Control and management of brine disposal for inland desalination plants

摘要

Desalination is a solution for a range of water supply problems. A higher recovery rate is an important goal because it increases production and improves cost effectiveness. As the recovery ratio increases, however, the concentration of dissolved ions in the brine becomes high enough to form scaling caused by precipitation of super-saturated salts. These precipitates might form a scale not only on membranes' surfaces but also in the brine disposal line. In order to prevent scale formation, special antiscalants are added to the reverse osmosis feed. It is important to emphasize that antiscalants only delay the onset of precipitation, resulting in possible scale precipitation in long outlet pipes. In addition to the tendency of scaling, brine disposal can be a serious environmental concern that needs to be studied and considered when building a desalination plant. Marine brine disposal can cause three possible hazards: precipitation on the pipe walls, soil and marine contamination. Since 2004, Mekorot has exclusively operated and maintained a unique 30-km long brine disposal pipeline to the Mediterranean Sea with the required permission from the Ministry of Environmental Protection. The pipe is used to dispose brine streams from the Gat and Granot BWRO desalination plants, which are located in southwestern Israel near the city of Ashkelon. A brine disposal pipe was developed by Mekorot as part of a coastal aquifer rehabilitation project and was chosen as the most economic solution for these two plants. A few years ago, an experimental system was run to obtain the design parameters for preventing scale deposition from a concentrate solution. Through the design of optimal operation of brine pipes, we prevent soil contamination and avoid scale deposition from concentrate solutions from both desalination plants. This paper reviews the management and control of the brine disposal pipe, including early scale detection, as well as the standard and special monitoring programs for the long brine disposal pipe at Mekorot.