Brine Reuse in Ion‐Exchange Softening: Salt Discharge, Hardness Leakage, and Capacity Tradeoffs

Abstract

Ion-exchange water softening results in the discharge of excess sodium chloride to the aquatic environment during the regeneration cycle. In order to reduce sodium chloride use and subsequent discharge from ion-exchange processes, either brine reclaim operations can be implemented or salt application during regeneration can be reduced. Both result in tradeoffs related to loss of bed volumes treated per cycle and increased hardness leakage. An experimentally validated model was used to compare concurrent water softening operations at various salt application quantities with and without the direct reuse of waste brine for treated tap water of typical midwestern water quality. Both approaches were able to reduce salt use and subsequent discharge. Reducing salt use and discharge by lowering the salt application rate during regeneration consequently increased hardness leakage and decreased treatment capacity. Single or two tank brine recycling systems are capable of reducing salt use and discharge without increasing hardness leakage, although treatment capacity is reduced. Water Environ. Res., 84, 535 (2012).

Increasing RO efficiency by chemical-free ion-exchange and Donnan dialysis: Principles and practical implications

“…First of all, preliminary experiments were conducted to evaluate the regeneration capacity of the resin using NaCl versus KCl solutions, since the RO concentrate could contain high concentrations of both Na þ and K þ (see Table 1). Traditionally, IEX resins for softening are regenerated using at least 2 bed volumes of a 80e120 g/l NaCl solution (Flodman and Dvorak, 2012). For this experiment, 10 bed volumes (to Fig.…”

CO2 electrolysis in seawater: calcification effect and a hybrid self-powered concept

“…The presence of calcium in seawater is found not only decreased the stability of the Ag catalyst; but also decreased the selectivity in CO conversion. To minimise the impact of Ca 2+ in seawater in the direct electrochemical CO2 conversion, existing technologies, such as ion exchange resins, 38,39 and precipitation agents 40 are readily available to remove Ca 2+ from seawater before being employed as an electrolyte.…”

Salt‐free softening by thermo‐reversible ion‐adsorbing hydrogels

“…3,4 Regeneration of IEX typically involves high temperatures [5][6][7] or consecutive washing steps involving brine or acid and caustic, 8 leading to a large amount of waste salt. 9,10 The disposal of these salts cause salinization of surface waters and soil, which is an increasing burden for the environment. There is upcoming regenerate disposal legislation, where several US states, like California, already installed partial softener bans to deal with salinization of surface waters.…”

“…A few examples have been published in which the lower critical solution temperature (LCST) of PNIPAAm is used as a switch between adsorption and desorption. 34,35 However, most of these hydrogels deal with ion adsorption at elevated temperatures (40-50 C) and ion desorption at ambient temperature levels (10)(11)(12)(13)(14)(15)(16)(17)(18)(19)(20) C). This is not practical for most applications, since multivalent ions often need to be adsorbed from natural water sources, generally found at ambient temperature levels.…”