Environmental Engineer:
Applied Research and Practice

A Multi-Plant Study to Understand the Chemicals and Process Parameters Associated with Biosolids Odors

Authors: Matthew J. Higgins, Yen-Chih Chen, John Novak, Dietmar Glindemann, Robert Forbes, Zeynep Erda, Jay Witherspoon, David McEwen, Sudhir Murthy, J. Ronald Hargreaves and Gregory Adams

Abstract

The main objectives of this research were to determine the compounds associated with odors during the digestion and handling of biosolids and understand the process operational factors which impact the production of these odor causing compounds. To accomplish these goals, a comprehensive sampling of 11 full-scale wastewater utilities with anaerobic digestion was performed in which samples were collected from most locations throughout the liquid and solids processing scheme. The samples were analyzed for a number of inorganic and organic constituents such as metal concentration, anions, pH, temperature, and the samples were placed in sealed headspace bottles for headspace analysis of possible odor causing compounds. The results indicated that biosolids odors after dewatering were generally much higher than odors produced from other sample locations in a plant. A direct correlation was found between the sulfur compound concentration, especially the volatile organic sulfur compounds, and the dilution thresholds measured by an odor panel, indicating that sulfur compounds were a main contributor to odors. The main sulfur compounds measured included hydrogen sulfide, methanethiol, dimethyl sulfide, and dimethyl disulfide. The odor descriptors most frequently cited by the odor panel were "offensive" "putrid" "chemical" and "garbage". Few of the operational parameters were correlated with biosolids odorant production, such as influent wastewater characteristics, ratio of primary and secondary to digestion, and residual biosolids activity. Digester SRT was weakly, negatively correlated to the concentration of VOSCs produced during storage and no correlation was found between the percent volatile solids reduction and VOSCs.

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