Inhibitory effects of sulfide on nitrifying biomass in the anaerobic-anoxic-aerobic wastewater treatment process

BACKGROUND: Long pipeline transportation of wastewater usually generates high concentration of sulfide; however, information on nitrification inhibition by sulfide in the anaerobic-anoxic-aerobic (AAO) process is still scarce. This study focused on how sulfide could inhibit nitrification activity in the AAO process, and the inhibitory effect of initial sulfide concentration and anaerobic exposure time on the behavior of nitrifying biomass. RESULTS: The net maximum specific growth rate (μ_AUT-b_AUT) was, respectively, 0.06 ± 0.01 and 0.31 ± 0.03 d^-1 at 15 and 20°C in a full-scale AAO wastewater treatment plant for long-pipeline transported wastewater. The μ_AUT-b_AUT was not affected by 6.2 mg L^-1 sulfide under aerated condition, but reduced by 75.9% after unaerated exposure for 0.5 h. The first-order kinetic constant of sulfide inhibition under anaerobic conditions was 0.658 h^-1, and half maximal inhibition concentration of sulfide on nitrification was 36.0 and 10.0 mg L^-1 after 1.0 h and 1.5 h anaerobic exposure, respectively. CONCLUSION: Nitrifying biomass was sensitive to the presence of sulfide under anaerobic conditions. The inhibitory reaction of sulfide on nitrifying biomass under anaerobic conditions conformed to the first-order kinetic reaction, while the effect of initial sulfide concentration on nitrification inhibition matched the modified Monod model.