Nitrate Removal by Continuous Electropermutation Using Ion-Exchange Textile

Abstract

Water with nitrate concentrations above 100 ppm has been treated with continuous electropermutation which partially substitutes the nitrate with chloride. The performance of a textile anion exchanger as conducting spacer in the feed compartment of an electropermutation cell was investigated. Experiments with and without textile are compared and the influence of the textile is discussed. The process could, using the textile, successfully treat feed water with 105 ppm nitrate to produce a water with less than 25 ppm nitrate. The importance of establishing a good contact between the membranes and the textile spacer was pointed out. The experimental results were compared to model predictions and a good agreement was found.

Modeling continuous electropermutation with effects of water dissociation included

“…In a previous paper, a steady state model of the FC, filled with an ion‐exchange textile as a conductive spacer, together with adjacent ion‐exchange membranes in an electropermutation cell was presented 6. In this article that model will be extended to include also the effect of water dissociation.…”

“…Continuous electropermutation4–7 is a process, which is similar to EDI in that it combines conventional ion‐exchange with an electromembrane process. Instead of removing all ions either the anions or the cations are selectively replaced by other more desirable ions.…”

“…In two previous papers,6, 7 the removal of nitrate by continuous electropermutation using ion exchange textile as conductive spacer was studied both experimentally and theoretically. From the experimental investigation, it was concluded that a conductive spacer is needed, in the FC, for the electropermutation process to be operated at reasonable current densities.…”

“…However, also with the ion‐exchange textile incorporated as a conductive spacer, it was noted that water dissociation was starting to become important at an average current density of 25 A/m 2 . The effect of water dissociation as a parasitic reaction was not considered in the electropermutation model presented in Ref 6…”

“…To include this additional phenomenon, a model of water dissociation, treated as a potential‐dependent heterogeneous reaction, was developed 8. An important task of this work is to test that model in a simulation of the entire electropermutation process, and to compare with the experimental results of Ref 7…”