have to be used for estimation of leachate quantity generation. It is recommended that such studies be conducted to estimate the quantity of leachate and design the leachate drainage, collection and removal facility.
Leachate control within a landfill involves the following steps:
- Prevention of migration of leachate from landfill sides and landfill base to the subsoil by suitable liner system.
- Drainage of leachate collected at the base of a landfill to the side of the landfill and removal of the leachate from within the landfill.
On a basis of review of liner systems adopted in different countries and in consideration with Indian conditions, it is recommended that for all HW landfills the liner system criteria be adopted in consultation with SPCB/PCC and commensurate with local area specified needs.
Leachate Drainage, Collection and Removal
A leachate collection system shall be designed at the base of all landfills. It shall comprise of a drainage layer, perforated pipe collection system, sump collection area, and a removal system.
The leachate collection layer (drainage layer) will usually be a 30 cm thick sand – gravel layer with a slope of 2% or higher and permeability of greater than 10-2 cm/sec (10-4 m/sec). A system of perforated pipes and sumps is provided within the drainage layer. The pipe spacing will be governed by the requirement that the leachate head shall not be greater than the drainage layer thickness.
Leachate will be removed from the landfill by one of the following ways:
- Pumping in vertical wells or chimneys.
- Pumping in side slope risers.
- By gravity drains through the base of a landfill in above ground and sloped landfills.
Side slope risers may be preferred to vertical wells to avoid any down drag problems. Submersible pumps have been used for pumping for several years; educator pimps are also being increasingly used. The leachate may be stored in a holding tank (for a few days) before being sent for treatment.
The design of following components should be undertaken:
- Leachate pipe and leachate trench network
- Leachate sumps and pumps
- Leachate well/side slope riser
- Leachate holding tank
- Backwashing/backflushing arrangement to prevent clogging/choking/head-loss.
The material used for pipes etc., should be such that it is not affected by the leachate quality.
- Offsite treatment of leachate: This involves storage, pretreatment and transportation of leachate to off-site facilities not associated with the landfill e.g. industrial effluent treatment facility etc. This will be feasible where offsite facilities are available at a reasonable distance and where pretreatment requirements for the leachate (such as adjustment of pH, reduction in concentration etc.) are not very stringent. Transportation of leachate to offsite facility will be undertaken through a manifest system in accordance with HWM rules of MoE.
- Onsite treatment of leachate: This involves complete treatment of the lechate at the landfill site to meet discharge standards for lined drains. Treatment processes may be biological, chemical or physical processes. Processes, which have been judged as having been “demonstrated”, should be adopted.
- Recirculation: One of the methods for treatment of leachate is to recirculate it through the landfill. This has two beneficial effects: (i) the process of landfill stabilization is accelerated and (ii) the constitutes of the leachate are attenuated by the biological, chemical and physical changes occurring with the landfill. Recirculation of a leachate requires the design of a distribution system to ensure that the leachate passes uniformly throughout the entire waste. Leachate recirculation has been used in some municipal waste landfills. Information on its efficacy in HW landfills is scanty.
Gaseous Emissions Management
Landfill gas is generated as a product of waste biodegradation or on account of presence of VOCs in the waste. Gas generation can be reduced or eliminated by avoiding disposal of biodegradable/organic wastes. For HW landfills where gaseous emissions are anticipated (as in the case of mixed waste having biodegradable components), the gas management strategy shall be:
- Controlled passive venting, or
- Controlled collection and treatment/reuse.
Final Cover System
A final landfill cover, comprising of several layers, each with a specific function shall be installed after each landfill phase reaches the full height. The final cover system shall enhance surface drainage, minimize infiltration, support vegetation to prevent erosion and control the release of landfill gases.
Surface Water Drainage System
Surface water management is required to ensure that rainwater run-off does not drain into the waste from surrounding areas and that there is no waterlogged/ponding on covers of landfills. A surface water drainage system comprising of channels, drains, culverts and basins shall be designed to ensure the following:
- Rainwater running off slopes above and outside the landfill area shall be intercepted and channelled to water courses without entering the operational area of the site. This diversion channel may require a low permeability lining to prevent leakage into the landfill.
- Rain falling on active tipping areas shall be collected separately and managed as leachate, via the leachate collection drain and leachate collection sumps to the leachate treatment and disposal system.
- Rainfall on areas within the landfill site, but on final covers of phases which have been completed and are not actively being used for waste disposal shall be diverted in drainage channels away from active tipping areas, and directed through a settling pond to remove suspended silt, prior to discharge.
- Any drainage channels or drains constructed on the restored landfill surface shall be able to accommodate settlement, resist erosion and cope with localized storm conditions.
- The horizontal surface of the final cover shall be provided a slope of 3 to 5% for proper surface water drainage. The slope of the cover on the sides will be higher and governed by slope stability considerations.
- All interceptor channels, drainage channels and settling ponds (storm water basins) shall be designed by a hydrologist using hydro-meteorological data.
- It shall be ensured that water collected by surface water drainage system and leachate collected by the leachate collection system do not get intermixed at any stage of collection or storage. This shall apply to the ‘active’ and ‘post closure’ periods of the landfill.
The design of following components shall be undertaken:
- Storm-water drains, diversion channels
- Storm-water basin
Base Stability, Slope Stability and Seismic Aspects
For landfills constructed on loose/soft soil, the base will be checked for stability against bearing failure or excessive settlements. The stability of side slopes of a landfill shall be checked for the following cases:
- Stability of excavated slopes.
- Stability of liner system along excavated slopes.
- Stability of temporary waste slopes constructed to their full height (usually at the end of a phase).
- Stability of slopes of above-ground portion of completed landfills.
- Stability of cover systems in above ground landfills.
The stability analysis shall be conducted using the following soil mechanics methods depending upon the shape of the failure surface:
- Failure surface parallel to slope.
- Wedge method of analysis.
- Method of slices for circular failure surface.
- Special methods for stability of anchored geomembranes along slopes.
In primary design of a landfill section, the following slopes may be adopted:
- Excavated soil slopes (2.5 horizontal : 1 vertical)
- Temporary waste slopes (3.0 horizontal : 1 vertical)
- Final cover slopes (4.0 horizontal : 1 vertical)
Slopes can be made steeper, if found stable by stability analysis results.
Acceptable factors of safety may be taken as 1.3 for temporary slopes and
1.5 for permanent slopes. In earthquake prone areas, the stability of all landfill slopes shall be conducted taking into account seismic coefficient as recommended by BIS codes.
A material balance shall be prepared for each material required for construction of a landfill, phase-by-phase, indicating materials required,
material available and deficient material to be imported or surplus material to be exported. If a borrow area is located within the landfill site it shall not become a part of an early phase to avoid stockpiling and double handling.
The following site infrastructure shall be provided at each HW landfill:
- Site Entrance and Fencing
- Administrative and Site Control Offices
- Access Roads
- Waste Inspection and Sampling Facility
- Equipment Workshops and Garages
- Signs and Directions
- Water Supply
- Vehicle Cleaning Facility
- Fire Fighting Equipment
Site entrance infrastructure should include:
- A permanent, wide, entrance road with separate entry and exit lanes and gates.
- Sufficient length/parking space inside the entrance gate till the weighbridge to prevent queuing of vehicles outside the entrance gate and onto the highway.
- A properly landscaped entrance area with a green belt of 20 m containing tree plantation for good visual impact.
- Proper direction signs and lighting at the entrance gate.
- A perimeter fencing of at least 2 m height all around the landfill site with lockable gates to prevent unauthorized access.
- Full time security guard at the site.
An accurate record of waste inputs is essential, hence good quality weigh bridges shall be used. For sites receiving more than 400 tons per day
of waste, twin weigh bridges to weigh both entry and exit weights may be located on either side of an island on which a weighbridge office room is located. The weighbridge office should be elevated and the weighbridge operators should be able to see entering vehicles as well as speak to drivers.
Administrative and site control offices should include: administrative office building (permanent); site control office (portable) near the active landfill area; stores (permanent) within or near administrative office; welfare facilities – toilets, shower room, first aid room, mess room, small temporary
accommodation; infrastructural services – electricity, drinking water supply, telephone, sewerage and drainage system and communication services
(telephone etc.) between site control office and administrative office and weighbridge office.
Environmental Monitoring System
Monitoring at a landfill site shall be carried out in four zones:
- On and within the landfill
- In the unsaturated subsurface zone (vadose zone) beneath and around the landfill
- In the groundwater (saturated) zone beneath and around the landfill
- In the atmosphere/local air above and around the landfill
The parameters to be monitored regulatory are:
- Long-term movements of the landfill cover
- Leachate head within the landfill
- Leachate quality within the landfill
- Gas quality (optional) within the landfill
- Quality of pore fluid in the vadose zone
- Quality pore gas (optional) in the vadose zone
- Quality of groundwater in the saturated zones
- Air quality above the landfill, at the gas control facilities, at buildings on or near the landfill and along any preferential migration paths
The indicators of leachate quality and landfill gas quality must be decided after conducting a study relating to the type of the waste, the probable composition of leachate and gas likely to be generated and the geotechnical as well as hydro-geological features of the area.
A monitoring programme must specify:
- A properly selected offsite testing laboratory capable of measuring the constituents at current detection levels
- A methodology for acquiring and storing data
- A statistical procedure for analyses of the data
The following instruments/equipment shall be used for monitoring:
- Groundwater samples for groundwater monitoring wells.
- Leachate samplers for leachate monitoring within the landfill and at the leachate tank.
- Vacuum lysimeters, filter tip samplers, free drainage samplers for leakage detection beneath landfill liners.
- Surface water samplers for collection of sample from sedimentation basin.
- Down-hole water quality sensors for measuring conductivity, pH, DO, temperature in leachate wells, groundwater wells and sedimentation basins.
- Landfill gas monitors (portable) for onsite monitoring of landfill gases.
- Active and passive air samplers for monitoring ambient air quality.
It is recommended that the location of each type of instrument/equipment be finalized in conjunction with an expert on the basis of the topography of
the area and the layout of the landfill. A minimum of 4 sets of ground water monitoring wells (one up-gradient and three down gradient) for sampling in
each acquifer are considered desirable at each landfill site.
Closure and Post-Closure Maintenance Plan
A statement on the end-use of landfill site is an essential part of the plan for landfill closure and post-closure maintenance. Some possible uses of closed landfill sites near urban centres include parking area, recreational area etc. a closed landfill should be aesthetically landscaped. A closure and post-closure plan for HW landfills must be evolved and should indicate the following components:
- Plan for vegetative stabilization of the final landfill cover and side slopes
- Plan for management of surface water run-off with an effective drainage system
- Plan for periodical inspection and maintenance of landfill cover and facilities
- Plan for post-closure management of leachate and gas
- Plan for post-closure environment monitoring
The term hazardous waste landfill (HW Landfill) is used to designate a waste disposal unit designated and constructed with the objective of minimum impact to the environment. This term encompasses other terms such as “secured landfill”, “engineered landfill”, “waste mounds”, “waste piles” etc.
HW Landfills shall not be located within a certain distance of the following lakes, ponds, rivers, wetlands, flood plains, highways, habitation, critical habitat area, water supply wells, Airports, coastal zone. If it is absolutely essential to site a landfill within the restricted zone, then appropriate design measures are to be taken and prior permission from the SPCB/PCC should be obtained.
- Lake or Pond: No landfill shall normally be constructed within 200 m of any lake or pond. Because of concerns regarding run-off of waste contaminated water, a surface water monitoring network with approval of SPCB/PCC shall be established.
- River: No landfill shall be constructed within a 100 m of a navigable river or stream.
- Flood Plain: No landfill shall be constructed within a 100-year flood plain. A landfill may be built within the flood plains of secondary streams if an embankment is built along the stream-side to avoid flooding of the area. However, landfills must not be built within the flood plains of major rivers unless properly designed protection embakements are constructed around the landfills.
- Highway: No landfill shall be constructed within 500 m of the right of way of any state or national highway.
- Habitation: A landfill site shall be at least 500 m from a notified habitated area. A zone of 500 m around a landfill boundary should be declared a no development buffer zone after the landfill location is finalized.
- Public Parks: No Land fill be constructed within 500 m of public park.
- Critical Habitat Area: No landfill shall be constructed within critical habitat areas including reserved forest areas. A critical habitat area is defined as the area in which one or more endangered species live. It is sometimes difficult to identify a critical habitat area. If there is any doubt then the SPCB/PCC shall be consulted be consulted for clarification.
- Wetlands: No landfill shall be constructed within wetlands. It is often difficult to identify a wetland area. Maps may be available for some wetlands, but in many cases such maps are absent or are incorrect. If there is any doubt, then the SPCB/PCC shall be consulted for clarification.
- Airport: No landfill shall be constructed within a zone around airports as notified by the regulatory authority or the aviation authority.
- Water Supply: No landfill shall be constructed within 500 m of any water supply well.
- Coastal Regulation Zone: No landfill shall be sited in a coastal regulation zone.
- Ground Water table level: No landfill shall be located in areas where the ground water table will be less than 2 m below the base of the landfill.
- Other criteria may be decided by the planners in consultation with SPCB/PCC commensurate with specific local requirements such as presence of monuments, religious structures etc.
Hazardous waste landfills should preferably be located in areas of low population density, low alternative land use value, low ground water contamination potential and at sites having high clay content in the subsoil. A HW landfill will be selected following the guidelines published by MoE. The step by procedure will be as follows:
1. Earmarking a’ search area’ taking into account the location of the waste generation units and a ‘search radius’ (typical 5 to 250 km). The search area will be so chosen that it minimizes the number of HW landfills in any region or state.
2. Identification of a list of potential sites on the basis of:
- Availability of land
- Collection of preliminary data
- Restrictions listed in the locational criteria
3. Collection of preliminary data as follows:
- Topographic Maps: A topographic map will help find sites that are not on natural surface water drains or flood plains.
- Soil Maps: These maps, primarily meant for agricultural use, will show the types of soil near the surface. They are of limited use as they do not show types of soil a few metre below the surface.
- Land Use Plans: These plans are useful in delineating areas with definite zoning restrictions. There may be restrictions on the use of agricultural land or on the use of forest land for landfill purposes.
- Transportation Maps: These maps, which indicate roads and railways and locations of airports, are used to determine the transportation needs in developing a site.
- Water Use Plans: Such maps are usually not readily available. A plan indicating the following items should be developed: private and public tube wells indicating the capacity of each well, major and minor drinking water supply line(s), water intake wells located on surface water bodies and open wells.
- Flood Plain Maps: These maps are used to delineate areas that are within a 100 year flood plain. Landfill siting must be avoided within the flood plains of major rivers.
- Geologic Maps: These maps will indicate geologic features and bedrock levels. A general idea about soil type can be developed from a geological map.
- Aerial Photographs / Satellite Imagery: Aerial photographs or satellite imageries may not exist for the entire search area. However, such information may prove to be extremely helpful. Surface features such as small lakes, intermittent stream beds and current land use, which may not have been identified in earlier map searches, can be easily identified using aerial photographs.
- Ground Water Maps: Ground water contour maps are available in various regions which indicate the depth to ground water below the land surface as well as regional ground water flow patterns. Such maps should be collected from Ground Water Boards or Minor Irrigation Tube well Corporations.
- Rainfall Data: The monthly rainfall data for the region should be collected from the Meteorological Department.
- Wind Map: The predominant wind direction and velocities should be collected from the Meteorological Department.
- Seismic Date: The seismic activity of a region is an important input in the design of landfills. Seismic coefficients are earmarked for various seismic zones and these can be obtained from the relevant BIS code or from the Meteorological Department.
- Site Walk Over and Establishment of Ground Truths: A site reconnaissance will be conducted by a site walk-over as a part of the preliminary data collection. All features observed in various maps will be confirmed. Additional information pertaining to the following will be ascertained from nearby inhabitants: (a) flooding during monsoons; (b) soil type; (c) depth to G.W. table (as observed in open wells or tube wells); (d) quality of groundwater and (e) depth to bedrock.
- Preliminary Boreholes and Geophysical Investigation: At each site, as a part of preliminary data collection, one to two boreholes will be drilled and samples collected at every 1.5 m interval to a depth of 20 m below the ground surface. The following information will be obtained: (i) soil type and stratification; (ii) permeability of each strata; (iii) strength and compressibility parameters (optional); (iv) ground water level and quality and (v) depth to bedrock. In addition to preliminary boreholes, geophysical investigations (electrical resistivity/seismic refraction/others may be undertaken to assess the quality of bedrock at different sites.
4. Selection of two best ranked sites from amongst the list of potential sites on the basis of the ranking system stipulated by MoE.
5. Environmental Impact Assessment for the two sites for the following parameters: (a). ground water quality; (b) surface water quality; (c) air quality gases, dust, litter, odour; (d) land use alteration; (e) drainage alteration, soil alteration, (f) soil erosion; (g) ecological impacts (h) noise; (i) aesthetics visual, vermin, files; (j) traffic alteration; and (k) others.
6. Assessment of public perception for the two sites.
7. Selection of final site.
8. The above site selection procedure shall not be applicable for location of facility within industrial areas of State Industrial Development Agencies.
SITE INVESTIGATION CRITERIA
The data collected during site selection is not sufficient for landfill design. To be able to undertake detailed design of a landfill at a selected site, it is essential to characterize the landfill site and evaluate the parameters required for design. It is necessary that all data on preliminary data be collected for site characterization. If some data has not be collected, the same should be obtained before site investigations are undertaken for characterization. The following additional data will be collected through a detailed site investigation programme at the chosen site.
A detailed site investigation programme will comprise of subsoil investigation, ground water/hydrogeological and geological investigation. The output expected from each investigation is listed below:
a. Subsoil Investigation: A detailed investigation plan may be drawn up in consultation with a geotechnical engineer. The output from such an investigation should yield the following:
- Stratification for subsoil – type of soil and depth.
- Depth to ground water table and bedrock (if located within 15m of base of landfill).
- Permeability of various strata beneath the landfill.
- Strength and compressibility properties of subsoil.
- Extent of availability of liner material, drainage material, top soil and protective soil in adjacent borrow areas.
- Subsoil properties along approach road.
A minimum of 3 boreholes per hectare of landfill area upto 15m beneath the base of the landfill shall be drilled and insitu tests as well as laboratory tests shall be performed for permeability, strength, compressibility and classification of soils. In addition, test pits and boreholes should be drilled at borrow are for liner and cover materials as well as along approach road.
b. Ground Water/Hydrogeological Investigation: A detailed investigation plan may be drawn up in consultation with a ground water specialist or a hydrogeologist. The output from such an investigation should yield the following:
- Depth to groundwater table and its seasonal variations.
- Ground water flow direction.
- Baseline ground water quality parameters – all drinking water quality parameters.
c. Topographical investigation: Construction of a landfill involves a large quantity of earthwork. It is essential to have an accurate topographical map of the landfill site to compute earthwork quantities precisely. A map of 0.3 m contour interval is considered desirable.
d. Hydrological Investigation: The objectives of a hydrological investigation is to estimate the quantity of surface run-off that may be generated within the landfill to enable appropriate design of drainage facilities. If additional run off from areas external to the landfill, this quantity should also be estimated to design interception ditches and diversion channels. Such an investigation shall yield estimates of peak flows. If seasonal rivers or streams run close to the site, hydrological investigation should indicate the possibility of flooding of the site under one in 100 year flood flows. Surface water samples for water quality analysis may be collected from during hydrological studies.
e. Geological Investigation and Seismic Investigation: Geological investigations shall delineate the bedrock profile beneath the landfill base, if not confirmed by subsoil investigations. Geophysical surveys may be designed in consultation with a geologist. In hilly areas or in quarried rocks, geological investigations should indicate the quality of superficial rock, depth to sound rock and the landfill base in the rock mass. Detailed seismic data may be obtained as a part of geological investigations (if required) in seismically active areas.
API Gravity – An arbitrary scale of the American Petroleum Institute for measuring the density of oils.
Baume Gravity – A unit of measurement of specific gravity used in the chemical industry. We use for caustic and acid.
A.S.T.M. DISTILLATION – The standard procedure of the American Society for Testing Materials for determining the boiling range of petroleum distillates.
SPECIFIC GRAVITY – The ratio of the weight of a volume of a body to the weight of an equal volume of some standard sub-stance. In the case of liquids and solids, the standard is water; and in the case of gases, the standard is air.
VISCOSITY – A test to determine the internal friction or resistance to flow. It is measured by the number of seconds required for a sample to pass through a standard opening or orifice at a specified temperature.
REID VAPOUR PRESSURE – A test that indicates the volatility of a liquid by measuring the amount of pressure generated in a bomb at a specific temperature (70 °F).
COLOUR-SAYBOLT – A test used for determining the color of gasoline and burning oils - range from 30 for gasoline to -16 for furnace oils.
A.S.T.M. – UNION – A test for determining the colour of furnace oils and heavier products - range from 0 for clear oils to 10 for dark oils.
FLASH POINT – A test designed to determine the lowest temperature at which a petroleum product forms vapour, under specified conditions, at a rate sufficient to produce a momentary flash when a small flame is passed over it.
OCTANE NUMBER – A test to determine the anti-knock properties of a gasoline sample. It is performed by burning a sample in a gasoline motor and comparing its performance with reference fuels (iso-octane: 100 octane number and normal heptane: 0 octane number). The octane is the percent of iso-octane in a mixture of iso-octane and heptane that matches the performance of the sample.
POUR POINT – A test which determines the lowest temperature at which oil will flow when chilled under prescribed conditions.
ABSORBER – A tower or column in which contact is caused between rising gases and falling liquid so that part of the gas may be taken up by the liquid. For example, a Gas Plant has a tower that absorbs butane and propane from the gases charged to it.
ABSORPTION OIL – The oil used in an absorption tower, usually in the range of kerosene or heating oil.
ACCUMULATOR – A vessel for the temporary storage of a liquid or gas, usually used for collecting sufficient material for a continuous charge or reflux.
ATMOSPHERIC TOWER – A distillation column operated at nearly atmospheric pressure.
ATOMIZER – A nozzle device used to break fuel oil into a fine spray so that the oil may be brought into more intimate contact with the air in the combustion chamber.
BAFFLE – A partial restriction, generally a plate located to change the direction, guide the flow or promote mixing within the equipment in which it is installed. (Example: heat exchanger).
BAROMETRIC CONDENSER – Equipment for maintaining a partial vacuum on a refinery tower or steam turbine by condensing the vapours from it by direct contact with sprayed water.
BARREL – A standard unit of measurement of liquids in the petroleum refining industry. It contains 42 U.S. standard or 35 Imperial gallons at 60 °F.
BATTERY – A series of stills or boilers operated as a unit.
BATTERY LIMITS – The outer boundaries of the area assigned to a unit or battery.
BLANK OFF – To place a metal disk between pipe flanges so that flow is halted or prevented. A safety measure during shut-downs or when welding or working inside a vessel.
BLEEDER – A connection consisting of a nipple and a valve located at a high or low spot in a line or vessel. Used for sampling, drawing off gas, water, etc.
CATALYST – A material which will increase or decrease the speed of a chemical reaction without changing its own chemical identity.
CHANNELLING – Flow through process equipment where most of the fluid, due to poor distribution, coking, etc., flows through certain portions of the bed or equipment, bypassing other portions.
CHARGE – Feedstock to a refinery processing unit.
CHECK VALVE – A valve which permits fluids to flow in only one direction by automatically closing when the flow attempts to reverse.
CUT – A petroleum fraction obtained by distillation.
CYCLONE – A cone-shaped vessel for separating solids or liquids from a gas.
DAMPER – A device for regulating the flow of flue gases in a chimney, thus controlling the amount of excess air to the furnace.
DOWN-COMER – The conduit or overflow pipe in a distillation tower through which the liquid from one tray enters and is distributed to the tray below.
DRAW OFF – A connection which allows liquid to flow from the side or bottom of a vessel.
ETHYL FLUID (Tetra-ethyl Lead) – A chemical which retards the tendency for gasoline to pre-ignite in an internal combustion engine.
EXPANSION JOINT – A type of joint used in piping. It usually contains a telescoping section or a bellows to absorb strain caused by expansion or contraction due to changes of temperature or other forces.
FEED WATER – The water supplied to a boiler to make up for evaporation and boiler blow down.
FIRE WALLS – Earthen banks or concrete walls built around storage tanks or other equipment containing oil to prevent its spread in case of fire or run over.
FLOATING HEAD – The end of a heat exchanger bundle not attached to the shell so as to allow for expansion.
FLUE GASES – Gases from the combustion of fuel. Their heating potential having been substantially spent, they are discarded to the flue or stack. They consist primarily of CO2-CO-O2-N2 and water vapour.
FOAMITE – A preparation used to extinguish fires. It consists of two solutions which, on mixing, produce a thick foam which will cover a surface and smother a fire.
FRACTIONATING TOWER – The vertical cylindrical vessel which separates components of a liquid mixture in a distillation process.
FURNACE OIL – A light fuel oil primarily used in home heating systems.
GAUGE – To measure, such as to gauge the level in a tank. Also, an instrument for measuring, such as a pressure gauge.
HEAD – Pressure of a fluid upon a system due to the height at which the surface on the fluid stands above the point where the pressure is taken. The discharge pressure of a pump is sometimes referred to as the pump head and expressed as feet of fluid.
HEAD – The removable end plate of an exchanger or the bolted plate over a tower or tank opening.
HEADER – A common manifold to which two or more pipes or tubes are connected. Headers in a heater have plugs that can be removed for cleaning.
HEATER – A furnace used for heating oil or gas for a unit. The portion where the burners are located is called the fire box or furnace. The fluid to be heated is flowing through tubes in the heater. The tubes visible to the fires are called the radiant section, and the tubes heated by combustion gases are called the convection section.
HEAT EXCHANGER – A piece of equipment having a tubular piping arrangement which effects the transfer of heat from a hot to a relatively cool process stream by conduction through the tube walls.
HYDROMETER – A graduated instrument used in determining API or Baume gravities.
IMPELLER – The moving part of a centrifugal pump or compressor which consists of a set of vanes attached to a central hub.
IMPINGEMENT – The contact of flame with the tubes in a furnace, usually undesirable.
FORCED DRAFT – Air supplied to a furnace, cooling tower, or exchanger, by means of a fan or blower, which force air through the equipment.
INDUCED DRAFT – Air supplied to a furnace, cooling tower, or exchanger, by means of a fan or blower, which pulls air through the equipment.
INERT GAS – Unreactive; will not support combustion. In refinery use is generally nitrogen or CO2 (carbon dioxide) (flue gas).
INHIBITOR – A chemical additive put in oils to prevent or slow down unwanted reactions, usually oxidation or gum formation. A chemical added to cooling towers or process stream to prevent corrosion.
INSULATION – A material applied to equipment to prevent the transfer of heat.
MERCURY – An element; a silver coloured liquid at ordinary temperatures used extensively in instruments: thermometers – manometers – gauges, etc. It is a great deal heavier than water, having a specific gravity of 13.5.
METER CONSTANT – The numerical constant which must be multiplied by the number of meter divisions to determine the flow through the meter.
MOLECULE – The smallest unit into which a substance can be divided and retain all of its chemical and physical properties.
MOLECULAR WEIGHT – The sum of the atomic weights of the atoms in a molecule. Example: methane (CH4) (Carbon 12) (Hydrogen 1) = 12 + 4 = 16.
ON STREAM – The period of time a refinery processing unit is in actual production.
ORIFICE – A device to restrict the flow through a pipe line.
ORIFICE METER – An instrument which measures the flow through a pipe by means of measuring the difference in pressure on the upstream and downstream sides of an orifice plate.
OUTAGE – The distance from the top of a container to the surface of the liquid in the container.
PISTON – A cylindrical device which reciprocates in a cylinder, causing fluid to enter and leave the cylinder.
PREHEAT – Heat added to a fluid prior to an operation performed on that fluid.
PRESSURE DROP – The decrease in pressure, due to friction, which occurs when a liquid or gas passes through a pipe, vessel, or other piece of equipment.
PARTIAL CONDENSER – A condenser (heat exchanger) sometimes located at the top of the tower that furnishes sufficient cooling to condense a part of the overhead vapours.
PRIMING – A violent intermittent action resulting in the throwing of slugs of boiler water over with the steam, similar to the agitation when water is boiled in an open vessel. The filling of the liquid end of a pump with liquid to remove vapors present and eliminate the tendency to become vapor bound or lose suction.
PUMP – A machine for moving a liquid by taking energy from some other source and transferring it to the liquid. Common types are as follows:
- CENTRIFUGAL – A pump in which fluid movement is developed primarily by the action of centrifugal force (whirling action). No valves.
- MULTI-STAGE – A centrifugal pump which has two or more impellers mounted on the same shaft. The discharge from one impeller is conducted to the suction eye of the next impeller. This type is used to obtain high differential pressure between suction and discharge.
- RECIPROCATING – A positive dis-placement type of pump consisting of plunger or piston moving back and forth within a cylinder. Liquid is pumped with every stroke of a double acting pump. Liquid is pumped only when the piston is moving in one direction (every other stroke) in a single acting pump.
- DUPLEX – A reciprocating pump that has two or more liquid cylinders, each having its individual drive. Duplex pumps have a more steady discharge pressure than do simplex pumps.
- SIMPLEX – A reciprocating pump that has one liquid cylinder on a single drive. Usually used on lubricators, chemical injectors, etc.
- ROTARY – A positive displacement pump with a fixed casing containing the rotating element or elements consisting of gears, cams, screws, vanes or modifications of these elements. Suitable for pumping viscous liquids or where high vacuums are required.
CAVITATION – A condition inside a pump wherein the liquid being pumped partly vaporizes due to temperature, pressure drop, etc. It can be identified by noisy operation and erratic discharge pressure. It can cause excessive wear on the impeller and case. This can often be remedied by increasing the pressure on the pump, usually by raising the level of liquid being fed to the pump, or else by decreasing the flow rate through the pump.
REACTOR – The vessel in which all or at least the major part of a reaction or conversion takes place. On most units this will be the vessel in which the catalyst is located.
REBOILER – A part of a fractionation tower designed to supply all or a portion of the heat to the tower. Liquid is withdrawn from the bottom of the tower and heated in the reboiler. The vapours formed are returned to the tower. The remaining liquid may or may not be returned to the tower. Heat may be furnished by oil circulated through a heater, bottoms from some other tower, or by steam.
RECYCLE – Continuous circulation without withdrawing a product from the system, or that part of the product that is returned to the system.
REFLUX – Liquid that is returned to a fractionating tower to control temperatures and increase the efficiency of separation.
REGULATOR – A valve which directly controls the flow of liquid or gas through a line usually actuated by an instrument to control temperature, pressure, level, or flow conditions.
RUNNING TANK – A tank to which a product from a unit is continuously pumped or from which a unit is charged.
SAFETY VALVE – A pre-set valve to release excessive pressure on a vessel or system.
SODIUM HYDROXIDE (NaOH) CAUSTIC SODA – Lye used in treating oils.
SOUR – Ill smelling; a petroleum fraction or gas having a bad odour caused by mercaptans or hydrogen sulfide.
SPLIT TUBE – A crack or break in a heater or exchanger tube due to mechanical failure — corrosion or overheating. If this occurs in a heater, it is usually followed by a fire.
STABILIZER – A tower that separates high vapour pressure hydrocarbons from gasoline so that the gasoline will meet vapour pressure specifications.
STATIC PRESSURE – Acting by mere weight without motion.
STEAM-LIVE – Water vapour which does not contain entrained water droplets (usually high pressure).
STEAM-EXHAUST – Low pressure steam which has already been used for some purpose (from a pump, compressor or electric generator).
STEAM-SUPERHEATED – Water vapour heated above the saturation temperature at a given pressure. Usually used in towers, heaters, strippers, etc.
STEAM-WET – Steam containing entrained water.
STRAIGHT RUN – A material produced by distillation of crude oil without appreciable cracking or alteration of the molecules in the product.
STRIPPER – A vessel which strips off the light ends of a side cut from the main fractionating tower. Superheated steam is usually injected into the stripper bottom to improve this separation.
SUPER HEATER – A heating apparatus (usually tubes) which imparts to a material more heat than is required for vaporization.
SURGE DRUM – A vessel or accumulator which serves as a reservoir for liquid flowing through a system, thereby overcoming fluctuations in the rate of flow.
SWEET – Having a good odour. Negative to the doctor test.
THIEF – A device for drawing samples of oil from a tank at various levels.
THIEF ROD – A rod used to measure the depth of water in a tank.
TUBE BUNDLE – A group of fixed parallel tubes, such as is used in a heat exchanger. The tube bundle includes the tube sheets with the tubes, the baffles, and the spacer rods.
TUBE STILL – A still in which heat is applied to the oil while being pumped through a coil or series of coils or tubes arranged in a suitable firebox.
TURBINE – A machine for producing power activated by the expansion of steam on a series of curved vanes in an impeller attached to a central shaft.
VACUUM JETS – Steam ejectors for removing air and non-condensible gases.
VAPOUR LOCK – Occurrence of air pockets or formation of vapor in a line or pump causing interruption of flow or loss of suction.
The education of engineers must be a multi-frontal effort. The basic fundamentals of engineering must be instilled into the student. The economics of how to manage an enterprise must be taught and the practical method of problem solving must be applied.
One of the key phrases is “the betterment of mankind”. This definition of engineering is now used as a yard stick in reputable engineering schools to grade PhD theses. Any new technology must be commercialized and used by consumers before it can be valuable to society and any new technology that is not utilized for betterment of mankind is not valuable to society. This definition will improve the way engineering is taught at the bachelor and post-graduate level.
Many of today’s leaders are engineers. A list of Prime Ministers, Presidents and CEOs will contain many engineers. What are the qualities that we wish to have in tomorrow’s leaders? Most people will agree engineering education is the best training to nurture thinking and the thought process. Therefore, how do we tune our engineering education to produce the best cognitive thinking? What is the best way to tap the resources of both sides of the brain; left and right- neurolinguistic and programming? How to remove the filters that alter our responses to conditions and pre conditioning – be able to realize a paradigm shift. To be extroverted and introverted at the same time – to be the best whether in a big community or among the private few. Command the ability to think and yet feel, to judge and yet perceive, to make decision in both regimented and chaotic situations. Our current engineering education already contains many such elements.
One who is trained or professionally engaged in a branch of engineering
The first tool in the required set of tools is scientific knowledge, the fundamental basics of engineering – fundamental principals and laws. These must be taught and understood. An engineer should be able to perform higher-level math and science correctly due to the decision-making he or she will be required to make in the job duties. Many times calculations performed will have an impact on personnel, and these calculations have to be accurate.
When you drive over a bridge or sit down in an air-plane seat, you are trusting that an engineer performed the calculation correctly. As engineering educators, it is our main task to instil the engineering fundamentals. A second task is to instil integrity. When you drive over a bridge or sit down in an air-plane set you trust that engineer has faithfully performed the calculations.
Before 1800, the study of engineering was by apprenticeship, which led engineering students into specific areas like mining and bridge design. At West Point in the early 1800s, there was mechanics and military engineering, which then translated to our more formal form of civil engineering.
Next, the auto-mobile era arrived along with mechanical engineering. Then the air-plane era arrived along with aerospace engineering. Next humans wanted to go to space and came up with aerospace engineering. Along the way came other needs – electricity, computers and chemicals, which all were economically driven and thus the formal teaching of engineering was established.
Engineering is reaction process that formalizes the obvious in mathematical terms to the public. Presently, biological chemical engineering and nano engineering are being studied do to market demand. The educational institutions must keep abreast of the needs of society in terms of the new demands. The breakdown of engineers required at different stages of country development also varies. In a developing country, graduating aerospace engineers might not be optimal if water, sanitation hygiene or basic necessities were not resolved first. In a developed country graduating 50%, agricultural engineers may not be the optimal.
The current employability of engineers in the field of engineering is rather surprising. Many graduate engineers never get to practice engineering but only apply the expertise gained to contribute in their respective different career paths.
Numbers of employability also tells a story:
|Ease of Employability Courses|
|Architecture & city planning||100|
|Medicine & dentistry||100|
|Computer science & IT||46|
|Economy & business||33|
|Science & similar||28|
|Arts & similar||24|
|Technical & similar||20|
|Arts & humanity||16|
|Agriculture & related||0.7|
The system is producing more engineers but only 62% are employed in engineering, therefore another 38% look at other economic growth areas. The question is not having the right number but the right type of engineering background. Therefore, part of the debate should be on how to tally the supply-demand. Future plans should decide where education emphasis should be concentrated.
A person who uses scientific knowledge to solve practical problems
The key of engineering education is scientific knowledge. Engineering education should not be modified to align with the current and latest fashions. Engineering fundamentals do not change and have to be instilled in the young engineers.
Having said this, engineers can and should serve the society. They should learn business and public administration after their engineering education, or they should seek partners who are purely trained in these disciplines. Leaders capitalize on their strengths and seek partners to make up where they are weak.
One who operates an engine
Many engineers today operate very complex engines. Common names include chemical plants, automobile manufacturing, and power generation. At engineering colleges, the instructors will put tools into the students toolbox. On the job, the engineering manager instructs the new engineer how to utilize his tools, based on the type of engine that the engineer is operating. The engineer manager will arrange on the job training that utilizes the engineer’s set of tools for a peculiar industry.
Given the rapid advancement of technology, specific job training will not prepare engineers for an entire career, therefore engineers should not be trained for specific jobs, but educated in the basic engineering skills and be prepared for lifelong learning.
Many factors are influencing the engineering industry and are changing the work place environment. Some of the factors include:
- Increased use of teams – Industry and academe will need to support the development of professional skills.
- Globalization – Engineers will be interfacing with colleagues and clients in other countries. When doing so they must protect their employers’ intellectual assets. They must also demonstrate that their contributions are worth their labour costs.
- Growth of small business – More engineers will work for smaller employers in environments that require an even broader range of skills and knowledge.
- Scientific advances – As new technologies are developed, engineers will need to retool more frequently.
- High throughput techniques and speed-based R&D – As the means of developing new products and processes change, so will the responsibilities and job scope of engineers.
- Economic uncertainty – Job market fluctuations will require engineers to have increased flexibility and mobility. Engineers will need to allow for opportunities outside their geographic areas and be prepared to relocate as necessary. Maintaining skill sets and institutional knowledge will become more of a challenge for employers as engineers relocate.
One who skillfully or shrewdly manages an enterprise
The engineer progresses from someone who barely knows how to take his or her tools out of the tool box to a master craftsman. They become a manager of an enterprise. The manager has several roles. They must train the new engineers, must operate the engine correctly, and they must review the economics of the enterprise. They must have technical, economic and people skills - not a commonly found combination. It is easily to find two of the three; it is difficult to fine all three skills in one person.
To have successful careers, engineering will need to:
- Be masters of their discipline
- Recognize the risks inherent in a changing industry
- Develop critical thinking skills
- Demonstrate the ability to learn
- Pursue lifelong learning
- Embrace the emergent technologies
- Look for rewarding and stimulating opportunities
- Be curious (play ‘what if…’)
- Find mentors and be a mentor
- Be effective communicators
- Be goal-oriented, but flexible
- Understand the strategies to improve corporate performance (operational excellence, product leadership, or customer service) and align personal development strategies appropriately
- Determine how to contribute to success of company
- Be responsible and exercise caution with new materials and technologies
- Be committed to leverage science against the needs and wants of our society
A person who harnesses resources for betterment of mankind and his environment
What type of person can harness resources for the betterment of mankind? Meyers and Briggs has a 16-type system where they rate personalities based on answers to a questionnaire. People are either:
- Introverted or Extroverted
- Sensing or Intuition
- Thinking or Feeling
- Judgemental or Perceiving
Most engineers are rated Introverted – Sensing -Thinking and Judgmental (ISTJ).
Extroverted people are outgoing and get their energy from others, and they feel comfortable with and like working in groups. Introverted people are not normally good at public speaking therefore, they should select the correct media to communicate their agenda. For example, the incoming CEO of a Fortune 500 Company was a very reserved person. Therefore, he set up an internal blog site to communicate his ideas and reach out to all employees. In the blog site’s forum, employees can voice anything anonymously. Anything he promised on the forum itself is executed. This is how he communicates and displays his accountability - despite not a charisma speaker.
Sensing people describe object and situations with direct output of five senses. Display skills by hands-on execution of work. This is the traditional strength of an engineer.
Intuition people work from the big picture to the facts. They place great trust in insights, symbols, and metaphors and less in what is literally experienced.
Feeling types of people believe that being tactful is more important than telling the “cold truth”. Thinking people believe telling the whole truth is more important than being tactful.
Thinking is not just to solve a problem and an engineer, who solves a problem, has solved only one problem. Today and tomorrow we need strategists – an engineer, who fore sees a problem and solicited resources to resolve the situation before the problem evolves, therefore eliminating the issue. The strategist put the first engineer out of job but reduced the cost of a product/service for the benefit of consumers. This may sound ironic but the first engineer is a cost, an expense and a liability to the society.
Perceiving people sometimes focus so much on adapting to the moment that they do not settle on a direction or plan. Judgemental people create systems to judge, regulate, audit and improve. The motivation must be improve and create value, therefore do not judge if does not create value. This is the greatest weakness of many engineers is that they diminish value for sake of correctness, and again society does not gain from this type of engineer.
To meet the challenge of employability or marketability the engineer will still be judged by what tools he or she has in their toolbox. In the future engineers, as well as other people, will need to have more skills to stay employable. Today in developed countries as much as 25% percent of the population has 16 or more years of education.
The question for individual engineers is what are they intending to contribute as an engineer. They then therefore must better equip themselves with technical know how or risk being phased out. As a manager, their toolbox must include materials such as business and public administration.
Many factors have the potential to reshape or redirect the engineering world. In the event of a crisis, drastic changes are likely to occur. However, the world will continue to evolve at an increasingly rapid pace even without the impact of unpredictable events. The significant changes in responsibilities and expectations for engineers that have occurred over the last ten years will continue during the next ten years. Given the rapid advancement of technology, specific job training will not prepare engineers for an entire career – they will need a solid foundation of basic engineering fundamentals along with the ability and desire to continue learning.