Water Journal : Water Journal May 2011
new products & services water MAY 2011 113 Each analyser/controller is built to the customer's specification so the customer is only paying for the functionality they need and not for the functionality they don't. A multi-colour backlight means that alarm conditions are clearly visible for up to 100 metres. The CRONOS is available as a residual chlorine analyser, a swimming pool controller, a DO meter, a pH meter, an ORP meter, a suspended solids meter, an ozone analyser and chlorine dioxide analyser. For more information please visit: www. processinstruments.net/products/cronos. php or contact George Benca, National Sales Manager, Bintech Products on (03) 9467 7300 or email: email@example.com MANAGEMENT OF RO MEMBRANE FOULING AT THE YABULU WATER RECYCLING FACILITY TRILITY Pty Ltd operates and maintains the Yabulu Water Recycling Facility, where they utilise Reverse Osmosis (RO) membranes to treat tailings water from the Queensland Nickel ore refining facility. These membranes are subject to a wide array of both organic and inorganic fouling that must be managed effectively so the treatment process is not impaired. Fouling is a common hindrance across all membrane processes. No matter the membrane size, type or process application, fouling is always an important factor to consider in the design and operation in membrane processes, as there are a wide array of mechanisms for it to occur. An increase in fouling can lead to a number of detrimental events such as increased breakdowns and equipment failure, as well as the deterioration of both quality and quantity of water produced. The Yabulu WRF membranes are subject to water of varying extremes, and because of this their operation and maintenance needs to be heavily monitored. Tailings water from QN Yabulu Refinery is variable in its constituents, containing varying levels of heavy metals, organics and inorganics. The Yabulu WRF has systems in place to prevent the more common types of fouling such as permeate flushing and acid/alkaline cleans. However, in spite of a well prepared operating system, occasionally incidents occur that require significant engineering and investigation to remediate. The Yabulu WRF has experienced both major types of fouling, organic and inorganic. Organic fouling The first major fouling incident was caused by organics. After an extended plant shutdown to undertake installation of new 8-inch membranes, it was noticed upon plant restart that there were higher- than-usual Differential Pressures (DP) being experienced in the system. Further investigation revealed organic fouling, believed to be a form of iron bacteria, which had grown on almost every internal surface. These organics formed a slick coating on all pipe walls, pump internals, and the faces of the lead membranes within each train (Figures 1 and 2). The build-up of these organics on the membranes themselves led to the increased operational pressures experienced, and required removal. Figure 1: The level of fouling of the Yabulu Refinery WRF internal systems by iron bacteria. This photograph was taken at the discharge side of an RO feed pump. Initially, the biocide DBNPA (2,2-dibromo- 3-nitrilopropionamide) was dosed into the system to kill the bacteria and inhibit further growth. This worked effectively in neutralising the bacteria; however, remnants of the organisms still existed physically within the system. Although no longer viable, another issue was created due to the now dead bacteria coating detaching from the WRF internals in 'flakes' and causing greater physical blockages of the membrane faces (see Figure 3). As a result, the entire WRF internals were pressure cleaned and flushed to remove all traces of the organic foulants. Figure 3: Organic fouling after biocide dosing. Note the patches of pipework where the bacteria have 'flaked' off. Figure 2: Fouling on an RO feed pump that has been removed and partially cleaned.
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