Identification of Seasonal Variations in Volatile Sulfur Compound Formation and Emission from the Secondary Treatment System at a Large Wastewater Treatment Plant
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. Sensory olfactometric data corroborated the results from the chemical analysis. This investigation established that settled solids inventory in the anaerobic environment of the secondary sedimentation basin was the primary cause of the formation of VSCs in the 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 had the potential to greatly reduce odor emissions from this process.