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

Effluents from X-ray film developing processes feature high contaminant load (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 sulphonated/hydroxylated derivatives and dimers yielded from the developing agents hydroquinone and phenidone were found to be the main organics contributing to the contaminant load of these effluents. Their potential degradation by oxidation with both photo- and thermal-Fenton reactions was investigated and the optimal degradation conditions were determined. Under these conditions the initial COD was reduced by about 97% within 6 h of treatment. The intermediates detected by LC-(EI)MS in the oxidation of hydroquinone and phenidone during the treatment were essentially hydroxylated derivatives and dimers and the residual organic matter was mainly made up of carboxylic acids. Reaction pathways for the oxidation of the developing agents hydroquinone and phenidone were proposed. The presence of many organic and inorganic components 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 thermal-Fenton reaction without affecting the degradation degree and quality of the discharge.