Improved Stability of Anaerobic Digestion through the Use of Selective Acidogenic Culture

Abstract

Accumulation of volatile fatty acids (VFAs) under overloading conditions in anaerobic reactors is a common problem. There is a need to stop this accumulation to improve reactor stability. In this study, propionate-, butyrate-, and acetate-degrading cultures were enriched and used as inocula in a mesophilic two-stage reactor to improve system stability. The performance of a test reactor was compared with that of a control reactor that was not seeded with specific VFA-degrading inocula under normal and overloading conditions. The reactors were fed with simulated wastewater having a chemical oxygen demand (COD) of 10,000 mg L−1. The test reactor inoculated with VFA-degrading cultures showed better performance in terms of methane production, COD removal, and VFA degradation. Also, after two consecutive organic shocks (influent COD 20,000 mg L−1) the test reactor recovered within four days and low levels of VFAs, especially propionate (429 mg L−1), were observed. In contrast, in the control reactor the concentration of VFA did not decline to preshock levels, even after five days of two consecutive shocks. PCR-denaturing gradient gel electrophoresis analysis using 16S rRNA gene amplicons also indicated a significant difference in archaeal community structure in the control and test reactors. Methanosarcinaceae was found dominant in the test reactor whereas in the control reactor an equal abundance of both Methanosaetaceae and Methanosarcinaceae was observed. Specific methanogenic activity also suggested higher acetoclastic and hydrogenotrophic activity of the sludge in the test reactor. Overall, using enriched culture as inocula resulted in a more balanced and robust methanogenic consortium and in improved system stability, with efficient degradation of the high concentration of VFAs.