Again, microorganisms in the upper aerobic region of the ponds remove dissolved organic carbon for food. The microorganisms coagulate and settle to the anaerobic bottom of the lagoon. These systems are least expensive to install and operate. However, they produce the lowest quality effluent of the processes discussed. They are generally used for animal waste and in developing countries.
Sludge treatment reduces the volume, offensiveness, and number of pathogens in sewage solids.
Ultimately offensive sewage solids are converted to humus. List and briefly describe the four steps in sludge treatment. The first step in sludge treatment is thickening or concentration of the solids. Thickening reduces the volume of the sludge so that it will be less expensive to treat. The second step is sludge stabilization where the odiferousness, volume, and the number of pathogens are reduced.