The generation of CO2 in sewage sludge treatment systems: life cycle assessment

Abstract

Life cycle assessment (LCA) on total sewage sludge treatment systems including thickening, anaerobic digestion, dewatering, and incineration/melting was performed to estimate a global warming impact as carbon dioxide (CO2) emission. As representative processes for the assessment, the most typical and widely used processes were selected. Generally, the life cycle of actual treatment facilities consists of three stages: construction, operation and dismantlement. In this study, the amount of CO2 produced from the life cycle steps of existing unit sludge treatment processes, was calculated by inventory analysis of input materials. In addition, for all processes investigated, individual CO2 emission units (CEUs), i.e. the amount of emitted CO2 for treating a unit weight of sludge, were also calculated. Byusing the obtained CEU matrix, it was possible to simulate the CO2 production from various types of complex treatment systems as well as to trace the dominant cause of CO2 production in individual treatment processes.