Effect of High Carbon Ash on Biosolids Odor Emissions and Microbial Activity

Quantitative measurements of odor emissions from biosolids were conducted relating odor units (odor intensity as perceived by people) to chemical odorant concentrations. Chemical odorant emissions from biosolids wereidentified using gas chromatography/mass spectrometry andincluded dimethyl disulfide (DMDS), dimethyl sulfide (DMS),carbon disulfide (CS₂), ammonia (NH₃), trimethylamine (TMA), and acetone. Odor unit emissions werepositively correlated with DMDS, DMS, CS₂, NH₃,TMA, and acetone emissions, demonstrating that the identifiedodorant emissions are associated with biosolids odor. To control biosolids odor, wood ash containing 32% carbon wasincorporated with biosolids at 1:1, 0.67:1, 0.33:1, and 0.11dry weight ratios. The high carbon ash additions reduced odor unit, DMDS, DMS, CS₂,TMA and acetone emissions when compared to a biosolids control. Although ash addition sometimes reduced NH₃ emissions, reduction was not consistently significant. Using SCREEN3 dispersion model (U.S. EPA) maximum dimethyldisulfide, NH₃, and trimethyl amine concentrations from a 1 ha 21 Mg biosolids application (dry wt.) were estimated to be 29.8, 3.3, and 1.0 times higher than publishedhuman detection limits, respectively, while maximum CS₂,DMS, and acetone concentrations were predicted to be 0.004, 0.01, and 0.04 times below published human detection limits, respectively. High carbon wood ash incorporation with biosolidseliminated DMDS odor and trimethyl amine odor, while wood ash did not significantly reduced the NH₃ odor.