Electrochemical Removal of Aqueous Sulfide from Swine Manure

Abstract

Hydrogen sulfide (H_2 S) produced in swine manure pit storage is a safety hazard to both human and animals. An electrochemical treatment based on low carbon steel electrodes was developed to reduce aqueous sulfide and emitted H_2 S concentration from manure storage. At the selected condition (Applied voltage = 0.7 V, immersed electrode surface area = 19 cm^2/L, initial sulfide concentration = 5 - 6 mM, operation temperature = 19 °C), the process achieved an average sulfide removal rate of 2.60 mg S^(2-)/(cm^2⋅day) for the zero order kinetic model, and a rate coefficient of 0.275 /day for the 1st order kinetic model. Constant disturbance created to simulate the pumping event was found greatly accelerated the H_2 S release directly from the manure liquid; however, removals of over 90% sulfide and H_2 S significantly reduced the risk. Methane concentration went higher as the sulfide removal; 46% higher concentration was found at 95% sulfide removal from the initial concentration over 6 mM. Different from the electrochemical sulfide removal from less viscous wastewater, low voltage applied in this study was proved feasible to maximize the precipitation and minimize the flotation in swine manure. The installation of this technology may reduce the risk of manure pump-out in terms of H_2 S over-exposure and may be applied in similar circumstances where H_2 S poses threats to health and life.