Caracterização da diversidade molecular microbiana e simulação computacional da produção de biogás a partir de lodo de ETE

Abstract

Anaerobic digestion (AD) is an effective biological process for treating various types of organic waste and producing energy in the form of biogas. Bacteria and Archaea form microbial consortia, with methane gas (CH4) as the product. AD and the stability in biogas formation, crucial for reactor operation, are not yet fully understood. Identifying the microorganisms (MO) involved in the process allows understanding the system's metabolic potential. In this investigation, Anaerobic Digestion Model No. 1 (ADM1) was used to simulate CH4 production in an anaerobic reactor (RA), and an associated Biochemical Methane Potential (BMP) assay on a bench scale was conducted using sewage sludge (SS) from Alegria/RJ municipal wastewater treatment plant (WWTP) as the raw material. The SS presented the following physicochemical characteristics: pH (7.4 - 7.6), alkalinity (2,382 ± 100 mg CaCO3 L-1), tCOD (21,903 ± 1000 mg L-1), COT (895 ± 100 mg L-1), ST, STV, and SSV (2.0%, 1.1%, and 0.8%, respectively). The BMP assay was performed in six replicates under mesophilic anaerobic conditions (37 ± 0.1°C) for 11 days with CH4 yield of 137.6 ± 6.39 NmL CH4 or 124 ± 6.72 CH4 g-1 VS-1. By comparing the results obtained in BMP with the data generated by computational model ADM1, similar cumulative CH4 production curves were obtained, indicating the calibration and validation of ADM1 model. Using Illumina MiSeq platform, 16S rRNA gene sequencing revealed a core bacterial community in the solid material, showing notable variations in profiles. Before AD, the relative abundance in SS was composed of: Proteobacteria > Bacteroidota > Actinobacteriota. Post-AD, the relative abundance changed to Firmicutes > Synergistota > Proteobacteria, with Sporanaerobacter and Clostridium emerging as dominant genera. The methanogenic community underwent a shift from acetoclastic to hydrogenotrophic metabolic pathway in the laboratory-scale reactors. At the genus level, Methanosaeta, Methanolinea, and Methanofastidiosum initially predominated, while post-AD, Methanobacterium, Methanosaeta, and Methanospirillum took precedence. This metabolic transition may be linked to the increased abundance of Firmicutes, particularly Clostridia, harboring acetate-oxidizing bacteria facilitating acetate conversion into hydrogen. Firmicutes was the dominant phylum during AD, followed by Synergistota. Sporanaerobacter and Clostridium were dominant genera in BMP reactors. The change from Methanosaeta to Methanobacterium in the methanogenic archaeal community may be related to increased Firmicutes and Synergistota phyla in the reactors, affecting the degree of substrate fermentation, which contains acetate-oxidizing bacteria converting acetate into H2 eliminated by methanogens, making the reaction thermodynamically feasible for these groups. The microbial profiles observed in this study expand the current knowledge on potential syntrophic relationships between H2-producing bacteria and hydrogenotrophic methanogenic archaea in SS. The results obtained help envision new horizons for future studies of microbial ecology and improvement of biogas production in WWTPs.