Syntrophic acetate oxidation in industrial CSTR biogas digesters

• 10 out of 13 randomly selected biogas plants showed syntrophic acetate oxidation (SAO).
• High SAO bacteria (SAOB) abundance despite differences in operation parameters.
• Stable levels of SAOB under variable operating conditions.
• SAOB correlated positively with low abundance of aceticlastic methanogens.
• The thermophilic SAOB T. phaeum correlated with high ammonia levels.

The extent of syntrophic acetate oxidation (SAO) and the levels of known SAO bacteria and acetate- and hydrogen-consuming methanogens were determined in sludge from 13 commercial biogas production plants. Results from these measurements were statistically related to the prevailing operating conditions, through partial least squares (PLS) analysis. This revealed that high abundance of microorganisms involved in SAO was positively correlated with relatively low abundance of aceticlastic methanogens and high concentrations of free ammonia (>160 mg/L) and volatile fatty acids (VFA). Temperature was identified as another influencing factor for the population structure of the syntrophic acetate oxidising bacteria (SAOB). Overall, there was a high abundance of SAOB in the different digesters despite differences in their operating parameters, indicating that SAOB are an enduring and important component of biogas-producing consortia.