Interactions among sulfate reducers, acetogens, and methanogens in anaerobic propionate systems

Abstract

The complex process of propionate oxidation in anaerobic systems in the presence of excess sulfate is based on combinations of six biological reactions. Laboratory batch and continuous experiments were conducted to study which of these reactions were predominant in propionate oxidation by sulfate-reducing bacteria in the presence of acetogens and methanogens. The engineering significance of the feed propionate to sulfate ratio was studied. In batch serum bottle experiments, sulfidewas more toxic to sulfate-reducing bacteria (SRB) than to acetogens and methanogens. Acetate was the least favored substrate for sulfate reduction. Two mechanisms appear possible under sulfate-limited conditions: (I) propionate use by both SRB and non-SRB acetogens and acetate and hydrogen use by methanogens and (2) propionate use by non-SRB acetogens followed by acetate use by methanogens and hydrogen use by both SRB and methanogens. In the chemostats, at a feed propi· onate:sulfate ratio of 2.2 (sulfate-limited condition), the acetate formed was primarily used by methanogens. With a gradual decrease in feed propionate:sulfate ratio from 2.2 to 0.44 (sulfate-rich condition), SRB outcompeted methanogens for acetate. In the chemostat study un-ionized H2S concentrations of up to 178 mg S/L (total sulfide 464 mg S/L) did not inhibit sulfate reduction. Water Environ. Res .. 67,330 (1995).

Methanogenic community changes, and emissions of methane and other gases, during storage of acidified and untreated pig slurry

“…The nature of inhibition of methanogens at pH 5Á5 (Farm A) and near-neutral pH (Farm B) may differ. At near-neutral pH, successful competition for H 2 by sulphate-reducing bacteria in the sulphate-rich environment of acidified slurry may account for the reduction in CH 4 emissions (Uberoi and Bhattacharya 1995). According to Chen et al (2008), methanogens are sensitive to hydrogen sulphide rather than total sulphide, and therefore the potential for toxic effects was much higher in slurry from Farm A acidified to pH 5Á5.…”

System Performance in UASB Reactors Receiving Increasing Levels of Sulfate

“…As a bacterial product, H2S can be controlled by selectively inhibiting SRB [9], purging the system by scrubbing [7] or precipitation with metal salts [10]. Inhibition by sulfate at levels above 1000 mg SO 4 L -1 in the influent starts to affect methane production [11] by providing favorable conditions to SRB in the competition for necessary substrates with methanogens.…”

Thermophilic sulfate reduction and methanogenesis with methanol in a high rate anaerobic reactor

“…Since hydrogen apparently is the main electron source for the methanogens in the sludge, very likely the competition between SRB and MA for hydrogen plays an important role in the fate of electron equivalents derived from methanol. This would explain why sulfate reduction ultimately dominates over methanogenesis in the reactors, because it is well known that SRB outcompete MA for hydrogen when sufficient sulfate is present (Harada et al, 1994;Uberoi and Bhattacharya, 1995;Visser et al, 1993). This presumably can be attributed to more favourable kinetic parameters of SRB (Oude Elferink et al, 1994;Widdel, 1988) or a lower hydrogen threshold level (Lovley et al, 1982) over MA.…”