Brine discharges from desalination in Morocco: what two impact assessments show, and what the draft decree would measure

Abstract

Morocco is rapidly developing seawater desalination. This production comes with brine discharges whose impact depends not only on their salinity, but also on their dilution and dispersion once they reach the sea. To see how these discharges are assessed, we examined the impact assessments published for the Jorf Lasfar and Safi plants, then compared their data with the Moroccan draft decree on coastal discharges. Our analysis covers only publicly available documents; it does not rely on any on-site measurement.

Both assessments describe the brine and its mixing with cooling water before discharge. However, the salinities stated for these mixtures cannot be recovered from the figures provided: the calculation gives 35.7 g/l instead of 35.4 at Jorf Lasfar, and 47.8 g/l instead of about 45 at Safi. Nor do the documents show how the saline plume disperses at sea, or what happens to the discharge if the cooling-water flow decreases.

The draft decree is a step forward, but its general limits appear ill-suited to effluents derived from seawater. Its conductivity threshold is close to that of natural seawater at 25 °C, while its limits for magnesium, calcium and sulfate are below the concentrations naturally present in the sea. The challenge is therefore to define specific rules that can be verified at each site: a salinity threshold in the receiving environment, a clearly located measurement point, reproducible mixing balances, and consideration of the dependence on cooling circuits. This finding prejudges neither the actual quality of the discharges nor any non-compliance.