Water. Desalination + reuse
Issue link: https://fhpublishing.uberflip.com/i/513849
May-June 2015 | Desalination & Water Reuse | 37 | TECHNOLOGY Stuck: self-cleaning flters clogged with fsh debris in 2013 after an overwhelming wave of jellyfsh followed by an algal tide brought a major player in the Oman's economy to a halt. need for high-dose dechlorination using sodium metabisulphite also has a negative impact on the RO membranes. Through its biocidal and oxidizing effects, chlorine breaks down large organic chains into smaller molecules that are much more readily used by microorganisms as food. The RO membrane vendor Hydranautics was consulted on the bio- fouling issue. It recommended a high- pH cleaning regime with warm water fushing which yielded positive results on fux (fgure 1) and brought differential pressures under control. REsiLiENCE The conditions at Majis provide a severe test of the resilience of pretreatment and RO systems to the extreme biofouling derived from the notorious HABs of the Gulf coast. Nevertheless, with the introduction of tailored cleaning regimes and modifcations to pretreatment operation, MF followed by RO was proven to be effective even under the most arduous of conditions. Testing conditions Majis operates a recently constructed seawater reverse osmosis plant (RO1) with a production capacity of 20,000 m 3 /d. A second RO plant (RO2), in its planning stage, will have a capacity of around 28,000 m 3 /d. RO1 consists of a microfltration pre-treatment system followed by fve seawater RO trains each producing 4 Ml/d. Two trains are dedicated to produce process water and two are for potable water for the Public Authority for Electricity and Water at the Oman capital, Muscat. The ffth lane is designed to produce either process or potable quality water. Majis' screened and chlorinated seawater is supplied from a seawater intake pumping station which has an open intake. And the water it receives comes from a shallow lagoon – only 4m deep – which provides an ideal environment for algal blooms. Furthermore the intake at Sohar Port is prone to frequent obstruction by jellyfsh shoals and the seasonal HABs in the form of a Red Tide and/or a suspension of green algae. Over the past fve to six years HABs have caused serious disruption to the water supply facilities at Sohar. Other signifcant challenges include high silt density indices of greater than 30, as well as high turbidity, and total organic carbon. To enhance its defences against HABs and jellyfsh, Majis is currently collaborating with Sohar University and Sohar Industrial Port Company to develop an early warning system to abate the economic impact of HABs. l