The use of phosphorus-free antiscalants in BWRO desalination plants and brine disposal pipelines

Abstract: Today, most RO desalination plants are using phosphorus-based antiscalants for preventing salt precipitation (scaling) and to achieve high membrane performance, as measured by reduced trans-membrane pressure, salt passage and increased permeate flow. However, phosphorus antiscalants in brine disposal can be an environmental issue that should be considered and studied when installing a desalination plant. The purpose of this research is to examine different types of phosphorus-free antiscalants and to find combinations of good membrane performance (varied recovery rates) and environmental antiscalants. Together, the Granot and Lahat BWRO desalination plants will produce approximately 30 Mm³ in 2014. They are part of a large project: “The Aquifer Rehabilitation,” which aims to protect the Israeli costal aquifer from saline infiltration. The concentrate from these inland BWRO desalination plants is sent along a unique 30-km-long brine disposal pipeline to the Mediterranean Sea (“Granot-Ashkelon” pipeline). Obviously, the preferred phosphorus-free antiscalant should prevent salt precipitation (scaling) in both the RO membranes and the lengthy brine disposal pipeline. The use of phosphorus-free antiscalant should achieve stable membrane performance. To date, five different antiscalants (four of them, phosphorus free) were tested at a pilot plant at the Granot site. This BWRO pilot plant contains two systems: (i) the desalination branch, which has similar alignment and pre-treatment as the Granot desalination plant, and (ii) a brine flow system that simulates true brine flow conditions. This system was used to validate the possibility of salt precipitation in the long brine pipeline. Experiment results carried out on four phosphorus-free antiscalants show that stable membrane performance did not occur. This research continues in pursuit of compounds that can satisfy the increasingly stringent environmental requirements in this field. According to the experiments schedule, additional phosphorus-free antiscalant will be tested in Granot BWRO pilot plant.