Anaerobic digestion of industrial dairy wastewater and cheese whey: Performance of internal circulation bioreactor and laboratory batch test at pH 5-6

Abstract

This study pointed out the performance of a full-scale internal circulation (IC) bioreactor (140 m(3)) inoculated with anaerobic granular sludge for the treatment of dairy wastewater for 91 days. The average COD removal was 80% and the average biogas was 69.8 m(3) per influent COD/L per day. Then the anaerobic digestion of cheese whey (CW) at a pH 5-6 was examined at a laboratory level as a strategy to reduce the requirement for alkalinity. First, anaerobic granular sludge from IC bioreactor (pH 7-7.5), was exposed to pH 5-6 while utilizing acetic acid for 7 months. This laboratory adapted anaerobic granular sludge when fed with CW showed 30% higher methane generation under batch conditions compared to non-acclimatized granular sludge under the same conditions (pH 5-6). Higher percentage of hydrogenotrophic methanogens (mostly Methanolinea) and increase of Clostridium at the anaerobic granular sludge exposed to pH 5-6 compared to initial granular sludge was found. Propionic acid was the reaction limiting step for granular sludge under pH 5-6. Anaerobic digestion at moderately low pH required 68% less NaOH (50 %v/v) per m(3) of CW however it can theoretically produce 53% less kWh per day compared to digestion at neutral pH. (C) 2019 Elsevier Ltd. All rights reserved.