Ultrapure Water Production by Continuous Electrodeionization Method: Technology and Economy

Abstract

Electrodeionization (EDI) and mixed bed deionization (MBDI) processes usually occupy the same position in the technological scheme of ultrapure water production, being used for the additional purification (conditioning) of reverse osmosis (RO) permeate (see, [1, 2]). A comparative analysis of the main differences of EDI and MBDI allows these methods to be more expediently used in water conditioning technology. The MBDI process has been used on a commercial scale for more than three decades, mostly in combination with a two-stage RO process. For this method, the content of active chlorine in the initial water flow is maintained within 0.05 – 0.08 mg liter in order to provide for a 3 – 4 month cellulose acetate regeneration cycle in the RO membranes. The ion exchanger is regenerated by treatment with strong acid and alkali solutions, which yields considerable volumes of highly mineralized waste waters implying the need for thoroughly monitoring the pH level. The EDI technology does not involve chemicals and does not require scrubbers for the flow neutralization after acid and alkali regeneration, reservoirs for the storage of concentrated acids and alkalis, the corresponding pumping equipment and valves, and double pipelines of corrosion-resistant steel, which significantly reduces both capital equipment and operating costs.