Water Journal : Water Journal May 2011
new products & services 114 MAY 2011 water water business To prevent the same issues recurring, system shutdowns are kept to a minimum length of time, and a number of internal areas are inspected prior to restarting the system after a prolonged shutdown to check for bacteria growth. Biocide and associated dosing facilities are also kept on site in case they are required for future use. Inorganic fouling The second major fouling incident involved high levels of inorganic sulfates being discovered within the system. This caused fouling of the lead membranes of each of the trains and created an increase in operational pressures. At one point there was, in fact, significant organic and inorganic fouling of the membranes simultaneously (see Figure 4). The presence of these sulfates was thought to have been a product of higher levels of sulfates within the influent water. This formed a varying amount of sulfate salts with other available ions within the system. The increased level of sulfates quickly fouled the lead membranes to such a large degree that they could not be easily cleaned using the usual mechanisms. To add to this, it was also discovered upon inspection that there was a slight amount of fouling attributed to ABS swarf from recent pipework modifications that involved both cutting and drilling of the pipe, which had partially blocked and damaged a number of lead membranes. The high pressure experienced within the system resulted in the swarf deeply embedding itself within the membrane faces, separating the wound sheets and reducing effectiveness (see Figure 5). The lead membrane faces were pressure cleaned to remove all visible fouling, although this did not reduce the deeply embedded sulphate compounds within the lead element. Under guidance from membrane suppliers Woongjin and Australian representative Vitachem, the lead membranes were swapped with the lag membranes and rotated 180 degrees so the 20-bar operating pressure would effectively 'blow' the fouling out the back end of the system, with the membranes to be returned to their original positions after a short period. Due to the variable nature of the influent water, sulfate salts and other inorganic foulants always have the potential to appear within the system regardless of the preventative measures in place. To help combat this, an asset management strategy has been put in place where the lead membrane in each operational vessel is replaced on an annual basis. This aims to control the flux and operational pressure, resulting in a more balanced and consistent operation. Fouling is always going to be an issue with RO membrane systems, with the type and level of fouling differing depending on the site, environmental and process applications. It is important to ensure that comprehensive preventative measures and routine maintenance procedures are in place, as it is much easier and less costly to prevent a fouling incident than to fix it. This article was supplied by TRILITY Pty Ltd (previously United Utilities Australia). For more information contact amedlock@ trility.com.au HUBER DISC THICKENER The Huber Disc Thickener is a unique sludge thickening machine designed for smaller municipal and industrial treatment plants. Applications include thickening of waste-activated sludge, primary sludge and all sludge types produced in the sewage, food processing, brewery, meat processing and dairy industries. Depending on the sludge type, the capacity ranges from 10--38 m3/h. Typically sludges can be thickened to 6%, resulting in a volume reduction of up to 75%. The unit can handle an influent solids concentration of 0.2--3% w/w solids. The Disc Thickener is totally enclosed, which contains aerosols and odours. The main case includes inspection hatches for visual examination of the thickening process. The main case, filtration disc and supports are fabricated in stainless steel, which allows the machine to be installed outdoors. The machine offers two sizes, with the biggest size being 2013mm in diameter, significantly smaller than other thickener types for the same capacity. Operating costs are minimal due to low power consumption. http://www.solarwasser.eu/ Figure 4: Showing both organic and inorganic fouling on the face of an 8-inch lead membrane. Figure 5: Sulfate and swarf build-up on the face of one of the 8-inch membranes. It can be seen towards the centre that the membrane sheets are beginning to separate due to the swarf embedding.
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