Optimizing anaerobic digestion of textile wastewater: the critical role of the inoculum

Introduction: Among other resources, the textile industry consumes substantial volumes of water, thus producing highly contaminated effluents. These effluents are typically highly coloured and contain various chemical compounds (such as surfactants and dyes) and high salt concentrations, resulting in elevated chemical oxygen demand (COD), biochemical oxygen demand (BOD), and conductivity levels. Therefore, they require appropriate treatment before being discharged into water bodies or reused in other processes (Pereira and Alves, 2012). Textile effluent valorisation by anaerobic digestion (AD) helps to reduce the environmental impact while fostering a circular economy, but the efficiency of the AD process is highly affected by the recalcitrant composition of these effluents. This study evaluated the effect of two different anaerobic inocula on biogas yield from textile effluent. Methodology: The textile effluent applied in the study was collected from the homogenization tank of a textile company in the North of Portugal. The anaerobic biodegradation potential of the effluent was evaluated through BMP (Biochemical Methane Potential) assays under anaerobic conditions at 37 °C, without agitation (Angelidaki et al., 2009; Holliger et al., 2016). The effluent was incubated with (60% (v/v)) inoculum. Two different inocula were tested: (i) a mixture of 50% anaerobic granular biomass and 50% anaerobic sludge collected from wastewater treatment plants anaerobic digesters, and (ii) anaerobic granular biomass collected from an anaerobic digester at a textile company. The microbial community was analyzed through 16S rRNA gene sequencing. Results: The methane produced by inoculum (i) was lower than that produced in the blank assay, showing a potential toxic effect of the effluent on the anaerobic microbial consortium. With inoculum (ii), the methane produced from effluent was almost 7 times higher than the methane produced in the blank assay. In this assay, a methanation percentage of nearly 35% was obtained. In the control assays, more than 80% of the microcrystalline cellulose was converted into CH for both inocula, indicating their good activity. The most abundant microorganisms present in microcosms were identified, and insights into the relationships between bacteria and methanogens were obtained. Conclusions: The origin and microbial composition of the inoculum were a crucial factor in the management, treatment, and valorization of textile wastewater through AD.