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 systems1-4 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