A B S T R A C TAll over the world, the reverse osmosis (RO) desalination plants are providing populations and industries with high quality freshwater. There are various requirements on water quality produced by RO desalination plants depending on final purpose of water usage. In recent years, the requirement for low Boron concentrations in RO permeate was the main parameter to be considered in designing many seawater RO systems. Beside the development of new RO membranes with improved Boron rejection, there are also other design options which can help to achieve required product quality. One of such options is also Split Partial Second Pass (SPSP) RO design.The principle of a SPSP design is based on the fact, that front elements in RO pressure vessel are always producing better permeate quality than elements at the back of the pressure vessel. In order to take advantage of better permeate quality at the front of the vessel in SPSP design, permeate is collected from both sides of the pressure vessel. Low TDS front permeate is than sent directly to final product line, while higher TDS back permeate is treated by partial second pass RO plant. At the end of the process, both permeate streams are blended together to create the final product of required quality. The SPSP design allows to select the right ratio between front and back permeate in order to obtain final product of required quality in terms of Boron, TDS and other quality parameters. The SPSP design provides cost effective option by minimizing the size of the second pass RO, which allows substantial savings on capital investments as well as in operating cost of the plant. This paper will present in more details the SPSP design option and requirements, the important parameters influencing SPSP design and different ways of the control, and finally it will discuss benefits and savings resulting from this RO design option. It will also present actual operating data from seawater RO plant using this design option.

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Operation of wastewater treatment plants can be very challenging due to the high fouling tendency of wastewater. Much knowledge has been gained over the past few years to guide design engineers on the optimum design for wastewater reverse osmosis (RO) plant. The implementation of this knowledge helps to improve the operation and performance of many wastewater plants. One such example is the SAFI (BESIX Group Company) plant in Ajman, UAE. Here, an microfiltration (MF) and RO plant was installed in 2010 to treat sewage effluent in order to supply high quality water for industrial and domestic reuse. The 6,800 m 3 /d plant treats secondary effluent with MF and RO. There are two RO trains designed to operate at 18.6 l/m 2 h and 75% recovery, for treating municipal treated effluent with 2,000-4,000 mg/l of total dissolved solids (TDS). When operation started in 2010, the rate of fouling on RO membranes was extremely high, with up to 66% flow decline in 3 months of operation. This was eventually attributed to higher than design operation temperatures, lack of regular biocide disinfection, absence of flushing and cleaning system, and no flux balance between the RO stages. A detailed analysis was made of the fouled elements, and it was found that the primary issue was biofouling. This paper will review the actions that were taken to correct the fouling issue and stabilize the RO performance. One of the key factors, which ultimately resolved the problem was the membrane change, from single element type to two different types of membranes, on each RO stage to better balance the flux between RO stages. This and other changes have resulted in the plant now to achieve the production goals with stable operation.

ab s t r ac tKindasa Water Services (KWS) derived its name "Kindasa" from the first seawater desalination plant built in Jeddah in the early 19th century. KWS is a limited liability company January 2000. KWS owns and operates desalination plants for supply of water to various industries, compounds etc. Recently KWS has built and is operating sea water reverse osmosis (SWRO) desalination plant in Jeddah Islamic Port with Hydranautics's integrated membranes system (IMS®). KWS has selected hybrid pretreatment system consisting of conventional dual media filtration in conjunction with the latest state-of-the-art ultrafiltration (UF) process to produce stable RO feed water quality that remains unaffected by the seasonal changes of the seawater quality. KWS's SWRO plant is the largest IMS operating already for two years in very difficult water. A pretreatment system was successfully commissioned in June 2006, and reverse osmosis section was commissioned in August-September 2006. There are different views in desalination industry on the use of membrane pretreatment utilizing or upstream of seawater reverse osmosis systems. Up to date unbiased information about real long term operational experience is not available. On the contrary, there are quite a few papers presenting membrane pretreatment as a "magic solution" to reverse osmosis performance problems. Two years of successful operational experience of this large SWRO IMS® working in very difficult raw water conditions has shown that this technology is viable, but it has also shown that this technology still needs proper attention and tuning and can create disappointment on end-user's side if certain design aspects and operational aspects are not properly addressed at the early stage of operation. Information will be provided which shows that close cooperation between technology supplier and user can solve these operational issues. Kindasa SWRO IMS® is designed for product capacity of 25,500 m³/d at 95% availability. The present plant production is 26,840 m³/d. The seawater is treated by 8 ultrafiltration racks equipped with Hydranautics HydraCap 60 and downstream by seawater reverse osmosis trains equipped with Hydranautics SWC3 seawater reverse osmosis membranes operating at 50% recovery. Product water is further treated in partial second pass trains utilizing Hydranautics low energy ESPA 2 membranes. The paper presents long term experience, operational data as well as normalized data and discusses all aspects of the plant operation and performance in detail. The plant is a key reference for future development of SWRO plants for difficult waters in the Middle East area as well as for global view of SWRO desalination and serves as "model plant" to demonstrate viability of MF/UF as pretreatment upstream of SWRO.

Operators in the Middle East have embarked on projects to explore and produce oil and gas from unconventional reservoirs by hydraulic fracturing (fracing). Many unique challenges exist for each reservoir under consideration but one that is common amongst all of these operations is the access to water to frac with. Companies responsible for conducting the frac have learned a lot about water management through the experience gained in North America about using sources other than fresh water such as brackish water, flowback water, and produced water but often the required level of treatment is minimal. This is because there is access to fresh water, which allows for dilution to get the waste water to the minimum required level for use in a frac. This coupled with advances in the development of high salinity tolerant frac fluid chemicals (Lebas et. al. 2013) eliminates the need to use advanced water treatment processes such as membranes. In contrast, there are many barriers to similar long term access to fresh water sources in the Middle East. Therefore other water sources must be considered, such as subsurface brackish water or seawater, and subsequently other treatment options must be considered, such as membranes. These technologies are mature in many other applications but for this particular application, there are challenges with implementing and deploying these systems resulting from the required flexibility of the systems and the environment in which the systems are to be operated. In order to overcome these obstacles, it is important that the stakeholders openly communicate the expectations to develop a mutual understanding for the requirements of these systems such that design measures can be implemented and operating protocols can be developed to make the systems fit for the purpose. The authors of this paper have taken the approach of identifying likely issues and providing an approach to the design of the process and operational protocol for these applications to provide guidance to those considering utilizing these processes. Also, references are made to similar challenges faced in other applications to those in this application to help with identifying possible solutions. The goal of this paper is not to provide solutions to each and every scenario, because it is impossible to do so, but rather to identify the critical factors that should be considered to enable the project stakeholders with the tools for development of a good design and operating protocol. By providing some clarity to the risks and potential solutions it is the authors’ ambition that those who make the investment in the technology are able to obtain the expected results and return on their investment.