RO treatment at elevated pH

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The third and fi nal treatment step is the RO. This equipment is made up of standard components that are readily available from suppliers. Caustic is fed to the inlet of the RO to elevate the operating pH. Silica is highly soluble at elevated pH and therefore does not limit the recovery of the RO unit. Unlike conventional RO that is limited to approximately 150 mg/l SiO2 in the reject, an RO operating in the elevated pH mode can concentrate silica to 2000 mg/l and greater. This characteristic makes these processes well suited for treatment of cooling tower blowdown and other such concentrated wastewater streams. The elevated pH has the additional advantages of eliminating biofouling potential, emulsifying any oil that may exist in the wastewater supply, and enhancing the rejection of organic constituents.

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