Effects of sulfate concentration and sludge retention time on the interaction between methane production and sulfate reduction for butyrate

Abstract

The effects of sulfate concentration and COD/S ratio on the anaerobic degradation of butyrate were investigated by using 2.0 L anaerobic chemostat-type reactor at 35°C. The study was conducted over a wide range of the COD/S ratio (1.5 to 148) by varying COD concentrations (2500–10000 mg/L) and sulfate concentrations (68–1667 mg-S/L) in the substrate. The sludge retention time at each COD/S ratio was changed from 5 to 20 days. The interaction between methane producing bacteria (MPB) and sulfate-reducing bacteria (SRB) was evidently influenced by COD/S ratio in the substrate. When COD/S ratio was 6.0 or more, methane production was the predominate reaction and over 80% of the total electron flow was used by MPB. At the COD/S ratio of 1.5, SRB utilzed over 50% of the total electron flow. A large amount of sulfate reduction resulted in not only the decrease of methane production, but also the rapid increase of the bacterial growth. The degradation pathway of butyrate and the composition of bacterial populations in the reactor were also dominated by COD/S ratio. In sulfate depleted condition, butyrate was degraded to methane via acetate and hydrogen by MPB. On the other hand, butyrate was firstly degraded into sulfide and acetate in sulfate rich conditions by SRB, and the produced acetate was then degraded by acetate consuming MPB and SRB. The methanogenesis from acetate was inhibited by the high concentration of sulfide.

Biological sulfate removal from acrylic fiber manufacturing wastewater using a two-stage UASB reactor

“…The growth of the SRB would be sulfate-limited, and it enabled the MPA to outcompete the SRB, and made MPA predominate in the reactor. This agreed with Mizuno et al (2007) that at high COD/SO 2− 4 , the MPA predominated while at lower COD/SO 2− 4 the SRB were more competitive (Mizuno et al, 1994). FISH results were also in accordance with the sulfate reduction shown in Section 2.1.…”

Effect of Sulfide Inhibition and Organic Shock Loading on Anaerobic Biofilm Reactors Treating a Low‐Temperature, High‐Sulfate Wastewater

“…Many studies have emphasized the COD/sulfate ratio as an important operational parameter for sulfate fed systems (Choi and Rim 1991;Maillacheruvu et al 1993;McCartney and Oleszkiewicz 1993;Mizuno et al 1994;Parkin et al 1991;Weijma et al 2002). This ratio gives an indication of the amount of sulfate available for SRB metabolism.…”

System Performance in UASB Reactors Receiving Increasing Levels of Sulfate

“…Anaerobic digestion of sulfate-rich wastewaters promotes the activity of sulfate-reducing bacteria (SRB), resulting in toxicity from H2S produced from the sulfate reduction [1] and competition for substrates: H2 and acetate with methanogens (decreasing methane production), and shortchain volatile fatty acids (butyrate, propionate) with acetogenic bacteria [2][3][4][5]. H2S is a highly toxic compound which denatures cell proteins [6][7][8].…”

“…Sulfate-reducing bacteria can use a wide variety of organic matter [12] and outcompete methanogens under substrate-limited conditions [13] due to their higher substrate affinity. Organic matter to sulfate (COD/SO4) ratios higher than 4 will promote methanogenic activity [3,6] and under long-term, non-substrate-limiting conditions, SRB will tend to use a low percentage of organic matter [14][15][16]. Also, high-rate (low hydraulic retention time (HRT)) reactors are not advantageous for SRB due to their low retention and biofilm/ floc forming ability [15][16][17].…”