ABSTRACT
The main objective of this research was to test the hypothesis that bioavailable protein and, more specifically, the sulfur-containing amino acids within the protein, can be degraded by proteolytic enzymes to produce odor-causing compounds--mainly volatile sulfur compounds (VSCs)--during biosolids storage. To achieve these objectives, samples of digester effluent and cake solids were collected at 11 different wastewater treatment plants in North America, and the samples were analyzed for protein and amino acid content and general protein-degrading enzyme activity. At the same time, cake samples were stored using headspace bottles, the concentration of VSCs were measured using gas chromatography, and olfactometry measurements were made by a trained odor panel. The results showed that the bound cake protein content and methionine content was well-correlated with VSC production and the detection threshold measured by the odor panel.
Subject(s)
Amino Acids, Sulfur/metabolism , Odorants/analysis , Proteins/metabolism , Sewage/chemistry , Waste Disposal, Fluid/methods , Amino Acids, Sulfur/analysis , Anaerobiosis , Bacteria, Anaerobic , Biotransformation , Proteins/analysis , Volatilization , Water Purification/methodsABSTRACT
Eleven dewatered sludge cakes collected from anaerobic digesters at different treatment plants were evaluated for the amount, type, and pattern of odorous gas production. All but one of the sludge cakes were from mesophilic anaerobic digesters. One was from a thermophilic digester. The pattern and quantities of sulfur gases were found to be unique for each of the samples with regard to the products produced, magnitude, and subsequent decline. The main odor-causing chemicals were volatile sulfur compounds, which included hydrogen sulfide, methanethiol, and dimethyl sulfide. Volatile sulfur compound production peaked in 3 to 8 days and then declined. The decline was a result of conversion of organic sulfur compounds to sulfide. In one side-by-side test, a high-solids centrifuge cake generated more odorous compounds than the low-solids centrifuge cake. The data show that anaerobic digestion does not eliminate the odor potential of anaerobically digested dewatered cakes.
