Boron removal from brackish ground water - case study on the ""Hij"" BWRO plant

Some water resources in particular brackish ground water are reported to have high concentration of boron, making them unsuitable for human consumption and irrigation. Boron is a vital element for organism growth, but excessive exposure can cause detrimental effects to plants, animals, and possibly humans. Many technologies have proved the ability to remove boron, for example: coagulation, precipitation, ion exchange and reverse osmosis. However, it is usually requires a double step treatment and combination of processes, as they are either not effective to remove boron and meet current World Health Organization guidelines for drinking water quality (i.e., 0.5 mg/L) or they are very costly, making them unaffordable for full scale utilization. In general, reverse osmosis technology has high efficiency to remove boron from brackish water as well as sea water and it is considered as one of the best available technologies in spite of draw back factors. This research aimed to study various RO system configurations to improve the removal of boron below 0.5 mg/L in brackish water reverse osmosis (BWRO) permeate of Hij plant in Oman and to calculate the anti‐scalant dose for each design configuration. Also, the risk associated with each alternative in case of any failure in the system was evaluated. Three different scenarios were considered in the study: single pass RO, double pass RO and NF combined with RO. Six commercial programmes were used to project boron removal and to calculate antiscalant dose. RO projection programs included: IMS‐Desing (Hydranautics), ROSA (Dow) and TORAY. They were used to determine the optimum conditions for boron removal. Anti‐scalant calculations programs included: Genesys, 4Aqua and Hydrex; they were used to determine the required anti‐scalant dose at each design. Finally, multi‐criteria analysis program was performed to evaluate the alternatives. The three scenarios were projected at different recovery, flux, pH, membrane brand and age. Also, anti‐scalant dose was calculated for each system configuration. Moreover, the risk associated with each alternative was evaluated. At the end, the multi‐criteria evaluation determined the best option considering technical and economical effectiveness such as costs; permeate quality and reliability of the system. The results shows that all proposed design configurations can remove boron for Hij case up to the desired level of WHO guideline. However, single RO design requires some change in the operating conditions (e.g., pH > 9.0) and installation of high boron rejection membrane is required. On the other hand, double pass RO and nano‐filtration plus RO designs can be operated at natural pH. Accordingly, the risk potential associated with first scenario is higher compared with second and third scenarios because the system cannot match the quality parameters in case of any failure in pH correction system. In summary, the boron rejection in RO plant depends on feed water salinity, pH value, membrane elements properties and age, system design and operational parameters such as average permeate flux and recovery. And it seems that, double pass RO is the most feasible option recommends for future application