Mesophilic aeration of autothermal thermophilic aerobically digested biosolids to improve plant operations

Autothermal thermophilic aerobic digestion (ATAD) has been observed to exhi bit a greater polymer demand for acceptable biosolids dewatering when compa red with conventional mesophilic aerobic digestion. Field studies indicated that an increase in thermophilic detention time promoted the release of pr oteins and polysaccharides from the biosolids to the bulk solution with cor responding increases in cationic polymer demand and dewatered biosolids fil trate chemical oxygen demand (COD). Tests indicated that mesophilic aeratio n reduced the polymer demand necessary for acceptable dewatering through re moval of proteins and polysaccharides from solution. Reduction in polymer d emand after aeration seems to depend on both thermophilic and mesophilic ae robic detention times, whereas the dewatered cake solids seemed to be unaff ected. Other process improvements produced by mesophilic aeration included reduction of odor, filtrate foam, filtrate COD, and filtrate phosphate.