Ion Exchange Regeneration Process Utilizing Membrane Distillation

摘要

Method for treating effluent waste from a cation-exchange column regeneration cycle, including backwashing the column; regenerating the column using rinse water and a regenerant brine having a temperature warmer than room temperature, thereby forming a waste effluent containing divalent cations; precipitating the divalent cations in a precipitation reactor at a temperature warmer than room temperature; filtering the precipitation effluent; optionally, adjusting the filtered precipitation effluent pH; concentrating the filtered precipitation effluent via membrane-based water recovery, thereby forming separated concentrated salt and pure rinse water; and recirculating the separated concentrated salt and pure rinse water back to the column for a subsequent regeneration cycle. Also, a system including an exhausted cation-exchange column; a chemical precipitation reactor; a filtration unit; an optional pH adjustment unit; and a membrane-based water recovery unit, wherein the system is a closed-loop through which salt and rinse water having a temperature warmer than room temperature recirculate.

主权项

1. A method comprising
i) a backwashing step, wherein an exhausted cation-exchange column is backwashed with backwash water; ii) a regeneration step, wherein rinse water having a temperature of from about 40° C. to about 60° C. and a regenerant brine comprising sodium chloride and having a temperature of from about 40° C. to about 60° C. are passed over the exhausted cation-exchange column, thereby forming a waste effluent having a temperature of from about 40° C. to about 60° C. and containing divalent cations and sodium chloride; iii) a precipitation step, wherein the waste effluent is fed at a temperature of from about 30° C. to about 50° C. to a precipitation reactor where the divalent cations are precipitated as carbonates or hydroxides, thereby forming a treated effluent; iv) a filtration step, wherein the treated effluent proceeds through a filtration unit to remove unsettled particles, thereby forming a filtered effluent; v) an optional pH adjustment step, wherein the filtered effluent is neutralized with acid, thereby forming a pH-adjusted effluent; vi) a membrane-based water recovery step, wherein the filtered effluent leaving the filtration step of iv) or the pH-adjusted effluent of the optional pH adjustment step of v) is concentrated via a membrane-based water recovery unit, thereby forming separated concentrated sodium chloride and pure rinse water having a temperature of from about 60° C. to about 70° C.; and vii) a recirculation step, wherein the separated concentrated sodium chloride and pure rinse water leaving the membrane-based water recovery unit are fed back to the cation-exchange column for a subsequent regeneration cycle; wherein ii)-vii) are repeated at least one time.