Anaerobic Digestion of Agro-Industrial Wastewater with high sulfate rates: The issues of its reduction into sulphide and its consequences onto the biodigester’s stability.

GIRARDI, VALENTINA; OLIVERA, CAMILA; FATTOBENE, LUCÍA; TONDO, MARÍA LAURA; HERRERO, MARÍA SOL; PÉREZ, LEONARDO MARTÍN; SALVATIERRA, LUCAS M.

Buenos Aires

Congreso; WCCE11 - 11th WORLD CONGRESS OF CHEMICAL ENGINEERING IACCHE - XXX INTERAMERICAN CONGRESS OF CHEMICAL ENGINEERING CAIQ2023 - XI ARGENTINIAN CONGRESS OF CHEMICAL ENGINEERING CIBIQ2023 - II IBEROAMERICAN CONGRESS OF CHEMICAL ENGINEERING; 2023

World Chemical Engineering Council

The study of circular economy has brought attention to the potential use of agro-industrial wastewater as feedstock in fermentation or green chemical processes to produce new valuable products. When such strategies are not feasible, anaerobic digestion (AD) is the best alternative to convert stored chemical power into energy, while also avoiding the release of large amounts of organic matter into the environment. However, the presence of high sulfate levels in the substrate can hinder the application of AD by stimulating the growth of sulfate-reducing bacteria (SRB), which not only compete with other prokaryotes for substrates but also generate toxic levels of H2S that affects methanogens and other microorganisms [1]. Hence, the generation of wastewater with high levels of sulfate and organic matter by several industries, including pulp and chemical plants, pharmaceuticals, and food processing facilities [2], emphasizes the need for greater attention and consideration.In this experiment, the impact of high sulfate concentration in an agro-industrial wastewater (SS) on AD was investigated. Six independent anaerobic bioreactors were used, each with a 3-liter inoculum and designed to operate in semi-continuous mode. During the stabilization stage, the bioreactors were supplied with a constant volumetric organic loading rate (ORL, equal to 2g COD/liter.day) by providing a base effluent (BS) with a chemical oxygen demand (COD) of 200 g/l and negligible sulfate concentration. The feeding composition of the bioreactors was then modified by increasing the proportion of SS (a substrate with a COD of 100 g/l, pH of 4, and sulfate concentration of 25 g/l) while maintaining the ORL constant. Therefore, bioreactor R1: 100% BS = control; R2: BS 90% - SS 10%; R3: 70% BS - 30% SS; R4: 50% BS - 50% SS; R5: 30% BS - 70% SS; and R6: 100% SS.The 50-day experiment evaluated several parameters, such as pH, production and quality of biogas (relative concentrations of CH4, CO2, O2, and H2S), sulfur balance, COD, etc. DNA extractions and metagenomic sequencing were conducted on the V3-V4 region of the 16S rRNA gene using the Illumina MiSeq platform. Results showed that an inhibitory process occurred as the proportion of SS increased, as evidenced by changes in the relative abundance of SBRs. Volatile sulfur compounds (VSCs) were observed when H2S levels exceeded 10,000 ppmv, and MeSH, EtSH, and DMS were strongly correlated with SRBs, such as Desulfocella, Desulfobacteraceae, and Desulfocarbo. PICRUSt analysis also predicted an increase in the abundance of dissimilatory sulfate reduction enzymes. A significant decrease in the archaeal abundance and CH4 production between bioreactors was noted: This could be due to the competition between methanogenic archaea and SRBs for substrates, as well as the heightened sensitivity of methanogens to H2S toxicity.