(368c) Pilot-Scale Testing of Electrochemical Removal of Hydrogen Sulfide in Deep-Pit Swine Manure Storage

The presence of hydrogen sulfide (H₂S) is a widespread issue in organic waste storage, and this toxic air contaminant causes serious concerns over environment, health and safety. One example is the deep-pit manure storage, a common practice for swine facilities in upper-Midwestern states. It occasionally experiences human or animal fatal overexposure to manure gas that contains H₂S. In this study, we developed an electrochemical-based oxidation method to remove or greatly reduce sulfide generation in the stored liquid manure. The treatment system needed some equipment installation and retrofit of the current storage pit with little maintenance requirement, low electricity consumption, and low chemicals usage. Lab-scale experiments were conducted in simulated swine manure storage, and systematically analyzed sulfide removal kinetics at varying total solids contents, initial sulfide concentrations, pH, applied voltages, electrode surface areas, electrode distances, and temperatures. An on-farm pilot-scale study was then performed to further confirm the treatment performance in close-to-real environment, and provide necessary data for techno-economic assessment. An electrochemical treatment device was designed and installed in two manure pump-out accesses in a testing barn that held about 200 growing-finishing pigs. Each pit access was divided to two compartments, one for control and the other for treatment installation. Perforated sheets of two electrode materials of low carbon steel (LCS) and stainless steel Type AISI 304 (SS) were installed in accesses and tested in 97 days’ operation. From the monitored H₂S concentration in pit headspace during the treatment, it can be seen that the LCS treatment decreased a substantial amount of H₂S concentration, achieving removal efficiency of 56%-78% depending on the applied voltage of between 0.6 and 0.7 V. SS treatment removed 13%-38% of H₂S. LCS treatment required a lower voltage application but achieved better removal performance, and is more economically feasible compared to SS installation according to techno-economic assessment. However, electrode material cost accounted for 76%-87% of the net present cost of the treatment assuming 20 yrs’ life-time of the treatment device. Cheaper material, lower surface area, or more effective material will have to be optimized in order to decrease the treatment cost.