Recent findings on biosolids cake odor reduction--results of WERF phase 3 biosolids odor research.

The Water Environment Research Foundation (WERF) has sponsored three phases of a long-term project entitled "Identifying and Controlling Odors in the Municipal Wastewater Environment." The current (third) phase focuses on reduction of odors from dewatered biosolids cakes, and is entitled "Biosolids Processing Modifications for Cake Odor Reduction." This phase encompasses nine research agenda items developed from the results of the prior phase of research (Phase 2), which was completed in December 2003 as WERF Report No. 00-HHE-5T and was entitled "Impacts of In-Plant Parameters on Biosolids Odor Quality." The current phase (Phase 3) was a 2.5-year project, the first half of which was dedicated to testing several of the more promising hypotheses from Phase 2 in the laboratory to help determine the cause-effect relationships of odor generation from biosolids, and to develop odor reduction techniques. It is important to note that this research project covers the reduction or prevention of odorous emissions from dewatered biosolids cake, not odor control by means of containment or adsorption or absorption of malodorous emissions. In the remainder of the Phase 3 project, promising laboratory findings are being applied to biosolids handling processes at one or more wastewater treatment plants (WWTPs), with the goal of achieving significant cake odor reduction in a realistic, full-scale setting. The Phase 3 laboratory results were used to identify the relative effectiveness of methods for reducing biosolids cake odors, using techniques and measurements of biosolids cake odor production potential that have been developed by the WERF Project Team. Plans to demonstrate the most promising research findings at full-scale biosolids digestion and dewatering facilities constitute the final, fourth phase of the project. Contacts have been made with wastewater treatment facilities that have an interest or need to reduce their biosolids cake odors. The main goal of the next phase of the project will be to match wastewater or biosolids facilities that need to reduce biosolids odors with specific technologies, chemicals, or biological agents, in order to demonstrate the efficacy of promising laboratory findings full scale at a real WWTP.

Role of protein, amino acids, and enzyme activity on odor production from anaerobically digested and dewatered biosolids.

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.

Generation pattern of sulfur containing gases from anaerobically digested sludge cakes.

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.