The removal of natural organic matter (NOM) is a
primary concern for the drinking water industry,
but little attention has been paid to the practice of
enhanced softening, its benefits, and associated challenges.
Additionally, no previous reports had included
the effects of softening on the formation of disinfection
byproducts. This article provides utilities that use softening
with a blueprint for studying how their own operations
might be altered to achieve better NOM removals
and reduced disinfection byproduct formation
Utilities that use softening will be interested in
the study results describing removal of NOM in
softening, as well as the effects of silica on softening
and NOM removal and the effects of bromide on the
speciation of trihalomethanes. The authors also
discuss how enhanced softening may be able to
achieve the US Environmental Protection Agency's
requirements for removal of NOM without complete
precipitation of magnesium hydroxide [Mg(OH)2].
Although Mg(OH)2 is a more efficient adsorbent of
NOM, calcium carbonate, which precipitates at
lower pH and therefore requires lower lime dosage
in softening, is also capable of substantial NOM
removal. Includes 20 references, tables, figures.