ANAEROBIC DIGESTION OF RICOTTA CHEESE WHEY: EFFECT OF PHASE SEPARATION ON METHANE PRODUCTION AND MICROBIAL COMMUNITY STRUCTURE

Different process configurations for the energetic valorization of Ricotta Cheese Whey (RCW), a dairy byproduct, were investigated by mesophilic Anaerobic Digestion (AD) under continuous operation mode using a Mono-phase (MPR) and two Bi-phase (BPR1 and BPR2) Continuous Stirred-Tank Reactors (CSTRs). The results showed an increase in CH4 production (21,4%-17.3%) and in CH4 content in biogas (19%-4%), in BPR1 and BPR2 respectively, compared to MPR (9.59 +/- 0.54NLCH(4)/d; 56.3 +/- 0.65% CH4). Although in BPR1 first phase, it was found negligible H-2 production (BPR1=0.07 +/- 0.002NLH(2)/d; 1.1 +/- 0.4% H-2; BPR2=3.91 +/- 0.50 NLH2/d; 39 +/- 2% H-2), a methane production comparable to BPR2 was achieved, showing that the fermentation processes that occurred in the first phase can increases the final production of CH4 regardless of the metabolic pathway. Low H-2 production in BPR1 contrasts with the high acetic acid concentration detected (19.30 +/- 1.4 mM), suggesting the establishment of an alternative pathway, the homoacetogenesis, which consumes H-2 and CO2 to produce acetic acid. In order to investigate the effect of phase separations in BPR1 and BPR2, the microbial community composition was analyzed in methanogenic reactors by Fluorescent In Situ Hybridization (FISH) in terms of Eubacteria vs Archaea and, inside the acetotrophic methanogenic guild, for Methanosarcina vs Methanosaeta. FISH analysis reveal the predominance in BPR1 of Methanosarcina (9,4% vs 16,5% of total acetotrophic Archaea), compared to Methanosaeta, which predominate in BPR2 (8,4% vs 16.8%). Performing an economic feasibility analysis, the energetic valorization of dairy wastewater was result sustainable and profitable, pursuing the biorefinery concept.