Arrested methanogenesis digestion of high-strength cheese whey and brewery wastewater with carboxylic acid production

•Developed a new anaerobic digestion process to valorize high-strength wastewaters.•Total acid concentration of 78 g/L achieved in 15 d at 40 °C and near-neutral pH.•Total acid productivity was 16 g/(Lliq·d) with 66% substrate conversion at HRT 4 d.•Robust open culture was developed for acid production and wastewater treatment.•Methane-arrested anaerobic digestion has potential for large-scale applications. A new anaerobic digestion process based on arrested methanogenesis (AM) was developed to treat high-strength cheese whey and brewery wastewater with simultaneous carboxylic acid production. This study specifically determined the links between wastewater characteristics, microbial community structure, and the operation of AM digesters at the bench scale. The highest total carboxylic acids concentration (78 g/L) was achieved after 15 days under batch condition at 40 °C and near-neutral pH. Lactate conversion to chain-elongated volatile fatty acid was observed. Under fed-batch conditions, the highest total acid productivity was 16 g/(Lliq·d) with substrate conversion of 0.66 g CODdigested/g CODfed at hydraulic residence time (HRT) of 4 days. Fed-batch digestion with biomass recycling resulted in a 2-fold increase in VFAs concentration (30 g/L) and a higher diversity in the microbial consortia. Experimental results show that highly efficient, robust, and productive community structure was established for sustainable carboxylate production from widely varying high-strength wastewaters.