A study of toxicity, biodegradability, and some by-products of ozonised nitrophenols

Treatment performances of ozonation applied for the degradation of nitrophenols (NPs) were assessed in terms of biodegradability improvement, and toxicity reduction. Among the by-products formed during the ozonation of 4-nitrophenol and 2,4-dinitrophenol at initial pH 9.5 4-nitrocatechol, p-quinone, and hydroquinone were identified. The by-products of NPs ozonation were much more biodegradable than NPs. The degree of organically bounded nitrogen conversion to nitrate was 66-100% at pH 2.5 and 38-87% at initial pH 9.5. The reduction of ozone consumption and acceleration of NPs degradation rate was achieved during the ozonation of NP mixture at initial pH 9.5. According to Daphnia magna acute toxicity test, a complete detoxification of ozonised solutions was achieved. Thus, ozonation can be applied as a very effective treatment method for detoxification and biodegradability improvement of NPs containing wastewater. The achieved biodegradability improvement and detoxification of treated NPs supports the potential use of ozonation to improve the capacity of conventional biological treatment to remove these toxic and poorly biodegradable compounds. (C) 2002 Elsevier Science Ltd. All rights reserved.