INFLUENCE OF SOLIDS CHARACTERISTICS AND DEWATERING PROCESS ON VOLATILE SULFUR COMPOUND PRODUCTION FROM ANAEROBICALLY DIGESTED BIOSOLIDS

This study focused on the evaluation of impacts of solids characteristics and dewatering equipment on volatile sulfur compound (VSC) production from anaerobically digested biosolids. Biosolids cakes were obtained from full-scale and laboratory-scale dewatering trials and were anaerobically stored for several days. The headspace of the samples was analyzed for VSC. To understand the impact of upstream solids characteristics on VSC production, three biosolids cake samples that were dewatered using the same dewatering equipment type, but on different dates (several months apart) were anaerobically stored and analyzed for VSCs. The VSC production characteristics from the cakes varied considerably for the three sample dates, even though the upstream anaerobic digestion process was operating in a consistent manner with similar volatile solids destruction efficiency and volatile solids remaining for the three sample dates. It is hypothesized that the cause (still undetermined) of solids characteristics and VSC production variation may lie further upstream of the digestion process (in the influent wastewater or the liquid treatment process). In the next experiment, three types of dewatering processes were evaluated for VSC production characteristics. The type of dewatering equipment (for similar cake solids) impacted VSC production characteristics considerably. The cakes obtained from a high-solids centrifuge produced the highest amount of VSC. The cakes obtained from a lowsolids centrifuge produced the next highest amount of VSC. The cakes obtained from a belt filter press (BFP) simulator produced no detectable VSC. Additional BFP simulation tests showed that the desiccation of cakes (using a desiccant) followed by storage did not generate VSC emissions. Air-drying of cakes to 35% dry solids content and subsequent anaerobic storage also did not generate VSC. The shearing of BFP cake with subsequent anaerobic storage resulted in VSC production (dimethyl sulfide). It is hypothesized that the cause of the VSC production during dewatering may therefore be due to labile protein generation from shear during dewatering and subsequent degradation during anaerobic storage. In a final experiment, the variation of high-solids centrifuge parameters resulted in substantial changes in VSC production rates. It is hypothesized that the variation in these centrifuge parameters results in changes to cake characteristics that results in subsequent changes to VSC production characteristics.