(1)
Reactor dose
monitoring approaches. One of the following UV reactor dose-monitoring
approaches shall be used:
(A)
UV
intensity setpoint approach. This approach relies on one or more
"setpoints" for UV intensity that are established during validation testing,
pursuant to the requirements contained in 252:626-9-11(e)(2)(C), to determine
UV dose. During operations, the UV intensity as measured by the UV sensors must
meet or exceed the setpoint(s) to ensure delivery of the required dose. In the
UV intensity setpoint approach, UV transmittance does not need to be monitored
separately. Instead, the intensity readings by the sensor account for changes
in UV transmittance. The operating strategy can be with either a single
setpoint (one UV intensity setpoint is used for all validation flow rates) or a
variable setpoint (the UV intensity setpoint is determined using a lookup table
or equation for a range of flow rates).
(B)
Calculated dose approach.
This approach uses a dose monitoring equation to estimate the UV dose based on
the measured flow rate, UV intensity, and UV transmittance. The dose monitoring
equation shall be developed through validation testing, pursuant to the
requirements contained in 252:626-9-11(e)(2)(C). During reactor operations, the
UV reactor control system inputs the measured parameters into the dose
monitoring equation to produce a calculated dose. The water system operator
divides the calculated dose by the validation factor and compares the resulting
value to the required dose for the target pathogen and log inactivation
level.
(2)
Design. The following criteria shall be included in the design of
the UV system:
(A)
Flow rate.
Maximum instantaneous flow rates shall be stated in the validation report
pursuant to the requirements contained in 252:626-9-11(e)(2)(C).
(B) Target pathogen(s) and log inactivation.
The log inactivation for the target pathogen(s) must be determined before
sizing the UV reactor. The target microorganism(s) and their log-inactivation
level shall be stated in the engineering report. The required UV doses for
Cryptosporidium and Giardia inactivation are lower than those needed for the
inactivation of viruses. Most viruses can be easily inactivated with
chlorine.
(C)
Validation. To ensure the validation testing and data analysis is
conducted in a technically sound manner and without bias, a person independent
of the UV reactor manufacturer shall oversee the validation testing.
Individuals qualified for such oversight shall include engineers experienced in
testing and evaluating UV reactors and scientists experienced in the microbial
aspects of biodosimetry. Appropriate individuals should have no real or
apparent conflicts of interest regarding the ultimate use of the UV reactor
being tested. The range of validated operating conditions must be included in
the validation testing and submittal of a validation report shall be required.
The validation testing shall be completed in accordance with procedures
outlined in the publication, "Ultraviolet Disinfection Guidance Manual for the
Final Long Term 2 Enhanced Surface Water Treatment Rule," EPA 815-R-06-007,
(2006).
(D)
Sizing. A
fouling aging factor of 0.70 shall be used to size the UV reactor.
(E)
Required UV dose. The
validation process shall determine the dose monitoring for the required dose
over the range of flow, UVT, lamp aging and fouling that will occur at the
water treatment plant.
(F)
Water quality. The following water quality parameters shall be
included in the design of the system:
(i)
Fouling factors, which include, temperature, pH, turbidity, iron, calcium,
manganese, alkalinity and total hardness;
(ii) UV transmittance at 254 mn;
and
(iii) UV transmittance from
200-300 mn for MP reactors only.
(G)
Operating pressure. Provide
the expected operating pressures for the UV system. The maximum operating
pressure to be withstood by the lamp sleeves and UV reactor housing.
(H)
UV sensors. A germicidal
spectral response shall be specified. A minimum of one UV sensor shall be
specified per UV reactor. The actual number shall be the same as used during
the validation process pursuant to the requirements contained in
252:626-9-11(e)(2)(C). The following shall also be required:
(i) UV sensors used during validation shall
read within 10% of the average of 3 or more reference sensor
measurements.
(ii) UV sensors
during operation shall be calibrated with 3 or more reference UV sensor
measurements. Reference UV sensors are off-line UV sensors that shall be at
least as accurate as the duty UV sensors and shall be constructed identically,
unless changes are made to the reference sensor to make said sensor more
accurate.
(iii) Reference UV
sensors shall have calibration traceable to one of the following national
standards:
(I) The National Physical
Laboratory;
(II) The National
Institute of Standards and Technology;
(III) Deutsche Vereinigung des Gas- und
Wasserfaches (GVDW); and
(IV)
Osterreichisches Normungsinstitut (ORNORM).
(I)
Hydraulics. The following
hydraulic information shall be provided:
(i)
The maximum system pressure at the UV reactor;
(ii) The maximum allowable head loss through
the UV reactor;
(iii) Special surge
conditions that may be experienced; and
(iv) The hydraulic constraints based on the
site-specific and validated conditions.
(J)
Location constraints. Do not
install UV disinfection upstream of filtration for surface and GWUDI water
treatment plants due to the potential of particles interfering with UV
disinfection.
(K)
Lamp
Sleeves. The following shall be applicable to all lamp sleeves
installed:
(i) Lamp sleeves shall be annealed
to minimize internal stress;
(ii)
Lamp sleeve specifications shall describe the type of lamp sleeve cleaning
system to be used, whether an off-line chemical clean, an off-line mechanical
clean, or an on-line mechanical and/or chemical clean method is used. Indicate
how the capacity of the system will be affected by the chosen cleaning system;
and
(iii) Provide piping and valves
necessary to properly dispose of chemicals used during the cleaning of the lamp
sleeves.
(L)
Alarms. At a minimum, the following UV reactor alarms shall be
specified:
(i) Lamp or ballast
failure;
(ii) Low UV intensity or
low validated UV dose;
(iii) High
temperature;
(iv) Operating
conditions outside of validated range; and
(v) Wiper failure.
(M)
Instrumentation. At a
minimum, the following signals and indicators shall be specified:
(i) UV lamp status;
(ii) UV reactor status;
(iii) All signals used in the dose monitoring
algorithm (e.g. at a minimum lamp output, UV intensity, flow, and
UVT);
(iv) Lamp cleaning cycle and
history;
(v) Accumulated run time
for individual lamps or banks of lamps and reactors; and
(vi) Influent flow rate.
(N)
Controls. At a minimum, the
following UV reactor controls shall be specified:
(i) UV dose setpoints, UV intensity set
points or UV transmittance setpoints as appropriate;
(ii) UV lamps, on and off control;
(iii) UV reactor, on and off
control;
(iv) UV reactor manual and
automatic control;
(v) UV reactor
local and remote control;
(vi)
Manual lamp power level control;
(vii) Manual lamp cleaning cycle control;
and
(viii) Automatic lamp cleaning
cycle setpoint control.
(O)
Startup Criteria. The
equipment installed shall meet the performance requirements contained in the
specifications. The following specific performance criteria shall be included
in the specifications:
(i) Allowable head
loss at each design flow rate;
(ii)
Estimated power consumption under the design operating conditions;
(iii) Disinfection capacity of each reactor
under the design water quality conditions;
(iv) Sensitivity of equipment to variations
in voltage or current; and
(v)
Reference UV sensor, duty UV sensor, and UV transmittance analyzer
performance.
(P)
Warranties. A physical equipment warranty for a minimum of one
year is required. Lamps shall be warranted to provide the lamp intensity under
design conditions and warranted for a minimum number of operating hours taking
into consideration the fouling and aging of the lamp.
(Q)
UV transmittance analyzer.
When a UV transmittance analyzer is provided, a calibrated spectrophotometer is
required, capable to measure UV absorbance and/or UVT at 254 nm, across a 4 cm
or 5 cm pathlength.
(R)
Back-up power supply. Power surges and the appropriate power
conditioning equipment must be addressed in the specifications.