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Many claims have been made regarding the effectiveness of chemical additives and amendments (A&As) to reduce the potential for odors from organic residuals. Various A&As have been added to biosolids during conditioning and dewatering, or directly to dewatered cake, with limited success. The Philadelphia Water Department (PWD) annually produces >200,000 wet tons of biosolids via anaerobic digestion, followed by high speed centrifuge dewatering. Nuisance odors were reported during staging/ storage of biosolids cake at the Philadelphia Biosolids Recycling Center, and land application sites. This manuscript summarizes results for several A&As that was evaluated relative to their potential to reduce odors in staged and/or stored PDW biosolids. Conventional head space sampling from incubated biosolids samples and GC-MS analysis was coupled with human sensory evaluation. Of the A&As selected for study, none were effective for both staging and storage odor mitigation situations. Lime kiln dust performed best for staging, and high carbon wood ash performed best for storage. Correlation of specific odorant gasses with odor panel results revealed mixed findings.

Short-term (<60-d) stockpile-curing of dewatered municipal wastewater biosolids has been suggested as a practice to reduce malodors during subsequent field application. Biosolids from the City of Philadelphia were evaluated following stockpile-curing for 3-d, 10-d, and 50-d. Each material was top-dressed on small grain stubble in 37-m diameter rings. Four trained odor assessors were positioned in the center of each odor ring and olfactory observations were performed at: pre-application (background); 45-60 min, 4-hrs, 10-hrs, and 20-hrs following field application. Comparison of 10-minute Best Estimate Dilution Threshold (BET 10 ) odor concentrations found no statistical difference between the 3-d and 10-d treatments, but 50-d BET 10 levels were statistically greater (α=0.05). Odor character, intensity, and hedonic-tone observations were similar and triangular forced-choice dynamic olfactometer testing of flux chamber whole-air samples revealed no statistical differences. Sensory odor quantification techniques employed to assess the total effect of field malodors showed remarkably consistent results. Analytical analyses were unsuccessful in identifying a single odorant in whole-air field samples. This study was not able to confirm that short-term biosolids stockpile curing produces a less odorous product for field application.

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