UV System Selection: What Information Is Required?
Flow rate, UV transmittance (UVT), target dose, line conditions and pre-treatment: the parameters that determine UV reactor sizing and how to gather them.
Five Inputs That Determine Selection
- Flow rate: minimum, nominal and maximum flow (m³/h). The reactor must deliver the target dose at maximum flow and worst-case water quality.
- UVT: UV transmittance of the water (T10, %) and its variation over time. Alongside flow rate, this is the second key parameter governing reactor size.
- Target: which microorganism and how many logs of reduction; or a process function such as chlorine/ozone destruction or TOC reduction.
- Line conditions: fluid temperature, pressure, CIP/SIP, connection type and mounting orientation.
- Validation and integration: third-party validated dose requirement, 4-20 mA / Modbus connectivity, and power supply voltage.
For series overviews see UV disinfection systems, and for maintenance see UV lamp replacement.
What Do Dose, Intensity, RED and UVT Mean?
Terms are summarized from the glossary of the Nuvonic (Hanovia) operation and maintenance manual.
| Term | Meaning | Unit |
|---|---|---|
| Dose (fluence) | UV energy delivered per unit area; the product of UV intensity and exposure time | mJ/cm² |
| Intensity | UV power per unit area; measured by the dry UV sensor | W/m² |
| RED | Reduction Equivalent Dose: the validated dose delivered by the system | mJ/cm² |
| UVT (T10) | Percentage of UV light transmitted through water; defined in the manual's Modbus register table as "UV transmittance over a 10 mm path" | % |
| Quartz sleeve (thimble) | Quartz tube closed at one end that separates the lamp from the water | - |
The dose applied by a reactor depends on three factors: the output power of the arc lamp, the geometry of the irradiation chamber, and the residence time of the water inside the chamber (Hanovia D10 form). In the field, light intensity decreases as the lamp ages, as the quartz sleeve fouls, and as water transmittance drops; according to the manual, transmittance drops as turbidity and the concentration of UV-absorbing substances increase.
Under Which Dose and UVT Are Catalog Flow Rates Stated?
The flow rates of the two ECO families below are calculated with different UVT assumptions; the numbers cannot be derived from one another.
| Model | Lamps | Power (W) | PharmaLine ECO flow (m³/h) | PureLine ECO flow (m³/h) |
|---|---|---|---|---|
| ECO 4 | 1 | 90 | 3.4 | 4.1 |
| ECO 8 | 1 | 150 | 9 | 8.6 |
| ECO 15 | 1 | 250 | 16.5 | 17.8 |
| ECO 32 | 1 | 360 | 30.5 | 32 |
| ECO 40 | 1 | 380 | 34 | 41 |
| ECO 85 | 2 | 750 | 68 | 86 |
| ECO 125 | 3 | 1,080 | 116 | 125 |
PharmaLine ECO flow rates are stated for a 30 mJ/cm² dose and 98% T10, and PureLine ECO flow rates for RED 30 mJ/cm² and 99% T10, both at end-of-lamp-life conditions (datasheet footnotes). According to the manual, light intensity decreases as water transmittance drops, and dose depends on exposure time (flow rate); therefore, a flow rate in the table does not apply to a different dose or UVT. Flow rate alone is not enough to select a model: the worst-case UVT value and target dose must be specified in writing.
Minimum T10 values in datasheets
| Series | Minimum T10 (%) | Note |
|---|---|---|
| PharmaLine D AF, PQ AF, PureLine D AF, PQ AF | 60 | All models; low-pressure amalgam |
| PureLine S PH | 15 – 30 | S 0015: 15, S 0010: 20, S 0005 / 0060 / 0080: 30 |
| PharmaLine DC PH | 85 | Free chlorine destruction; DC PH 100–500 |
| PureLine D PH | 62 – 93 | Model-dependent (D PH 0070: 64; 0080: 91; 0400: 62; 0300: 93) |
The PureLine S, PureLine D AF and D PH datasheets state that the wet UV monitor is fitted only when T10 is above the minimum threshold; for water below the minimum T10, reactor sizing and monitoring method are evaluated separately. The control panel includes flow and UVT meter inputs; when these inputs are connected, lamp power is steplessly adjusted and dose is calculated according to actual process conditions.
Target Dose and Log Reduction
The target dose is derived from the D10 value of the organism and the required log reduction. D10 is the dose that reduces a population by 90%; twice the dose gives 99% (2 log), and three times the dose gives 99.9% (3 log). Examples from the Hanovia D10 form:
| Organism | D10 (mJ/cm²) | For 3 log (3 × D10) |
|---|---|---|
| Legionella pneumophila | 2.04 | 6.1 |
| Staphylococcus aureus | 2.6 | 7.8 |
| Escherichia coli (in water) | 5.4 | 16.2 |
| Pseudomonas aeruginosa | 5.5 | 16.5 |
| Bacillus subtilis spores | 12 | 36 |
| Aspergillus niger (mold spores) | 100 | 300 |
These values indicate organism sensitivity under laboratory conditions; the actual dose delivered by a reactor in the field depends on flow hydraulics. Because the dose equations and sizing of the PQ series are independently derived by a third party in accordance with the USEPA UV Disinfection Guidance Manual, the PQ family is selected for critical lines with a defined target dose (pharmaceutical purified water distribution, drinking water barriers, water reuse). Validation scope varies by series: USEPA, DVGW, NWRI, NVI.
If your goal is dechlorination, chlorine dioxide or ozone destruction, or TOC reduction, the target is a chemical process function rather than a microorganism: DC PH and DCD PH (chlorine, chlorine dioxide), DO series (ozone) and 185 nm TOCLine ECO are designed for these duties; specify your inlet concentration and target outlet level (mg/L, ppb).
Temperature, Pressure and CIP
Values are taken from the datasheets on the product pages.
| Series | Fluid temperature | Pressure | CIP |
|---|---|---|---|
| PureLine PQ AF | 5–40°C | 10 bar | 130°C (0005–0016), 95°C (0030–0090, cabinet isolated) |
| PharmaLine ECO | 5–40°C | Not stated on datasheet | 95°C (cabinet isolated) |
| PureLine S PH | 1–80°C | 10 bar (datasheet) | 95°C (cabinet isolated) |
| TOCLine ECO | 0–40°C | 10 bar | 95°C (cabinet isolated) |
| ProLine WW IL, SwimLine PQ IL | 1–60°C | 6 bar (positive pressure only) | - |
| UVShield | 5–45°C | 6 bar | - |
| PharmaLine DC PH | 1–60°C (80°C without wiper) | Not stated on series page | - |
On lines undergoing CIP/SIP, the lamp is switched off first; the manual for MP series requires waiting for any active wiper cycle to finish before CIP, isolating the cabinet at the isolator, and waiting for the line to cool below 40°C before restarting the lamp. Mounting orientation for the PureLine PQ AF must be horizontal. For hygienic lines, specify tri-clamp connections and sub-0.38 µm internal surface finish options (PharmaLine D AF H, PQ AF H).
What Should Be Upstream and Downstream of UV?
- Turbidity and suspended solids: lower UVT. In wastewater, UV is placed downstream of a clarifier, sand filter or membrane unit (ProLine WW IL, PQ WW AL/IL).
- Iron and carbonate hardness: scale on the quartz sleeve and reduce UV intensity. For hard water deposits, the manual describes cleaning with 5% citric acid followed by rinsing with water and IPA. An optional automatic wiper reduces deposit buildup.
- RO and EDI train: upstream of RO, UV reduces biofouling to protect membranes and pre-treatment equipment; if residual free chlorine is a concern for RO and EDI, the DC PH series removes chlorine. For the pure water train, see our EDI system selection guide.
- Water quality monitoring: online sensors measuring 254 nm absorption (TriOS LISA-254, SAC254) track UV absorbance of the sample and help detect changes in UVT.
According to the manual, lamps are sized for expected end-of-lamp-life performance; nevertheless, if process water quality changes or the quartz sleeve fouls, performance may drop. An automatic wiper helps maintain performance under fouling conditions.
Dose Output, Alarms and SCADA
On the Nuvonic PQ AF series, the dry UV sensor continuously reads intensity and the calculated RED dose, issuing a low-dose warning when needed. Active 4-20 mA outputs transmit dose or UV intensity, while 24 V DC outputs report lamp on, fault, warning, system ready, remote control and bleed valve status; RS485 Modbus connects to the plant control system over a single cable. The UVGuard™ windowed sensor can be checked against a reference sensor while the system is running. The PQ AF is powered from 230 V (207–253 V), 50/60 Hz; PH series operate across wider voltage ranges depending on cabinet and model (for example, 380–480 V for DC PH 320–500). Specify your voltage, communication protocol (Modbus, Ethernet) and I/O requirements from the start.
What to Include When Contacting Us
- Minimum, nominal and maximum flow rate (m³/h)
- Water UVT (T10) value and worst-case UVT value
- Target microorganism and log reduction; or inlet and target outlet levels for chlorine/ozone/TOC
- Fluid temperature, operating pressure, CIP/SIP method and temperature
- Line diameter, connection type (flange, tri-clamp) and installation footprint
- Application: drinking water, wastewater, food and beverage, pharmaceutical pure water, swimming pool, aquaculture
- Pre-treatment train (filter, RO, EDI, storage tank) and position of UV in the line
- Validation requirement (USEPA, DVGW, NWRI, NVI) and hygienic design specification
- Supply voltage, SCADA protocol, and make/model of any existing UV system
Frequently Asked Questions About UV System Selection
Required sizing inputs, UVT, target dose, pre-treatment and flow rate relationship.
What information is required to select a UV system?
At least five items of information: flow rate (minimum, nominal, maximum m³/h), water UV transmittance (T10, %) and its range of variation, target (which microorganism and how many logs of reduction; or chlorine/ozone destruction, TOC reduction), line conditions (fluid temperature, pressure, CIP/SIP, connection), and validation requirements. Pre-treatment status and integration details such as supply voltage and communication protocol are also requested at the proposal stage.
What is UVT (UV transmittance) and how is it measured?
UVT is the percentage of UV light that passes through a medium. In Nuvonic manuals it is denoted as T10, representing transmittance across a 10 mm optical path. It can be measured in the laboratory on a sample; for continuous online monitoring, a 4-20 mA UVT meter input is provided on the reactor control panel. As turbidity and the concentration of UV-absorbing compounds increase, UVT drops and the dose delivered by the same lamp decreases.
Under what conditions are catalog flow rates stated?
Every catalog flow rate is tied to a specific dose and UVT assumption. PharmaLine ECO flow rates are calculated for a 30 mJ/cm² dose and 98% T10, while PureLine ECO flow rates are calculated for RED 30 mJ/cm² and 99% T10, both at end-of-lamp-life conditions (datasheet footnotes). For example, 68 m³/h is stated for the PharmaLine ECO 85 (750 W, 2 lamps) and 86 m³/h for the PureLine ECO 85. For any other dose or UVT, the flow rate must be recalculated; the two tables cannot be derived from one another.
How is the target dose determined?
It starts from the D10 value of the target organism and the required log reduction: 1 × D10 gives 90%, 2 × D10 gives 99%, and 3 × D10 gives 99.9% reduction. In the Hanovia D10 table, D10 for E. coli is 5.4 mJ/cm², so 16.2 mJ/cm² is required for 3-log reduction; D10 is 12 mJ/cm² for Bacillus subtilis spores and 100 mJ/cm² for Aspergillus niger. Because the actual dose delivered by a reactor depends on flow hydraulics, a reactor with an independently validated (PQ) dose equation is preferred.
What pre-treatment is needed upstream of a UV system?
UV itself does not filter particles; turbidity and suspended solids lower UVT, while iron and carbonate deposits adhering to the quartz sleeve reduce intensity. In wastewater, UV is typically installed downstream of a clarifier, sand filter or membrane unit (ProLine WW IL and PQ WW series). In hard water, the sleeve may need cleaning with 5% citric acid. If free chlorine is present upstream of RO, the DC PH series destroys free chlorine.
Which missing parameter most often leads to an undersized system?
The most frequently missing datum is UVT. Even when the flow rate is accurate, assuming an overly high UVT leads to an undersized reactor. According to the manual, lamps are sized for end-of-lamp-life performance, meaning margins are included for lamp aging and sleeve fouling alongside UVT. If process water quality fluctuates, always report the worst-case UVT value.
Send the make and model of your current instrument to [email protected] — our engineers will propose the equivalent with the same connection and measuring range.
Planning a project? Send us your flow rate, feed water source and target water quality to [email protected] — our engineers will reply with a technical proposal.