Algal bloom—critical to designing SWRO pretreatment and pretreatment as built in Shuwaikh, Kuwait SWRO by Doosan

The growing demand for fresh water in many areas in the world is due to drought, water shortages, population increases, and the desire for high- quality drinking water. The reverse osmosis (RO) process is pressure-driven and filtered seawater is pressurized beyond the osmotic pressure the solution to overcome the permeation barrier of membrane and the water molecules in the seawater able to pass through the membranes. In recent years, the number and size of these water projects have increased noticeably. RO membranes are expensive and susceptible to fouling due to contamination in the feed water; hence, it is utmost important to care for particular feed water treatment in maintaining ongoing performance and avoiding significant problems in downstream process equipments. In recent, days the additional risks are due to naturally occurring events like algal blooms or red tide, due to ingress of marine algae, planktonic bloom with small particles and colloidal material released from algae cause for pretreatment failure almost regularly. As algal bloom life cycle peaks and decays, a significant amount of organic material is released upon cell death. Also, bacteria feed on the decaying material and release their own extracellular polymeric substance (EPS) that has the potential to escape out pretreatment and foul RO membranes. There are many pretreatment procedures for seawater reverse osmosis (SWRO) plant, and the basis of selection of right system depends on seawater quality and the price. Doosan built facility in Shuwaikh in Kuwait is having the pretreatment configuration with combination of dissolved air flotation and ultrafiltration to take care of difficult water condition with highly suspended solid value arise for various reasons. Pretreatment combination is found to be working well in providing plant availability and quality. But the main concern is that it is impossible to avoid deposition of EPS on SWRO membrane surface with present pretreatment technology—it may happen in future with new generation of technology, it will be possible to overcome the situation at added cost.