Treatment of Phenol, Formaldehyde and their Mixtures by Photocatalytic and Biological Methods

Abstract

Phenol and formaldehyde are toxic compounds present in many industrial wastewaters. Particularly, in synthetic resin producing industries the concentrations of one or both of these organics can reach concentrations of grams per litre. In the present work, the degradation of phenol, formaline (formaldehyde: methanol mixture) and their mixtures with photocatalytic and biological methods has been studied to determine the best strategy for the treatment of wastewaters containing those organics. Photocatalytic studies in batch and in continuous (by dosing) have been performed. Experiments in batch showed that formaline slows down phenol degradation. Another set of experiments with phenol-methanol mixtures revealed that the presence of this alcohol also slows down the degradation of phenol but less than the mixture formaldehyde: methanol. FTIR studies indicated the formation of 4-hydroxybenzaldehyde as a result of phenol-formaldehyde interaction with the catalyst surface. Thus, the lower phenol degradation rate is attributed to the formation of this aldehyde on the surface of the catalyst in addition to the ·OH scavenging effect of methanol. This inhibitory effect in the degradation was overcome by dosing the influent into the photocatalytic reactor. In the present work the biological systems have been employed to optimise and speed up the degradation process of phenol-formaldehyde mixtures. These systems have shown lower detoxification efficiency of the samples in comparison with that of the photocatalytic method with dosing. Taking into account the obtained results of degradation and toxicity, a novedous process consisting of a biological treatment followed by a photocatalytic one with dosage for the treatment of formaldehyde-phenol containing wastewaters is proposed.