Microbial Ecology of Authothermal Aerobic Digestion (ATAD): Diversity, Dynamics and Activity of Bacterial Communities Involved in Treatment of a Municipal Wastewater

Authothermal thermophilic aerobic digestion (ATAD), or liquid composting, is a versatile new thermophilic process for the treatment and stabilization of high strength wastes of slurry consistency. The process has initially been applied for the treatment of pharmaceutical and industrial wastewater but has more recently been used to stabilize municipal wastes. There have been a number of studies focusing on reactor performance and the pattern of inactivation of various pathogenic organisms, but little focus on investigating the microbial population associated with the thermophilic step where microbial activity increases the temperature to 55-65°C during the biodegradation of municipal sludge. We have investigated the thermotolerant and thermophilic bacterial community responsible for efficient performance of ATAD by analysis of a clone library constructed of ATAD bacterial community 16S rDNA genes. A prevalence of thermophilic Bacillus, Paenibacillus, and Peptostreptococcaceae species was found. 8% of the clones were affiliated to Symbiobacterium thermophiiums often found associated with Bacillus species, while 40% of the clones have high similarity (>90%) to 16S rDNA sequences of compost-associated bacteria Most of the phylogenetic affiliations discovered in this study have previously been characterized as physiologically active microorganisms associated with elevated temperature niches. Monitoring of the operating parameters has demonstrated that there is on average a 35% removal of soluble COD, a 31% reduction in total solids (TS) and a 46% VS (volatile solids) reduction during the treatment of domestic waste sludge via ATAD.