New findings on the anaerobic co-digestion of thermally pretreated sludge and food waste: laboratory and pilot-scale studies

Co-digestion of thermally pretreated sewage sludge with food waste is an innovative strategy that could improve the balance and availability of nutrients needed to increase the efficiency of anaerobic digestion in terms of biogas production. In this context, the aim of this research was to evaluate the impact of different proportions of sewage sludge/food waste in laboratory- and pilot-scale reactors. Special focus was placed on the impact of the variability of food waste composition on the behaviour of the pilot digester. Our results show that by adding 40% of co-substrate, a higher biogas production was possible during laboratory operation. Interestingly, using a co-substrate of variable composition had no negative impact on the reactor's stability at pilot-scale, promoting an increase in biogas production through a more efficient use of organic matter. In both the lab and pilot experiences there was an impact on the amount of nitrogen in the digestate compared to digester operating in monodigestion. This impact is more significant as the proportion of co-substrate rises. Overall, our results show that co-digestion of thermally pretreated sewage sludge with food waste allows better management of food waste, especially when their composition is variable. HIGHLIGHTS Thermally pretreated sewage sludge is being co-digested with industrial waste.; At laboratory-scale, the highest biogas yield was obtained using 40% FW as co-substrate.; ACoD with FPW of variable composition has no negative impact on digester stability.; ACoD with FPW led to more biogas and a more efficient use of the organic matter.