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Calcimator

UV Disinfection Calculator

Calculate UV dose and reactor sizing for pathogen inactivation based on flow rate, UVT, and target log reduction.

Inputs

MGD

Results

Design UV Dose

26 mJ/cm²

Required Power

142 kW

≈ 9 homes' peak draw

UV Lamps Required947
Reactor Vessels48
Estimated Capital Cost$2,873,500.00
Annual Operating Cost$318,787.00
Annual Power Cost$124,387.00
Annual Lamp Replacement$189,400.00
Headloss through Reactor24 ft
Quartz Sleeve CleaningBi-weekly
No Disinfection ByproductsYes — No disinfection byproduct formation
How to Use This Calculator
  1. Enter Design Flow Rate (MGD) — use the maximum design flow for conservative sizing.
  2. Select Target Pathogen (Cryptosporidium, Giardia, or virus) and set the Target Log Reduction required by your permit.
  3. Enter UV Transmittance (UVT %) from your source water or post-filter measurements — lower UVT requires more power.
  4. Set Safety Factor (typically 1.2-1.5) and review Design UV Dose (mJ/cm²) calculated for the log credit claimed.
  5. Review Required Power (kW), UV Lamps Required, and Reactor Vessels for equipment procurement and electrical planning.
  6. Check Estimated Capital Cost and Annual Operating Cost for budget development and life-cycle cost comparisons with chlorination.

What each input means

Design Flow Rate
Peak flow rate through the UV reactor.
Target Pathogen
1 = Bacteria, 2 = Virus, 3 = Giardia, 4 = Cryptosporidium (UV is highly effective against Crypto).
Target Log Reduction
Desired log reduction (3-log = 99.9% inactivation, 4-log = 99.99%).
UV Transmittance (UVT)
Percentage of UV light transmitted through a 1-cm water sample at 254nm. Lower UVT requires more power.
Safety Factor
Design safety factor applied to the required dose. Typical: 1.2-2.0.

How this is calculated

Worked example, using the default values

  1. Identify Input Parameters
    4 parameters
    Design Flow Rate = 3, Target Pathogen = 4, Target Log Reduction = 3, UV Transmittance (UVT) = 85 = 5 input(s) provided
  2. Calculate Design UV Dose
    26 = 26
  3. Calculate Required Power
    Required Power
    142 = 142
  4. Calculate UV Lamps Required
    UV Lamps Required
    947 = 947
  5. Calculate Reactor Vessels
    Reactor Vessels
    48 = 48

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