NOVELTY - The method comprises contacting the solution with an anion exchange resin having an affinity for the oxyanion to produce an effluent (5) having reduced oxyanion content and an oxyanion-loaded ion exchange resin, and contacting the oxyanion-loaded ion exchange resin with a regenerant solution (6) e.g. a brine to form a treated anion exchange resin having a reduced oxyanion load relative to the oxyanion-loaded ion exchange resin and a spent regenerant solution having an increased oxyanion content relative to the regenerant solution.    USE - The method is useful for reducing the content of an oxyanion e.g. nitrate in an aqueous solution e.g. water sourced for drinking (claimed).    ADVANTAGE - The method is capable of simply, effectively and economically reducing the content of the oxyanion in the aqueous solution, prevents the loss of salt during the water treatment, and provides high-quality product brine combined with minimal waste.    DETAILED DESCRIPTION - The method comprises contacting the solution with an anion exchange resin having an affinity for the oxyanion to produce an effluent (5) having reduced oxyanion content and an oxyanion-loaded ion exchange resin, contacting the oxyanion-loaded ion exchange resin with a regenerant solution (6) e.g. a brine to form a treated anion exchange resin having a reduced oxyanion load relative to the oxyanion-loaded ion exchange resin and a spent regenerant solution having an increased oxyanion content relative to the regenerant solution, treating the spent regenerant solution in an anoxic membrane bio-reactor (MBR) under anoxic conditions to produce an anoxic treatment effluent having a reduced oxyanion content relative to the spent regenerant solution, treating a waste sludge in an aerobic MBR under aerobic conditions to produce an aerobic treatment effluent having a reduced sludge content, and recycling the anoxic treatment effluent and/or the aerobic treatment effluent to the anion exchange resin via storage tanks, for use as the regenerant solution, or as a component of the regenerant solution. The anoxic treatment effluent comprises clarified brine. The regenerant solution is an aqueous solution having dissolved in a quantity of monovalent alkali metal salt to provide a salinity of 3%. The anoxic MBR is operated at relatively short solids retention times of 12-72 hours. The aerobic MBR is operated at relatively long solids retention times of 10-100 days. The anoxic MBR and the aerobic MBR comprise submerged membranes, which are microfiltration membranes with an average pore size of 0.1-1 microns or ultrafiltration membranes with an average pore size of 0.01-0.1 microns. INDEPENDENT CLAIMS are included for:    (1) a water treatment system for reducing the content of an oxyanion present in an aqueous solution; and    (2) an apparatus for reducing the content of an oxyanion present in an aqueous solution.    DESCRIPTION OF DRAWING(S) - The diagram shows a schematic view of a method for reducing the content of an oxyanion in which an ion exchange regenerant solution is recycled.    First anoxic membrane bioreactor (1)    Second aerobic treatment tank (2)    Ion exchange chromatography resin (4)    Effluent (5)    Regenerant solution. (6)