Disinfection may be accomplished with gas and liquid chlorine,
calcium or sodium hypochlorites, chlorine dioxide, ozone, or ultraviolet light.
Other disinfecting agents will be considered, providing reliable application
equipment is available and testing procedures for a residual are recognized in
"Standard Methods for the Examination of Water and Wastewater," referenced in
Subsection 002.02, or an equivalent means
of measuring effectiveness exists. The required amount of primary disinfection
needed shall be specified by the Department. Consideration must be given to the
formation of disinfection by-products (DBP) when selecting the disinfectant.
See Section 531, Facility Design Standards -
Design Standards for Chemical Application. For public water systems using only
ground water and that voluntarily chlorinate, see Subsection
552.04. (3-24-22)
01.
Chlorination. (3-24-22)
a. In addition to the requirements of Section
531, chlorination equipment shall
meet the following requirements: (3-24-22)
i.
Solution-feed gas chlorinators or hypochlorite feeders of the positive
displacement type must be provided. (3-24-22)
ii. Standby or backup equipment of sufficient
capacity shall be available to replace the largest unit. Spare parts shall be
on hand to replace parts subject to wear and breakage. (3-24-22)
iii. Automatic proportioning chlorinators are
required where the rate of flow or chlorine demand is not reasonably constant.
(3-24-22)
iv. Each eductor
(submerged jet pump) must be selected for the point of application with
particular attention given to the quantity of chlorine to be added, the maximum
injector waterflow, the total discharge back pressure, the injector operating
pressure, and the size of the chlorine solution line. (3-24-22)
v. The chlorine solution injector/diffuser
must be compatible with the point of application to provide a rapid and
thorough mix with all the water being treated. (3-24-22)
vi. Automatic switch-over of chlorination
treatment units shall be provided, where necessary, to assure continuous
disinfection. (3-24-22)
b. Effective contact time and point of
application requirements are as follows: (3-24-22)
i. Effective contact time sufficient to
achieve the inactivation of target pathogens under the expected range of raw
water pH and temperature variation must be demonstrated through tracer studies
or other evaluations or calculations acceptable to the Department. Improving
Clearwell Design for CT Compliance, referenced in Section
002.02, contains information
that may be used as guidance for these calculations. Additional baffling can be
added to new or existing basins to minimize short circuiting and increase
contact time. (3-24-22)
ii. At
least two (2) contactors shall be provided which are each capable of providing
the required effective contact time at one-half (1/2) of the plant design
capacity. Alternatively, a single contactor that can provide effective contact
time at plant design capacity may be designed with separate sections and bypass
piping to allow sections to be cleaned or maintained individually during low
flow conditions. Any system that produces water on an irregular schedule may
provide documentation for the Department's review and approval that a single
contactor would be an acceptable design by demonstrating there would be
adequate time for maintenance and cleaning during operation shutdowns.
(3-24-22)
iii. At plants treating
surface water, except slow sand filtration systems: (3-24-22)
(1) Unless otherwise approved by the
Department, in addition to the injection point prior to the disinfection
contact tank, injection points shall also be provided for applying the
disinfectant to the raw water, settled water, and water entering the
distribution system. (3-24-22)
(2)
Unless otherwise approved by the Department, chemical piping or tubing shall be
installed from the disinfectant feed system to each injection system during the
initial construction. (3-24-22)
iv. For pipeline contactors, provision shall
be made to drain accumulated sediment from the bottom of the contactor if the
discharge from the contactor is not located at the bottom.
(3-24-22)
c. Chlorine
residual test equipment recognized in the "Standard Methods for the Examination
of Water and Wastewater," referenced in Subsection
002.02, shall be provided for
use by the operator. All surface water treatment plants that serve a population
greater that three thousand three hundred (3,300) must have equipment to
measure chlorine residuals continuously entering the distribution system. A
sample tap shall be provided to measure chlorine residual and shall be located
at a point after receiving the required contact time and at or prior to the
first service connection. (3-24-22)
d. Chlorinator piping requirements: (3-24-22)
i. Cross connection protection: The
chlorinator water supply piping shall be designed to prevent contamination of
the treated water supply by sources of questionable quality. At all facilities
treating surface water, pre- and post-chlorination systems must be independent
to prevent possible siphoning of partially treated water into the clear well.
The water supply to each eductor shall have a separate shut-off valve. No
master shut-off valve will be allowed. (3-24-22)
ii. The pipes carrying elemental liquid or
dry gaseous chlorine under pressure must be Schedule 80 seamless steel tubing
or other materials recommended by the Chlorine Institute (never use PVC).
Rubber, PVC, polyethylene, or other materials recommended by the Chlorine
Institute must be used for chlorine solution piping and fittings. Nylon
products are not acceptable for any part of the chlorine solution piping
system. (3-24-22)
02.
Disinfection with Ozone.
Systems that are required to maintain a disinfectant residual in the
distribution system shall supplement ozone disinfection with a chemical
disinfectant. (3-24-22)
a. The following are
requirements for feed gas preparation: (3-24-22)
i. Feed gas can be air, oxygen enriched air,
or high purity oxygen. Sources of high purity oxygen include purchased liquid
oxygen conforming with AWWA Standard B-304; on site generation using cryogenic
air separation; or temperature, pressure or vacuum swing (adsorptive
separation) technology. In all cases, the design engineer must ensure that the
maximum dew point of -76°F (-60°C) will not be exceeded at any time.
(3-24-22)
ii. Air compression:
(3-24-22)
(1) Air compressors shall be of the
liquid-ring or rotary lobe, oil-less, positive displacement type for smaller
systems or dry rotary screw compressors for larger systems. (3-24-22)
(2) The air compressors shall have the
capacity to simultaneously provide for maximum ozone demand, provide the air
flow required for purging the desiccant dryers (where required) and allow for
standby capacity. (3-24-22)
(3) Air
feed for the compressor shall be drawn from a point protected from rain,
condensation, mist, fog and contaminated air sources to minimize moisture and
hydrocarbon content of the air supply. (3-24-22)
(4) A compressed air after-cooler,
entrainment separator, or a combination of the two (2) with automatic drain
shall be provided prior to the dryers to reduce the water vapor.
(3-24-22)
(5) A back-up air
compressor must be provided so that ozone generation is not interrupted in the
event of a break-down. (3-24-22)
iii. Air drying: (3-24-22)
(1) Dry, dust-free and oil-free feed gas must
be provided to the ozone generator. Dry gas is essential to prevent formation
of nitric acid, to increase the efficiency of ozone generation and to prevent
damage to the generator dielectrics. Sufficient drying to a maximum dew point
of -76°F (-60°C) must be provided at the end of the drying cycle.
(3-24-22)
(2) Drying for high
pressure systems may be accomplished using heatless desiccant dryers only. For
low pressure systems, a refrigeration air dryer in series with heat-reactivated
desiccant dryers shall be used. (3-24-22)
(3) A refrigeration dryer capable of reducing
inlet air temperature to 40°F (4°C) shall be provided for low pressure
air preparation systems. The dryer can be of the compressed refrigerant type or
chilled water type. (3-24-22)
(4)
For heat-reactivated desiccant dryers, the unit shall contain two (2) desiccant
filled towers complete with pressure relief valves, two (2) four-way valves and
a heater. In addition, external type dryers shall have a cooler unit and
blowers. The size of the unit shall be such that the specified dew point will
be achieved during a minimum adsorption cycle time of sixteen (16) hours while
operating at the maximum expected moisture loading conditions.
(3-24-22)
(5) Multiple air dryers
shall be provided so that the ozone generation is not interrupted in the event
of dryer breakdown. (3-24-22)
(6)
Each dryer shall be capable of venting "dry" gas to the atmosphere, prior to
the ozone generator, to allow start-up when other dryers are "on-line."
(3-24-22)
iv. Air
filters: (3-24-22)
(1) Air filters shall be
provided on the suction side of the air compressors, between the air
compressors and the dryers and between the dryers and the ozone generators.
(3-24-22)
(2) The filter before the
desiccant dryers shall be of the coalescing type and be capable of removing
aerosol and particulates larger than 0.3 microns in diameter. The filter after
the desiccant dryer shall be of the particulate type and be capable of removing
all particulates greater than 0.1 microns in diameter, or smaller if specified
by the generator manufacturer. (3-24-22)
v. Piping in the air preparation system can
be common grade steel, seamless copper, stainless steel or galvanized steel.
The piping must be designed to withstand the maximum pressures in the air
preparation system. (3-24-22)
b. The following requirements apply to the
ozone generator: (3-24-22)
i. Capacity.
(3-24-22)
(1) The production rating of the
ozone generators shall be stated in pounds per day and kWhr per pound at a
maximum cooling water temperature and maximum ozone concentration.
(3-24-22)
(2) The design shall
ensure that the minimum concentration of ozone in the generator exit gas will
not be less than one (1) percent (by weight). (3-24-22)
(3) Generators shall be sized to have
sufficient reserve capacity so that the system does not operate at peak
capacity for extended periods of time resulting in premature breakdown of the
dielectrics. (3-24-22)
(4) The
production rate of ozone generators will decrease as the temperature of the
coolant increases. If there is to be a variation in the supply temperature of
the coolant throughout the year, then pertinent data shall be used to determine
production changes due to the temperature change of the supplied coolant. The
design shall ensure that the generators can produce the required ozone at
maximum coolant temperature. (3-24-22)
(5) Appropriate ozone generator backup
equipment must be provided. (3-24-22)
ii. Electrical. The generators can be low,
medium or high frequency type. Specifications shall require that the
transformers, electronic circuitry and other electrical hardware be proven,
high quality components designed for ozone service. (3-24-22)
iii. Cooling. Adequate cooling shall be
provided. The cooling water must be properly treated to minimize corrosion,
scaling and microbiological fouling of the water side of the tubes. Where
cooling water is treated, cross connection control shall be provided to prevent
contamination of the potable water supply. (3-24-22)
iv. Materials. To prevent corrosion, the
ozone generator shell and tubes shall be constructed of Type 316L stainless
steel. (3-24-22)
c. The
following requirements apply to ozone contactors: (3-24-22)
i. Bubble diffusers. (3-24-22)
(1) Where disinfection is the primary
application, a minimum of two (2) contact chambers, each equipped with baffles
to prevent short circuiting and induce countercurrent flow, shall be provided.
Ozone shall be applied using porous-tube or dome diffusers. (3-24-22)
(2) The minimum contact time shall be ten
(10) minutes. A shorter contact time (CT) may be approved by the Department if
justified by appropriate design and "CT" considerations. (3-24-22)
(3) Where taste and odor control is of
concern, multiple application points and contactors shall be considered.
(3-24-22)
(4) Contactors shall be
separate closed vessels that have no common walls with adjacent rooms. The
contactor must be kept under negative pressure and sufficient ozone monitors
shall be provided to protect worker safety. (3-24-22)
(5) Contact vessels can be made of reinforced
concrete, stainless steel, fiberglass or other material which will be stable in
the presence of residual ozone and ozone in the gas phase above the water
level. If contact vessels are made of reinforced concrete, all reinforcement
bars shall be covered with a minimum of one and one-half (1.5) inches of
concrete. (3-24-22)
(6) Where
necessary, a system shall be provided between the contactor and the off-gas
destruct unit to remove froth from the air and return the other to the
contactor or other location acceptable to the reviewing authority. If foaming
is expected to be excessive, then a potable water spray system shall be placed
in the contactor head space. (3-24-22)
(7) All openings into the contactor for pipe
connections, hatchways, etc. shall be properly sealed using welds or ozone
resistant gaskets such as Teflon or Hypalon. (3-24-22)
(8) Multiple sampling ports shall be provided
to enable sampling of each compartment's effluent water and to confirm "CT"
calculations. (3-24-22)
(9) A
pressure/vacuum relief valve shall be provided in the contactor and piped to a
location where there will be no damage to the destruction unit.
(3-24-22)
(10) The depth of water
in bubble diffuser contactors shall be a minimum of eighteen (18) feet. The
contactor shall also have a minimum of three (3) feet of freeboard to allow for
foaming. (3-24-22)
(11) All
contactors shall have provisions for cleaning, maintenance and drainage of the
contactor. Each contactor compartment shall also be equipped with an access
hatchway. (3-24-22)
(12) Aeration
diffusers shall be fully serviceable by either cleaning or replacement.
(3-24-22)
ii. Other
contactors, such as the venturi or aspirating turbine mixer contactor, may be
approved by the Department provided adequate ozone transfer is achieved and the
required contact times and residuals can be met and verified.
(3-24-22)
d. The
following requirements apply to ozone destruction units: (3-24-22)
i. A system for treating the final off-gas
from each contactor must be provided in order to meet safety and air quality
standards. Acceptable systems include thermal destruction and thermal/catalytic
destruction units. (3-24-22)
ii.
The maximum allowable ozone concentration in the discharge is 0.1 ppm (by
volume). (3-24-22)
iii. At least
two (2) units shall be provided which are each capable of handling the entire
gas flow. (3-24-22)
iv. Exhaust
blowers shall be provided in order to draw off-gas from the contactor into the
destruct unit. (3-24-22)
v.
Catalysts must be protected from froth, moisture and other impurities which may
harm the catalyst. (3-24-22)
vi.
The catalyst and heating elements shall be located where they can easily be
reached for maintenance. (3-24-22)
e. Piping materials: Only low carbon 304L and
316L stainless steels shall be used for ozone service with 316L preferred.
(3-24-22)
f. The following
requirements apply to joints and connections: (3-24-22)
i. Connections on piping used for ozone
service are to be welded where possible. (3-24-22)
ii. Connections with meters, valves or other
equipment are to be made with flanged joints with ozone resistant gaskets, such
as Teflon or Hypalon. Screwed fittings shall not be used because of their
tendency to leak. (3-24-22)
iii. A
positive closing plug or butterfly valve plus a leak-proof check valve shall be
provided in the piping between the generator and the contactor to prevent
moisture reaching the generator. (3-24-22)
g. The following requirements apply to
instrumentation: (3-24-22)
i. Pressure gauges
shall be provided at the discharge from the air compressor, at the inlet to the
refrigeration dryers, at the inlet and outlet of the desiccant dryers, at the
inlet to the ozone generators and contactors, and at the inlet to the ozone
destruction unit. (3-24-22)
ii.
Each generator shall have a trip which shuts down the generator when the
wattage exceeds a certain preset level. (3-24-22)
iii. Dew point monitors shall be provided for
measuring the moisture of the feed gas from the desiccant dryers. Where there
is potential for moisture entering the ozone generator from downstream of the
unit or where moisture accumulation can occur in the generator during shutdown,
post-generator dew point monitors shall be used. (3-24-22)
iv. Air flow meters shall be provided for
measuring air flow from the desiccant dryers to each of the other ozone
generators, air flow to each contactor, and purge air flow to the desiccant
dryers. (3-24-22)
v. Temperature
gauges shall be provided for the inlet and outlet of the ozone cooling water
and the inlet and outlet of the ozone generator feed gas and, if necessary, for
the inlet and outlet of the ozone power supply cooling water.
(3-24-22)
vi. Water flow meters
shall be installed to monitor the flow of cooling water to the ozone generators
and, if necessary, to the ozone power supply. (3-24-22)
vii. Ozone monitors shall be installed to
measure zone concentration in both the feed-gas and off-gas from the contactor
and in the off-gas from the destruct unit. For disinfection systems, monitors
shall also be provided for monitoring ozone residuals in the water. The number
and location of ozone residual monitors shall be such that the amount of time
that the water is in contact with the ozone residual can be determined.
(3-24-22)
viii. A minimum of one
ambient ozone monitor shall be installed in the vicinity of the contactor and a
minimum of one shall be installed in the vicinity of the generator. Ozone
monitors shall also be installed in any areas where ozone gas may accumulate.
(3-24-22)
h. Safety
requirements are as follows: (3-24-22)
i. The
maximum allowable ozone concentration in the air to which workers may be
exposed must not exceed one-tenth part per million (0.1 ppm) by volume.
(3-24-22)
ii. Noise levels
resulting from the operating equipment of the ozonation system shall be
controlled to within acceptable limits by special room construction and
equipment isolation. (3-24-22)
iii.
Emergency exhaust fans must be provided in the rooms containing the ozone
generators to remove ozone gas if leakage occurs. (3-24-22)
iv. A sign shall be posted indicating "No
smoking, oxygen in use" at all entrances to the treatment plant. In addition,
no flammable or combustible materials shall be stored within the oxygen
generator areas. (3-24-22)
03.
Disinfection with Chlorine
Dioxide. Chlorine dioxide may be considered as a primary and residual
disinfectant, a pre-oxidant to control tastes and odors, to oxidize iron and
manganese, and to control hydrogen sulfide and phenolic compounds. When
choosing chlorine dioxide, consideration must be given to formation of the
regulated by-products, chlorite and chlorate. (3-24-22)
a. Chlorine dioxide generation equipment
shall be factory assembled pre-engineered units with a minimum efficiency of
ninety-five (95) percent. The excess free chlorine shall not exceed three (3)
percent of the theoretical stoichiometric concentration required.
(3-24-22)
b. Other design
requirements include: (3-24-22)
i. The design
shall comply with all applicable portions of Subsections
530.01.a. through 530.01.d.
(3-24-22)
ii. The maximum residual
disinfectant level allowed shall be zero point eight (0.8) milligrams per liter
(mg/l), even for short term exposures. (3-24-22)
iii. Notification of a change in disinfection
practices and the schedule for the changes shall be made known to the public;
particularly to hospitals, kidney dialysis facilities and fish breeders, as
chlorine dioxide and its by-products may have effects similar to chloramines.
(3-24-22)
04.
Other Disinfecting Agents. Proposals for use of disinfecting
agents other than those listed shall be submitted to the Department for
approval prior to preparation of final plans and specifications.
(3-24-22)