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Module 6: EFFLUENT TREATMENT AND RESIDUALS MANAGEMENT Program for North American Mobility in Higher Education.

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Presentation on theme: "Module 6: EFFLUENT TREATMENT AND RESIDUALS MANAGEMENT Program for North American Mobility in Higher Education."— Presentation transcript:

1 Module 6: EFFLUENT TREATMENT AND RESIDUALS MANAGEMENT Program for North American Mobility in Higher Education

2 Structure of this module This module is divided into 3 tiers, each with a specific goal: Tier 1.- Basic introduction Tier 2.- Case study of the pulp & paper sector Tier 3.- Open-ended problem

3 Tier 1. Contents: 1. Introduction 2. Industrial pollution problems. The petroleum industry. The petroleum industry. The pulp and paper industry. The pulp and paper industry. 3. Programs for reducing pollution. 4. Treatment processes. 5. Process selection. 6. Volume and disposal reduction.

4 Tier 1 Tier I: Introductory concepts Effluent Treatment and Residuals Management

5 G o a l s: Tier 1 To provide information about the significance of treating effluents from industry and others facilities (or sources) To extreme the necessity of minimize pollutant concentration in the effluents and reduce the wastes production, and, To suggest strategies to reduce pollutant wastes production and their emission to the environment

6 What is pollution? Pollution means: …changes in the physical, chemical and biological characteristics of air, land and water …harms for the human and other living species, and, …degradation of the ecosystems...the undesirable state of the natural environment being contaminated with harmful substances as a consequence of human activities For example, Water Pollution refers to contaminants in aquatic ecosystems (streams, lakes, etc) which render them unfit for a particular use. Tier 1

7 Pollutants can reach: 1. Air 2. Water 3. Solid waste This module focuses on water pollution from industrial sources Tier 1

8 Water standards: Drinkable Recreation: swimming, fishing. Irrigation Water impurities may or may not be harmful; it depends on: The amounts and nature of these impurities, The next use to which the water will be put, and The tolerance of these impurities for the next use. Tier 1

9 Types and characteristics of wastewaters: Contaminants Reason for importance Physical suspended solids They can lead to the development of sludge deposits. Chemical biodegradable organics When discharged untreated to the environment, they lead to the depletion of natural oxygen resources. Nutrients If discharged, they can lead to water pollution. Hazardous Because of their characteristics (e.g.,toxicity, flammability) are dangerous for human health and the environment. Heavy metals They can negatively impact upon biological waste treatment processes. Dissolved inorganic solids They are result of water use, and may have to be removed if the wastewater is to be reused. Biological pathogens Communicable diseases can be transmitted by the pathogenic organism in wastewater. Tier 1

10 Water standards Tier 1 Industrial effluent standards ParameterMexico a USA b Canada c Total suspended solids, (mg/l) BOD 5, (mg/l) pH

11 Tier 1

12 BOD What is BOD? BOD By definition, BOD is the quantity of oxygen required for the stabilization of the oxidizable organic matter present over 5 days of incubation at 20 o C; that can be explained as a measure of the oxygen required by microbes to degrade a sample of effluent. The organic content of the water can be estimated by the BOD. Tier 1

13 Why should we minimize the use of water? Water is such an important part of many manufacturing processes that we must consider Effluent Treatment as a part of the main process because of the great amount always involved. Water is abstracted from aquifers and rivers, treated and supply to industries and homes for different uses; used water is supposed to be treated and discharged again into the rivers. Most of the times, this water returns to its natural environment but unfortunately, with a greater heat content or with some substances added. Tier 1

14 It is also important to minimize use of water because of several reasons: Fresh water is often scarce. High costs involved operating effluent treatment plants. Fresh water is often scarce. High costs involved operating effluent treatment plants. Difficult to separate all the elements that pollute water. Difficult to separate all the elements that pollute water. Tier 1 Why should we minimize the use of water?

15 Industrial pollution problems Tier 1

16 Industrial pollution problems: The main pollution problems are related to : Increasing use of water for agriculture. The increase of aqueous effluent to receiving water. Population growth. Industrial products and services. The mental, technical, financial, regulatory and institutional barriers to implement preventive modern technologies. RESULTS: Ecosystems decline. Industrialization social costs. The increase of human diseases The increase of human diseases. Tier 1

17 The petroleum industry

18 The Petroleum Industry: Crude oil refining operations involve extracting useful petroleum products from crude oil. Crude oil contains fractions of napthas, gasoline, gas oils, diesel fuel, asphalt, jet fuel and lubrication fuels. Large quantities of production wastes are produced during exploration and production: Wastewater Solid waste Toxic pollutants Tier 1

19 Production wastes in the petroleum industry can be grouped broadly into 2 classes: Wastes related to drilling including chemical additives: treatment and disposal of oil drilling wastes takes place either on or off the drilling site. Wastes related to oil production, primarily produced water: The volume of produced water exceeds the volume of drilled wastes. If environmental quality standards are not exceeded the remainder may be discharged to surface waters. The majority of produced water is disposed of underground through injection wells and it is permitted under U.S. EPA control programs. The Petroleum Industry: Tier 1

20 What is refinery effluent? Petroleum refineries use large volumes of water in their processes. The wastewater contains hazardous chemicals: Tier 1

21 Refinery wastes: Emissions from refineries include Emissions from refineries include: Sulfur oxides Nitrogen oxides Benzene, toluene and xylene VOC Wastewater containing BOD levels Heavy metals Tier 1

22 PollutionApproximate Quantities Cooling systems m 3 of wastewater generated per ton of crude. Polluted wastewater BOD mg/l COD mg/l phenol mg/l oil mg/l (desalted water) oil 5000 mg/l in tank bottom benzene mg/l heavy metals mg/l Solid waste and sludge 3 to 5 kg per ton of crude (80 % should be considered as hazardous waste because of the heavy metals and toxic organic presence). VOC emissions 0.5 to 6 kg/ton of crude. Others emissions BTX (Benzene, Toluene and Xylene) 0.75 to 6 g/ton of crude Sulfur oxides kg/ton of crude Nitrogen oxides kg/ton of crude Tier 1 Wastes generated: (Pollution Prevention and Abatement Handbook World Bank Group)

23 Tier 1 The pulp and paper industry

24 How paper is made: Most of the raw material needed for paper manufacture is supplied by trees. The main steps in the pulp and paper manufacture are raw material preparation, such as wood debarking, and chip making; pulp manufacturing; pulp bleaching; paper manufacturing and fiber recycling. Pulp mills and paper mills may exist separately or as integrated operations. The characteristics of the paper (smoothness, glazed finish) are given by a process called calendering. The paper undergo coating, whereby a thin layer of coating pigment or filler is spread onto the paper surface. Tier 1

25 Pulp and paper industry: The pulp and paper industry has made significant steps toward conserving water and energy. Significant water reductions are achieved through better reuse methods and by separating cooling water from process water. The waste streams generated in this industry are best classified by their origins as show in the next slide. Tier 1

26 Types of waste products in the pulp and paper industry: Material originated in raw materials (dirt and bark with wood). Nonfiber components in wood. Contaminants in waste paper and make-up chemicals. Reaction products (dissolved wood substance from mechanical or chemical action). Fiber fragments. By-products of chemical recovery and combustion. Fiber and nonfiber process looses and discharges of water, air and heat. Tier 1

27 The pulp and paper industry Water use and effluent discharges: Liquids discharges Liquids discharges from the process contain solids, mainly fiber, fillers, and colloidal and dissolved material. The fiber and fillers are minimized and reused. Colloidal and dissolved materials are by-products of the refining of the fibers or carried over from the pulp mill. Discharges of dissolved material are minimized by washing the stock and displaced carryover from pulp mills and by practicing good water reuse strategies that reduce the volume and concentrations of waste in wastewater. Tier 1

28 Programs for reducing pollution Tier 1

29 Government programs for reducing pollution: For sustainable development, governmental pollution prevention programs can best counteract the pressure to invest in end of pipe pollution solutions by demonstrating the economic and environmental benefits of a source reduction approach, making technical information available and providing technical assistance. EPA has been working with industry and government representing environmental, community and work force issues to prevent pollution at the source prior to end of pipe treatment. Tier 1

30 Laws such as NEPA, TCSA, CAAA and PPA remain outside the scope of most pollution control work. The following options were suggested for USEPA for moving forward interaction in the US: 1. Add multi-media provisions to the existing regulations. 2. Correct laws in other policy sectors with environmental measures. 3. Make NEPA a stronger statute. 4. Make TSCA a law which can use EPA programs to control and reduce toxic substances. 5. Establish pollution prevention approaches. Tier 1 Government programs for reducing pollution:

31 Programs for reducing pollution: Manufacturers could implement a variety of improved management procedures that would aid pollution reduction: Environmental audits. Identify (inventory) and correct problems (strategies to achieve reductions) that generate wastes. Regular preventive maintenance. Inspection, maintenance and replacement of equipment. Material handling and storage. Emissions of hazardous material must be avoided. There should be labels of all containers and first aid recommendations. Employee training. Well informed employees are better able to make valuable waste reduction suggestion. Operating manual and record keeping. Good facility documentation: process procedures, control parameters, hazards and operator responsibilities. Tier 1

32 Environmental programs: Some industries may see no difference between end of pipe pollution control and a front end pollution prevention control. The importance is that those industries may not go beyond the first stage of waste reduction. As the environmental concern deepens, industries have to move further up the production chain: End of pipe solution to wastes and pollutants; and later End of pipe solution to wastes and pollutants; and later Internal process modifications to reduce emissions and wastes, and eventually Internal process modifications to reduce emissions and wastes, and eventually Redesign products to achieve a maximum level of recycling of raw materials and minimization of wastes after the products are used. Redesign products to achieve a maximum level of recycling of raw materials and minimization of wastes after the products are used. Tier 1

33 Some measurements to save water: Keep water effluent streams separated. Keep water effluent streams separated. Reuse water as close to source as possible. Reuse water as close to source as possible. Recycling whenever it is possible. Recycling whenever it is possible. Better control of usage with automated systems. Better control of usage with automated systems. Checking and control of leaks. Checking and control of leaks. When buying new equipment, evaluate water-efficiency models including accessories. When buying new equipment, evaluate water-efficiency models including accessories. Reducing the quantities of chemicals so that the amount of dilution water will be reduced. Reducing the quantities of chemicals so that the amount of dilution water will be reduced. Tier 1

34 Reusing water: It is not only possible but necessary to reuse wastewater of a process stream before it leaves the plant accomplished by piping, diluting or treating some of the effluents before using them again. Some plants are now using closed systems, so that there are no water discharges. Zero discharges has been practiced in locations where water is scarce, and may involve technologies for removing suspended and dissolved solids. Complete demineralization is relatively expensive, however, in some cases wastewater discharges can be reduced significantly with other less expensive technologies. Tier 1

35 Treatment processes Tier 1

36 Expectations of a water treatment program: The expectations from a water treatment program should be integrated to include all aspects of the program, from the proposal through to the implementation stages. Tier 1

37 Treatment Program As we will see in the next diagram, the expectations that a good treatment program should give us are listed below: Overview of a new or existent problem. Overview of a new or existent problem. Lab study of all system and water composition. Lab study of all system and water composition. Submit a proposal. Submit a proposal. Program implementation. Program implementation. Monitoring to optimize. Monitoring to optimize. Use of modern treatment techniques. Use of modern treatment techniques. Tier 1 Program under control

38 Treatment Program New or Problem System Plant Study Lab Study Proposal Implement Program Follow-up New Product Technology System under control Tier 1

39 Wastewater treatment processes: Wastes are generated by every industrial enterprise, and this wastes can either be liquids or solids. Wastewater treatment can be divided into three stages: 1.Primary treatment 1.Primary treatment that uses physical operations to remove free oil and/or suspended solids. 2.Secondary treatment 2.Secondary treatment to remove dissolved contaminants through chemical or biological action, and 3.Tertiary treatment 3.Tertiary treatment for the removal of residual contaminants. Tier 1

40 Separation order This list shows how separation is carried out: Primary treatment Sedimentation Aeration Secondary treatment Tertiary treatment Tier 1

41 Treatments… Primary treatment prepares the wastewater for biological treatment. Large solids are removed by screening, and grit. Equalization in a mixing basin, levels out the flows variation and concentrations. Neutralization, where required, follows equalization. Oils, greases and suspended solids are removed by flotation, sedimentation of filtration. Secondary treatment is a biological degradation of soluble organic compounds from input levels of mg/l BOD or greater to effluent levels under 15 mg/l. Aerobic treatment in an open vessel is done. After biotreatment, the microorganisms and solids suspended are allowed to settle. Tier 1

42 Treatments… The tertiary treatment remove specific residuals. By filtration, suspended colloidal solids can be removed; adsorption removes organics by granular activated carbon (GAC); and chemical oxidation also removes organic compounds. Tertiary systems have to treat great amounts of wastewater, so they are expensive. When streams rich in heavy metals, pesticides or other substances that may pass through primary treatment and inhibit biological treatment are present, in-plant treatments are necessary. Precipitation, activated carbon adsorption, chemical oxidation, air or steam stripping, wet air oxidation, ion exchange, reverse osmosis are some of the methods useful when in-plant treatments are to be used. Tier 1

43 The tertiary treatment… Tertiary treatment is a polishing step. Its importance is that rather than have to find solutions at the end of pipe, where primary and secondary treatments are used to, it is possible to minimize some toxics or hazardous components in the process before they are combined with other less hazardous. Biological treatment usually produces a 30/20 effluent with no more than 30 mg/l suspended solids and 20 mg/l BOD. Tier 1

44 Tertiary treatment However, river flows have decreased owing to drought conditions. In these circumstances, new limits are imposed on the quality of the final effluent. The treatment processes beyond the secondary treatment to achieve the required limits in the process are well known as tertiary treatments. Tier 1

45 In plant treatment Before end of pipe wastewater treatment, a program of waste minimization should be initiated. 1.Recirculation 1.Recirculation. In the paper board industry, white water from a paper machine can be put through a save all to remove the pulp and fiber and recycled to various points in the process. 2.Segregation 2.Segregation. Clean streams are separated for direct discharge. 3.Disposal 3.Disposal. In many cases, the total discharge BOD and suspended solids can be reduced by removal of residue in semidry state for disposal. 4.Reduction 4.Reduction. The use of automatic cutoffs can reduce the wastewater volume. 5.Substitution 5.Substitution. The substitution of chemical additives of a lower pollutional effect in processing operations. Tier 1

46 . Wastewater treatment processes: Process selection

47 Figure 1. Conceptual treatment program for organic and toxic industrial wastewater Tier 1 Organic streams Streams containing heavy metals Mineral streams Source control Figure 3. EqualizationNeutralization Oil/grease removal Suspended solids Biological treatment Final disposal Biodegradable volatile Toxic and/or nonbiodegradable To define the wastewater treatment problems, a preliminary analysis should be carried out: For wastewaters containing nontoxic organics, process design criteria can be obtained from lab studies. (Eckenfelder, 2000)

48 Source treatment: Source reduction is any activity that reduces or eliminates the generation of hazardous wastes at the source The fundamental goal is to enact changes in consumption, use and waste generation patterns associated with products Tier 1

49 Source treatment: Source treatments involves different definitions of source reduction, but the general consensus appears to be that include any in- plant actions to reduce the quantity or the toxicity of the waste at the source. Examples include equipment modification, design and operations changes of the process and products and substitution of raw materials. Tier 1

50 Figure 2. Laboratory studies for heavy metals/volatile organics Tier 1 Priority pollutants scan and bioassay Fed batch reactor Long-term biodegradation Priority pollutants scan and bioassay Equalized sample Air or steam stripping Chemical oxidation reduction Precipitation Source treatment Granular activated carbon Powder activated carbon Reverse osmosis Ion exchange Nondegradable/ toxic Degradable VOC/NH 3 Heavy metals Priority pollutants/toxic TDS/inorganics start (Eckenfelder, 2000) When toxic and nontoxic organics and inorganics are present, it is necessary to evaluate the existence of heavy metals or volatile organics.

51 Figure 3. Treatment of toxic wastewater: In-plant treatment Tier 1 Ionexchange Filtration Precipitation Oxidationreduction Polymericresins Granularcarbonadsorption Anaerobictreatment Wet air oxidation Chemicaloxidation Reverseosmosis Air or steam stripping ProcesswastewaterHeavymetalsOrganicchemicals Volatileorganicsammonia To discharge recycle or treatment If the wastewater is nonbiodegradable or toxic, it should be considered source treatment or in-plant modification. (Eckenfelder, 2000)

52 Methods for suspended solids removal Sedimentation is the more common technique in wastewater treatment because it involves little mechanical equipment and it is very stable to operate. However, there are some situations where flotation is a better choice. Flotation is a good technique for solids removal when the density difference between water and the solids is marginal, or the solids have a high fat or oil content. Tier 1

53 Methods for suspended solids removal Coagulation is employed for removal of waste materials in suspended or colloidal form. Colloids are particles within the size range of 1 nm to 0.1 nm, do not settle out on standing and can not be removed by conventional physical treatment processes. Precipitation. In the water treatment, the precipitation process is used for softening (removal of the hardness caused by calcium and magnesium) and removal of iron and manganese. Tier 1

54 Sedimentation: Reduce solids by at least 50%, with proportional reduce of BOD. Addition of chemicals to assist settlement by coagulating particles or chemical precipitation can be essential. Can have acceptable discharge standards with regular desludging without a secondary treatment. Primary tanks are desludged at intervals of between 8 and 24 hours. Secondary settlement follows any form of biological aeration or filtration to produce an effluent low in solids. Particularly demanding discharge consents may dictate a tertiary treatment to remove solids and BOD by a further 50%. Tier 1

55 Flotation: Dissolved air flotation, which is a common technique. This technique basically consists on injecting an aqueous stream containing dissolved air into the wastewater. The dissolved air forms bubbles when it comes out of solution and carries suspended particles, which tend to concentrate at the bubble wastewater interface, to the surface, where they form an emulsion. Tier 1

56 Flotation: General diagram for flotation methods:

57 Coagulation: Paperboards wastes can be effectively coagulated with low dosages of alum. Silica or polyelectrolyte will aid in the formation of a rapid settling floc. Wastes that contain emulsified oil can also be clarified by coagulation. For effective coagulation, alkalinity should first be added,. After addition of alkali and coagulant, a rapid mixing is recommended. Tier 1

58 Precipitation: Chemical precipitation in wastewater treatment involves the addition of chemicals to alter the physical and chemical state of dissolved and suspended material and to facilitate their removal. It is usually combined with coagulation, flocculation, separation. Principle: Dissolved compounds, for instance heavy metal ions, are brought into their insoluble hydroxides by pH increase through dosing of lime or NaOH. Using coagulation, flocculation techniques these small hydroxide nuclei become larger flocs for separation. With proper precipitants these flocs also serve as entrapment for other dissolved (organic) compounds; a form of co-precipitation. Tier 1 Chemical precipitationChemical precipitation in wastewater treatment involves the addition of chemicals to alter the physical and chemical state of dissolved and suspended material and to facilitate their removal. It is usually combined with coagulation – flocculation – separation.PrincipleDissolved compounds, for instance heavy metal ions, are brought into their insoluble hydroxides by pH increase through dosing of lime or NaOH. Using coagulation, flocculation techniques these small hydroxide nuclei become larger flocs for separation. With proper precipitants these flocs also serve as entrapment for other dissolved (organic) compounds ; a form of co-precipitation.Chemical precipitationChemical precipitation in wastewater treatment involves the addition of chemicals to alter the physical and chemical state of dissolved and suspended material and to facilitate their removal. It is usually combined with coagulation – flocculation – separation.PrincipleDissolved compounds, for instance heavy metal ions, are brought into their insoluble hydroxides by pH increase through dosing of lime or NaOH. Using coagulation, flocculation techniques these small hydroxide nuclei become larger flocs for separation. With proper precipitants these flocs also serve as entrapment for other dissolved (organic) compounds ; a form of co-precipitation. Chemical precipitationChemical precipitation in wastewater treatment involves the addition of chemicals to alter the physical and chemical state of dissolved and suspended material and to facilitate their removal. It is usually combined with coagulation – flocculation – separation.PrincipleDissolved compounds, for instance heavy metal ions, are brought into their insoluble hydroxides by pH increase through dosing of lime or NaOH. Using coagulation, flocculation techniques these small hydroxide nuclei become larger flocs for separation. With proper precipitants these flocs also serve as entrapment for other dissolved (organic) compounds ; a form of co-precipitation.Chemical precipitationChemical precipitation in wastewater treatment involves the addition of chemicals to alter the physical and chemical state of dissolved and suspended material and to facilitate their removal. It is usually combined with coagulation – flocculation – separation.PrincipleDissolved compounds, for instance heavy metal ions, are brought into their insoluble hydroxides by pH increase through dosing of lime or NaOH. Using coagulation, flocculation techniques these small hydroxide nuclei become larger flocs for separation. With proper precipitants these flocs also serve as entrapment for other dissolved (organic) compounds ; a form of co-precipitation.

59 Heavy Metals Removal: Tier 1 HEAVY METALS REMOVAL TECHNOLOGIES Conventional precipitation Hydroxide Sulfide carbonate coprecipitation Enhanced precipitation Dimethyl thio carbamate Diethyl thio carbamate Trimercapto-s-triazine, trisodium salt Other methods Ion exchange Adsorption Recovery opportunities Ion exchange Membranes Electrolytic techniques

60 The Biological Treatment Tier 1 Influent wastewater Physical and chemical treatment Biodegradable High strength Anaerobic treatment Discharge PACT Inhibitory Nondegradable fraction Polished effluent Dispersed growth system Complete mix system Readily degradable Nitrogen removal required Fixed Growth system Discharge Intermittent process Nitrification/ Denitrification system Plug flow system Selector system Polished effluent Highstrength Yes No (Eckenfelder, 2000) When biological treatment is needed, there are several options:

61 The biological treatment The biological treatment: typical operating parameters and dimensions Tier 1 Treatment method Mode of operation Degree of treatment Land requirementsEquipmentRemarks Lagoon Intermittent or continuous discharge; facultative or anaerobic Intermediate Earth dug; days retention Odor control frequently required Activated lagoons Completely mixed or facultative continuous basins High in summer; less in winter Earth basin, 8-16 ft deep, 8-16 acres/(million gal/d) Pier-mounted or floating surface aerators or subsurface diffusers Solids separation in lagoon; periodic dewatering and sludge removal Activated sludge Completely mixed or plug flow; sludge recycle > 90% removal of organics Earth or concrete basin; 12p20 ft deep; ft3/(million gal/d) Diffused or mechanical aerators; clarifier for sludge separation and recycle Excess sludge dewatered and disposed of Trickling filter Continuous application; may employ effluent recycle Intermediate or high, depending on loading ft /(million gal/d) Plastic packing ft deep Pretreatment before POTW or activated sludge plant RBC Multistage continuousIntermediate or highPlastic disks Solids separation required Anaerobic Complete mix with recycle; upflow or downflow filter, fluidized bed; upflow sludge blanket Intermediate Gas collection required; pretreatment before POTW or activated sludge plant Spray irrigation Intermittent application of waste Complete; water percolation into groundwater and runoff to stream gal/(min.acre) Aluminum irrigation pipe and spray nozzles; movable for relocation Solids separation required; salt content in waste limited (Eckenfelder, 2000)

62 Advanced wastewater treatments Advanced wastewater treatment is defined as the processes that remove more pollutants from wastewater than the conventional treatments. This term may be applied usually as tertiary treatment, but most of their goals are to remove nitrogen, phosphorus, and suspended solids. Advanced treatments include: Chemical coagulation of wastewater Granular media filters Ultrafiltration Nanofiltration Wedge-wire screens Microscreening Diatomaceous earth filters Tier 1

63 Volume and disposal reduction

64 Volume reduction Volume reduction can be used to reduce treatment cost and to reduce handling and disposal costs for residues remaining after treatment. Volume reduction can be accomplished by using a variety of methods: Reuse of treated wastewater and wastes Reuse of treated wastewater and wastes Treatment modifications to reduce solid residues Treatment modifications to reduce solid residues Segregated treatments to reduce hazardous waste mixtures Segregated treatments to reduce hazardous waste mixtures Incineration to reduce waste volume and to render a hazardous waste nonhazardous. Incineration to reduce waste volume and to render a hazardous waste nonhazardous. Tier 1

65 Reduction of waste production and disposal volumes Simple dewatering: the sludge is discharged into a series of tanks and allowed to settle. Top water can then be decanted. This method reduce the volume of sludge for disposal. Composting: the material is mechanically turned at intervals, force aerated and often contained in a building where heat losses, odor and water content can be controlled. Tier 1

66 Digestion: is the slow degeneration of the organic content of sludge by obligate anaerobic bacteria to simpler compounds- carbon dioxide, water and anions (nitrate, sulphate, phosphate). Digestion is one of the few sludge treatment processes in which a significant reduction of pathogens is possible. The digestor gas produced is 65-70% methane, 30-34% carbon dioxide, and traces of sulphur compounds. The collected gas is burnt in a boiler to keep the digestor warm and the excess put to further heating or power generation purposes. Tier 1 Reduction of waste production and disposal volumes

67 Incineration: its main advantages lie in the complete destruction of organic compounds, the ash being inert and usually less than 25% of the original sludge volume. Most incinerators are of the fluidized bed variety. Tier 1 Reduction of waste production and disposal volumes

68 A waste management diagram… Tier 1 Waste disposal Waste treatment Waste recycle Upgrade operation Redesign process Substitute raw material Increasing Effectiveness of waste management

69 Multiple choice questions Tier 1

70 Tier 1: Quiz 1. What is pollution? a) Pollution refers to harmful environmental contaminants and to the act or process of polluting the environment. b) Any undesirable change in the characteristics of the air, water, soil or food that can affect the health called pollution. c) Unwanted chemicals or other materials found in the environment. Pollutants can harm human health, the environment, and property. d) All of the above. Tier 1

71 2. What is BOD? a) The quantity of oxygen required for the stabilization of the oxidizable organic matter present over 7 days of incubation at 20 o F. b) An empirical test used for measuring waste, evaluating the measure of the oxygen required by microbes to degrade a sample of effluent. c) A test used to evaluate the quantity of oxygen present in the stream. d) The quantity of oxygen required to develop a biochemical test. Tier 1: Quiz Tier 1

72 3. Why is it important to reduce hazardous contaminants? a) Because if discharged, they can lead to water pollution. b) Because of its radioactive characteristics, its effects on human health and development of cancer. c) Communicable diseases can be transmitted when in contact to them. d) Because of their dangerous characteristics for human health and the environment. Tier 1 Tier 1: Quiz

73 Tier 1 Tier 1: Quiz


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