Modelling of the anaerobic semi-continuous co-digestion of sewage sludge and wine distillery wastewater
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 CODT (7–8% higher) for HRT = 8 d. The methane productivity at HRT = 8 d (18.0 LCH4 kgVS−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 kgCH4 kgCOD−1) was higher than SS (0.094 kgCH4 kgCOD−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.