The aim of this work was to study the degradation of three azo dyes, Orange II, Methyl red and Biebrich Scarlet by electro-Fenton and the effect of the electrochemical pre-treatment on the biodegradability of the solutions. The electrochemical pre-treatment showed that an electrochemical reduction on the carbon felt electrode was mainly responsible for the decolorization of the azo dyes. Indeed, the electrochemical behaviour of the azo dyes highlighted their electroactivity, electrolysis with and without ferric ions led to the same decolorization yield, namely 99% at 15 min for Methyl red, and stable COD values were recorded during decolorization. In a second step and owing to the absence of by-products electroactivity in reduction, the formation of hydroxyl radicals 2 by the Fenton reaction led to the oxidation of by-products from the electrochemical reduction. It was illustrated by the decrease recorded for the COD values. The results also showed that the azo bond cleavage occurring during the electrochemical reduction was not sufficient to significantly reduce recalcitrance as shown from BOD 5 /COD ratio examination below the limit of biodegradability (0.4). Contrarily, a positive trend was recorded for Orange II during the electro-Fenton reaction, with a BOD 5 /COD ratio of 0.81 after 28h of pre-treatment.

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The aim of this work was to determine easily and quickly the operating conditions for the industrial production of lactulose (rate of isomerisation, rate of lactose degradation, reaction time, temperature, pH). The kinetic equations of lactulose formation and lactose degradation in an alkaline medium (NaOH) were determined. Experiments were carried out at different OH− concentrations (0·5 × 10−2–19 × 10−2 mol dm−3) and at different temperatures (328–353 K). A kinetic model is presented which can be used to describe the experimental results and hence a procedure for industrial production.