AWWA ACE63124

This slide presentation outlines a study on enchanced silicon and boron removal during precipitative softening. Information on silicon and boron is outlined and includes: Silicon - clogging of distribution system piping, reverse osmosis (RO) membranes;Boron - toxicity to plants at fairly low levels(~ 0.3-1 mg/L forinitial symptoms), possible human health concerns;Lifetime Health Advisory of 0.6 mg/L issued in 1992; and, WHO 0.5 mg/L; EU 1.0 mg/L. Topics outlined include: results from recent U.S. survey; Ames, Iowa WTP schematic; Ames data; current understanding of Si and Bremoval during softening; In situ ppt of Mg for Si and B removal; mineral stability diagram; X-ray difraction; known and unknown parameters; equations; model results; Boron jar test data; and, Freundlich Isotherm fit. Conclusions indicated:silicon removal during softening via am-Mgsub2/subSiOsub4/sub;enhanced boron removal via sorption to am-Mgsub2M/subSiOsub4/sub; and,boron removal estimated by Freundlich isotherm. Includes figures.



Keywords: Boron; Softening; Ames, Iowa; Public Health; Modeling; Toxicity; Jar Tests; Reverse Osmosis; Sorption; Membranes