Influence of Raw Sludge Quality on the Efficiency of Microaerobic Sulfide Removal during Anaerobic Digestion of Sewage Sludge

Biogas produced by anaerobic digestion of organic substances is often polluted by hydrogen sulfide (H₂S) when organic matter containing sulfur compounds is digested. Energy use of biogas is complicated by H₂S content and it must be removed. Microaeration has recently been proven as a relatively simple and highly efficient biological method for sulfide removal regarding anaerobic digestion of biosolids. Our experience with a long term operation of the microaerobic digester confirms feasibility of highly efficient H₂S removal (about 99 %). However, a reliable control for air dosing according to raw sludge quality is a necessary condition for high and stable efficiency for microaerobic H₂S removal. It was observed that H₂S concentration in biogas varied significantly even at stable concentrations of sulfur compounds in raw sludge. Results prove that concentration of H₂S is significantly influenced not only by occurrence of sulfur compounds but also by presence of metals capable of binding to insoluble sulfide. Fe³⁺ and Al³⁺, most commonly used phosphorus removal agents during wastewater treatment, have a completely different impact on distribution of sulfide compounds.