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The acids and bases used for ion exchange regeneration contribute significantly to the increasing salinity of potable water supplies. This research investigated the use of bipolar membrane electrodialysis (BMED) for producing acids and bases from dilute salt solutions that are produced during reverse osmosis or evaporative cooling. Using single pass BMED, acids and bases were produced with concentrations equal to ∼75% of the feed salt concentration with current utilizations >75%. Current utilization increased with increasing feed salt concentrations due to decreased leakage current through the monopolar membranes. The maximum current density at which the BMED stack could be operated depended on the feed salt concentration and the flow velocity and was limited by water dissociation at the interface between the diluate solutions and the monopolar membranes. The stack resistance was dominated by the bipolar membranes, even for the most dilute feed solutions. The energy required per mole of acid or base produced increased linearly with increasing current density. The energy costs for producing acids and bases were significantly less than costs for purchasing bulk HCl and NaOH, and the process is scalable to large systems.

The effect of current density on dosing rates and energy requirements for iron and aluminum electrodes in a bench-scale electrocoagulation (EC) reactor have been investigated. Dissolution rates of the iron and aluminum anodes were independent of bulk solution pH values. Iron dosing rates followed Faraday's law, but aluminum dosing rates averaged 83% greater than those predicted by Faraday's law. Chemical corrosion of both the anode and cathode contributed to the extra-faradaic aluminum dosing. A method was developed to determine the faradaic power consumption as a function of the current density. An equation describing power dissipation by ohmic and faradaic mechanisms was derived and used to estimate energy consumption per unit coagulant dose for EC reactors operating over a wide range of conditions. The derived equation can be used to compare the operational costs for EC with those using chemical additives, such as alum or ferric chloride.

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