Water Treatment for Small Public Supplies

摘要

Reverse osmosis (RO) and electrodialysis (ED) were shown to be successful methods for upgrading current drinking water supplies for small New Mexico communities to meet drinking water standards. A mobile demonstration unit was operated 500-2000 hours in each of nine communities visited, using feed from the current drinking water supply. In all cases, product water from the demonstration unit (as certified by the appropriate agency) met drinking water standards. Engineering design data are presented for the evaluation of ED, RO, and ion-exchange unit operations for application in the drinking water systems. The potential for selective removal of ionized cationic contaminants by precipitation as their sulfides was also assessed (for cadmium, mercury, and zinc), using a developed stopped-flow spectrophotometry technique. Preliminary data indicated the appropriateness of sulfide precipitation under special conditions (e.g., low total dissolved solids, high concentrations of only 1-2 of the cations). Application of this technique to the removal of fluoride as calcium fluoride required a large excess of calcium for reasonable precipitation/sedimentation rates; any effect of the added calcium on drinking water quality should be considered.