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Membrane fouling is the main problem during the nanofiltration (NF) process of brackish water desalination due to the existence of natural organic matter, especially humic acid (HA). Moreover, the conventional membrane cleaning method would do great harm to the environment because large amount of chemicals were employed. In order to control organic fouling, a novel cleaning method via direct osmosis backwash (DOBW) by injecting high salinity (HS) solution was developed. Different operating conditions for HS-DOBW technology in the actual process were systematically investigated. The results demonstrated that there was a strong driving force to lift and sweep the foulants from the membrane surface which would be carried over to the brine. The optimal conditions in terms of HS (150 kg/m 3 NaCl solution) flow rate of 0.121 L/min were selected for the subsequent experiments. The results showed that the fouling could be almost fully reversible (more than 99.78% permeate water flux recovery), and the membrane needed to be cleaned for about 10 min because of the appearance of HA on membrane surface at the fouling time of 24 h. Most importantly, the HS-DOBW technology is very effective in keeping the membrane continuously clean and ensuring stable permeate production. [ABSTRACT FROM AUTHOR]

A pilot-scale ultrafiltration (UF)–nanofiltration (NF) integrated membrane system (IMS) which included a self-cleaning crossflow UF filtration process and a dual-stage NF process with a capacity of 100 m 3 ·d − 1 NF permeation water was established for seawater softening investigation. The separation performance of the dual-stage NF process under different conditions, such as operating pressure, recovery rate, and inlet flowrate, was extensively investigated; long-term performance and energy consumption of the dual-stage NF process were analyzed as well. The results showed that during the long-term operation, UF could provide qualified filtrate for NF. The dual-stage NF process achieved high separation performance with good permeate quality, especially high rejection of Ca 2 + and Mg 2 + (> 90%). In addition, the dual-stage NF process showed good anti-fouling characteristics, with the normalized NF permeate flux maintaining at an essential constant value of about 14 L·m − 2 ·h − 1 at 3.5 MPa, and DOC rejection around 90% during the long-term experiment. Energy consumption of the dual-stage NF process increased with the increase of the operating pressure and the decrease of the raw seawater temperature, which was about 1.8 kWh·m − 3 at 3.5 MPa and 25 °C. [ABSTRACT FROM AUTHOR]