Carbon Emission Calculations and Reductions in Membrane Water Treatment: A Review

Membrane technology has become a key common technology to solve major problems in the fields of global water resources, energy, and the environment and is one of the most developed high-tech methods in the 21st century. However, due to the high cost and low reuse rate of membrane technology, its energy consumption and carbon footprint are still high, which is the main factor limiting its use. Therefore, we need to clarify the method used to calculate greenhouse gas emissions from this technology and put forward effective emission reduction programs. Based on the life cycle assessment method, the accounting boundary of greenhouse gas emissions from membrane technology is defined. According to this boundary, the greenhouse gas emissions in the whole life cycle of membrane technology are divided into direct emissions, indirect emissions, and carbon compensation, and the measured emission factor method is used to calculate the greenhouse gas emissions. Then, we discuss the effective pathways for reducing carbon emissions by this technology: (1) reduce energy consumption by optimizing operating conditions and coupling membrane systems with clean energy; (2) recover and utilize organic matter byproducts and recycled water; and (3) recycle waste membrane components in whole or in part. Studies have found that membrane technology can overcome its current challenges and even achieve net zero emissions under a recycling scheme, but quantitative data are still lacking. Finally, we hope to provide a valuable reference for carbon emission accounting and carbon emission reduction in studies of membrane technology.