Membrane fouling control in ultrafiltration technology for drinking water production: A review

Abstract

Ultrafiltration is a promising process to produce qualified drinking water. The application of ultrafiltration for drinking water production has undergone accelerated development during the past decade. Membrane fouling may be the main obstacle for wider implementation of ultrafitration, which usually causes higher costs of energy, operation, and maintenance. Fouling is formed due to pore blocking, pore stricting and cake formation. Pretreatments (e.g. coagulation, adsorption, and pre-oxidation) can in various degrees alleviate the fouling by pre-reacting with the foulants in the feed water. However, adverse effects from the pretreatment are also claimed. Moreover, modest operation methods (e.g. running modes, rinsing modes, chemical cleaning, and air scouring) can effectively obtain the fouling reduction. In this report, fouling control in ultrafiltration technology for drinking water production is reviewed in terms of different effective pretreatments and operation methods. Specific mechanisms and future research required are also discussed based on the literature reviewed.

Introduction

Millions of preventable deaths in developing countries are due to microorganisms, which come from the polluted drinking water. Ultrafiltration (UF) can be such a way to remove the contaminants from the drinking water [1], with a relatively low cost compared with nanofiltration and reverse osmosis. With the intense regulatory activity and scarce high quality source water, UF is considered as a very promising process for drinking water production because of its compactness, easy automation, and high removal rate of turbidity, organic matters (such as humic substances), Giardia and also virus [2], [3], [4], [5]. UF is recognized as a low-pressure membrane filtration process; it is usually defined to be limited to membranes with pore diameters from 10 A to 1000 A. When the source water is passing through the filter under a trans-membrane pressure provided by the gravity or a pump, the bacteria and most viruses can be removed, the water-related disease and death from microorganisms can be prevented, the drinking water quality can be satisfied for consumers, and the use of chemicals, capital, and operating cost can be reduced. With the decreasing cost of the ultrafiltration membrane, UF technology is gradually accepted by the developing countries compared to other low-pressure membrane technologies, and is expected to be more widely applied due to the more stringent water environment.

Today, UF, as a fast-growing industry, has a significant growth for drinking water production. Though the ultrafiltration grew fast during the past twenty years, the membrane fouling problem is always the critical issue which inhibits its wider application for drinking water production [6]. Therefore, fouling reduction has been the focus for its practical application in recent years. Researchers endeavor to find a moderate pretreatment method to integrate higher removal of contaminants, lower rate of losing permeability, and lower cost of the whole process.

Previous reviews focused on the application of low-pressure membrane processes, including MF, UF, and NF, in drinking-, waste-, and industrial-water treatment. Differently, it is possibly the first time to review the application of UF as a membrane process for drinking water production in this report, and a relative comprehensive understanding of the fouling reduction by different measures is depicted.

This report is organized in four sections as bellows: 1) mechanisms of ultrafiltration and characteristics of foulants; 2) mechanisms of different pretreatment options, their performances when combined with UF with respect to the aquatic contaminants, and their contributions to the fouling control of the UF membrane; 3) fouling control through operation changes; 4) and future research and outlook of ultrafiltration for drinking water production.