Pilot study of seawater nano fi ltration softening technology based on integrated membrane system

A pilot-scale ultrafiltration (UF)–nanofiltration (NF) integrated membrane system (IMS) which included a selfcleaning crossflow UF filtration process and a dual-stage NF process with a capacity of 100 m3·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 Ca2+ and Mg2+ (N 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. © 2015 Elsevier B.V. All rights reserved.

1.8 We have comprehensively tested the crossflow-circulation UF pretreatment and the dual-stage NF process for seawater softening based on a 100 m3·d− 1 pilot-scale UF–NF IMS. The following conclusions can be drawn: 1.7 1.6 1.5 2.0 2.5 3.0 3.5 4.0 Operating pressure (MPa) Fig. 15. The power consumption of the dual-stage NF process with operating pressure. (Feed temperature: 25 °C; influent flowrate: 7 m3·h−1).