Nanofiltration (NF) application in drinking water treatment plants and the challenges of its concentrate management in China

Nanofiltration (NF) technology, employed for water purification through size exclusion and charge separation, faces certain challenges. This review offers a comprehensive summary of the application of NF technology in drinking water treatment plants (DWTPs) across various regions in China, and the characteristics of NF concentrate (NFC). The quality of NFC exhibits variability at recovery rates of 40-60 %, despite consistent pollutant rejection across various NF membranes. Over a seven-year study, continuous operation of NF membranes was found to induce fouling, necessitating more frequent cleaning that damages the membrane structure. This leads to a doubling of NFC yield and a 30 % decrease in the retention of monovalent ions like chloride, with minimal impact on the retention of total hardness and sulfate. Temperature influences NF membrane recovery rates, which are 5-15 % higher in summer. Influent quality, productivity, and rejection efficiency variations significantly stress the final stage of a three-stage NF system. This review includes a study at two DWTPs using NF90 and NF270 membranes for treating saline groundwater and surface water contaminated with trace organic compounds (TrOCs), respectively. The study highlights challenges in managing NFC due to elevated levels of water quality parameters such as total dissolved solids, sulfate, chloride, total phosphorus, and TrOCs. Additionally, NF retains beneficial elements like strontium. It also assesses NFC composition and regional discharge standards for water bodies. This review offers valuable insights into the research and application of NF membranes in DWTP in China, and the water quality characteristics of NFC, facilitating a more comprehensive understanding of NF technology.