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UF membranes with new Multibore design were tested in a pilot unit at the Addur SWRO Desalination Plant, Bahrain as pre-treatment for RO. The seawater at Addur is known for its extremely bad condition, mainly caused by industrial and residential waste disposals and high organic contents and bioactivity. Feed water for the pilot plant was taken from the Addur seawater supply line (intake 1.2 km offshore, chlorinated) directly, without making use of the existing media filtration. The existing UF/RO plant at Addur is suffering from heavy fouling and scaling problems. The pilot unit was started in March 2003. A first set of trials was done to test different operational modes and cleaning procedures under extreme fouling conditions. Based on these trials new modified UF modules were installed inMarch 2004 and operated until July 2005. During these 16 month of service the newMultibore UF membranes performed successfully. During summer month 2004 no membrane cleaning except normal backwash procedures with sodium hypo chloride was necessary for stable operation. The use of not chlorinated seawater as feed to the UF was tested in October 2004 and during the outage of the Addur plant February-April 2005. This water was taken by a newly installed 3’’ intake pipe from a location about 200 m offshore from a depth of 1.5 m only. This so called ‘‘raw beach water’’ turned out to be not suitable for UF filtration due to its extremely high fouling potential. The injection of flocculants into feedwater was tested to further improve the UF output and filtrate quality. The dosing of very small amounts of Fe proved to be beneficial. During summer 2005 the UF operation with Fe injection was stable with a flux of 70 l/m2h at a differential pressure around 250 mbar only. Filtrate SDI was always well below 3, even below 2 in July 2005. An additional RO pilot unit was installed inMay 2004 to directly test the fouling potential of the filtrate from the UF pilot plant. In the RO pilot plant a permeator as it is used at the Addur SWRO plant was installed. The fouling of this permeator was remarkably lower compared to the fouling in the Addur SWRO desalination plant. This proves the high quality of the UF filtrate in addition to the low SDI values. Because of the low consumption of cleaning chemicals, low differential pressure and no need for media filtration the operating costs for Multibore UF membranes would be remarkably lower compared to the operating costs of the existing arrangement at Addur. The pilot test under the extreme seawater conditions of Addur revealed that these new UF membranes are a very promising alternative for pre-treatment for SWRO desalination plants.

One of the largest seawater reverse osmosis (SWRO) desalination plants in the world commissioned at Addur, Kingdom of Bahrain survived the numerous obstacles that brought down the plant's production capacity to its lowest level. The drastic production loss, ever increasing heavy chemical cleaning programs, fouling of RO membranes and subsequent replacement within a short period of commissioning mystified the desalination world and drew the attention of experts in this field. Experiments and trials were conducted to identify the problems and rectify them. Ultrafiltration membrane technology emerged as the best viable alternative and was selected to improve the quality of the feedwater thereby to restore productivity. Based on that, the rehabilitation program was implemented with major changes in the infrastructure of the pretreatment section of the plant and ultrafiltration membranes were installed and operated. Soon, it became evident that the UF needed further refinement. A number of shortfalls in the UF system affected the operation and reduced the production capacity of the plant letting the operating cost to soar high. Under ‘The Addur SWRO desalination plant rehabilitation —production improvement works’ project, a team of experts investigated the probable methods to improve the production of the plant and suggested improvements with an enhanced model of UF membranes and entirely different type of RO membranes. The trials for this project were conducted at the pilot plant level; the tests were successful and the results were hopeful. With all positive expectations, ‘the production improvement works’ would be executed soon in the coming months with the improved UF membranes and use of cellulose acetate membrane type in one RO desalination production train. This paper attempts to describe the operational and mechanical problems encountered in the plant from the commissioning period till date and analyses them in view of before and after rehabilitation and sheds light on the reasons that lead to ‘the rehabilitation — the production improvement works’. The current status of the plant also is touched upon.

In 1984, the State of Bahrain commissioned its first high brackish water RO plant (13,000 ppm, TDS designed for 19,000 ppm) at Ras Abu Jarjur. The design capacity of the plant is 46,000 m3/d at a recovery rate of 65%. During recent years the plant has been subjected to many modifications with the objective of operating the plant at the minimal possible running costs and at the same time improve the overall performance of the plant, in particular the micron guard filters and the permeators. Based on extensive monitoring, trials and tests, the plant′s operating philosophy has been modified to optimize the operational costs and improve the overall plant performance. The modification works primarily covered the change of antiscalant chemical, reduction of dosing chemicals, bypassing of some pretreatment units, cleaning cycles for the membranes, and other off-line procedures which in turn directly reflected on the operational philosophy of the plant. This paper outlines all the achievements which resulted on the plant′s operating cost optimization and performance upgrade at the Ras Abu Jarjur, RO plant.