Kinetic modelling of anaerobic co-digestion of sewage sludge and Sherry-wine distillery wastewater: Effect of substrate composition in batch bioreactor

Batch thermophilic anaerobic co-digestion of sewage sludge (SS) and Sherry-wine distillery wastewater (SW-DW) was investigated through biochemical methane potential tests (BMP). The results pointed out that biodegrad-ability and biomethane potential were enhanced proportionally to the percentage of SW-DW of the feedstock, whose soluble biodegradability fraction is 10-fold higher than SS. Specifically, organic matter removal increases from 37 % (employing sole SS as feedstock) to 60 % (employing sole SW-DW as feedstock). SW-DW almost doubles methane yield in comparison to SS (302 +/- 15 and 175 +/- 9 NL/kg, respectively). A structured kinetic model was developed considering hydrolysis, acidogenic and methanogenic steps of anaerobic digestion. A non-linear multiple-response regression was employed to estimate the kinetic parameters for each feedstock (0%(v/v) SW-DW, 25%(v/v) SW-DW, 50%(v/v) SW-DW, 75%(v/v) SW-DW, and 100%(v/v) SW-DW). The first-order kinetic parameter estimated of the hydrolysis step varies inversely proportional to the percentage of SW-DW content in the feedstock. Whereas, there is no significant influence of feedstock compo-sition on kinetic parameters value regarding acidogenesis and methanogenesis. These results showed that rate-limiting step switched during the fermentation and the addition of SW-DW favours acidogenic and meth-anogenic steps. In summary, the proposed kinetic model was able to predict batch experimental data, supporting the application of biogas production from anaerobic co-digestion of SS and DW-DW.