INVESTIGATING THE DYNAMICS OF VOLATILE SULFUR COMPOUNDS FROM PRIMARY AND SECONDARY SYSTEMS IN WASTEWATER RESOURCE RECOVERY FACILITIES
Bazemo, Ulrich Yoan Yanick
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This study quantifies volatile sulfur compounds (VSCs) emissions from Wastewater Resource Recovery Facilities (WRRFs) and investigate their mechanisms of generation. In primary treatment, of the VSCs analyzed, hydrogen sulfide (H2S) and methyl mercaptan (MM) concentrations in the off gas were dominant, while dimethyl sulfide (DMS) and dimethyl disulfide (DMDS) were under their odor threshold for most sampling dates. H2S emission in primary settling tanks was mainly the result of the stripping of dissolved sulfide (64%) generated in the sewers. MM emission was more dependent on the conditions in the primary clarifiers (only 16% stripping). Most significant prevention of odor emission in primary settling tanks can be achieved by managing biofilms and microbial reactions in the sewer network. This would control the biomass seeding and fermentation product availability in the primary settling tanks directly and will decrease the observed kinetics of H2S and MM production. Overall, management of sludge blanket heights and thus avoiding time at low oxidation reduction potential (ORP) minimized odor emission independent of sewer conditions. Our investigations in secondary reactors have shown that MM was 2 to 3 order of magnitude higher than dissolved MM in primary effluent, revealing that the production of MM took place in the activated sludge process itself, and the stripping of MM from the feed was very minimal. Furthermore, data showed that the depth of secondary sludge blanket plays an important role on the extent of MM emission. At high sludge blanket height, high MM emission was observed. It was concluded that low ORP conditions in sludge blanket, selector zones and RAS was the major source of VSCs. Increasing ORP could decrease odor emissions by targeting the zones where MM is emitted. This could be achieved by addition of nitrate in secondary settling tanks.