Biodegradability enhancement of refractory pollutants by ozonation: A laboratory investigation on an azo-dyes intermediate

The effectiveness of ozone treatment for improving the biodegradability of recalcitrant pollutants has been proved by investigating the ozonation reaction of FAST-VIOLET-B (FVB) a bioresistant chemical intermediate of ate-dyes. Laboratory scale experiments have been carried out, at room temperature, by bubbling, for 90 min, ozonated air (9ppmO(3)/min) into 0.35 l of an alkaline (pB=11) aqueous solution (50 ppm) of FVB. The experimental results indicate that during the ozonation, even though complete FVB degradation occurs in 10 min, ozone consumption goes on for a further 20-min after which time most degradation reactions are completed. The main ozonation by-products, identified by HPLC, IC, and GC-MS are formaldehyde, acetaldehyde, glyoxal, acetone, acetic-, formic-, oxalic- and carbonic-acid, plus six FVB derivatives scarcely biodegradable. At the end of the ozonation, i.e. after 30 min., the initial values of TOC (35 mgC/l) and COD (103 mgO(2)/l) are respectively 27 and 25 and correspond to a relative removal of about 23% and 76%. As for FVB solution biodegradability expressed as (BOD5)/COD) ratio, during the first 10 min its value regularly increases from zero up to a maximum of 0.75 that corresponds to an ozone consumption of 2.4 mg per each mg of organic carbon initially present in the solution. (C) 1998 Published by Elsevier Science Ltd. All rights reserved.