SULFIDE INHIBITION OF ANAEROBIC DEGRADATION OF LACTATE AND ACETATE

Bench-scale batch anaerobic degration of lactate and acetate was investigated using three sets of serum bottles. All serum bottles were fed 1g1(-1) COD and 15.6 mM (1.5 g1(-1) SO(4)2- at the start of the experiment. Set one (S(L)) used lactic acid, set two (S(A)) used acetic acid, and set three (S(M)) used a 1:1 mixture on a COD basis of the two organic acids. Each set consisted of 10 serum bottles of which 5 were started at a pH of 7 and 5 at a pH of 8. Each pH subset reactor had a different initial total sulfide (TS) concentration, which varied from 3.13 to 31.3 mM (100-1000mg1(-1)). Acetate removal followed first order reaction kinetics and proceeded without any significant sulfate reduction. Inhibition of acetate removal by aqueous hydrogen sulfide (H2S) was modeled using an exponential function. Both propionate removal and sulfate reduction were inhibited proportionally to the concentration of TS. This suggests a crucial role for the sulfate reducing bacteria in mediating propionate degradation to acetate. In the low pH subset of S(M), complete inhibition of sulfate reduction occurred at only 17% inhibition of methanogenesis. Complete COD removal occurred in all the serum bottles of the high pH subsets, indicating the important role of H2S in sulfide inhibition.