Mesophilic Aeration of Autothermal Thermophilic Aerobically Digested Biosolids To Improve Plant Operations

Abstract

Autothermal thermophilic aerobic digestion (ATAD) has been observed to exhibit a greater polymer demand for acceptable biosolids dewatering when compared with conventional mesophilic aerobic digestion. Field studies indicated that an increase in thermophilic detention time promoted the release of proteins and polysaccharides from the biosolids to the bulk solution with corresponding increases in cationic polymer demand and dewatered biosolids filtrate chemical oxygen demand (COD). Tests indicated that mesophilic aeration reduced the polymer demand necessary for acceptable dewatering through removal of proteins and polysaccharides from solution. Reduction in polymer demand after aeration seems to depend on both thermophilic and mesophilic aerobic detention times, whereas the dewatered cake solids seemed to be unaffected. Other process improvements produced by mesophilic aeration included reduction of odor, filtrate foam, filtrate COD, and filtrate phosphate.