Abstract: A filter element having a perforated tubular core and a plurality of layers of strand material wound about the tubular core. The outermost layer has the ability to retain particles smaller than those retained by the innermost layer. The size range of particles retained by the outermost layer is from one to twenty-five microns and the size range of particles retained by the innermost layer is from twenty-five to one hundred microns.According to the method of invention, the filter element is used to purify liquids through the steps of precoating, delivering liquid through the filter, periodically backwashing the filter, and precoating the filter again.

Abstract: The invention relates to a method for converting strong-base anion exchange resins from the monovalent anion form to the hydroxide form. A .?.solution.!. .Iadd.source .Iaddend.of polyvalent anions is first passed through the resin to displace the monovalent anions. A solution of alkali metal hydroxide is then passed through the resin to convert it to the hydroxide form, and to produce an effluent solution of hydroxide ions and polyvalent anions. This effluent solution is then neutralized with an acid containing .Iadd.a source of .Iaddend.polyvalent anions, and the neutralized solution is passed through a second batch of resin in the monovalent anion form. In the preferred embodiment, a portion of the effluent is retained without neutralization and is delivered to the second batch of resin after the neutralized effluent to perform a portion of the hydroxide regeneration.