Analyses of Methanogenic Population as Key Indicator for Anaerobic Digestion: A Case-Study in the Organic Fraction of Municipal Solid Waste Treatment

Purpose The anaerobic digestion of the organic fraction of municipal solid waste (OFMSW) is a treatment biologically optimizable. The analysis of the microbial balance within the digester allows not only to describe and improve the efficiency of the system but also to foresee potential variations after biochemical interventions. This work aims to highlight methanogenic population variations in two similar parallel digesters to identify bio-indicators for digestion performance after the inclusion of an additive. Methods The analysed industrial case study involved the two parallel, pilot-scale, bio-digesters of ACEA Pinerolese Industriale. They had analogous design and fed by the same OFMSW except for an additive inclusion. The analyses by qRT-PCR, on both bio-digesters, have been performed to determine an impact of the additive on the growth and metabolic activity of total methanogens, Methanosarcina spp., Methanocorpuscolum spp., and Methanospirillus spp. Results Collected data showed that the addition of biopolymers extracted from compost produced both total methanogens and Methanosarcina decrease (7.67 vs. 7.48 and 6.05 vs. 5.69 Log gene copies/mL sludge respectively, T-test p < 0.01) affecting slightly the methane yield (-8%). Methanosarcina was the highest expressed methanogen; however, the results suggested the involvement of a highly complex and heterogeneous methanogen community. Conclusions Total methanogens and active Methanosarcina modulations are able to highlight major bio-methane production even if their shift is slight. Globally only 3–4% of the present and 12–13% of the active methanogens were described. However, biological approach can supply a proxy of production performance of the digester also concerning the feeding peculiarities.