High-solids anaerobic co-digestion of sewage sludge and food waste in comparison with mono digestions: Stability and performance

System stability and performance of high-solids anaerobic co-digestion of dewatered sludge (DS) and food waste (FW) in comparison with mono digestions were investigated. System stability was improved in co-digestion systems with co-substrate acting as a diluting agent to toxic chemicals like ammonia or Na+. For high-solids digestion of DS, the addition of FW not only improved system stability but also greatly enhanced volumetric biogas production. For high-solids digestion of FW, the addition of DS could reduce Na+ concentration and help maintain satisfactory stability during the conversion of FW into biogas. System performances of co-digestion systems were mainly determined by the mixing ratios of DS and FW. Biogas production and volatile solids (VSs) reduction in digestion of the co-mixture of DS and FW increased linearly with higher ratios of FW. A kinetic model, which aimed to forecast the performance of co-digestion and to assist reactor design, was developed from long-term semi-continuous experiments. Maximum VS reduction for DS and FW was estimated to be 44.3% and 90.3%, respectively, and first order constant k was found to be 0.17 d−1 and 0.50 d−1, respectively. Experimental data of co-digestion were in good conformity to the predictions of the model.

► The first study on high-solids anaerobic co-digestion of dewatered sludge and food waste.
► Better system stability was obtained in co-digestion than in mono digestion system.
► Relationship of dynamic performance between mono- and co-system was demonstrated.
► A model was developed from mono digestions to help predicting co-system performance.
► Experiment data of co-system was in good conformity to the predictions of the model.