DEGRADATION OF THE POLYSACCHARIDE ALGINIC ACID - A COMPARISON OF THE EFFECTS OF UV-LIGHT AND OZONE

Oxygenated aqueous solutions of alginic acid, a model compound for polyuronic acids contained in surface waters, were photolyzed in UV light (λ = 254 nm), treated with ozone, or reacted with radiolytically generated hydroxyl radicals. The average molecular weight decrease upon such treatment was measured by viscosimetry. At a fluence of 250 J m2, which is generally considered sufficient to disinfect drinking water, 0.0005 strand breaks per macromolecule are effected. Alginic acid is capable of complexing ferric ions. Their presence increases photolytic strand-break formation. At an iron concentration of 10−6 mol dm−3, such as may prevail after flocculation with iron salts, 0.004 strand breaks per macromolecule are detected at the above fluence. Hydroxyl radicals, produced by subjecting the N2O/O2-saturated aqueous alginic acid solution to ionizing radiation from a 60Co γ source, cause strand breakage with an efficiency of 22%, while superoxide radicals are released from the polymer peroxyl radicals with an efficiency of 71%. The efficiency of ozone in producing a strand break is 18%, relative to the total of the ozone consumed. The destruction of the alginic acid by ozone is mainly caused by the intermediate hydroxyl radicals. The polysaccharide peroxyl radicals that are formed by OH attack and subsequent addition of O2 eliminate superoxide radicals, which in turn stimulate further hydroxyl radical production by reacting rapidly with the ozone. © 1990, American Chemical Society. All rights reserved.