The Shuwaikh seawater reverse osmosis (SWRO) plant is a large-scale desalination plant in the Persian Gulf. It is the first desalination plant in Kuwait to use RO technology for seawater treatment and also the world’s largest SWRO plant using dissolved air flotation (DAF) and pressurized inside-out ultrafiltration (UF) as pretreatment steps. The combination of DAF and UF was chosen to guarantee reliable plant operation as the seawater in the area is highly saline, rich in organic components and known for occasional harmful green algae blooms.
Together, DAF and UF can efficiently remove high concentrations of suspended solids (SS) and small-sized colloidal particulates. As a result, the high-quality RO feed water that is produced has a consistent silt density index (SDI) value of less than 3.0 at all times.
red tide events
The Shuwaikh SWRO site faces occasional red tide events that can last up to 10 days at a time, and green algae blooms. During such events, the combined DAF and UF pretreatment has proven successful in removing the increased number of particles caused by the abnormal growth of algae with turbidity levels of up to 31 NTU. The high turbidity of the seawater leads to a higher effluent turbidity from the DAF units, which can have negative effects on the UF performance. First, the increased number of particles and colloids can plug the membrane pores. Also, extracellular polymeric substances excreted from algae can lead to increased membrane fouling, which is difficult to remove with normal water backwash.
During the last red tide event in May 2012, it was proven that only small measures need to be taken to guarantee a reliable operation of the UF system and provide optimum pretreatment for the RO system. To control the high turbidity, coagulation of DAF is enhanced and chemically enhanced backwash (CEB) frequency of the UF system is increased. These two simple actions ensure a continuous supply of high-quality pretreated seawater to the SWRO system, thereby preventing production reductions or shutdown and ensuring a reliable supply of potable water to the city of Kuwait.
As an example of the UF performance, below the operating data from one UF skid in operation is shown before, during and after the red tide event (May 5-10, 2012). The top graph shows development in membrane permeability over time.
The bottom graph shows development of transmembrane pressure (TMP) of the UF unit. The UF performance data confirms that the UF skids operated during the red tide event, which allowed continuous operation of the SWRO desalination plant.
scope of supply
5840 x Seaguard 40 UF
membrane 20 x Skids
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Applied in large-scale desalination systems, Seaguard UF membranes provide an excellent pretreatment method for SWRO plants with feed water containing suspended solids levels of up to 75 mg/L.