Effect of Chemical addition on Production of Volatile Sulfur Compounds and Odor from Anaerobically Digested Biosolids

Abstract

A study was performed to determine the effect of chemical addition both pre- and post-dewatering on volatile sulfur compound (VSC) and odor production. The chemicals investigated included cationic polymer, FeCl3, calcium nitrate with anthraquinone, potassium nitrate, calcium hypochlorite, and calcium hydroxide. The chemicals were added at varying dosages. In the case of cationic polymer and FeCl3 addition, these chemicals were added in a full-scale test prior to dewatering on medium solids centrifuges. The other chemicals were added directly to the cake after dewatering. The cake samples were collected after chemical addition and 100 g of cake was stored in 750 mL PETE bottles and headspace samples were analyzed for methyl mercaptan (MT), dimethyl sulfide (DMS), and dimethyl disulfide (DMDS). In addition, the headspace samples of the polymer dose and FeCl3 study were analyzed by an odor panel for hedonic tone and intensity. Two different biosolids cake sources were used for the experiments. Increasing polymer dose, 6.6, 8.5, and 11 g/kg dry solids (DS), resulted in the production of greater concentrations of MT and DMS and the odor panel also reported increased intensity and worse hedonic tone. The increased odors associated with the polymer dose was correlated to the amount of protein sequestered by the polymer and deposited in the cake. Protein is considered one of the main precursors for VSC production. Therefore, minimizing polymer dose will aid in reducing VSC associated odors. Addition of FeCl3 (0, 24, 63, 125 g FeCl3/kg DS) resulted in a decrease in the VSC production as well as odors measured by the odor panel. The decrease in odors was proportional with the FeCl3 dose and thought to be associated with the binding of sulfur compounds by the iron. Addition of nitrate compounds also reduced VSCs and odors, as well as calcium hydroxide and calcium hypochlorite. The results provide some preliminary information on methods to control odors in cake solids and suggest a combination of minimized polymer dose and chemical addition could be used as a control strategy for odor production. Additional research is needed to further exam these effects as well as develop cost data to determine the economic feasibility of these treatments.