Pretreatment options for large scale SWRO plants: case studies of UF trials at Kindasa, Saudi Arabia, and conventional pretreatment in Spain

Kindasa Water Services (KWS) currently operates an RO facility at Jeddah Port on the Red Sea in Saudi Arabia, using conventional pre-treatment, to provide a 14 mld output. Due to an increasing requirement for treated water services, a contract has recently been placed with Weir Westgarth for a new desalination facility to expand the capacity of RO treated water from 14 to 40.5 mld (3.7 to 10.7 MGD). The original system has operated well for most of the time since it was brought into supply in 2000. However, occasional poor quality conditions have occurred during storms, or periods of algal bloom, which have resulted in SDI’s to the RO exceeding target levels. Accordingly, an interest was expressed in utilizing ultrafiltration (UF) as an alternative to conventional pre-treatment, to improve RO feed quality, and guarantee on-stream time. The UF trial was highly successful in achieving stable membrane permeability and a consistent filtrate SDI when operated under optimized process conditions. Utilizing ferric chloride dosing, with acidification, the trial has operated at a flux of 95 LMH, and at a transmembrane pressure of 0.15–0.20 bar. The recovery was 94%. An average SDI of 2.2 has been obtained in the UF filtrate, approximately 2 units better than the existing conventional treatment. By utilizing an air enhanced backwash on a regular basis, the trial has shown that filtrate SDI’s of less than 3.0 can be obtained at all times, even under the poor feed quality conditions that occur during algal blooms. In the final phase of the trial, we have been able to obtain UF filtrate SDI values well below 2. Hydranautics has gained experience with UF pre-treatment to RO in 3 other case studies in the Gulf of Mexico, the Red Sea, and the Mediterranean. In each case, UF was demonstrated to *Corresponding author. Presented at the EuroMed 2004 conference on Desalination Strategies in South Mediterranean Countries: Cooperation between Mediterranean Countries of Europe and the Southern Rim of the Mediterranean. Sponsored by the European Desalination Society and Office National de l’Eau Potable, Marrakech, Morocco, 30 May–2 June, 2004. 0011-9164/04/$– See front matter © 2004 Elsevier B.V. All rights reserved

• Performance of the HYDRAcap module is • • • • • excellent with a stable TMP of <0.2 bar at an average flux of 95–98 L/m2h, including without FeCl3 dosing. Permeate SDI’s have averaged 2.2 in the first three phases and around 1 in the fourth phase, after AEB was correctly implemented; projected values for a main plant operation average 2.0, with all values falling below 3.0. This is at least 2 SDI units below the current DMF, and would reduce fouling material on the RO by approximately 75%. If Hydranautics provide both UF and RO stages, UF quality ceases to be a guarantee parameter due to the IMS guarantee. Recovery is 94%, with backwash and rinse volumes at around 6% of forward flow. Hypochlorite back flushing (20 ppm) maintains the TMP at normal low levels. Acid or caustic chemically enhanced back flushing have only been necessary when no dosing was employed, or when there were dosing problems; when used, baseline flux and TMP have quickly been re-established. Case studies at 3 locations on similar seawater feeds utilizing Hydranautics’ UF and RO have shown that the RO has operated for 6 months downstream of UF without the need for cleaning and that no problems have been experi- • • • • enced with RO fouling by dissolved organics passing through the UF. After comparing existing data from the UF pilot unit compared to large installations with conventional pretreatment, it can be seen that HYDRAcap technology is a more reliable pretreatment than the open water intake SWRO plants. Price of the whole conventional pretreatment compared to the UF pretreatment is still a key point but the additional cost of UF is reduced by the security of operation and on-stream time. RO membrane replacement is reduced significantly. Low space – >33% saving with UF Reduced requirement for RO disinfection and cleaning; avoidance of downtime or production loss.