SULFATE-REDUCING BACTERIA IN ANAEROBIC PROPIONATE SYSTEMS

The design of anaerobic treatment systems for sulfate containing high- strength wastewater requires the understanding of interactions between sulfate reducers and other anaerobes. The objectives of this research were to study the effects of the feed propionate:sulfate ratio on the interactions among the sulfate-reducing bacteria (SRB), acetogens, an d methanogens, and to determine the kinetics of anaerobic biological r eactions for propionate degradation under sulfate-limited and sulfate- rich conditions. Both continuous and batch experiments were conducted to meet these objectives. In sulfate-limited chemostats with propionat e as the sole carbon source, the effluent sulfate concentration was go verned by the propionate utilizing SRB and was below 10 mg/L. In sulfa te-rich systems the effluent sulfate concentration was governed by ace tate utilizing SRB and could not be maintained below 400 mg/L without controlling the sulfide concentration. Under these sulfate-rich condit ions, a decrease in SRT from 30 to 13 d decreased the extent of acetat e utilization by SRB. The propionate utilizing SRB outcompeted the pro pionate utilizing acetogens in the chemostats. This was attributed to lower Monod-half velocity coefficient, K-s, for propionate utilization by SRB (4.5 mg-Pm), than the K-s for propionate utilization by acetog ens (20.4 mg-Pr/L). The rate constants (k) for SRB and acetogens in te rms of mg of propionate/mg of volatile suspended solids (VSS) per day were approximately 5.2 and 3.1 mg-Pr/mg-VSS-d, respectively. In sulfat e-rich conditions, propionate was utilized by SRB, and the intermediat e acetate was utilized by both SRB and methanogens.