Anaerobic co-digestion of food waste and domestic wastewater – Effect of intermittent feeding on short and long chain fatty acids accumulation

Abstract

Abstract This work investigates the anaerobic co-digestion of a mixture of food waste and domestic wastewater (0.09, v/v) using an upflow anaerobic sludge blanket (UASB) reactor to generate renewable energy in form of biogas. The reactor was operated under the conditions of mesophilic temperature (35 °C), pH 7.2, and 10 days of hydraulic retention time (HRT). The chemical oxygen demand (COD) removal efficiency and the methane content were 80 ± 1.3% and 56%, respectively, when the reactor was operated continuously at the organic loading rate of 2 g COD/L/d in 2 days of operation, while the COD removal efficiency started decreasing and reached 61 ± 1.7% after 10 days, with the methane content of 37%. The deterioration of reactor efficiency on converting organic matter to methane was attributed to the accumulation of long chain fatty acids (LCFAs) onto the sludge. To overcome the physical and metabolic inhibition by LCFAs, the application of intermittent feeding mode (48 h feed and 48 h feedless) was chosen and applied at different organic loading rates (OLRs; 2–4.5 g COD/L/d) to evaluate the reactor performance in terms of COD removal, methane content, accumulation of LCFAs and short chain fatty acids (SCFAs). The COD removal efficiency and methane content were 82 ± 1.1%, 75 ± 0.9%, and 62 ± 1.5% and 58%, 56%, and 51% at the OLR of 2, 3, and 4.5 g COD/L/d, respectively. The 48 h feed/48 h feedless cycle seemed a promising alternative to treat real food wastewater. However, further studies are still necessary to better evaluate the application of intermittent feeding to treat different mixtures of food waste and domestic wastewater at higher organic loading rates.