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Title: Identification of Seasonal Variations in Volatile Sulfur Compound Formation and Emission From the Secondary Treatment System at a Large Wastewater Treatment Plant

Author
item SEKYIAMAH, KWEKU - PBS&J
item KIM, HYUNOOK - SEOUL UNIV, KOREA
item MCCONNELL, LAURA
item TORRENTS, ALBA - UNIV MD, COLLEGE PARK
item RAMIREZ, MARK - DCWASA

Submitted to: Water Environment Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/1/2008
Publication Date: 12/1/2008
Citation: Sekyiamah, K., Kim, H., Mcconnell, L.L., Torrents, A., Ramirez, M. 2008. Identification of Seasonal Variations in Volatile Sulfur Compound Formation and Emission From the Secondary Treatment System at a Large Wastewater Treatment Plant. Water Environment Research. 80(12):2261-2267.

Interpretive Summary: Offensive odors associated with gaseous emissions from wastewater treatment plants (WWTPs) are a nuisance to residential communities that exist in close proximity to these facilities. Excessively high odor levels may result in local litigation and new regulatory requirements to reduce emissions from these treatment plants. The purpose of this study was to identify, quantify and determine source locations of significant volatile sulfur compounds (VSCs) associated with the activated sludge treatment process at the District of Columbia’s Water and Sewer Authority’s (DCWASA’s) Blue Plains WWTP. Direct air emissions and wastewater headspace sampling techniques were used to capture odorous gases associated with the secondary activated sludge treatment process. Field measurements for DO, temperature, ORP, and pH were recorded. VSCs were extracted using the headspace-solid phase microextraction (HS-SPME) method. A GC/MS/HS-SPME chemical analytical method was used to quantify VSC concentration. Olfactometric analysis was also performed to corroborate the results from the chemical analysis. This investigation established that settled solids inventory in the anaerobic environment of the secondary sedimentation basin might be the primary cause of the formation of VSCs in the secondary treatment system. The stripping effect caused by the secondary aeration basins was responsible for the emission of VSCs into the atmosphere. The study concluded that the efficient management of settled solids inventory in the secondary sedimentation basins would have the potential to greatly reduce odor emissions from the secondary activated sludge process.

Technical Abstract: Offensive odors associated with gaseous emissions from wastewater treatment plants (WWTPs) are a nuisance to residential communities that exist in close proximity to these facilities. The purpose of this study was to identify, quantify and determine source locations of significant volatile sulfur compounds (VSCs) associated with the activated sludge treatment process at the District of Columbia’s Water and Sewer Authority’s (DCWASA’s) Blue Plains WWTP. Direct air emissions and wastewater headspace sampling techniques were used to capture odorous gases associated with the secondary activated sludge treatment process. The result from this study has established that DMS, DMDS and other major VSCs are formed in the biosolids blanket at the bottom of the secondary sedimentation basins. The VSCs formed in the biosolids blankets are returned by the return activated sludge (RAS) process back to the secondary aeration basin where the intense interaction with compressed air causes the VSCs to strip out of the wastewater. A strong statistical correlation between VSC concentration and biosolids blanket depth was established [DMDS: r = 0.86 (p < 0.001, df = 25) and DMS: r = 0.72 (p < 0.001, df = 25). Odor intensity and VSC concentration in the gas emission from the secondary aeration basin was also strongly statistically correlated [DMS: r = 0.85 (p < 0.001, df = 13) and DMDS: r = 0.81 (p < 0.001, df = 13). In conclusion, the effective management of solids inventory in the activated sludge of the secondary sedimentation basins, can minimize the formation of VSCs and therefore mitigate the odor problem associated with the wastewater treatment process.