RESEARCH CORNER
INNOVATION FOR CHEMICAL FREE DESALINATION By Dr. Ahmed Al Amoudi, Dr. Byungsung Park, Dr. Seungwon Ihm, and Eng. Nikolay Voutchkov, Desalination Technology Research Institute (DTRI), Saline Water Conversion Corporation (SWCC) Recent desalination industry shifts toward chemical-free desalination and recovery of valuable minerals and rare metals from concentrate are expected to transform desalination into one of the most environmentally sound and sustainable water supply alternatives of the 21-st century. At present the desalination industry uses chemicals for: (1) intake bio-growth control; (2) coagulation and flocculation of source seawater; (2) prevention of membrane scale formation; (3) membrane cleaning; (4) and desalinated water post treatment. Latest two key industry trends aimed at reducing and ultimately eliminating chemicals used for production of desalinated water are: (1) treatment process optimization to reduce chemical demand and, (2) use of green chemicals – generation of chemicals from seawater and brine. Intake Bio-growth Control At present, most desalination plants worldwide use sodium hypochlorite for intermittent injection in the desalination plant intake area to suppress growth of shellfish along the source water conveyance pipelines. Majority of the desalination plants worldwide have adopted generation of sodium hypochlorite from seawater thereby eliminating the use of commercial chemical. Recent trend is the development and use of systems for generation of high-purity chlorine dioxide from brine for biogrowth control. Latest generation chlorine dioxide systems do not generate any oxidants 50
harmful for the reverse osmosis membranes, thereby eliminating the use of sodium bisulfite for dichlorination. Since chlorine dioxide is generated from bine – the intake bio-growth control chemicals are green and their production is sustainable. Coagulation and Flocculation Ferric chloride is the most commonly used coagulant for pretreatment of seawater at present. Recently, the desalination industry has adopted an automated monitoring of seawater quality and automated adjustment of the coagulant dosage proportionally to the actual content of suspended solids in the
