NTPC Transactions on Energy Research

India is a water-stressed country, having only 4% of the world’s water resources available for 18% of the world’s population. Multi-stage Reverse osmosis (RO) in combination with wastewater RO(WW-RO) is in practice now for the Indus-trial demineralization process actualizing the zero liquid discharge concept. The design of the de-mineralization plant depends upon the quality of the water source. Natural water holds a considerable amount of silica (SiO₂) up to 100 mg/L. The factors affecting RO membrane performance were studied, of which, silica fouling in combination with minerals and organics is found to be the main factor among other factors. The silica is hence complex in nature and silica fouling is generally not easy to control, thereby, resulting in performance failure of RO membranes. The present study discusses the effect of dolomite treatment, soluble magnesium compounds and sparingly soluble magnesium compounds on silica removal in boiler-feed water. It is found that the dolomite treatment in the pre-treatment step is ineffective for silica removal. The effective silica removal with soluble magnesium compounds increases the conductivity in the treated waters, and with sparingly soluble magnesium compounds is found only 40% effective; for increased effectiveness up to 86% pre-acidification was the condition which caused conductivity increase. In the present study, 90% of silica removal is achieved without pre-acidification along with the co-benefit of conductivity re-duction of feed water to the RO system. Therefore, the developed solution is efficient, cost-effective and environmentally friendly, which has not reported so far and is unclear in the literature available.