Environmental and economic life cycle assessment of emerging sludge treatment routes

Abstract

Before implementing large-scale emerging sludge treatment methods, it is crucial to conduct a comprehensive analysis of their environmental impacts and economic costs at the system level. This study utilizes standardized Life Cycle Assessment (LCA) and Life Cycle Cost (LCC) accounting methods to evaluate four emerging sludge treatment routes: anaerobic fermentation (AF), pyrolysis (PY), hydrothermal carbonization (HTC), and alkaline thermal hydrolysis (ATH). These routes are compared with two traditional sludge treatment routes, anaerobic digestion (AD) and aerobic composting (AC). The results indicate that the conventional route AD is the optimal choice in terms of environmental pollution, carbon emission control, and life cycle cost. The emerging routes AF and ATH have significant environmental benefits from carbon source recovery and protein recovery. However, they require approximately twice the cumulative energy demand of AD and additional consumption of chemicals, which imposes a greater environmental burden. While PY and HTC outperform the conventional sludge treatment routes in terms of the total environmental impact (1.79E-10, 1.72E-10) due to energy recovery and the use of clean energy sources. AF and PY demonstrate better economic performance (842.11 and 712.00 CNY) compared to the traditional route AC (905.06 CNY). However, both HTC and ATH incur costs approximately 1.3 times higher than AC due to their high energy and material demands. Furthermore, sensitivity analysis reveals that emerging treatment routes are highly influenced by energy and resource recovery and consumption. Therefore, reducing the energy and resource inputs for emerging routes could significantly decrease their environmental impact and cost, maximizing their resource recovery advantages.