Seawater Quality, Distillation, Desalination, Brine Concentrate, Water Supplies and Sustainability

Seawater quality is impacting due to the release of stormwater discharged into the sea. The stormwater has low dissolved solids in it, but volumes are huge resulting addition of huge load of contaminants and dissolved solids in the sea water. It is estimated that seawater contains dissolved solids around 35,000 mg/L.

Oceans are the largest distillation pot and sink for salts accumulated due the process of evaporations. Any salt dumped into the sea remains there forever. It means that slat levels are increasing with the age of earth. Evaporations resulting in rains bring stormwater containing low dissolved solids to oceans.

There are more than 20,000 desalination plants worldwide that are operated to meet water demands for potable and industrial water demands. This number will be increasing further to meet water demands.

The operation of desalination plants contributes to the generation of concentrated side streams that have high total dissolved solids (TDS). It is estimated that concentrated brine has TDS of more than 70,000 mg/L which is discharged back to oceans. This implies that one litre of potable water dumps around 70g of salts into seas. From the above assumptions one can estimated that 100 MLd desalination plant would generate brine and 7000-ton salts that will be dumped into the sea. This estimate may change when recovery rates of potable water are low. The amount of salt generated from more than 20,000 desalination plants will change the water quality is a big concern and alarming.

The provision of water supply schemes needs serious review and ensure that stormwater/surface water are used at maximum to minimise the use of seawater for the production of potable water.

The sustainability of current practices needs detailed review to maintain water quality of seawater before it reached to salt toxicity. Presently, concentrated brine is allowed into sea considering dilution and distribution of salts in the disposal areas.