Ultraviolet
(UV) Disinfection for Domestic Wastewater
The vast majority of domestic wastewater
treatment facilities in Florida use chlorination for disinfection.
However, there are some rather significant concerns associated with
chlorination including the production of potentially hazardous
byproducts (chlorinated organic compounds), toxicity concerns from
chlorine residual for the biota in receiving surface waters, and the
potential hazards associated with handling the chlorine at the
treatment plant.
Recognizing the potential adverse impacts of chlorination, the
State of Florida encourages the use of alternative disinfection
methods. Rule
62-600.440(1)
(123 KB), Florida Administrative Code (F.A.C.),
states that:
"The Department (of Environmental Protection) is aware
of the possible harmful effects of chlorine used in conjunction
with wastewater treatment and encourages the use of alternative
disinfection methods."
UV Disinfection
Many utilities are beginning to evaluate and implement
alternative disinfection methods, with UV irradiation among the most
popular. UV has long been recognized as an effective disinfectant.
However, unlike chlorine, UV does not pose disinfection byproducts,
toxicity, or hazardous materials concerns.
The knowledge base related to UV disinfection has increased
rapidly over the last two decades. For example, 10 years ago the
conventional wisdom was that UV was relatively ineffective against
Cryptosporidium (a protozoan pathogen). Today we know that UV is
very effective (more effective than chlorine) in inactivating
Cryptosporidium. It is interesting to note that Germany currently
makes widespread use of UV for disinfecting drinking water – a
disinfection application with significant public health
implications.
UV Disinfection
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Domestic
Wastewater and UV Disinfection
Most domestic
wastewater treatment facilities in Florida must meet either "basic
disinfection" (applies to most surface water discharges) or "high-level
disinfection" (applies to many reuse systems). These two levels of
disinfection are described in Rule 62-600.440, F.A.C.
UV
can be reliably used to meet basic disinfection criteria. Basic
disinfection essentially requires that the effluent after disinfection
contain less than 200 fecal coliforms per 100 mL [see
Rule 62-600.440(4) , F.A.C.(123 KB),
for detailed requirements]. There are a number of treatment facilities
that use UV for basic disinfection applications in Florida.
The use of UV for
high-level disinfection historically has posed more concern to the
Department. High-level disinfection, which is used in conjunction with
some types of reuse projects (including use of reclaimed water to irrigate
residential lawns, areas accessible to the public, and edible food crops),
essentially requires that fecal coliforms be reduced below detection [see
Rule 62-600.440(5), F.A.C., for detailed requirements]. Filtration is
required ahead of the disinfection process and serves as an important and
integral part of the overall high-level disinfection process. Florida's
high-level disinfection criteria were designed to ensure that the
reclaimed water would be essentially virus free.
The 2000 NWRI
guidelines provide detailed guidance for the design of UV systems that
meet high-level disinfection. The 2000 NWRI guidelines include a
well-defined testing protocol, and are applicable to UV systems designed
to meet California, Florida, and other state standards.
DEP will accept UV
designs that comply with the 2000 NWRI guidelines, and are supported with
validation testing reports as a means for providing reasonable assurance
that the domestic wastewater treatment facility can meet the high-level
disinfection criteria.
Both chlorination and
UV irradiation are effective disinfectants that can be effectively and
safely used to disinfect wastewater, reclaimed water, and drinking water.
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For
More Information Contact:
Domestic Wastewater Section
2600 Blair Stone Road, MS 3540
Tallahassee, Florida 32399-2400
(850) 245-8605
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