Life Cycle Energy-Carbon-Water Analysis and Integrated Ranking of Sludge-To-Energy Processes Based on Multi-Criteria Decision Analysis

Sludge-to-energy technologies have gradually been recognized by more researchers because they can promote the development of circular economy and contribute to realizing a sustainable society. Hence, it is necessary to have a comprehensive recognition of the performances of different technologies on various perspectives to make a suitable decision. However, current assessment studies majorly focus on the environmental impacts and economic influences while less of them work on the analysis for water recycling and energy flows. This paper is conducted to provide a life cycle analysis for the six sludge-to-energy technologies with the respect of energy recovery, carbon emissions, and water consumption. The evaluated alternatives include dewatering, composting, drying, incineration, incinerated sludge melting, and dewatered sludge melting. The fuzzy best-worst method is applied to integrate the performance score together to obtain a comprehensive ranking for the selected scenarios. Results indicate that the scenario of gasification and melting is the superior option under the context of emphasizing on energy recovery and drying is the worse alternative due to the bad performances on all the aspects. However, the scenarios with considerable energy production, i.e., the latter three options, are also accompanied with relatively high carbon emissions and water consumptions. Future efforts are still required to improve the energy recovery rates and the entire performances of the technologies. Government supports on finance and technique may also necessary to promote the development of relevant industries and research