Biological pre-treatment of wastewater containing sulfate using anaerobic immobilized cells.

Biological reduction of sulfate to sulfide using sulfate reducing bacteria (SRB) was investigated. A respirometer was used to study the sulfide toxicity in the systems fed glucose, the results showed that sulfide would start to inhibit methanogens when the dissolved sulfide and total sulfide concentrations were 276.4 and 304.6 mg/L, respectively. When chemostats were used to study the Monod kinetic coefficients, Y, kd, Ks, and k were 0.36 mg VSS (volatile suspended solids) using SRB/mg SO4-S, 0.05/day, 147.30 mg SO4-S/L, and 6.50 mg SO4-S/mg VSS using SRB-d, respectively. Using pure cultural techniques, SRB were found to be 29.45% of the VSS in the chemostats. Sulfate removal using an upflow anaerobic filter packed with immobilized cells was also investigated. Under sulfate loading rates of 0.2 and 0.4 g SO4-S/L day, and a hydraulic retention time (HRT) of 2 days, a sulfate removal efficiency greater than 93% could be achieved. When the filter was operated under COD (chemical oxygen demand)/S from 10/1 to 5/1 and HRTs of 2, 1 and 0.5 days, sulfate removal efficiency was between 98.1 and 70.9%. It is believed that protection by the immobilized cell structure caused the microbial cells in the filter to tolerate higher dissolved sulfide (447.8 mg/L) and total sulfide (940.3 mg/L) levels, allowing a much higher biomass concentration (13.2-13.5 g VSS/L) to be reached.