IS REVERSE OSMOSIS THE MOST SUITABLE SEAWATER DESALINATION PROCESS FOR ALGERIA?

Abstract

Algeria lies between two seas: the Mediterranean Sea to the north, an open sea, and the fossil sea to the south, an underground sea. These seas possess enormous water resources, but they are saline and undrinkable. To eliminate the salt, Algeria opted for reverse osmosis. Eighteen desalination plants and more than fifteen demineralization plants produce 1.35 billion m³/y of fresh water. However, the plants' output has not reached the expected level. The reverse osmosis process is not well-suited to the raw water treated in Algeria. Reverse osmosis encounters difficulties during the rainy season. The polluted water discharged by the 50 Rivers (riverbeds) into the sea seeps into the plants' water intakes. To prevent turbidity in the raw water, the intakes must be located further from the treatment plants. For brackish water demineralization plants, reverse osmosis is not suitable for raw water at a temperature of 60°C. A cooling tower is necessary to lower the temperature to 30°C. The distillation process does not require a pretreatment step. It is better suited to warm and even turbid water. Distillation produces a green brine containing only salts and no chemical additives. In contrast, the brine discharged by reverse osmosis contains salts and chemical additives used during the pretreatment phase. Storing brine from a demineralization plant using distillation in evaporation ponds is not a viable solution, as it results in the loss of land and significant amounts of water through evaporation for just a few kilograms of salt. The most effective solution for brine from a demineralization plant is its direct discharge into the salt flats (chotts). However, for seawater desalination, brine in the sea without chemicals remains the only viable option at present. So, even though reverse osmosis consumes less energy, considering the parameters mentioned in the article, distillation is a much more favorable process than reverse osmosis.