Autoheating and pathogen destruction during storage of dewatered biosolids with minimal mixing

Long-term storage with occasional mixing of biosolids was investigated for its ability to meet Class A, pathogen destruction requirements for unrestricted beneficial use of biosolids on land as de fined by the Environmental Protection Agency. Field studies were conducted to evaluate the survival of pathogenic bacteria (Salmonella typhimurium, Yersinia enterocolitica, and Campylobacter jejuni), and Ascaris suum eggs in stored, digested, dewatered, and air-dried wastewater biosolids. Screen-enclosed biosolids columns, seeded with the pathogens, were incorporated into elongated, triangular biosolids-storage piles established at five wastewater treatment plants in Utah. Storage piles were either nonmixed, mixed once a month, or mixed twice a month. Biosolids piles at the Central Weber wastewater treatment plant that were mixed once and twice each month were autoheated to 50 degrees C and 57 degrees C, respectively. Pathogenic organisms were reduced to below detection levels in all the piles within a year irrespective of whether the piles were turned or if autoheated temperatures were attained. Storage time was most important in the destruction of A. suum eggs.