Chlorine photolysis and subsequent OH radical production during UV treatment of chlorinated water

• Published in: Water research (Oxford) Vol. 41; no. 13; pp. 2871 - 2878
• Main Authors: Watts, Michael J., Linden, Karl G.
• Format: Journal Article
• Language: English
• Published: Oxford Elsevier Ltd 01-07-2007; Elsevier Science
• Subjects: Applied sciences; chemical residues; chlorination; Chlorine; Chlorine - chemistry; disinfectants; Disinfection; drinking water; Exact sciences and technology; free radicals; Halogenation; halogens; hydroxides; Hydroxyl radical; Hydroxyl Radical - chemistry; hydroxylation; irradiation; Monochloramine; new methods; optimization; Other industrial wastes. Sewage sludge; oxidation; photochemical reactions; Photolysis; Pollution; pressure treatment; Quantum yield; reaction kinetics; Ultraviolet; ultraviolet radiation; Ultraviolet Rays; Wastes; Water Purification - methods; water treatment; Water treatment and pollution; yields; Monochloramine; Disinfection; Ultraviolet; Quantum yield; Chlorine; Hydroxyl radical; Drinking water treatment; Water treatment; Chlorination; Pollutant behavior; Tosylchloramide sodium; Nitrates; Radical scavenger; Pollution; Ultraviolet radiation; Ultraviolet;Chlorine;Monochloramine;Quantum yield;Hydroxyl radical;Disinfection; Water quality; Hydroxyl radicals; Kinetics; Photochemical degradation
• ISSN: 0043-1354; 1879-2448
• DOI: 10.1016/j.watres.2007.03.032

The photodegradation of chlorine-based disinfectants NH
2Cl, HOCl, and OCl
− under UV irradiation from low- (LP) and medium-pressure (MP) Hg lamps was studied. The quantum yields of aqueous chlorine and chloramine under 254
nm (LP UV) irradiation were greater than 1.2
mol
Es
−1 for free chlorine in the pH range of 4–10 and 0.4
mol
Es
−1 for monochloramine at pH 9. Quantum yields for MP (200–350
nm) ranged from 1.2 to 1.7
mol
Es
−1 at neutral and basic pH to 3.7
mol
Es
−1 at pH 4 for free chlorine, and 0.8
mol
Es
−1 for monochloramine. Degradation of free chlorine was enhanced under acidic water conditions, but water quality negatively impacted the MP Hg lamp degradation of free chlorine, compared to the LP UV source. The production of hydroxyl radical via chlorine photolysis was assessed along with the rate of reaction between
OH and HOCl using radical scavengers (parachlorobenzoic acid and nitrobenzene) in chlorinated solutions at pH 4. The quantum yield of OH radical production from HOCl at 254
nm was found to be 1.4
mol
Es
−1, while the reaction of HOCl with OH radical was measured as 8.5×10
4
M
−1
s
−1. NH
2Cl was relatively stable in all irradiated solutions, with <0.3
mg
L
−1 increase in nitrate following a UV dose of 1000
mJ
cm
−2. For water treatment plants, no significant changes in chlorine concentration would be expected under typical pH levels and UV doses; however, the formation of
OH could have implications for chlorinated byproducts or decay of unwanted chemical contaminants.