SECTION 252:626-9-11. Disinfection

(a)   General.

(1)   Surface and GWUDI. All surface and GWUDI supplies require disinfection.

(2)   Groundwater. Full-time disinfection of a groundwater supply is required whenever the record of bacteriological tests indicates the water is or was ever bacteriologically unsafe pursuant to252:626-7-4(a)(2).

(3)   Modification to disinfection process. Do not make any changes to the disinfection process unless approved by the DEQ.

(4)   CT Standards. Design the system to meet the CT standards in accordance with 40 CFR § 141.72. CT shall provide 4.0 log inactivation for viruses.

(5)   Accomplished log inactivation. Total log removal/inactivation required for Giardia, Cryptosporidium and viruses shall be accomplished through filtration and disinfection as described in the "Microbial and Disinfection Byproduct Rules Simultaneous Compliance Guidance Manual," EPA 815-R-99-015.

(b)   Chlorination.

(1)   Chlorinators. Provide solution-feed-gas-type chlorinators positive displacement hypochlorite feeders or tablet chlorinators. Only NSF approved tablet chlorinators are allowed.

(2)   Capacity. Design the capacity of chlorine feeders to produce a free chlorine residual of at least 2 mg/l in the water after a contact time needed to meet the required CT Value. The equipment must accurately operate over the desired feeding range.

(3)   Stand-by equipment. Provide stand-by equipment to replace the largest unit during shutdowns and adequate spare parts for chlorinators. Hypochlorinators of adequate capacity may temporarily replace gas-type chlorinators in small plants.

(4)   Proportioning. Provide automatic proportioning chlorinators where the rate of flow or chlorine demand is not constant.

(5)   Contact time and point of application.

(A)   At plants treating surface water, make provisions for applying disinfectant to raw water, water applied to filters, filtered water, and water entering the distribution system. At plants treating ground water, make provisions for applying chlorine to the detention basin inlet and water entering the distribution system.

(B)   Design all basins used for disinfection to minimize short-circuiting and increase contact time.

(C)   If primary disinfection is accomplished using ozone, chlorine dioxide, or any other chemical that does not provide a residual disinfectant, then chlorine or chloramines must be added to provide a residual disinfectant.

(6)   Testing equipment. Provide chlorine residual test equipment recognized in the latest edition of "Standard Methods for the Examination of Water and Wastewater" published by AWWA, APHA, and WEF. Public water supply systems that serve a population greater than 3,300 shall have equipment that continuously measures and records chlorine residuals at the entry point to the distribution system.

(7)   Chlorinator piping. Design the chlorinator water supply piping to prevent contamination of the treated water supply by back-siphonage or cross connections with non-potable water. At all facilities treating surface water, pre-chlorination and post-chlorination systems must be independent to prevent possible siphoning of partially treated water into the clear well.

(c)   Chloramines. Disinfection with chloramines is not allowed for primary disinfection to meet CT requirements.

(d)   Chlorine dioxide. Perform an oxidant demand study before selecting chlorine dioxide as a primary disinfectant.

(e)   Chlorine dioxide testing equipment. When treatment with chlorine dioxide is used, provide equipment for testing concentrations of chlorine dioxide and chlorites.

(f)   Ultraviolet disinfection. UV drinking water disinfection applications shall be closed channel reactors. Full-scale drinking water applications generally use UV low-pressure, UV low-pressure high-output, or UV medium pressure mercury vapor lamps. There are several factors to determine which lamp to use, including the number of lamps needed, lamp life, power usage, start-up time and germicidal efficiency.

(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 in252:626-9-11(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.

[Source: Added at 18 Ok Reg 1612, eff 6-1-01; Amended at 25 Ok Reg 2304, eff 7-11-08; Amended at 31 Ok Reg 1301, eff 9-12-14]