Chapter 10 - Environmental and techno-economic assessment of thermochemical treatment systems for sludge

Abstract

This chapter describes and discusses the most relevant investigations regarding environmental, technical, and economic evaluations of thermochemical methods commonly used for sludge treatment. Individually, gasification, incineration, pyrolysis, hydrothermal liquefaction, and hydrothermal carbonation technologies are assessed. As we describe here, significant discrepancies in the performance of these thermochemical treatments can be found in the literature because many factors strongly affect the authors’ conclusions. Thus, variations in selected system boundaries, diverse technical assumptions, and differences in economic environments make direct comparisons problematic. Likewise, data scarcity is an additional difficulty to developing these assessments, particularly for hydrothermal processes. As general rules, three main conclusions could be extracted from this study: sludge moisture is the most important parameter in energy performance for processes, coupling anaerobic digestion with thermochemical processes for sludge usually results in better environmental and economic profiles, and recovering valuable products (e.g., energy and nutrients) is mandatory for achieving feasible outcomes.