Anaerobic digestion is considered unsuitable for the bioremediation of tannery effluent due to process inhibition, mainly due to high concentrations of sulfur species, and the accumulation of ${\mathrm{H}}_2\mathrm{S}$ and/or ${\mathrm{NH}}_3$. This study using the standardized biochemical methane potential protocol showed that efficient processing is possible with slaughterhouse wastewater, provided sufficient functional biomass is present at the start of the process and the ${\mathrm{SO}}_4{}^{2-}$ concentration is below inhibition threshold. Methanogenic activity (K = 13.4–17.5 and µm = 0.15–0.27) and ${\mathrm{CH}}_4$ yields were high when reactors were operated ISR ≥ 3 and/or lower ${\mathrm{SO}}_4{}^{2-}$ ≤ 710 mg/L while high ${\mathrm{SO}}_4{}^{2-}$ ≥ 1960 mg/L and ISR < 3.0 caused almost complete inhibition regardless of corresponding ISR and ${\mathrm{SO}}_4{}^{2-}$. The theoretical optimum operating conditions (922 mg/L ${\mathrm{SO}}_4{}^{2-}$, ISR = 3.72) are expected to generate 361 mL biogas/gVS, 235 mL ${\mathrm{CH}}_4$/gVS with reduction efficiencies of 27.5% VS, 27.4% TS, 75.1% TOC, 75.6% ${\mathrm{SO}}_4{}^{2-}$, and 41.1% COD. This implies that tannery sludge will be reduced by about 27% (dry mass) and ${\mathrm{SO}}_4{}^{2-}$ by 76%, with a fraction of it recovered as ${\mathrm{S}}_0$. The models displayed a perfect fit to the cumulative ${\mathrm{CH}}_4$ yields with high precision in the order Logistic > Cone > modified Gompertz > first order.

Microbial communities in hybrid linear flow channel reactors and anaerobic sequencing batch reactors operated in series for remediation and beneficiation of tannery wastewater were assessed. Despite concurrent sulfidogenesis, more intensive pre-treatment in hybrid linear flow channel reactors reduced methanogenic inhibition usually associated with anaerobic digestion of tannery effluent and promoted efficiency (max 321 mLCH₄/gCOD_consumed, 59% biogas CH₄). Nitrification and biological sulfate reduction were key metabolic pathways involved in overall and sulfate reducing bacterial community selection, respectively, during pre-treatment. Taxonomic selection could be explained by the proteinaceous and saline character of tannery effluent, with dominant genera being protein and/or amino acid degrading, halotolerant and/or ammonia tolerant. Complete oxidizers dominated the sulfidogenic populations during pre-treatment, while aceticlastic genera dominated the methanogenic populations during anaerobic digestion. With more intensive pre-treatment, the system shows promise for remediation and recovery of biogas and sulfur from tannery wastewater in support of a bio-circular economy.