Search Results

Electrodialysis is used to remove salts from waste or other water streams, to yield a concentrated brine and a substantially deionized product water. During the electrodialysis process, the boundary layer adjacent to the ion selective membrane can become depleted of ions, resulting in severe pH changes sometimes accompanied by precipitation, and power losses, by a process known as “water-splitting.” In order to optimize the applied electric current density, to achieve maximum deionization without exceeding the limiting current at any point along the path, a simulation program has been created to plot ion concentrations and fluxes, and cell current densities and voltages, along the electrodialysis path. A means for tapering the current density along the path is recommended.

As the durations of manned space missions increase, so will the need for compact and reliable water recycling systems. Optimization of such water-recycling systems involves computer simulation of process elements and subsystems. The operations of water recycling systems are simulated at the Ames Research Center using commercial software called ASPEN-PLUS. Ion exchange is a part of the multifiltration subsystem, used for final polishing of recycled water and in some cases as a complete water treatment. Ion-exchange resins remove hazardous ions from solution by exchanging them with innocuous ions according to selection parameters. The ion-exchange operation is not provided in the ASPEN-PLUS multiprocess simulator package, but FORTRAN-callable modules may be added. Therefore we have adapted a FORTRAN program simulating multicomponent adsorption by ion-exchange resins, for use both as an ASPEN-callable module and as a free-standing simulator of the ion-exchange bed.