ABSTRACT
The purpose of secondary treatment is to remove the soluble and colloidal organics that escape the primary treatment and to provide further removal of suspended solids. Secondary levels of treatment can also be achieved by physical-chemical or natural systems. This chapter presents the theory and design of biological waste treatment processes. It discusses major treatment processes which include aerobic, anaerobic, and biological nutrient removal (BNR). The BNR processes use a combination of anaerobic, anoxic, and aerobic reactors. Since they achieve enhanced nitrogen and phosphorus removal in addition to biological oxygen demand (BOD) and total suspended solids (TSS) removal, they have gained a great deal of interest for designing medium and large wastewater treatment plants. The chapter includes the basic concepts of microbiology, growth phases, and substrate utilization requirements. There are three major types of suspended growth, anaerobic treatment processes: anaerobic digestion, anaerobic contact process, and upflow anaerobic sludge blanket (UASB) process.
