Degradation of medical X-ray film developing wastewaters by advanced oxidation processes

Effluents from X-ray film developing processes feature high contaminant loa d (COD about 200 g/l). Identification of the main organics present in these wastewaters was performed by using liquid chromatography-mass spectrometry in electron impact mode, LC-(EI)MS. Both, unconsumed ingredients and sulph onate/hydroxylated derivatives and dimers yielded from the developing agent s hydroquinone and phenidone were found to be the main organics contributin g to the contaminant load of these effluents. Their potential degradation b y oxidation with both photo- and thermal-Fenton reactions was investigated and the optimal degradation conditions were determined. Under these conditi ons the initial COD was reduced by about 97% within 6 h of treatment. The i ntermediates detected by LC-(EI)MS in the oxidation of hydroquinone and phe nidone during the treatment were essentially hydroxylated derivatives and d imers and the residual organic matter was mainly made up of carboxylic acid s, Reaction pathways for the oxidation of the developing agents hydroquinon e and phenidone were proposed. The presence of many organic and inorganic c omponents in the wastewaters did not affected the favoured oxidation route of these developers. The results obtained allow to assess the reduction of costs permitted in the treatment of X-ray effluents with the photo- and the rmal-Fenton reaction without affecting the degradation degree and quality o f the discharge. (C) 2001 Elsevier Science Ltd. All rights reserved.