Integrating wastewater treatment and incineration plants for energy-efficient urban biomass utilization: A life cycle analysis

Abstract

Abstract Sewage sludge and municipal solid waste, defined as urban biomass, are promising energy sources with the potential to lower fossil fuel consumption and reduce carbon dioxide emissions. However, the current process of extracting useable energy from urban biomass has two problems that must be addressed in order to achieve greater energy efficiency: (1) significant fossil fuel consumption is currently needed to dry sewage sludge in wastewater treatment plants, and (2) a huge amount of exhaust heat from incineration plants remains unused. One promising solution is to integrate wastewater treatment and incineration plants. In this way, total energy efficiency could be enhanced by utilizing the exhaust heat generated in the incineration plant to dry sewage sludge in the companion wastewater treatment plant. Aiming to clarify sustainable conditions for integrating the two plants, this paper proposes a method for conducting a life cycle analysis for urban biomass utilization. The proposed method combines scenario storylines and quantitative assessment to provide a better understanding of critical factors and their rationales. Each scenario is quantified by process network modeling and then evaluated in terms of their economic profit and carbon dioxide emissions. A case study involving a Japanese waste water treatment plant and a nearby incineration plant is conducted. The results show that the integration scenario reduces total annual costs by 35% and total annual carbon dioxide emissions by 1% relative to the status quo scenario. This is mainly due to the elimination of several system components, including a digestion tank, made possible by the integration.