Modelling of the anaerobic semi-continuous co-digestion of sewage sludge and wine distillery wastewater

Abstract

The semi-continuous mesophilic anaerobic co-digestion of sewage sludge and wine distillery wastewater was investigated. In this sense, the effects of reducing the hydraulic retention time (HRT, from 20 d to 8 d) on the degradation of organic matter and methane production were determined. The experimental results showed that anaerobic co-digestion enhanced the biodegradability of the mixture in terms of VS and COD_T (7–8% higher) for HRT = 8 d. The methane productivity at HRT = 8 d (18.0 L_CH4 kg_VS⁻¹ d⁻¹) was also enhanced (30% higher) compared to that obtained in the control experiment. In addition, a mathematical kinetic model was proposed to determine the rate-limiting step of the process. Stoichiometric parameters obtained for SS : WDW (0.115 kg_CH4 kg_COD⁻¹) was higher than SS (0.094 kg_CH4 kg_COD⁻¹), which means that co-digestion increased the rate of consumption because of the higher amount of biodegradable compounds. The kinetic study showed that anaerobic co-digestion favoured the methane production rate enhancing the acetate consumption step and making methanogenesis the rate-limiting step in this process.