Comparison and improvement of energy balance establishment methods for heat pretreatment prior to anaerobic digestion

The performance of the anaerobic digestion (AD) process is remarkably enhanced by heat pretreatment (HPT), while HPT process requires additional energy input, mainly including heat and electrical energy. Thus it is critical to determine whether biogas growth fulfills this energy requirement. Consequently, the energy assessment of HPT is more complex than that of other predominantly power-consuming pretreatment methods, leading to the poor homogeneity and comparability of reported HPT energy balance (EB) analysis methods. In view of this, the current study comprehensively summarizes the relevant reports to explore more universal EB analysis methods for the applying HPT. Based on the summary of previous studies, two EB analysis models were developed for the HPT process in present work. The design difference mainly derives from the fact that biogas is utilized in two different ways in practice: heat production only and cogeneration, and their calculation process is required to be separated from the AD process to improve the accuracy of the results. Finally, a re-evaluation of 15 reported records on HPT revealed that the electrical input of the HPT process is 0.43–5.0% of the heat energy input; only five groups obtained positive EBs under the heat utilization mode of biogas, whereas the EB results under the combined heat and power cogeneration mode showed that all the electrical EBs were positive, and two groups of data reported both positive heat and electrical EBs. Summaries of the current work and the constructed models can better assist users in making decisions regarding process selection.