Photocatalysis as a pre-treatment prior to a biological degradation of cyproconazole Original Research Article

The feasibility of coupling photocatalysis and a biological treatment (Pseudomonas fluorescens) to remove a fungicide, cyproconazole, in pure water was examined. Photocatalytic elimination of 85 10−3 g L−1 cyproconazole was almost complete after 500 minutes irradiation. In view of a subsequent biological treatment, the residual organic content should be significant and hence 255 minutes irradiation time was chosen, leading to 85.8% elimination yield, 38.5% mineralisation and 51.6% oxidation. COD on TOC ratio decreased during photocatalysis indicating a favourable trend, which however was not confirmed by a decrease of the toxicity, since the EC50 values were 61% and 64% initially and after 255 minutes irradiation. In addition, the presence of by-products from photocatalysis after P. fluorescens culture, showing their non-biodegradability, was also in disfavour of a coupling of the two operations. Therefore in the considered experimental conditions, photocatalysis prior to biological treatment with P. fluorescens is not really relevant to treat water containing cyproconazole.