Sulfate Reduction Relative to Methane Production in High-Rate Anaerobic Digestion: Microbiological Aspects

Abstract

acetate (medium A) or acetate together with ethanol (medium AE) digested in high-rate anaerobic reactors. The purpose of this paper is to examine in more detail why the SRB were apparently not able to scavenge the major part of the electron flow under those conditions. Several factors which could affect the activities of the SRB were investigated. These include the possible feedback inhibition of H2S on SRB, iron availability for the SRB, the effect of the SRB inocula, substrate concentration, and the capacity of the SRB to colonize and adhere in the carrier matrix of the reactor. The effect of iron availability was investigated because it has been reported that the SRB have an absolute requirement for iron (2, 13, 17). A deficiency of this element could severely affect the growth of the SRB.

Effect of influent COD/SO42− ratios on mesophilic anaerobic reactor biomass populations: physico-chemical and microbiological properties

“…These contradictory findings may be related to differences in acetate, sulphate and sulphide concentrations which prevailed in the systems under investigation, the pH and duration of the experiments and the reactor design. found that retained biomass reactors promoted dominance of AMBA over ASRB and this is supported by findings of the superior attachment properties of AMPA (Isa et al, 1986;Omil et al, 1996Omil et al, , 1997Shin et al, 1997). HSRB were found to play a more significant role in the conversion of hydrogen in the present study but did not become completely dominant.…”

“…These authors reported that SRB were never able to completely outcompete methanogens. The coexistence of SRB and methanogens in the presence of nonlimiting sulphate conditions has been reported in the literature (Isa et al, 1986;Nielsen, 1987;Yoda et al, 1987). SRB species are reported to occupy the outer layer (50-100 mm) (Santegoeds et al, 1999;Sekiguchi et al, 1999).…”

“…The DG1 (kJ/mol) for the OHPA reaction is 176.1 compared to -37.8 for propionate oxidation by SRB (Laanbroek et al, 1984). In conditions of excess sulphate, the growth kinetic properties of propionate degrading SRB clearly show that they have a competitive advantage over OHPA and this was shown to be true in many studies (Isa et al, 1986;Visser et al, 1993). In reactors operating at low influent sulphate concentrations (high COD : SO 4 2À ratios), the outcome of competition is not so clear.…”

“…Although pure cultures of sulphate reducing bacteria cultivated in the laboratory often aggregate in clumps or attach to surfaces (Widdel, 1988), the length of time taken for the SRB to form a biofilm or to granulate in anaerobic reactors is not clear (Visser, 1995). According to Isa et al (1986), the superior colonization capacity of MPA would enable these bacteria to successfully outcompete the SRB in biofilm reactors. On the contrary, Yoda et al (1987) assumed an equal attachment ability of SRB and MPA.…”

Effect of Sulfate Reduction on Chemical Oxygen Demand Removal in an Anaerobic Baffled Reactor

“…However, this competition is based on subtle interrelationships that remain unclear and caution must be exercised against oversimplified and trivial analysis that assumes the dominance of sulfate reduction based solely on kinetic and thermodynamic considerations (Speece, 1996). The reason is that many factors affect the delicate ecosystems involved, such as substrate composition and concentration, chemical oxygen demand-to-sulfate (COD:SO 4 2Ϫ ) ratios, sulfide levels, adhesion properties, hydrogen partial pressures, trace metals, nutrients, chelators and vitamin concentrations, changes in half saturation constant (K s , M/L 3 ) and maximum specific rate of substrate use (k max ,M substrate /M x ⅐t, where x is the cell concentration), thermodynamics, proximity (biofilm versus dispersed), temperature, longterm shifts, immobilization properties, substrate concentrations, reactor configurations (Speece, 1996), organic loading rate (Choi and Rim, 1991), pH (Koster et al, 1986), proximity of sulfate reduction with respect to methanogenesis, pH gradients (Colleran et al, 1995), and acclimatization (Isa et al, 1986b).…”