Drinking Water Quality for the 21 sl Century
281
bromine substitution. HOBr attacks more sites in the precursor than HOCI and
reacts with them faster than HOCI.
Ozone will oxidize bromide to bromate ion or hyprobromous acid, depending
on water-quality conditions. The formation of bromate, for example, is favored at
high pH, ozone doses, and bromide levels but an increased DOC concentration
will increase the ozone demand for NOM and lead to lower bromate yields (Song
et al. 1996). Organic bromide formation is favored at low pH, high bromide levels,
and high ozone to DOC ratios. It is, therefore, apparent that the type and amount
of brominated bypro ducts in distributed drinking waters will be a function of a
variety of parameters that will have to be carefully monitored in any treatment
plant survey in order to determine any meaningful correlations.
So with this background of challenges to our future drinking water quality, what
is available to the industry to provide additional barriers against compromises to our
supplies?
4 Treatment Technologies
4.1 Enhanced Coagulation
Kavanaugh (1978) and Babcock and Singer (1979) have shown coagulation to be
an effective method of NOM removal. Based on these and other findings, EPA
has required the implementation of enhanced coagulation - defined as modified
coagulation to attain greater NOM removal - for the treatment of surface water.
Based on raw water alkalinity and TOC concentration, a utility must achieve a
specific percent removal of NOM - using TOC as the surrogate - before the point
of continuous disinfection. If a utility cannot achieve the necessary TOC removal
by this method, it can meet the enhanced coagulation requirements by performing
coagulation at a coagulant dose and pH such that an incremental addition of 10 mg
rl of alum results in a TOC removal of 0.3 mg rl or less. This alternative method
has been referred to as the point of diminishing return (PODR) criterion.
White et al. (1997) have shown that water with a low TOC content and/or a
low specific UV absorbance (SUVA) value is not amenable to coagulation. To
increase NOM removal, ozonation and biofiltration treatment have been suggested
to aid coagulation (Semmens and Field 1980; Miltner et al. 1992; LeCourt et al.
1997). Ozone oxidizes NOM to form organic byproducts that are biodegradable
and can be removed by biofiltration (Speitel et. al. 1993; Krasner et al. 1993).
Therefore the combination of coagulation, ozonation, and biofiltration can be an
effective treatment scheme for removing NOM and, therefore, effectively
controlling DBP formation.
281
bromine substitution. HOBr attacks more sites in the precursor than HOCI and
reacts with them faster than HOCI.
Ozone will oxidize bromide to bromate ion or hyprobromous acid, depending
on water-quality conditions. The formation of bromate, for example, is favored at
high pH, ozone doses, and bromide levels but an increased DOC concentration
will increase the ozone demand for NOM and lead to lower bromate yields (Song
et al. 1996). Organic bromide formation is favored at low pH, high bromide levels,
and high ozone to DOC ratios. It is, therefore, apparent that the type and amount
of brominated bypro ducts in distributed drinking waters will be a function of a
variety of parameters that will have to be carefully monitored in any treatment
plant survey in order to determine any meaningful correlations.
So with this background of challenges to our future drinking water quality, what
is available to the industry to provide additional barriers against compromises to our
supplies?
4 Treatment Technologies
4.1 Enhanced Coagulation
Kavanaugh (1978) and Babcock and Singer (1979) have shown coagulation to be
an effective method of NOM removal. Based on these and other findings, EPA
has required the implementation of enhanced coagulation - defined as modified
coagulation to attain greater NOM removal - for the treatment of surface water.
Based on raw water alkalinity and TOC concentration, a utility must achieve a
specific percent removal of NOM - using TOC as the surrogate - before the point
of continuous disinfection. If a utility cannot achieve the necessary TOC removal
by this method, it can meet the enhanced coagulation requirements by performing
coagulation at a coagulant dose and pH such that an incremental addition of 10 mg
rl of alum results in a TOC removal of 0.3 mg rl or less. This alternative method
has been referred to as the point of diminishing return (PODR) criterion.
White et al. (1997) have shown that water with a low TOC content and/or a
low specific UV absorbance (SUVA) value is not amenable to coagulation. To
increase NOM removal, ozonation and biofiltration treatment have been suggested
to aid coagulation (Semmens and Field 1980; Miltner et al. 1992; LeCourt et al.
1997). Ozone oxidizes NOM to form organic byproducts that are biodegradable
and can be removed by biofiltration (Speitel et. al. 1993; Krasner et al. 1993).
Therefore the combination of coagulation, ozonation, and biofiltration can be an
effective treatment scheme for removing NOM and, therefore, effectively
controlling DBP formation.