Part I Wastewater Engineering 1 Wastewater Engineering: An Overview Every community produces both liquid and solid wastes and air emissions. The liquid waste-wastewater is essentially the water supply of the community after it has been used in a variety of applications. From arried wastes removed from residences. institutions. and commercial and industrial establishmer ogether with such groundwater surface water and stormwater as may be present. When wastewater accumulates and is allowed to go septic, the decomposition of the organic matter it contains will lead to nuisance conditions including the production of malodorous gases. In addition, untreated wastewater contains numerous pathogenic microorganisms that dwell in the human intestina tract. Wastewater also contains nutrients, which can stimulate the growth of aquatic plants, and may contain toxic compounds or compounds that potentially may be mutagenic or carcinogenic. For these reasons, the immediate and nuisance-free removal of wastewater from its sources of generation, followed by treatment, reuse, or dispersal into the environment is necessary to protect public health and the environment Wastewater engineering is that branch of environmental engineering in which basic principles of science nd engineering are applied to solving the issues associated with the treatment and reuse of wastewater. goal of wastewater engineering is the protection of public health in a manner commensurate with environmental, economic, social and political concerns. To protect public health and the environment. it is necessary to have knowledge of (D) environment,(3)the transformation and wastewater. and (5) methods for Combined sewer beneficial use or disposal of solids To provide an initial perspective on the field of wastewater engineering, common terminology is defined and introduced first Fig. 1-1 Schematic diagram of management infrastructure 1-1 Terminology In the literature, and in governmental regulations, a variety of terms have been used for individual constituents of concern in wastewater. The terminology used commonly for key concepts and terms in the field of wastewater management is summarized in Table 1-1 In some cases, confusion and undue negative perceptions arise with the use of the terms contaminants, impurities, and pollutants, which are often used interchangeably. To avoid confusion, the term constituent is used in this text in place of an individual compound or element, such as ammonia nitrogen. The term 1-1
1-1 Part I Wastewater Engineering 1 Wastewater Engineering:An Overview Every community produces both liquid and solid wastes and air emissions. The liquid waste-wastewater, is essentially the water supply of the community after it has been used in a variety of applications. From the standpoint of sources of generation, wastewater may be defined as a combination of the liquid or water-carried wastes removed from residences, institutions, and commercial and industrial establishments, together with such groundwater, surface water, and stormwater as may be present. When wastewater accumulates and is allowed to go septic, the decomposition of the organic matter it contains will lead to nuisance conditions including the production of malodorous gases. In addition, untreated wastewater contains numerous pathogenic microorganisms that dwell in the human intestinal tract. Wastewater also contains nutrients, which can stimulate the growth of aquatic plants, and may contain toxic compounds or compounds that potentially may be mutagenic or carcinogenic. For these reasons, the immediate and nuisance-free removal of wastewater from its sources of generation, followed by treatment, reuse, or dispersal into the environment is necessary to protect public health and the environment. Wastewater engineering is that branch of environmental engineering in which basic principles of science and engineering are applied to solving the issues associated with the treatment and reuse of wastewater. The ultimate goal of wastewater engineering is the protection of public health in a manner commensurate with environmental, economic, social, and political concerns. To protect public health and the environment, it is necessary to have knowledge of (1) constituents of concern in wastewater, (2) impacts these constituents when wastewater is dispersed into the environment, (3) the transformation and long-term fate of these constituents in treamtent processes, (4) treatment methods that can be used to remove or modify the constituents found in wastewater, and (5) methods for beneficial use or disposal of solids generated by the treatment systems. To provide an initial perspective on the field of wastewater engineering, common terminology is defined and introduced first. Fig. 1-1 Schematic diagram of a wastewater management infrastructure 1-1 Terminology In the literature, and in governmental regulations, a variety of terms have been used for individual constituents of concern in wastewater. The terminology used commonly for key concepts and terms in the field of wastewater management is summarized in Table 1-1. In some cases, confusion and undue negative perceptions arise with the use of the terms contaminants, impurities, and pollutants, which are often used interchangeably. To avoid confusion, the term constituent is used in this text in place of an individual compound or element, such as ammonia nitrogen. The term
characteristic is used to refer to a group of constituents, such as physical or biological characteristics The term "sludge"has been used for many years to signify the residuals produced from wastewater treatment, in 1994, the Water Environment Federation adopted a policy defining"biosolids as a primarily organic, solid wastewater treatment product that can be recycled beneficially. In this policy, " solids"are defined as the residuals that are derived from the treatment of wastewater solids that have been treated to the point at which they are suitable for beneficial use are termed"biosolids. In this text. the terms of solids and biosolids are used extensively, but"" continues to be used. especially in cases where 1-2 Impact of Regulations on Wastewater Engineering From about 1900 to the early 1970s, treatment obiectives were concerned primarily with(1) the removal of colloidal, suspended, and floatable material. (2)the treatment of biodegradable organics, and(3) the on of pathogenic organisms. Implementation in the United States of the Federal Water Pollution Control Act Amendments of 1972(Public Law 92-500). also known as the Clean Water Act(CWA stimulated substantial changes in wastewater treatment to achieve the obiectives of "fishable and swimmable"waters. Unfortunately, these objectives were not uniformly met From the early 1970s to about 1980, wastewater treatment objectives were based primarily on aesthetic and environmental concerns. The earlier objectives involving the reduction of biological oxygen demand ( BOD), total suspended solids(TSs), and pathogenic organisms continued but at higher levels. Removal of nutrients, such as nitrogen and phosphorus, also began to be addressed, particularly in some of the inland streams and lakes, and estuaries and bays. Major programs were undertaken by both state and federal agencies to achieve more effective and widespread treatment of wastewater to improve the quality of the surface waters. These programs were based on(D) an increased understanding of the environmental effects caused by wastewater discharges:(2)a greater appreciation of the adverse long-term effects caused by the discharge of some of the specific constituents found in wastewater: and (3 )the development of national concern for the protection of the environment. As a result of these programs, significant improvements have been made the quality of the surface waters Table I-I Terminology ly used in the field of wastewater engineerin Biosolids Primarily an organic, semisolid wastewater product that remains after solids are stabilized biologically or chemically and are suitable far beneficial use Class a biosolids Biosolids in which the pathogens are reduced below current detectable Class a biosolids Biosolids in which the pathogens are reduced to levels that are unlikely to pose a threat to the public health and the environment under specific use conditions. Class b biosolids cannot be sold or given away in bags or other containers or applied on lawns or home gardens Characteristics General classes of wastewater constituents such as physical, chemical (wastew biological and biochemical Composition The makeup of wastewater, including the physical, chemical, and biological constituents Constituents Individual components, elements, or biological entities such as Contaminants Disinfection Reduction of disease-causing microorganisms by physical or chemical Effluent The liquid discharged from a processing step Constituents added to the water supply through use Non-point sources Sources of pollution that originate from multiple sources over a relatively large area Nutrient An element that is essential for the growth of plants and animals Nutrients in wastewater, usually nitrogen and phosphorus, may cause unwanted algal and plant growths in lakes and streams Point sources Pollutional loads discharged at a specific location from pipes, outfall 1-2
1-2 characteristic is used to refer to a group of constituents, such as physical or biological characteristics. The term “sludge” has been used for many years to signify the residuals produced from wastewater treatment, in 1994, the Water Environment Federation adopted a policy defining "biosolids' as a primarily organic, solid wastewater treatment product that can be recycled beneficially. In this policy, “solids” are defined as the residuals that are derived from the treatment of wastewater. Solids that have been treated to the point at which they are suitable for beneficial use are termed “biosolids.” In this text, the terms of solids and biosolids are used extensively, but “sludge” continues to be used, especially in cases where untreated solid material and chemical residuals are referenced. 1-2 Impact of Regulations on Wastewater Engineering From about 1900 to the early 1970s, treatment objectives were concerned primarily with (1) the removal of colloidal, suspended, and floatable material, (2) the treatment of biodegradable organics, and (3) the elimination of pathogenic organisms. Implementation in the United States of the Federal Water Pollution Control Act Amendments of 1972 (Public Law 92-500), also known as the Clean Water Act (CWA), stimulated substantial changes in wastewater treatment to achieve the objectives of “fishable and swimmable”waters. Unfortunately, these objectives were not uniformly met. From the early 1970s to about 1980, wastewater treatment objectives were based primarily on aesthetic and environmental concerns. The earlier objectives involving the reduction of biological oxygen demand (BOD), total suspended solids (TSS), and pathogenic organisms continued but at higher levels. Removal of nutrients, such as nitrogen and phosphorus, also began to be addressed, particularly in some of the inland streams and lakes, and estuaries and bays. Major programs were undertaken by both state and federal agencies to achieve more effective and widespread treatment of wastewater to improve the quality of the surface waters. These programs were based, in part, on (1) an increased understanding of the environmental effects caused by wastewater discharges; (2) a greater appreciation of the adverse long-term effects caused by the discharge of some of the specific constituents found in wastewater; and (3)the development of national concern for the protection of the environment. As a result of these programs, significant improvements have been made in the quality of the surface waters. Table 1-1 Terminology commonly used in the field of wastewater engineering Term Definition Biosolids Primarily an organic, semisolid wastewater product that remains after solids are stabilized biologically or chemically and are suitable far beneficial use Class A biosolids Biosolids in which the pathogens are reduced below current detectable levels Class A biosolids Biosolids in which the pathogens are reduced to levels that are unlikely to pose a threat to the public health and the environment under specific use conditions. Class B biosolids cannot be sold or given away in bags or other containers or applied on lawns or home gardens Characteristics (wastewater) General classes of wastewater constituents such as physical, chemical, biological, and biochemical Composition The makeup of wastewater, including the physical, chemical, and biological constituents Constituents Individual components, elements, or biological entities such as suspended solids or ammonia nitrogen Contaminants Constituents added to the water supply through use Disinfection Reduction of disease-causing microorganisms by physical or chemical means Effluent The liquid discharged from a processing step Impurities Constituents added to the water supply through use Non-point sources Sources of pollution that originate from multiple sources over a relatively large area Nutrient An element that is essential for the growth of plants and animals. Nutrients in wastewater, usually nitrogen and phosphorus, may cause unwanted algal and plant growths in lakes and streams Parameter A measurable factor such as temperature Point Sources Pollutional loads discharged at a specific location from pipes, outfalls
and conveyance methods from either municipal wastewater treatment lants or industrial waste treatment facilities Pollutants water Reclamation Treatment of wastewater fur subsequent reuse application or the act of using treated wastewater The reuse of treated wastewater and biosolids for beneficial purposes R euse Beneficial use of reclaimed or repurified wastewater or stabilized Sludge and solids Solids removed from wastewater during treatment. Solids that are treated further am termed Since 1980, the water quality improvement objectives of the 1970s have continued, but shifted to the definition and removal of constituents that may cause long-term health effects and environmental impacts. Consequently while the early treatment obiectives remain valid today. the required degree of treatment has increased significantlv and additional treatment obiectives and goals have been added. Therefore, treatment obiectives must go hand in hand with the water quality obiectives Recent regulations that ies design inc beneficial use of biosolids. In the biosolids regulation promulgated in 1993. national standards were set for pathogen and heavy metal content and for the safe handling and use of biosolids. The standards are designed to protect human health and the environment where biosolids are applied beneficially to land The rule also promotes the development of a"clean sludge(U.s. EPA, 1999 The total maximum daily load (TMDL) program was promulgated in 2000 but is not scheduled to be in effect until 2002. The Tmdl rule is designed to protect ambient water quality. A TMDL represents the maximum amount of a pollutant that a water body can receive and still meet water quality standards. A TMDL is the sum of (1)the individual waste-load allocations for point sources,(2) load allocations fo nonpoint sources, (3)natural background levels, and(4)a margin of safety (U.S. EPA, 2000). To implement the rule a comprehensive watershed-based water quality management program must be undertaken to find and control nonpoint sources in addition to conventional point source discharges. With implementation of the TMDL rule. the focus on water quality shifts from technology-based controls to preservation of ambient water quality. The end result is an integrated planning approach that transcends jurisdictional boundaries and forces different sectors. such as agriculture, water and wastewater utilities and urban runoff managers, to cooperate. Implementation of the TMDL rule will vary depending on the specific water quality objectives established for each watershed and, in some cases, will require the installation of advanced levels of treatment 1-3 Health and Environmental Concerns in Wastewater Management As research into the characteristics of wastewater has become more extensive, and as the techniques for analyzing specific constituents and their potential health and environmental effects have become more comprehensive, the body of scientific knowledge has expanded significantly. Many of the new treatment methods being developed are designed to deal with health and enviro indings of recent research. However the advancement in treatment technology effectiveness has not kept ace with the enhanced constituent detection capability. Pollutants can be detected at lower concentrations than can be attained by available treatment technology Therefore, careful assessment of health and environment effects and community concerns about these effects becomes increasingly important in wastewater management The need to establish a dialogue with the community is important to assure that health and environmental issues are being addressed. Water quality issues arise when increasing amounts of treated wastewater are discharged to water bodies that are eventually used as water supplies. The waters of the Mississippi river and many rivers in the eastern United States are used for municipal and industrial water supplies and as repositories for the esulting treated wastewater. In southern California. a semiarid region. increasing amounts of reclaimed wastewater are being used or are planned to be used for groundwater recharge to augment existing potable water supplies. Significant questions remain about the testing and levels of treatment necessary to protect human health where the commingling of highly treated wastewater with drinking water sources results in indirect potable reuse. Some professionals obiect in principle to the indirect reuse of treated wastewater for potable purposes: others express concern that current techniques are inadequate for detecting all microbial and chemical contaminants of health significance. Among the latter concerns are(1)the lack of 1-3
1-3 and conveyance methods from either municipal wastewater treatment plants or industrial waste treatment facilities Pollutants Constituents added to the water supply through use Reclamation Treatment of wastewater fur subsequent reuse application or the act of reusing treated wastewater Recycling The reuse of treated wastewater and biosolids for beneficial purposes Reuse Beneficial use of reclaimed or repurified wastewater or stabilized biosolids Sludge and solids Solids removed from wastewater during treatment. Solids that are treated further am termed Since 1980, the water quality improvement objectives of the 1970s have continued, but the emphasis has shifted to the definition and removal of constituents that may cause long-term health effects and environmental impacts. Consequently, while the early treatment objectives remain valid today, the required degree of treatment has increased significantly, and additional treatment objectives and goals have been added. Therefore, treatment objectives must go hand in hand with the water quality objectives or standards established by the federal, state, and regional regulatory authorities. Recent regulations that affect wastewater facilities design include those for the treatment, disposal, and beneficial use of biosolids. In the biosolids regulation promulgated in 1993, national standards were set for pathogen and heavy metal content and for the safe handling and use of biosolids. The standards are designed to protect human health and the environment where biosolids are applied beneficially to land. The rule also promotes the development of a “clean sludge” (U.S. EPA, 1999). The total maximum daily load (TMDL) program was promulgated in 2000 but is not scheduled to be in effect until 2002. The TMDL rule is designed to protect ambient water quality. A TMDL represents the maximum amount of a pollutant that a water body can receive and still meet water quality standards. A TMDL is the sum of (1) the individual waste-load allocations for point sources, (2) load allocations for nonpoint sources, (3) natural background levels, and (4) a margin of safety (U.S. EPA, 2000). To implement the rule, a comprehensive watershed-based water quality management program must be undertaken to find and control nonpoint sources in addition to conventional point source discharges. With implementation of the TMDL rule, the focus on water quality shifts from technology-based controls to preservation of ambient water quality. The end result is an integrated planning approach that transcends jurisdictional boundaries and forces different sectors, such as agriculture, water and wastewater utilities, and urban runoff managers, to cooperate. Implementation of the TMDL rule will vary depending on the specific water quality objectives established for each watershed and, in some cases, will require the installation of advanced levels of treatment. 1-3 Health and Environmental Concerns in Wastewater Management As research into the characteristics of wastewater has become more extensive, and as the techniques for analyzing specific constituents and their potential health and environmental effects have become more comprehensive, the body of scientific knowledge has expanded significantly. Many of the new treatment methods being developed are designed to deal with health and environmental concerns associated with findings of recent research. However, the advancement in treatment technology effectiveness has not kept pace with the enhanced constituent detection capability. Pollutants can be detected at lower concentrations than can be attained by available treatment technology. Therefore, careful assessment of health and environment effects and community concerns about these effects becomes increasingly important in wastewater management. The need to establish a dialogue with the community is important to assure that health and environmental issues are being addressed. Water quality issues arise when increasing amounts of treated wastewater are discharged to water bodies that are eventually used as water supplies. The waters of the Mississippi River and many rivers in the eastern United States are used for municipal and industrial water supplies and as repositories for the resulting treated wastewater. In southern California, a semiarid region, increasing amounts of reclaimed wastewater are being used or are planned to be used for groundwater recharge to augment existing potable water supplies. Significant questions remain about the testing and levels of treatment necessary to protect human health where the commingling of highly treated wastewater with drinking water sources results in indirect potable reuse. Some professionals object in principle to the indirect reuse of treated wastewater for potable purposes; others express concern that current techniques are inadequate for detecting all microbial and chemical contaminants of health significance. Among the latter concerns are (1) the lack of
sufficient information regarding the health risks posed by some microbial pathogens and chemical constituents in wastewater, (2 )the nature of unknown or unidentified chemical constituents and potential pathogens, and (3)the effectiveness of treatment processes for their removal Other health concerns relate to:(I)the release of volatile organic compounds( vOCs) and toxic air contaminants(TACs) from collection and treatment facilities.(2)chlorine disinfection, and(3)disinfection byproducts( DBPs). Odors are one of the most serious environmental concerns to the public. Many industrial wastes contain vocs that may be flammable toxic and odorous and may be contributors Effluents containing chlorine residuals are toxic to aquatic life, and, increasingly, provisions to eliminate chlorine residuals are being instituted. Other important health issues relate to the reduction of disinfection byproducts(DBPs) that are potential atters. To achieve higher and ore consistent microbes inactivation levels improved performance of disinfection systems must be addressed. In many communities, the issues of safety in the transporting storing, handling of chlorine are also being examined Fig. 1-2 Covered treatment plant facilities for the control of odor emissions 1-4 Wastewater Characteristics Prior to about 1940. most municipal wastewater was generated from domestic sources. After 1940. as industrial development in the U.S. grew significantlv. increasing amounts of industrial wastewater have been and continue to be discharged to municipal collection systems. The amounts of heavy metals and synthesized organic compounds generated by industrial activities have increased, and some 10.000 new As technological changes take place in manufacturing changes also occur in the compounds discharge and the resulting wastewater characteristics. Numerous compounds generated from industrial processes re difficult and costly to treat by conventional wastewater treatment processes. Therefore, effective Enforcement of an industrial pretreatment, program is a daunting task and soz a ome of the regulated pollutants still escape to the municipal wastewater collection system and must be treated. In the future with the objective of pollution prevention, every effort should be made by industrial dischargers to assess the environmental impacts of any new compounds that may enter the wastewater stream before being pproved for use 1-5 Wastewater Treatment Wastewater collected from municipalities and communities must ultimately be returned to receiving waters or to the land or reused. The complex question facing the design engineer and public health officials is: what levels of treatment must be achieved in a given application-bevond those prescribed by discharge permits-to ensure protection of public health and the environment? The answer to this question quires detailed analyses of local conditions and needs, application of scientific knowledge and engineering judgement based on past experience, and considerations of federal, state, and local regulations Methods of treatment in which the application of physical forces predominate are known as unit operations. Methods of treatment in which the removal of contaminants is brought about by chemical or biological reactions are known as unit processes. At present time, unit operations and processes are grouped together to provide various levels of treatment known as preliminary primary, advanced primary ndary and tertiary treatment. See Tab 1-2. Tab 1-2 Levels of wastewater treatment Treatment level Description Preliminary Removal of wastewater constituents, such as rags, sticks, floatables, grit, and grease that may cause maintenance or operational problems with the treatment operations, processes, and ancillary systems
1-4 sufficient information regarding the health risks posed by some microbial pathogens and chemical constituents in wastewater,(2)the nature of unknown or unidentified chemical constituents and potential pathogens, and (3)the effectiveness of treatment processes for their removal. Other health concerns relate to: (1)the release of volatile organic compounds(VOCs) and toxic air contaminants(TACs) from collection and treatment facilities, (2)chlorine disinfection, and (3)disinfection byproducts(DBPs).Odors are one of the most serious environmental concerns to the public. Many industrial wastes contain VOCs that may be flammable,toxic, and odorous,and may be contributors to photochemical smog and tropospheric ozone. Effluents containing chlorine residuals are toxic to aquatic life, and, increasingly, provisions to eliminate chlorine residuals are being instituted. Other important health issues relate to the reduction of disinfection byproducts (DBPs) that are potential carcinogens and are formed when chlorine reacts with organic matters. To achieve higher and more consistent microbes inactivation levels, improved performance of disinfection systems must be addressed. In many communities, the issues of safety in the transporting, storing, and handling of chlorine are also being examined. Fig. 1-2 Covered treatment plant facilities for the control of odor emissions 1-4 Wastewater Characteristics Prior to about 1940, most municipal wastewater was generated from domestic sources. After 1940, as industrial development in the U.S. grew significantly, increasing amounts of industrial wastewater have been and continue to be discharged to municipal collection systems.The amounts of heavy metals and synthesized organic compounds generated by industrial activities have increased, and some 10,000 new organic compounds are added each year. As technological changes take place in manufacturing, changes also occur in the compounds discharged and the resulting wastewater characteristics. Numerous compounds generated from industrial processes are difficult and costly to treat by conventional wastewater treatment processes. Therefore, effective industrial pretreatment becomes an essential part of an overall water quality management program. Enforcement of an industrial pretreatment, program is a daunting task and some of the regulated pollutants still escape to the municipal wastewater collection system and must be treated. In the future with the objective of pollution prevention, every effort should be made by industrial dischargers to assess the environmental impacts of any new compounds that may enter the wastewater stream before being approved for use. 1-5 Wastewater Treatment Wastewater collected from municipalities and communities must ultimately be returned to receiving waters or to the land or reused. The complex question facing the design engineer and public health officials is: what levels of treatment must be achieved in a given application-beyond those prescribed by discharge permits-to ensure protection of public health and the environment? The answer to this question requires detailed analyses of local conditions and needs, application of scientific knowledge and engineering judgement based on past experience, and considerations of federal, state, and local regulations. In some cases, a detailed risk assessment may be required. Methods of treatment in which the application of physical forces predominate are known as unit operations. Methods of treatment in which the removal of contaminants is brought about by chemical or biological reactions are known as unit processes. At present time, unit operations and processes are grouped together to provide various levels of treatment known as preliminary, primary, advanced primary, secondary,and tertiary treatment. See Tab 1-2. Tab 1-2 Levels of wastewater treatment Treatment level Description Preliminary Removal of wastewater constituents, such as rags, sticks, floatables, grit, and grease that may cause maintenance or operational problems with the treatment operations, processes, and ancillary systems
Primary Removal of a portion of the suspended solids and organic matter from the Advanced Primary anced removal of suspended solids and organic matter from the wastewater Typically accomplished by chemical addition or filtration Secondar Removal of biodegradable organics, suspended solids. Disinfection is also ally included in the definition of conventional secondary treatment Tertian Removal of residual suspended solids, usually by granular medium filtration or microscreen. Disinfection is also typically a part of tertiary treatment. Nutrient In this Advanced Removal of dissolved and suspended materials remaining after normal biological treatment when required for various water reuse applications A listing of unit operations and processes used for the removal of major constituents found in wastewater is presented in Tab 1-3 Tab 1-3 Unit Operations and Processes used to Remove Constituents Found in Wastewater Constituent I Unit Operation or Process Suspended solids Screening, grit removal, sedimentation, high-rate clarification, flotation, depth filtration, surface filtration Biodegradable organics Aerobic suspended growth variations, aerobic attached growth variations, anaerobic suspended growth variations, anaerobic attached growth variations, lagoon variations, physical-chemical systems, chemical oxidation, advanced oxidation membrane filtration Nutrient-nitrogen Chemical oxidation, suspended growth nitrification and denitrification variations, fixed film nitrification and denitrification variations, air stripping, Nutrient-phosphorus Chemical treatment, biological removal Colloidal and dissolved Membranes, chemical treatment, carbon adsorption, ion exchange Volatile Air stripping, carbon adsorption, advanced oxidation compounds Odors Chemical scrubbers, carbon adsorption, biofliters, compost filters About 20 vears ago. biological nutrient removal(BNR) for the removal of nitrogen and phosphorus, was viewed as an innovative process for advanced wastewater treatment. Because of the extensive research into the mechanisms of bNR, the advantages of its use, and the number of placed into operations, nutrient removal, for all practical purpose become a part of conventional wastewater treatment. When compared to chemical treatment methods. BNR uses less chemical, reduces the production of waste solids. and has lower energy consumptions. Because of the importance of BNR in wastewater treatment, BNR is integrated into the discussion of theory, application, and design of biological treatment systems Land treatment processes, commonly termed"natural systems, "combine chemical, and biological treatment mechanisms and produce water with quality similar to or better than that from advanced wastewater treatment. Natural systems are used mainly with small treatment systems Current status Up until the late 1980s. conventional secondary treatment was the most common methods of treatment for the removal of BOD and TSS. In the United States, nutrients removal was used in special circumstances. uch as in the great Lakes area where sensitive nutrient-related water quality conditions were identified Because of nutrient enrichment that has led to eutrophication and degradation( due in part to point source discharges), nutrient removal processes have evolved and now are used extensively in other areas as well The municipal wastewater treatment enterprise is composed of over 16.000 plants that are used to treat a total flow of about 1400 cubic meters per second. Approximately 92 per cent of the total existing flow is handled by plants having capacity of 0.044 m/s and larger. Nearly one-half of the present design capacity is situated in plants providing greater than secondary treatment. In the last 10 vears. many plants have been designed using BNR. Effluent filtration has also been installed the effectiveness of disinfection especially for ultraviolet (UV disinfection systems. because(1) the removal of larger particles of suspended solids that harbor bacteria enhances the reduction in coliform bacteria and(2) the reduction of turbidity improves the transmittance of uv light Effluent reuse 1-5
1-5 Primary Removal of a portion of the suspended solids and organic matter from the wastewater Advanced Primary Enhanced removal of suspended solids and organic matter from the wastewater. Typically accomplished by chemical addition or filtration Secondary Removal of biodegradable organics, suspended solids. Disinfection is also typically included in the definition of conventional secondary treatment Tertiary Removal of residual suspended solids, usually by granular medium filtration or microscreens. Disinfection is also typically a part of tertiary treatment. Nutrient removal is often included in this definition. Advanced Removal of dissolved and suspended materials remaining after normal biological treatment when required for various water reuse applications A listing of unit operations and processes used for the removal of major constituents found in wastewater is presented in Tab 1-3. Tab 1-3 Unit Operations and Processes used to Remove Constituents Found in Wastewater Constituent Unit Operation or Process Suspended solids Screening, grit removal, sedimentation, high-rate clarification, flotation, chemical precipitation, depth filtration, surface filtration Biodegradable organics Aerobic suspended growth variations, aerobic attached growth variations, anaerobic suspended growth variations, anaerobic attached growth variations, lagoon variations, physical-chemical systems, chemical oxidation, advanced oxidation, membrane filtration Nutrient-nitrogen Chemical oxidation, suspended growth nitrification and denitrification variations, fixed film nitrification and denitrification variations, air stripping, ion exchange Nutrient-phosphorus Chemical treatment, biological removal Pathogens Chlorine compounds, chlorine dioxide, ozone, UV radiation Colloidal and dissolved solids Membranes, chemical treatment, carbon adsorption, ion exchange Volatile organic compounds Air stripping, carbon adsorption, advanced oxidation Odors Chemical scrubbers, carbon adsorption, biofliters, compost filters About 20 years ago, biological nutrient removal (BNR) for the removal of nitrogen and phosphorus, was viewed as an innovative process for advanced wastewater treatment. Because of the extensive research into the mechanisms of BNR, the advantages of its use, and the number of BNR systems that have been placed into operations, nutrient removal, for all practical purposes, has become a part of conventional wastewater treatment. When compared to chemical treatment methods, BNR uses less chemical, reduces the production of waste solids, and has lower energy consumptions. Because of the importance of BNR in wastewater treatment, BNR is integrated into the discussion of theory, application, and design of biological treatment systems. Land treatment processes, commonly termed “natural systems,” combine chemical, and biological treatment mechanisms and produce water with quality similar to or better than that from advanced wastewater treatment. Natural systems are used mainly with small treatment systems. Current Status Up until the late 1980s, conventional secondary treatment was the most common methods of treatment for the removal of BOD and TSS. In the United States, nutrients removal was used in special circumstances, such as in the Great Lakes area where sensitive nutrient-related water quality conditions were identified. Because of nutrient enrichment that has led to eutrophication and degradation (due in part to point source discharges), nutrient removal processes have evolved and now are used extensively in other areas as well. The municipal wastewater treatment enterprise is composed of over 16,000 plants that are used to treat a total flow of about 1400 cubic meters per second. Approximately 92 per cent of the total existing flow is handled by plants having capacity of 0.044 m3 /s and larger.Nearly one-half of the present design capacity is situated in plants providing greater than secondary treatment. In the last 10 years, many plants have been designed using BNR. Effluent filtration has also been installed where the removal of residual suspended solids is required. Filtration is especially effective in improving the effectiveness of disinfection, especially for ultraviolet (UV) disinfection systems, because (1) the removal of larger particles of suspended solids that harbor bacteria enhances the reduction in coliform bacteria and (2) the reduction of turbidity improves the transmittance of UV light. Effluent reuse