In the UV peroxide process UV spectrum photons react with hydrogen peroxide to form hydroxyl radicals as shown by the
simplified reaction below:
H2O2 → 2 •OH (in the presence of UV light)
The major components of a H2O2/UV system include: UV lamps, lamp sleeves, and lamp cleaning system, hydrogen peroxide storage and injection system, reactor chamber, in-line mixer, supply and discharge pumps and piping, monitoring and control systems. For the H2O2/UV system, higher radical generation results from the use of MP-UV lamps relative to the LP-UV lamps, due to the better absorptivity of H2O2 at lower wavelengths (see a brief discussion of UV lamps for water treatment).
The key design and operating parameters include the H2O2 dose, the UV lamp type and intensity, the reactor contact time, and the control systems (pH and temperature). The UV quartz sleeve cleaning frequency is a function of iron and other materials which could form scale on the tubes. The optimum dose of H2O2 should be determined for each water source based on bench and pilot-scale testing, but is commonly estimated at twice the TOC and not less than 1 to 2 mg/L.
The advantages and disadvantages of the H2O2/UV system are:
MP-UV irradiation can serve as an effective disinfectant for a variety of microorganisms in addition to activating the peroxide for organic destruction.
H2O2 is highly soluble and can be added to the source water at high concentrations, whereas O3 is a much less soluble gas that must be bubbled into the source water. Consequently, H2O2/UV processes can generate larger amounts of hydroxyl radicals than O3/UV processes for equal amounts of energy used to add the oxidants to the source water.
UV light penetration can be adversely affected by high turbidity and elevated nitrate concentrations and the tubes can become fouled with scale.
The theoretical yield of hydroxyl radicals via the H2O2/UV process is greater than that for the H2O2/O3 process; however, due to interfering compounds in the water, this theoretical yield can be decreased to below that of the H2O2/O3 process.
The presence of residual hydrogen peroxide in the water may require removal down stream of the process.