DEVELOPMENT OF A HYDROGEL-BASED REACTIVE MATRIX FOR REMOVAL OF CHLORACETANILIDE HERBICIDES FROM CONTAMINATED WATER

Biodegradable, high-affinity hydrogel-based beads may prove useful in the decontamination of waters containing pesticide residue. Ethanethio l-cellulose beads, with a thiol content of up to 160 mu mol -SH mL(-1) bead, were synthesized by a novel method using 1,1'-carbonyldiimidazo le followed by reaction with aminoethanethiol. The use of thiol-deriva tized beads to remove metolachlor from aqueous solutions, via a nucleo philic substitution reaction involving the alpha-carbon of the chloroa cetamido group of metolachlor and the thiol group of the bead (i.e., c ovalent bond formation), was investigated using batch reaction conditi ons and fixed-bed column techniques. In batch reaction studies, ethane thiol-cellulose beads (160 mu mol -SH mL(-1) bead) exhibited binding c apacities of up to 180 mu mol metolachlor mL(-1) bead (or about 1300 m u mol g(-1)) depending on the solution pH and temperature. When the et hanethiol-cellulose beads were suspended in an aqueous solution at pH 9 and incubated at 40 degrees C, their binding capacity for metolachlo r was about equal to that of activated carbon on a per gram adsorbent basis. Though the fixed-bed column studies revealed that the derivatiz ed beads (131 mu mol -SH mL(-1) bead) possessed a large capacity for m etolachlor, high effluent quality could not be maintained over extende d column operation under the conditions employed. Metolachlor was not removed from solution under batch reaction conditions or in the fixed- bed columns when unmodified cellulose beads replaced thiol-derivatized beads. The results of our investigation demonstrate that ethanethiol- cellulose beads can be used to decontaminate water containing metolach lor and possibly other pesticides with reactive electrophilic centers.