CHEMICAL CLEANING EXPERIMENTS FOR PERFORMANCE RESTORATION OF NF MEMBRANES OPERATED ON SEAWATER FEED1

The pioneering work of utilizing nanofiltration (NF) membranes for pretreatment of seawater feed to SWRO and MSF has gained attention of many in the desalination industries. During the performance evaluation study of NF membranes, one particular type of NF membrane experienced a decrease in their product flow along with increase in salt rejection and attempts to restore its performance by chemical cleaning was a failure, rather it produced an adverse affect on the membrane performance. As the attempts to restore the NF membrane performance failed, autopsy was conducted on 2 selected NF membranes out of 10 membranes after operation of about 1 year. Based on the autopsy results, chemical cleaning of the NF membranes was conducted to restore their performance. The cleaning was initially conducted on flat-sheet membranes cut from two NF membranes, which were autopsied. Since it was found that the major foulants were primary organic matter followed by iron, both low pH cleaning as well as high pH cleaning were tried utilizing standard chemicals such as citric acid, HCl, SBS, sodium lauryl sulfate, NaOH and high pH cleaning with Cl2 as well as a combination o