Expanding the Use of Activated Sludge at Biological Waste Water Treatment Plants for Odor Control

Odors from wastewater treatment plants (WWTPs) are composed of a mixture of gases, predominantly reduced sulfur compounds, such as hydrogen sulfide (H2S) and volatile organic carbon (VOC) compounds. Their emissions can be prevented by the biological and chemical constituents commonly found in activated sludge, which is often employed for biological wastewater treatment. The use of activated sludge for odor control may take place through a number of processes, including activated sludge diffusion (ASD) or activated sludge recycle (ASR). ASD operates by sparging foul air, collected from covered or contained sources, into an activated sludge bioreactor in place of normal ambient process air. ASR operates by pumping activated sludge mixed liquor from an activated sludge bioreactor or settled activated sludge from secondary clarification to the plant inlet works, capturing odorous compounds before they volatilize from the liquid phase. In this paper, the design issues, practicalities and performance of these technologies are discussed based on existing published technical papers as well as recent field experience by CH2M HILL. The use of an existing resource at a WWTP (activated sludge) can in certain situation offer the possibility to reduce or eliminate the high investment costs associated with conventional odor control measures to reduce operating costs and provide high performance odor control for wastewater treatment plants. The use of activated sludge (often considered as a waste product) should be considered at WWTPs as part of the odor control management.