Tartaric acid and barium chloride pretreatment of distillery spent wash enhances biomethanation efficiency and methanogenic diversity: insights from mcrA amplicon sequencing.

The distillery sector discharges approximately 40 billion litres of distillery spent wash (DSW) annually, a recalcitrant pollutant characterised by high organic loading, excessive potassium concentration (> 8000 ppm), elevated sulphate levels (> 600 ppm), heavy metals, high electrical conductivity (EC), and acidic pH. The indiscriminate discharge of untreated distillery spent wash presents a profound hazard to ecosystems and environmental integrity. Despite its considerable potential as an efficient feedstock for biogas production, the effluent's inhibitory components, mainly potassium and sulphate, require a strategic remediation strategy. This study elucidates the efficacy of selective chemical pretreatment using 1 M tartaric acid (1:1 v/v) and barium chloride (9.2 g L- 1), individually achieving 82 (± 0.03) % potassium and 86 (± 0.04) % sulphate removal. The combined pretreatment reduced potassium and sulphate concentrations by 80.78% and 83.28%, respectively. Biomethanation of this TA + BC-DSW (combined tartaric acid and barium chloride) mixed with cow dung (1:1 v/v) produced 12.10 L of biogas, a 6.8-fold increase over untreated DSW (1.79 L of biogas), while the methane content increased from 45.0% to 69.5%. Scale-up in a 12 L reactor yielded 62.56 L of biogas containing 73.5% methane. Amplicon (mcrA) gene-based nanopore sequencing revealed enrichment of methanogenic taxa, particularly Methanocorpusculum, and greater methanogenic diversity in pretreated samples. Overall, the integrated pretreatment-biomethanation approach offers a promising and potentially scalable strategy for converting inhibitory DSW into renewable biogas while mitigating its environmental pollution, thereby advancing sustainable waste valorisation and supporting circular bioeconomy practices.