coagulate and destabilize particles suspended in the water [39]. The suspended
particles are ultimately removed via clarification and/or filtration. Conventional
filtration includes pretreatment steps of chemical coagulation, rapid mixing, and
flocculation, followed by floc removal via sedimentation or flotation [36]. After
clarification, the water is filtered using common filter media such as sand, dualmedia, and tri-media. Direct filtration has several effective variations, but all include
a pretreatment of chemical coagulation, followed by rapid mixing. The water is
filtered through dual- or mixed-media using pressure or gravity filtration units
[31, 35, 36].
4.4 Lime Softening
In the lime-softening (LS) process, the pH of the water being treated is raised
sufficiently to precipitate calcium carbonate and, if necessary, magnesium hydroxide
to reduce water hardness. Some materials in solution are removed by incorporating
them into the particles of calcium carbonate/magnesium hydroxide and
coprecipitate, which are then separated by settling, filtration, or flotation [31, 35, 36].
5 Point-of-Use/Point-of-Entry Treatments
The SDWA identifies both point-of-entry (POE) and points-of- use (POU) treatment
units as options for compliance technologies for small systems. A POU treatment
device treats only the water at a particular tap or faucet, resulting in other taps in the
facility serving untreated water. POU devices are typically installed at the kitchen
tap. POU devices are listed as compliance technologies for inorganic contaminants,
synthetic organic contaminants, and radionuclides [34]. POU devices are not listed
for volatile organic contaminants because they do not address all routes of exposure.
POE treatment units treat all of the water entering a facility (household or other
building), resulting in treated water from all taps. POE devices are still considered
emerging technologies because of waste disposal and cost considerations.
POE and POU treatment units often use the same technological concepts as those
used in central treatment processes, but on a much smaller scale. Technologies that
are amenable to the POU and POE scale treatment include activated alumina, GAC,
reverse osmosis, ion exchange, and air stripping [37].
When POU and POE units are used by a public water system to comply with the
National Primary Drinking Water Regulations (NPDWRs), the SDWA requires that
the units be owned, controlled, and maintained by the public water system or by a
person under contract with the public water system. This is to ensure that the units
are properly operated and maintained to comply with the MCL or treatment techniques. This will also ensure that the units are equipped with the required mechanical
4 Endocrine Disruptors
187
particles are ultimately removed via clarification and/or filtration. Conventional
filtration includes pretreatment steps of chemical coagulation, rapid mixing, and
flocculation, followed by floc removal via sedimentation or flotation [36]. After
clarification, the water is filtered using common filter media such as sand, dualmedia, and tri-media. Direct filtration has several effective variations, but all include
a pretreatment of chemical coagulation, followed by rapid mixing. The water is
filtered through dual- or mixed-media using pressure or gravity filtration units
[31, 35, 36].
4.4 Lime Softening
In the lime-softening (LS) process, the pH of the water being treated is raised
sufficiently to precipitate calcium carbonate and, if necessary, magnesium hydroxide
to reduce water hardness. Some materials in solution are removed by incorporating
them into the particles of calcium carbonate/magnesium hydroxide and
coprecipitate, which are then separated by settling, filtration, or flotation [31, 35, 36].
5 Point-of-Use/Point-of-Entry Treatments
The SDWA identifies both point-of-entry (POE) and points-of- use (POU) treatment
units as options for compliance technologies for small systems. A POU treatment
device treats only the water at a particular tap or faucet, resulting in other taps in the
facility serving untreated water. POU devices are typically installed at the kitchen
tap. POU devices are listed as compliance technologies for inorganic contaminants,
synthetic organic contaminants, and radionuclides [34]. POU devices are not listed
for volatile organic contaminants because they do not address all routes of exposure.
POE treatment units treat all of the water entering a facility (household or other
building), resulting in treated water from all taps. POE devices are still considered
emerging technologies because of waste disposal and cost considerations.
POE and POU treatment units often use the same technological concepts as those
used in central treatment processes, but on a much smaller scale. Technologies that
are amenable to the POU and POE scale treatment include activated alumina, GAC,
reverse osmosis, ion exchange, and air stripping [37].
When POU and POE units are used by a public water system to comply with the
National Primary Drinking Water Regulations (NPDWRs), the SDWA requires that
the units be owned, controlled, and maintained by the public water system or by a
person under contract with the public water system. This is to ensure that the units
are properly operated and maintained to comply with the MCL or treatment techniques. This will also ensure that the units are equipped with the required mechanical
4 Endocrine Disruptors
187