BIOSOLIDS PROCESSING FROM ADVANCED DIGESTION SYSTEMS: EXPERIENCES WITH THE ATAD PROCESS

The dewatering properties of thermophilic aerobically digested biosolids, which have been found to be poor, were improved through the use of inorganic conditioners and through the implementation of post-mesophilic aeration. In one study, the use of inorganic conditioners substantially reduced additional polymer dose requirement. The reduction in polymer dose resulted in conditioning costs being reduced to half the original costs. Additionally, centrifuge throughput rates were increased by a third. Laboratory analyses show that conditioning with inorganic conditioners can result in a reduction in recycle COD. Postmesophilic aeration of thermophilic biosolids resulted in almost 40% reduction in polymer conditioning requirements. Through the oxidation of reduced odorous compounds, substantial odor mitigation of the biosolids product was achieved through post-mesophilic aeration as compared to conventional anaerobically digested biosolids. The results of this study may be applicable to other thermophilically digested biosolids that are difficult to process due to poor dewatering characteristics, high recycle nutrient and COD loads, and onsite and off-site odor generation potential. Dual-Conditioning costs for ATAD biosolids are currently in the 40–60 range, and are similar to anaerobically digested biosolids.