Methanogenic community change in a full-scale UASB reactor operated at a low F/M ratio

Abstract

A full-scale upflow anaerobic sludge blanket (UASB) reactor was investigated in terms of archaeal composition, acetoclastic methanogenic capacity and performance over a 2-year period. Performance of the reactor in terms of COD removal efficiency varied between 60% and 80% at organic loading rates (OLRs) in the range of 2.5–12 kg COD m^{− 3}d^{− 1}. The reactor had been operated under a F/M (food to microorganisms) ratio of 0.02–0.03 gCOD gTVS^{− 1} d^{− 1}, which is much lower than the typical values reported for similar reactors. According to specific methanogenic activity (SMA) tests the anaerobic sludge was operating at only 12–34% of its potential acetoclastic methanogenic capacity. These results demonstrated that the UASB reactor was under loaded compared to its maximum loading capacity. All other operational parameters had been maintained within their desired ranges. The SMA test and Fluorescence in situ hybridization (FISH) results revealed that a decrease in the acetoclastic methanogenic activity of the UASB sludge from 344 mL CH₄ gTVS^{− 1} d^{− 1} to 109 mL CH₄ gTVS^{− 1} d^{− 1}coincided with a decrease in the relative abundance of acetoclastic Methanosaeta from 90% ± 1.2 to 79% ± 1.4 of the archaeal population, and an increase in the relative abundance of hydrogenotrophic Methanobacteriales from non-detectable levels to 24% ± 0.7% of the archaeal population during the 2-year operation of the reactor. The relative abundance of archaeal cells within the UASB sludge was in the range of 15–17%.

Keywords:

• Fluorescence in situ hybridization
• specific methanogenic activity
• UASB reactor
• archaeal composition
• alcohol distillery effluents

Acknowledgments

This work was supported by the Scientific Research Projects of Istanbul Technical University (project no. 844 and 30696) and Bogazici University (projects no. 04Y105 and 02Y103D). Authors would also like to acknowledge Tekel Co., Turkey, for their cooperation.

Notes

*unitless.

^a Formamide concentration in the hybridization buffer.

^b Hybridization temperature.

^c Washing temperature.

^d NaCl concentration in the washing buffer.

^a (The number of cells detected with UNIV1392)/(Total cell count using SYBR Green).

^b (The number of cells detected with ARC915)/(The number of cells detected with UNIV1392).

^c (The number of cells detected with MX825)/(The number of cells detected with ARC915).

^d (The number of cells detected with MB310)/(The number of cells detected with ARC915).