Osmosis Inversa

8

The Open Chemical Engineering Journal, 2009, 3, 8-16

Open Access

Direct Osmosis for Reverse Osmosis Fouling Control: Principles, Applications and Recent Developments
Jian-Jun Qin*,1, Boris Liberman2 and Kiran A. Kekre1
1

The Centre for Advanced Water Technology, PUB Consultants Pte Ltd; 2IDE Technologies Ltd, Israel
Abstract: Reverse osmosis (RO) has been widely applied invarious water and wastewater treatment processes as a promising membrane technology. However, RO membrane fouling is a global issue, which limits it operating flux, decreases water production, increases power consumption and requires periodical membranes Cleaning-in-Place (CIP) procedure. This may result in low effectiveness, high cost and adds environmental issues related to the CIP solutions disposal.Forward osmosis (FO) or direct osmosis (DO) is the transport of water across a semi-permeable membrane from higher water chemical potential side to lower water chemical potential side, which phenomenon was observed in 1748. The engineered applications of FO/DO in membrane separation processes have been developed in food processing, wastewater treatment and seawater/brackish water desalination. Inrecent years, DO has been increasingly attractive for RO fouling control as it is highly efficient and environmentally friendly technique which is a new backwash technique via interval DO by intermittent injection of the high salinity solution without stoppage of high pressure pump or interruption of the operational process and allows keeping RO membrane continuously clean even in heavybio-fouling conditions and operating RO membranes at high flux. This paper provides the state-of-the-art of the physical principles and applications of DO for RO fouling control as well as its strengths and limitations.

Keywords: Backwash, direct osmosis, fouling control, reverse osmosis, salinity solution. INTRODUCTION Reverse osmosis (RO) is a pressure driven membrane process and has been widelyapplied in various water treatment processes as a promising technology. However, RO membrane fouling is a global issue, which limits it operating flux, decreases water production, increases power consumption and requires periodical membranes CIP procedure. This may result in low effectiveness, high cost and adds environmental issues related to the CIP solutions disposal. In past ten years,investigations on RO fouling and fouling control have been sharply increased as shown in Fig. (1), based on searching results from Engineering Village [1]. RO fouling is used to describe the potential deposition and accumulation of constituents in the feed stream on the RO membrane surface and it is usually classified into four major types: colloidal fouling organic fouling, inorganic fouling/scaling andbiofouling. Better understanding the factors that will cause fouling is a fundamental for subsequent fouling control. Thus this topic has been focused in a great number of studies [2-7]. Three types of factors in general that have been explored in most studies are (1) chemical composition of feed water; (2) operating condition; (3) membrane properties, which are reviewed by Hong & Elimelech [8]. Basedon the factors affecting RO membrane fouling, various preventive strategies have been investigated and performed to reduce fouling. This generally includes pretreatment of the feed water (such as removing most flocculants by microfiltration (MF)/ultrafiltration (UF), adjusting pH and adding antiscalant), improvement of operating conditions (including the initial flux and flow velocity) andmodification of membrane properties (like membrane hydrophilicity, surface roughness and charge via coating), and some other approaches. These typical preventive strategies and their effective results are described elsewhere [8]. Although all the above preventive strategies can slow the fouling rate to a certain extent, fouling is inevitable. Hence membrane cleaning is the long-term solution to remove...