UASB Treatment of Wastewater from the Food Industry: Performance, Kinetic Analysis, and Energy Recovery

The stabilization of two-stage bioenergy systems and optimization of the energy recovery efficiency have been found to be closely related to the management of VFA-rich effluent obtained after the dark fermentation of food waste. In this study, the performance of a mesophilic UASB reactor was investigated at different OLR levels. The focus of this study was to assess methane yield and substrate degradation during anaerobic digestion. The results revealed that the performance of the UASB reactor was stable within the range of 2.5–7.0 kg COD m−3 d−1. At this range, it was possible to convert VFAs into methane gas through the synergistic interaction of fermentative bacteria and methanogenic archaea. The methane content was 67.9%, TCOD removal efficiency was 89.7% at the optimal OLR of 7.0 kg COD m−3 d−1, and volumetric methane production rate was 2.41 LCH4 L−1 d−1. The increase in OLR to 10.0 kg COD m−3 d−1 resulted in instability of the anaerobic digestion process. The instability of the anaerobic digestion process was characterized by propionate accumulation and a high VFA/alkalinity ratio of 0.89. The Grau second-order and Modified Stover–Kincannon models were found to describe COD removal efficiency. The Monod model was found to show limited preliminary agreement under the conditions tested for high-rate granular sludge. The highest methane yield and efficiency of energy recovery were obtained at 7.0 kg COD m−3 d−1. The recoverable energy obtained at this OLR was 2.04 MJ d−1. The results of this study revealed that it is possible to integrate dark fermentation and anaerobic digestion through the use of UASB reactors.