Journal of Membrane Science 346 (2010) 8–14 Contents lists available at ScienceDirect Journal of Membrane Science journal homepage: www.elsevier.com/locate/memsci Development of novel backwash cleaning technique for reverse osmosis in reclamation of secondary effluent Jian-Jun Qin a,∗ , Maung Htun Oo a , Kiran A. Kekre a , Boris Liberman b a The Centre for Advanced Water Technology, PUB Consultants Pte Ltd, Singapore 608575, Singapore b IDE Technologies Ltd, Israel article info Article history: Received 3 May 2009 Received in revised form 16 July 2009 Accepted 5 August 2009 Available online 11 August 2009 Keywords: Reverse osmosis Backwash cleaning Direct osmosis High salinity Water reclamation abstract The objective of the study was to further develop a novel cleaning technique for reverse osmosis in reclamation of municipal secondary effluent. This technique is a new backwash method via direct osmosis (DO) by intermittent injection of the high salinity (HS) solution without stopping of high pressure pump and it is environment and membrane friendly technique. In the study, DO-HS trials were carried out with a UF-RO pilot system which was operated on site with the secondary treated effluent as the raw feed. Different operating conditions for DO-HS treatment in the actual process were investigated. It was found that the operation for implementation of the DO-HS cleaning technique developed was easy. For the first time, the actual profiles of HS concentration, DO backwash flow rate, brine flow rate and permeate pressure during DO-HS treatment have been demonstrated. It was observed that turbidity of the brine stream during DO-HS treatment at 3 NTU was 5 times higher than that before DO-HS treatment. The results from this study have confirmed the previous hypothesis with DO-HS treatment that there would be a strong driving force for DO backwash to lift and sweep the foulants from the membrane surface which would be carried over to the brine. The optimal plant operating conditions in terms of RO feed flow rate, HS concentration and HS injection time are ready for the DO-HS method to be adopted and validated in a long-term continuous plant operation. © 2009 Elsevier B.V. All rights reserved. 1. Introduction Reverse osmosis (RO) is a pressure driven membrane process and has been widely applied in various water treatment processes as a promising technology [1]. However, RO membrane fouling is a global issue. RO fouling is usually classified into four major types: colloidal fouling, organic fouling, inorganic fouling/scaling and bio- fouling. Hong and Elimelech [2] have reviewed the common fouling factors, typical preventive strategies and their effective results that have been explored in most studies. Of which, chemical cleaning is most widely used to control membrane fouling and maintain the membrane performance [3] although physical cleaning such as forward/reverse flushing and air sparging is effective for specific fouling [4]. However, these approaches will cause low effectiveness of production due to the downtime of frequent RO operation stop- page and create environmental issues related to the waste chemical disposal. Engineered applications of FO/DO in membrane separation processes have been extensively reviewed by Cath et al. [5] and Cornelissen et al. [6] and will not be discussed in this ∗ Corresponding author Tel.: +65 63262914; fax: +65 63262929. E-mail address: QIN Jianjun@pub.gov.sg (J.-J. Qin). paper. Development of forward osmosis (FO) or DO technology has been increasingly attractive for backwash cleaning of RO as it is highly efficient and environmentally friendly technique [7–18]. Spiegler and Macleish [7] investigated DO backwash of RO mem- branes about 30 years ago. That time, knowledge on DO backwash under realistic plant operating conditions was scarce although it was in practice known that periodic release of the brine pressure of a RO plant could create a forward flush and temporarily recover production rate which had gradually reduced in the course of the plant operation. In their lab scale studies, an osmosis technique was developed to clean and possibly to backwash contaminated cellulose acetate RO membranes. They found that the RO flux could be restored after DO backwash although the RO membranes were fouled with ferric hydroxide and performed significant flux decrease. However, it daily took at least 30 min for each operation of osmotic backwash. Ando et al. [8,9] invented a backwash method and treatment system for spiral wound membrane modules and employed a per- meate back pressure in the range of 0.05–0.3 MPa for backwash of a spiral wound RO membrane module. Rychen et al. [10] reported a new DO backwash process and device for producing pure water with RO and no pressure was supplied at the permeate side. In that method, the RO production process was stopped when the 0376-7388/$ – see front matter © 2009 Elsevier B.V. All rights reserved. doi:10.1016/j.memsci.2009.08.011