HETEROGENEOUS AND HOMOGENEOUS PHOTOCATALYT1C TREATMENT OF WASTEWATERS FROM BLACK TABLE OLIVES PROCESSING

摘要

The photocatalytic oxidation of an actual wastewater originating from black table olives processing was investigated. Experiments were conducted in an immersion well, batch type, laboratory scale photoreactor. Photocatalysis was applied in the presence of TiO_2. Eight crystalline forms of TiO_2 were tested for their photocatalytic activity and a synthetic TiO_2 catalyst prepared in the laboratory was found to be more active, in terms of phenolic compounds reduction, than the other commercially available photocatalysts. The extent of photocatalytic degradation was found to increase with increasing TiO_2 concentration up to 1.5 g/L TiO_2, above which degradation remained practically constant, reaching a plateau. To assess catalyst activity on repeated use, experiments were performed where the catalyst was recovered and reused. After two successive uses, TiO_2 had sufficiently retained its photocatalytic activity. Furthermore, effluent degradation was enhanced in the presence of hydrogen peroxide at concentrations 25, 50, 100mg/L At 100mg/L H_2O_2 the photocatalytic treatment achieved 47%, 72%, 61%, 94% reduction for COD, phenols, aromatics and color respectively. However, the use of H_2O_2 above 150mg/L suppressed degradation. Besides, the oxidative degradation of table olives wastewater was investigated by means of homogeneous photocatalysis in the presence of iron cations. Fe~2+ and Fe~3+ were tested in the form of FeSO_4 and FeCI_3respectively and the latter were found more efficient for photocatalytic treatment. In general, treatment performance improved with increasing Fe~3+ loading at values of 10, 31, 48, 104mg/L. The interference from Fe~3+ in the estimation of phenolic compounds was pointed out. Finally, it was observed that the addition of H_2O_2 to the homogeneous photocatalytic mixture enhanced the chemical oxidation to 19%, 80%, 56%, 73% for COD, phenols, aromatics and color reduction respectively.