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Client: Washington Suburban Sanitation Commission

Project: Biosolids Odor Mix Study
Project Type: Research and Innovative Projects
Industry: Utilities
Location: Washington, DC
Biosolids treatment plant.


Western Branch WRRF (WB) is a 30 mgd plant that generates an average of 80 wet tons (WT) of biosolids (20 – 25 %TS) per day. The biosolids are undigested and therefore disposed in landfills. However, landfills have expressed concerns over excessive odors. Finding suitable alternatives for disposal has become problematic. The purpose of this assignment was to assess the extent to which WB biosolids odors may be reduced through blending with composted yard-waste, lime, and/or sawdust. Several rounds of tests were performed as preliminary trials to gain a sense of the potential impact.

Biosolids treatment plant.


Material Matters, Inc. collaborated with the Penn State Odor Assessment Laboratory to arrange for a series of olfactometry assessments of various biosolids blend treatments to allow comparison of potential nuisance odor metrics. In all three rounds of tests were performed. Material Matters, Inc. reviewed and interpreted laboratory test results and presented findings in technical memorandums to WSSC. Notably, limited trial repetitions did not allow for statical evaluation.

A creek flowing through some woods.

Outcomes and Benefits

Findings from the study were variable as one may expect in a series of preliminary trials. In the first round of testing, amendment of WB biosolids cake with composted yard waste did not noticeably reduce odor concentration (Detection Threshold, DT) compared to the unamended cake. This was an unexpected finding. In the second round of testing, addition of lime and/or sawdust significantly improved DT (reduced odor concentration) relative to the unamended cake. In the third trial, non-aerated, lime-amended biosolids showed the lowest odor concentration relative to all other treatments, across all rounds. While very preliminary in nature, this series of initial odor trials demonstrates that it is possible to significantly reduce nuisance odor levels in WB biosolids. If further interest in blending to reduce WB nuisance odor is to be pursued, much more testing and a detailed cost/benefit analysis would be recommended.

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