Resource recovery from tannery wastewater using an integrated biological system: Towards a circular bioeconomy and net positive tannery operations

Anaerobic digestion (AD) of tannery effluents generated by beamhouse processes is limited by ammonia and sulfur species. High sulfate concentrations in beamhouse effluents (BHE) promote sulfidogenesis during AD, and the hydrogen sulfide that is generated inhibits methanogenesis. The feasibility of using a novel integrated biological system that comprised of hybrid linear flow channel reactor/s (HLFCR/s) and an anaerobic sequential batch reactor (AnSBR) connected in series mainly for the pre-treatment and recovery of elemental sulfur (S0) and methane (CH4) was investigated. The application of single-stage and two-stage HLFCR topology operating at 8 and 4 days’ hydraulic retention times (HRT), respectively, produced effluents that were ideal for AD. Single-stage HLFCR (8-days HRT) recovered 21% of the inlet sulfur and the downstream effluent treatment in continuously mixed AnSBR at 50 rpm achieved 238 mL CH4/gCODadded). The full-scale application of the system at a local medium sized tannery treating 2258 m3 of BHE would produce a floating sulfur biofilm with 33% S0, 3420 m3 of CH4, 50 m3 of irrigation water and 31 tonnes of biofertiliser. The sale of recovered resources and potential savings from a 72% reduction in electricity demand and 62% in sludge disposal had a potential revenue of US$5559. This study demonstrated the feasibility of a circular bioeconomy and net positive tannery operations through the conversion of tannery wastewater treatment plants into bio-refineries. [Display omitted] •Single-stage HLFCR (8-days HRT) recovered 21% of the inlet sulfur.•Single (8-days HRT) and two stage HLFCR effluents had ideal characteristics for AD.•Continuously mixed AnSBR at 50 rpm achieved the highest yield of 238 mL CH4/gCODadded.•Cone and Logistic model were used to simulate CH4 yields and determine AD kinetics.•Digestate and treated effluent were suitable for agricultural application.