Abstract
Influence of sulfide on the activities of sulfate-reducing bacteria (SRB) and hydrogenproducing proton-reducing bacteria (PRB) in anaerobic degradation of palmitate and propionate was investigated using four anaerobic sludge consortia (referred to as R1 through R4) derived from different sources.Four sludge consortia were categorized as follows according to the type of reactor and the level of sulfide for sludge cultivation: R1 as CSTR-low sulfide, R2 as CSTR-high sulfide, R3 as UASB-low sulfide, and R4 as UASB-high sulfide.
As for R1 sludge (CSTR, low sulfide), palmitate degradation activity (Pal-DA) by a symbiosis between palmitate-degrading PRB (Pal-PRB) and hydrogen-scavenging SRB (H-SRB) was 2.6 times as large as that by palmitate-oxidizing SRB (Pal-SRB).Pal-DA of R2 sludge (CSTR, high sulfide) by the symbiosis of Pal-SRB with H-SRB was only one-fifth of that of R1 sludge.As for R3 sludge (UASB, low sulfide), a symbiosis between PRB and hydrogen-scavenging methanogens (H-MPB) performed the same magnitude of propionate degradation activity (Pro-DA) as propionate-oxidizing SRB (Pro-SRB) did. Pro-DA of R4 sludge (UASB, high sulfide) was entirely attributable by Pro-SRB solely.
Two distinctive patterns were observed with respect to sulfide effect on Pal-DA and Pro-DA.Highsulfide sludge consortia, R2 and R4 showed a tendency to consistently decrease Pal-DA and Pro-DA, respectively, with increasing sulfide concentration.On the contrary, Pal-DA and Pro-DA of low-sulfide sludge, R1 and R3 possessed optima around 50 mg H2S-S·l-1, above which point both activities inhibited by sulfide in the same manner as the case of high-sulfide sludge.
