Inorganic fouling control in reverse osmosis wastewater reclamation by purging carbon dioxide

Inorganic fouling on the membrane surface is one of the major prevalent issues affecting the performance and cost of reverse osmosis system. Chemical dosage is a widely adopted method for the inhibition of inorganic scale on the membrane surface. In this study, CO₂ was used to control inorganic scale formation on surface of reverse osmosis (RO) membrane in wastewater reclamation. The pH of influent could be lowered by purging CO₂. It caused an increase in solubility of inorganic salts in water resulting in discharge of principle ions in concentrate stream. A pilot plant study was conducted with four different RO modules including control, with dosage of antiscalant, with purging CO₂ and with co-addition of antiscalant and CO₂. The effectiveness of CO₂ purging was assessed on the basis of operational analysis, in-line analysis and morphological results. Ryznar stability index was used to determine the scaling potential of system. The examined data indicated that CO₂ purging was successful to inhibit scale formation on the membrane surface. Moreover, CO₂ was found more eco-friendly than antiscalant, as no by-products were generated in concentrate stream.