Off-Gas Analyses Reflect Activated Sludge Operating Conditions

Abstract

Comprehensive odorous emissions sampling programs were recently conducted at the Blue Plains Advanced Wastewater Treatment Plant. Liquid and air emission samples were simultaneously collected at each of the wastewater treatment processes and the solids processing facilities. Air emission samples were analyzed for sulfur-containing compounds and olfactory parameters. Liquid samples were analyzed for a variety of parameters such as dissolved hydrogen sulfide, pH, dissolved oxygen (DO), oxidation reduction potential (ORP) and many other parameters.The results showed that the high rate activated sludge treatment process emits substantial quantities of odorous emissions and the main odorous compound is methyl mercaptan. The results also showed that the highest total reduced sulfur (TRS) and odor mass emissions occur when primary clarifier effluent is added to activated sludge mixed liquor in low DO and low ORP conditions and subsequently aerated. Long mixed liquor retention time in the secondary clarifiers also create conditions that are related to the high quantities of odorous emissions. However, continuous aeration can increase oxidative conditions in the activated sludge process and these conditions reduce the emissions of sulfur-containing compounds by 95 to 99%.