Taking Advantage of Waste Heat Resource from Vinasses for Anaerobic Co-digestion of Waste Activated Sludge under the Thermophilic Condition: Energy Balance and Kinetic Analysis

[Image: see text] Vinasses are not only an easily biodegradable substrate but also a heat energy resource. In this study, the energy balance and kinetic model of anaerobic co-digestion of waste activated sludge (WAS) with vinasses have been investigated in semicontinuous reactor experiments at 55 °C. Herein, the maximum energy balance value, the ratio of energy to mass, and the kinetic constants μ(max) and K of anaerobic digestion of WAS were −33.44 kJ·day(–1), −5.72 kJ·VS(–1)·day(–1), and 0.0894 day(–1) and 0.7294, respectively, at an organic loading rate (OLR) of 1.17 VS·L(–3)·day(–1); when the mixture ratio of WAS to vinasses was 2:1 (dry VS) for co-digestion, the maximum energy balance value, the maximum ratio of energy to mass, and the kinetic constants μ(max) and K of anaerobic co-digestion of WAS and vinasses were +39.73 kJ·day(–1), 8.1 kJ·VS(–1)·day(–1), and 0.2619 day(–1) and 1.9583, respectively, at an OLR of 1.73 VS·L(–3)·day(–1). The positive energy balance was obtained for two reasons: one is for making the best use of the high-temperature heat energy resource of vinasses and the other is for enhancing the amount of biogas yield. The bottleneck of the negative energy balance of thermophilic digestion of WAS can be broken by anaerobic co-digestion of WAS and vinasses. The results indicate a promising future in the application of anaerobic thermophilic co-digestion of WAS and vinasses. Methane production from digestion and co-digestion was also predicted by the Chen–Hashimoto kinetic model.