RESULTS OF TRIALS OF CHEMICALS, ENZYMES AND BIOLOGICAL AGENTS FOR REDUCING ODORANT INTENSITY OF BIOSOLIDS

One goal of Philadelphia's biosolids program is to produce neither nuisance odors at its processing plant nor in the communities to which biosolids is delivered, through improving its biosolids product quality. In this commitment, Philadelphia joins many other utilities. While a major thrust of the biosolids profession is on equipment innovation and process modification, one fruitful avenue for investigation, due to relatively low capital requirements and quick implementation timeframe, is use of enzymes, chemicals and microbial blends as additives within the biosolids “value chain.” Toward that end, the Philadelphia Water Department's biosolids and wastewater operators conducted trials of such amendments at its wastewater and biosolids facilities. These products have been recently termed CEBA, the initials for “chemicals, enzymes, and biological agents.” Three products were added directly to conventional anaerobic digesters; three products were dosed into the liquid wastewater solids just prior to centrifuge dewatering; two products were applied to biosolids cake prior to subsequent land application; one ash product was mixed into cake at the application site just prior to land spreading (a second ash was demonstrated on the bench top, but was not evaluated in field scale). Product performance was measured objectively by tracking the concentration of odorant emissions (i.e., methyl mercaptan and dimethyl sulfide) from field-gathered samples over time. Several effective products include: coal cogeneration ash used at the application site; a humic mineral product spread on the cake before placement in storage; and, application of a nutrient supplement to the digester and holding tank in advance of dewatering. Recent reports, not yet verified by field application, have suggested that alum, used as a partial replacement for polymer into the centrifuge during dewatering, produces a low-odor cake. Reductions of odorant concentrations of 50 percent to more than 90 percent were observed during these trials for several products, but others showed no improvement in odor characteristics in the biosolids. This research highlights the value of objectively evaluating odor control products as part of a comprehensive effort to eliminate odor nuisances in the biosolids value chain. The research also underscores the limited understanding of the physical, biological and chemical processes at work with CEBA products. The research also suggests that application of biotechnology to wastewater treatment might open up opportunities for achieving new treatment objectives, such as reduction of organic pollutants and energy production.