Effect of enhancing nutrient balance in anaerobic digester feedstock by co-substrate addition on the microbial diversity and energy production from municipal sewage sludge

Enhancement of methane production during anaerobic digestion of waste activated sludge (WAS) could improve the energy self sufficiency of the municipal wastewater treatment plants (WWTPs). Therefore, mixing WAS with organic wastes improved process performance and stability. In this work, the anaerobic co-digestion of WAS combined with the olive processing wastewater (OPW) was investigated and associated with the energetic benefits and microbial populations shifts. The bio-methane potential (BMP) of various WAS and OPW mixtures corresponding to increased phenols concentrations were tested. The anaerobic digestion of better proportions (90%/10% and 80%/20%) was performed in anaerobic sequencing batch reactors (ASBRs). The biodegradation of phenols at concentrations up to 0.76 g/L was confirmed by Sephadex gel filtration showing that ASBR, which is suspended growth reactor, can handle much higher concentration of toxic compounds. Microbial analysis showed that phenols induced significantly the archaea community dynamic, which showed highly richness and diversity in the well performed reactor. The dominant bacteria and archaea phylotypes were affiliated to Proteobacteria and Methanosarcinales, respectively. Therefore, OPW addition increased total energy production from 24.6 kWh/ton to 64.7 kWh/ton, which would provide 0.43 M€/year net benefits only from the electric power. In addition it brings a payback time on investment of 2 years for WWTPs modification, which was considered interesting.