Blending brackish water with desalted seawater as an alterative to brackish water desalination

Due to a severe water shortage and increasing salinity of natural sources, Israel is currently undergoing an intensive program of both large seawater reverse osmosis (SWRO) desalination plant construction and desalination of a number of wells shut down due to an increase of water salinity. There are some such wells in the vicinity of the planned large seawater desalination plants. Therefore, a proposed alternative of desalination of these sources is to use them to blend SWRO product whose salinity content has been reduced to a very low level by a second desalination pass. The foreseen specification of the desalted water regarding the upper limit of chloride and boron content in the coming international bids of large SWRO plants will probably be 70 mg/L chloride and 0.3 mg/L boron. Since a partial second pass for the SWRO is needed to achieve this specification, increasing the second pass to treat the entire or almost all the capacity of the first pass permeate can achieve product suitable for blending with some brackish source water. However, this option has to be competitive with direct desalination of the brackish water source. The comparative economics of these two alternatives is obviously dependent on the additional cost of reducing the SWRO permeate salinity vs. the cost of desalting the equivalent capacity of brackish water that could be blended with the permeate. The aim of this work was to analyze the comparative economics of these two alternatives for various types of brackish water sources.