Life Cycle Assessment and Life Cycle Cost of Sludge Dewatering, Conditioned with Fe2+/H2O2, Fe2+/Ca(ClO)2, Fe2+/Na2S2O8, and Fe3+/ CaO Based on Pilot-Scale Study Data

Numerous advanced oxidation processes (AOPs) have been developed for conditioning sewage sludge due to their excellent dewaterability, which can reduce the water content of sludge to below 60 wt %. However, the application of different chemical reagents for sludge dewatering inevitably causes varying degrees of environmental impact and economic pressure. It is still questionable whether advanced sludge dewatering processes can reduce environmental and economic burdens. In this work, life cycle assessment (LCA) and life cycle cost (LCC) of three types of AOPs (Fe2+/H2O2, Fe2+/Ca(ClO)2, and Fe2+/Na2S2O8) were compared to the traditional conditioner (Fe3+/CaO) for the first time based on pilot-scale study data to measure the optimal choice of environmental and economic performance. Fe2+/Ca(ClO)2 and Fe2+/H2O2 exhibited the highest and lowest environmental and economic burdens, respectively. Among them, the total environmental impact and total cost of Fe2+/H2O2 were equivalent to 54-62% and 56-66% of other processes, respectively. In the sludge treatment routes, the sludge conditioning and landfill stages were the largest contributors to the environmental impact and economic cost. The greenhouse gas emissions and particulate matter generation were the main impact indicators of LCA and LCC. In addition, the superior dewatering performance did not result in significant environmental benefits. The obtained LCA and LCC results will support the selection and application of sludge pretreatment processes in wastewater treatment plants and contribute to the improvement and development of the technology.