Weak-Electrolyte Ion Exchange in Advanced-Technology Water-Reuse Systems

摘要

Ion-exchange treatment can be used to purify wastewater in various ways, including selective removal of individual unwanted ionic species. Weak-acid and weak-base ion exchangers, relatively new on a commercial scale, furnish and exceptional range of performance capabilities with the prospect of unusually efficient and inexpensive regeneration. Column runs, as well as batch experiments, established the equilibrium isotherm behavior between typical exchangers and particular solutions. The equilibrium data fit the Law of Mass Action, with activity coefficients correcting satisfactorily for nonidealities in both solution and resin phase. Behavior of weak-electrolyte resins is more complex than for strong electrolytes. This produces fairly large nonidealities in dilation behavior and Donnan uptake, and probably also in intraparticle diffusion rates. Phosphate was used as a model impurity in this study, and a secondary municipal effluent high in phosphate was modeled. A combination of general salinity reduction with impurity removal increases the useability of product water. Nearly complete acidification gives the best results for phosphate uptake. A new technique, segmented-bed operation, has been developed to minimize the cost and use of regenerant chemicals, and the disposal of regeneration wastes.