Municipal Sewage Treatment (a)PRIMARY TREATMENT (b)SECONDARY TREATMENT (c)DISINFECTION AND RELEASE (Biological oxidation) Screening,skimming, ③Primary effluent Effluent is disinfected grinding of sewage. undergoes aeration: by chlorination and microorganisms released. 2 Solid matter oxidize organic Trickling filter settles out. matter. (see Figure 27.22) Primary Chlorinator Sewage Effluent Primary sedimentation tank Settling tank Activated Secondary sludge system effluent (see Figure 27.20) Primary sludge Secondary sludge from settling tank Sludge effluent Sludge is is dried. removed and disposed of Key Sludge in landfill or Physical ⑤Remaining sludge effluent agricultural processes is digested anaerobically. land. Microbial producing methane. processes Anaerobic sludge digester Chemical (d)SLUDGE DIGESTION (see Figure 27.23) Drying bed processes Figure 27.19Municipal Sewage Treatment Figure 27.19