UlWattage and flow rate are the most important factors
in achieving UV sterilization; the slower the flow rate, the
higher the kill rate for a given bulb wattage (Escobal, 1993).
For example, a 40-watt mercury vapor bulb with a flow
rate of 500 gallons per hour in a 2-inch-diameter pipe will
deliver approximately 11,530 μwatt-sec/cm2. Increasing the
pipe diameter to 3 inches (thereby reducing flow rate) will
increase the dosage to 17,530 μwatt-sec/cm2; cutting the
flow rate in half in that 3-inch pipe further increases the
dosage to 34,340 μwatt-sec/cm2 (Hoff et al., 2008).