In situ substrates for sulfidogens and methanogens in municipal anaerobic sewage digesters with different levels of sulfate

To clarify the interaction between sulfidogens and methanogens in municipal anaerobic digesters, in situ substrate utilization by the two microbial gr oups was characterized by the accumulation rates of substrates after the ad dition of specific inhibitors, 20 mM of molybdate for sulfidogens and 0.01% (v/v) of chloroform for methanogens in three anaerobic sludge digesters wi th different concentrations of sulfate (A, 1.2; B, 1.8; C, 2.7 mM). The rat es. of sulfate reduction and methane production in sludge C were the highes t and the lowest, respectively among the three sludges. The major substrate s for methanogens were acetate (35-58%), and propionate (17-22%) in all the sludges. Propionate should be utilized by methanogens after conversion to acetate and H-2 by syntrophic hydrogen-producing acetogens, as no methanoge ns are known to directly utilize propionate. Detectable accumulated substra tes for sulfidogens (< 20%) were propionate in sludges A and B and acetate in C. Still approximately 80% of substrates for sulfidogens were unknown. T hese results show that acetate or propionate is a common substrate for sulf idogens and methanogens but sulfidogens can mainly grow on the other substr ates in the municipal anaerobic sludges, implying nutritional segregation b etween sulfidogens and methanogens. (C) 2000 Elsevier Science Ltd. All righ ts reserved.