Challenges and achievements in the expansion of the granot BWRO plant: A part of Israel’s coastal aquifer rehabilitation project

The Granot inland BWRO (brackish water reverse osmosis) desalination plant is a part of the Aquifer Rehabilitation Project, which aims to prevent the salinization of the Israeli coastal aquifer. The main flow gradient of groundwater in the region is from a brackish aquifer in the east, to one of Israel’s main freshwater aquifers (the coastal aquifer) in the west. To prevent salinization of the freshwater aquifer, a buffer zone has been created in-between the two aquifers, comprised of approximately 40 wells. These wells act as a barrier to salinization by pumping the brackish water before it reaches the coastal aquifer. This brackish water feeds the Granot BWRO and Lahat BWRO desalination plants. This aquifer rehabilitation project consists of three main parts: (1) a line of wells along the boundary between the two aquifers, (2) the BWRO desalination plants, and (3) a unique, exceptionally long (30 km) brine disposal pipeline to the Mediterranean Sea. From the outset, this project was designed to accommodate expansions in the production capacity of the system as well as to cope with increasing salinity of the source water. Accordingly, since 2004 there has been a gradual expansion over the years, in the number of desalination units within the Granot Plant. Currently, three desalination units are in operation, and a fourth unit is targeted to initiate production in June 2015. The total capacity at the Granot plant will be 41,600 m³d^-1 in 2015, and subsequent to the planned fifth unit, production is expected to reach 52,900 m³d^-1. This paper discusses the optimal design of the desalination plant, including considerations of RO membrane type, configuration, and post-treatment processes. This design is chosen to meet the permeate water quality regulations, and to minimize energy consumption. The design and construction of the Granot Plant meets all of the regulations of the Israeli Water Authority and the Israeli Ministry of Health, including respective boron and chloride concentration limits in the permeate, of 0.35 ppm and 20 ppm, respectively. Mekorot has also overcome several issues in the design phase as a result of an expected increase TDS and silica concentrations which might increase the scaling tendency. TDS and silica concentrations (and consequently, scaling) are expected to increase further by more than 20% during the coming decade. Experiments were carried out to address the challenge of preventing scaling on the RO membrane and within the brine disposal pipeline. These experiments have led to adjustments in the design features of the desalination units, including the operational conditions and chemical usage.