Forschungs- & Entwicklungsinformationsdienst der Gemeinschaft - CORDIS

Coupling between ozone and biotreatment for decontamination of wastewater containing pesticides

The experimental conditions that lead to an optimisation of the ozone treatment of effluents containing recalcitrant organic substances such as the CADOX target compounds, i.e., alachlor, atrazine, chlorfenvinfos, diuron, isoproturon and pentachlorophenol,have been obtained. Particularly, it have been performed some experimental tests using aqueous solutions containing a mixture of the organic compounds previously mentioned and in the presence of T-824, R113675 (both, Janssen products)and the very high soluble organic compound femam (Deretil), as a model solution to carry out experimental research. The oxidation reactor used was a bubble column operating at atmospheric pressure. The liquid requiring treatment was re-circulated via a peristaltic pump in the column, while gas containing the ozone was continuously injected into the bottom of the column through a porous diffuser (semi-batch reactor). The tests were carried out at ambient temperature.

From the ozonation experiments, it is observed the establishment of two different kinetics. The first corresponding at the yellow coloration and discoloration of the effluent during the first twenty minutes, and the second corresponding at an other step of oxidation. In the first step, after a contact time of 20 minutes and an ozone rate of 900 mg/l, the treated effluent is turned from yellow to colourless. On the other hand, it has been observed that the COD is reduced as the pH of the effluent decreases until a value closed to 3. This acid pH obtained after ozonation is the suitable pH to apply a PhotoFenton procedure for decreasing even more the TOC of the effluent.A decrease of TOC with treatment time is observed, but is much lower than the observed for DCO, this leads to a reduction of the DCO/TOC ratio being an indication that the effluent becomes more oxidized with increasing ozonation time.

In view of the characteristics of the effluent and with relation to the design of the pilot plant, it is suggested the use of a Venturi injection system in a column by means of a diffuser. The diameter and height of the ozone reactor will depend on the gas volume flow and the concentration of ozone needed.

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Campus Universitario, Departament de Química.
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