Seawater quality at the brine discharge site from two mega size seawater desalination plants in Israel (Eastern Mediterranean)

Desalination is recommended by the United Nations, through the goals of Agenda 2030 for Sustainable Development, as an essential tool to provide clean water and sanitation to the world’s population. Five seawater reverse osmosis desalination plants located at the Mediterranean Sea coastline, supply about 80% of the total domestic and industrial water needs in Israel. The plants are among the largest in the world, producing close to 590 Mm³/y freshwater. As part of the brine discharge permitting process, the plants are required to perform biannual compliance monitoring surveys to assess the effects of brine on the marine environment. Here we present the results of the monitoring performed at the marine outfalls of Palmachim and Soreq plants, which are equipped with diffusers, and located at 20 m water depth, 0.8 km apart. Six years (2013-2018) monitoring have shown almost no impact on seawater quality. The brine dispersed near the bottom following its initial mixing, and was not detected near the surface. Maximal excess salinity at the salty layer ranged from 4.3 to 9.1% over the reference and the affected area was highly variable (2 km² - >13 km²). Brine increased seawater temperature by up to 0.7°C near the outfalls. It had no impact on oxygen saturation, turbidity, pH, nutrients (except for total organic phosphorus (TOP)), chlorophyll-a and metal concentrations. TOP, correlated with excess salinity, originated from the polyphosphonate-based antiscalant discharged with the brine. It is unknown if the results of this short term study represent a steady state, with temporal variability, or the beginning of a slow incremental impact. With plans to more than double desalination in Israel along its 190 km Mediterranean coast by 2050, a long term, adaptable, monitoring program, along with specific research and modeling, should be set up to assess and predict the impact of large scale brine discharge on the marine environment.