Water tools

Advanced oxidation: electrical energy per order, lamp power and peroxide absorption

The figure of merit for UV-based oxidation is the electricity needed to cut a contaminant by a factor of ten in a cubic metre. It sizes the lamps, and the water's own absorbance decides how much of that light the peroxide gets.

Lamp electrical powerkW

Flowm³/h

Contaminant inany unit

Contaminant outsame unit

Target EE/O for the sizingkWh/m³ per orderBelow about 0.27 is favourable; trichloroethylene 0.03 to 0.05, hard compounds 2 to 10.

Lamp efficiency (optical output over electrical)

Hydrogen peroxide dosemg/L

Water absorbance at 254 nm1/cm

Measured

EE/O of this system

0.216kWh/m³ per order

Orders of removal

1.00

Sizing

Optical power for the target EE/O

208.0kW

Electrical power for the target EE/O

693.3kW

Peroxide

Fraction of UV absorbed by peroxide

10.3%

The rest is absorbed by the water matrix and wasted.

How it works

E E / O = \frac{P}{Q \log_{10} (C_{i n} / C_{o u t})} P_{o p t i c a l} = E E / O \cdot Q \cdot \log_{10} \frac{C_{i n}}{C_{o u t}} P_{e l} = \frac{P_{o p t i c a l}}{η}

(1)

f_{H_{2} O_{2}} = \frac{ε_{H_{2} O_{2}} C_{H_{2} O_{2}}}{ε_{H_{2} O_{2}} C_{H_{2} O_{2}} + A_{w a t e r}} ε_{H_{2} O_{2}} = 19.6 \frac{L}{mol cm}

(2)

where

$E E / O$: electrical energy per order of removal, kWh per m³
$P$: lamp power, kW
$Q$: flow, m³/h
$C_{i n}, C_{o u t}$: contaminant in and out
$P_{o p t i c a l}$: optical output needed, kW
$P_{e l}$: electrical input, kW
$η$: lamp efficiency
$f_{H_{2} O_{2}}$: fraction of the UV absorbed by peroxide
$ε_{H_{2} O_{2}}$: molar absorptivity of peroxide at 254 nm, L/mol·cm
$C_{H_{2} O_{2}}$: peroxide concentration, mol/L
$A_{w a t e r}$: absorbance of the water at 254 nm, 1/cm

For pseudo first-order destruction the energy scales with the orders removed, so doubling the energy adds one order. The theoretical minimum for plug flow is a fraction of what mixed reactors achieve. Peroxide absorbs weakly at 254 nm, so natural organic matter and nitrate steal most of the photons in coloured waters; the useful dose is usually 0.5 to 2 mmol/L. Bicarbonate and organic carbon also scavenge the hydroxyl radicals.

Advanced oxidation: electrical energy per order, lamp power and peroxide absorption

How it works

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