energv-efficient processes and equipment. Large amounts of electricity are used for aeration that is needed for biological treatment. Tvpicallv. about one-half of the entire plant electricity usage is for aeration. In the design of wastewater treatment plants power use can be minimized by paying more careful attention to plant siting, selecting energy-efficient equipment, and designing facilities to recover energy for in-plant Changes in regulations and the development of new technologies have affected the design of disinfection disinfectant of choice for wastewater. With the increasing number of permits requ 3 systems. Gene probes are now being used to identify where specific groups of organisms are found in r particle-associated). Historically, chlorine has been nondetectable amounts of chlorine residual in treated effluents. dechlorination facilities have had to be added, or chlorination systems have been replaced by alternative disinfection systems such as ultraviolet (UV) radiation. Concerns about chemical safety have also affected design considerations of chlorination ns. Improvements that have been made in UV lamp and ballast design within the past 10 years have improved significantly the performance and reliability of UV disinfection systems Effective guidelines have also been developed for the application and design of UV systems. Capital and operating costs have also been lowered. It is anticipated that the application of UV for treated drinking water and for stormwater will continue to increase in the future. Because Uv produces essentially no troublesome byproducts and is also effective in the reduction of NDMa and other related compounds, its use for disinfection is further enhanced as compared to chlorine compounds Overflows from combined sewer and sanitary sewer collection systems have been recognized as difficul problems requiring solution especially for many of the older cities in the United States. The problem has become more critical as greater development changes the amount and characteristics of stormwater runoff and increases the channelization of runoff into storm, combined, and sanitary collection systems Combined systems carry a mixture of wastewater and stormwater runoff and, when the capacity of the interceptors is reached. overflows occur to the receiving waters. Large overflows can impact receiving water quality and can prevent attainment of mandated standards. Recreational beach closings and shellfish bed closures have been attributed to CSOs( Combined System Overflow). Federal regulations for CSOs e still under development and have not been issued at present A combination of factors has resulted in the release of untreated wastewater from parts of sanitary collection systems. These releases are termed sanitary system overflows(SSOs). The SSOs may be caused by(1) the entrance of excessive amounts of stormwater, (2) blockages, or (3)structural, mechanical,or electrical failures. Many overflows result from aging collection systems that have not received adequate upgrades, maintenance, and repair. The 40.000 overflows per vea occur from sanitary collection systems. The untreated wastewater of these overflows represents threats to public health and the environment. The U.S. EPa is proposing to clarify and expand permit requirements for municipal sanitary collection systems under the Clean Water Act that will result in reducing the frequency and occurrence of SSos(U.S. EPa 2001). The U.S. EPA estimates that nearly $45 billion is required for constructing facilities for controlling CSOs and SSOs in the United States(U.S. EPA, 1997a) The effects of pollution from nonpoint sources are growing concerns as evidenced by the outbreak of gastrointestinal illness in Milwaukee traced to the oocysts of Crytosporidium parum, and the occurrence of Pfiesteria piscicida in the waters of Maryland and North Carolina. Pfiesteria is a form of algae that is very toxic to fish life. Runoff from pastures and feedlots has been attributed as a potential factor that triggers the effects of these microorganisms Perhaps one of the significant future developments in wastewater treatment will be the provision of separate facilities for treating return flows from biosolids and other processing facilities. Treatment of return flows will be especially important where low levels of nitrogen are to be achieved in the treated effluent. Separate treatment facilities may include (1)steam stripping for removal of ammonia from biosolids return flows. now typically routed to the plant headworkS:(2)high-rate sedimentation for emoving fine and difficult-to- settle colloidal material that also shields bacteria from disinfection ()flotation and high-rate sedimentation for treating to reduce solids loading on metals removal by chemical precipitation to meet more stringent discharge requirements. The specific treatment sy used will depend on the will impact the wastewater treatment proc The control of odors and in particular the control of 71-7 energy-efficient processes and equipment. Large amounts of electricity are used for aeration that is needed for biological treatment. Typically, about one-half of the entire plant electricity usage is for aeration. In the design of wastewater treatment plants power use can be minimized by paying more careful attention to plant siting, selecting energy-efficient equipment, and designing facilities to recover energy for in-plant use. Changes in regulations and the development of new technologies have affected the design of disinfection systems. Gene probes are now being used to identify where specific groups of organisms are found in treated secondary effluent (i.e., in suspension or particle-associated). Historically, chlorine has been the disinfectant of choice for wastewater. With the increasing number of permits requiring low or nondetectable amounts of chlorine residual in treated effluents, dechlorination facilities have had to be added, or chlorination systems have been replaced by alternative disinfection systems such as ultraviolet (UV) radiation. Concerns about chemical safety have also affected design considerations of chlorination and dechlorination systems. Improvements that have been made in UV lamp and ballast design within the past 10 years have improved significantly the performance and reliability of UV disinfection systems. Effective guidelines have also been developed for the application and design of UV systems. Capital and operating costs have also been lowered. It is anticipated that the application of UV for treated drinking water and for stormwater will continue to increase in the future. Because UV produces essentially no troublesome byproducts and is also effective in the reduction of NDMA and other related compounds, its use for disinfection is further enhanced as compared to chlorine compounds. Overflows from combined sewer and sanitary sewer collection systems have been recognized as difficult problems requiring solution, especially for many of the older cities in the United States. The problem has become more critical as greater development changes the amount and characteristics of stormwater runoff and increases the channelization of runoff into storm, combined, and sanitary collection systems. Combined systems carry a mixture of wastewater and stormwater runoff and, when the capacity of the interceptors is reached, overflows occur to the receiving waters. Large overflows can impact receiving water quality and can prevent attainment of mandated standards. Recreational beach closings and shellfish bed closures have been attributed to CSOs (Combined System Overflow). Federal regulations for CSOs are still under development and have not been issued at present. A combination of factors has resulted in the release of untreated wastewater from parts of sanitary collection systems. These releases are termed sanitary system overflows (SSOs). The SSOs may be caused by (1) the entrance of excessive amounts of stormwater, (2) blockages, or (3) structural, mechanical, or electrical failures. Many overflows result from aging collection systems that have not received adequate upgrades, maintenance, and repair. The U.S. EPA has estimated that at least 40,000 overflows per year occur from sanitary collection systems. The untreated wastewater of these overflows represents threats to public health and the environment. The U.S. EPA is proposing to clarify and expand permit requirements for municipal sanitary collection systems under the Clean Water Act that will result in reducing the frequency and occurrence of SSOs (U.S. EPA 2001). The U.S. EPA estimates that nearly $45 billion is required for constructing facilities for controlling CSOs and SSOs in the United States (U.S. EPA, 1997a). The effects of pollution from nonpoint sources are growing concerns as evidenced by the outbreak of gastrointestinal illness in Milwaukee traced to the oocysts of Crytosporidium parvum, and the occurrence of Pfiesteria piscicida in the waters of Maryland and North Carolina. Pfiesteria is a form of algae that is very toxic to fish life.Runoff from pastures and feedlots has been attributed as a potential factor that triggersthe effects of these microorganisms. Perhaps one of the significant future developments in wastewater treatment will be the provision of separate facilities for treating return flows from biosolids and other processing facilities. Treatment of return flows will be especially important where low levels of nitrogen are to be achieved in the treated effluent. Separate treatment facilities may include (1)steam stripping for removal of ammonia from biosolids return flows, now typically routed to the plant headworks; (2)high-rate sedimentation for removing fine and difficult-to-settle colloidal material that also shields bacteria from disinfection; (3)flotation and high-rate sedimentation for treating filter backwash water to reduce solids loading on the liquid treatment process; and (4)soluble heavy metals removal by chemical precipitation to meet more stringent discharge requirements. The specific treatment system used will depend on the constituents that will impact the wastewater treatment process. The control of odors and in particular the control of