Desalination
PLANTS and their potential effect in San Quintín Bay
The salt and chemical concentration in brine can be toxic for marine species and the environment . Photo : Enrique Alfaro .
1
By César Guerrero and Antonieta Valenzuela
One of the main primary food supply sources in Northwestern Mexico and Southwestern United States is the agricultural area of Baja California , especially the San Quintín Valley , where water is undoubtedly the fundamental resource for agriculture .
Quality standards required in water available for agriculture are not met due to the absence of atmospheric precipitation and the excessive groundwater extraction in the San Quintín Valley .
The effects of saltwater intrusion into the groundwater levels — from which water for agriculture is extracted — are irreversible ; water with high concentrations of salts is not ideal for agriculture and it reduces ( or even prevents ) the performance of agricultural production .
Due to the undeniable need of maintaining agricultural production and the inability of providing faster methods of groundwater recharge , the technology of desalination plants is now being used to solve the problem in the short term , but with negative — and sometimes irreversible — effects when is not appropriately managed .
The desalination process using reverse osmosis consists in withdrawing large volumes of seawater of the ocean or coastal saline aquifers ( as is the case in San Quintín ) and filtering it for irrigation , industrial
processes , agriculture or human use . On average , a desalination plant withdraws 2 gallons of seawater , from which it produces 1 gallon of desalinated water . Wastewater ( brine ) with high salinity is a result of this process and is later discharged back into the sea ( Cooley et al . 2013 ).
Brine has a much higher saline concentration than that of the sea , and it can even present higher temperatures . It is composed of large quantities of suspended solids , variable pH and dissolved salts , as well as chemicals used during the desalination process like detergents , coagulants ( ferric chloride ), anti-scaling agents ( polyacrylate ), anticorrosive agents ( sodium bisulfite ) and biocide ( sodium hypochlorite ) ( Mauguin et al . 2005 ). It results evident that this salt and chemical concentration in brine can be toxic for marine species and the environment .
Currently , there are at least 11 brine discharge locations registered in San Quintín Bay and Laguna Figueroa ( a water body located north of the bay ). Their salinity levels reach up to 62 mg / L , almost duplicating the average seawater salinity of 35 mg / L .
The impact on the marine environment can be negative when brine discharge zones coincide with sensitive ecosystems , closed and shallow sites with a high concentration of marine life ( Latterman & Höpner , 2008 ). Likewise , marine resources in the
06 AUGUST 2016