Water. desalination + reuse

TECHNOLOGY Hot Standby Operation - Gold Coast Desalination Plant _________ Sean McCagh, Seqwater, and Scott Murphy, David Cohen and Yvan Poussade, Veolia Water Australia ___ Editor's Note: Much political capital has been made in Australia over its implementation of a desalination programme that has seen the country construct six major seawater reverse-osmosis plants. In still-dry Western Australia, Water Corporation's two plants are seen as a boon. With full dams elsewhere, desalination plants have had to be mothballed. This article looks at putting a plant on "hot standby". being located approximately 100 km from Brisbane City, is able through this network to provide a drought-resilient alternative supply to residents of Brisbane and the wider SEQ region. Given the connectivity of the plant into the SEQ water supply system and its ability to assist with water quality and supply challenges in the network, Hot Standby was an option which would allow the plant to continue to be available to supply into the system at up to 100% capacity. The objective then was to develop an operating regime which would minimise operating costs while sustaining this capability. Figure 1: Timeline - Water storage levels in South East Qld. leading to Hot Standby announcement. OWNERS AND OPERATORS of the newly constructed seawater desalination plants on the eastern seaboard of Australia have found themselves in a difficult situation: their alternative drought-proof supply is ready to go, but the local surface water supply reservoirs are full. In South East Queensland (SEQ), the Gold Coast Desalination Plant (GCDP) owned by Seqwater, and operated by an alliance partnership between Seqwater, Veolia Water Australia Pty Ltd and John Holland Pty Ltd has implemented a novel solution given the circumstances. Figure 1 illustrates the coincidence of commencement of the GCDP construction with the breaking of the 'millennium drought' in SEQ. This was not only a significant inconvenience on construction itself, but it meant that by the time the plant commenced potable water supply in early 2009, water storage levels had increased from a historical low of 17% to nearly 50%. GCDP is a 133,000 m3/d capacity conventional pretreatment plant that has been designed to deliver at 33%, 66% or 100% capacity. The plant operated largely at its minimum continuous capacity of 44,000 m3/d during 2009 and 2010 as rain continued to fall heavily in SEQ catchments, and dam levels increased to 77% and 98% respectively. During 2010 Queensland water authorities and Veolia investigated options to further reduce plant production. The SEQ water supply system (Figure 2) comprises a network of supply sources connected by bi-directional bulk transport pipelines to give maximum supply security for nearly 3 million people. GCDP, despite | 32 | Desalination & Water Reuse | August-September 2013 INvESTIGaTION Preliminary work was carried out to ensure that the operating mode did not pose any undue risks to the plant or supply system. The work comprised desktop studies, risk assessment and mitigation activities, and trials to help test the materiality of the perceived risks. The key constraints were identified as the following needs: l Prevent reverse osmosis (RO) membrane fouling and other undesirable effects including voiding the membrane warranty by regularly flushing membranes with permeate water. l Maintain water quality in the pipeline connecting the plant to the wider water network by regular turnover of the contents of the pipeline.

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