1、附附录录： Wastewater Biological Treatment Processes The objective of wastewater treatment is to reduce the concentration of specific pollutants to the level at which the discharge of the effluent will not adversely affect the environment or pose a health threat. Moreover , reduction of these constituent
2、s need only be to some required level. For any given wastewater in a specific location , the degree and type of treatment are variables that require engineering decisions . often the degree of treatment depends on the assimilative capacity of the receiving water . DO sag curves can indicate how much
3、 BOD must be removed from wastewater so that the DO of receiving water is not depressed too far . The amount of BOD that must be removed is an effluent standard and dictates in large part the type of wastewater treatment required . To facilitate the discussion of wastewater , assume a “ typical wast
4、ewater ”and assume further that the effluent from this wastewater treatment must meet the following effluent standards : BOD15mg/L SS15mg/L P1mg/L Additional effluent standard could have been established , but for illustrative purposes we consider only these three . The treatment system selected to
5、achieve these effluent standards includes 1. Primary treatment : physical processes that nonhomogenizable solids and homogenize the remaining effluent . 2. Secondary treatment : biological process that remove most of the biochemical demand for oxyen . 3. Tertiary treatment : physical , biological ,
6、and chemical processes to remove nutrients like phosphorus and inorganic pollutants , to deodorize and decolorize effluent water , and to carry out further oxidation . Primary treatment The most objectionable aspect of discharging raw sewage into watercourses is the floating material . Thus screen were the first form of wastewater treatment used by communities , and they are used today as the first step in treatment plants .Typical screens consist of a series bars that might be about 2.5
