Photocatalytic treatment of black table olive processing wastewater.

The photocatalytic treatment of an effluent from black table olive processing over TiO2 suspensions was investigated. The study focused on the effect of various operating parameters on the treatment efficiency including initial organic load, catalyst type, concentration and reuse, and addition of hydrogen peroxide. Initial organic load, expressed in terms of chemical oxygen demand (COD), was studied in the range 1-8 g/L, anatase TiO2 concentrations in the range 0.25-2 g/L and H2O2 concentrations in the range 0.025-0.15 g/L. Treatment efficiency, which was assessed in terms of COD, total phenols, aromatics and color reduction, generally increased with decreasing initial COD and increasing contact time, catalyst and H2O2 concentrations; however, for H2O2 there was a maximum dosage above which performance deteriorated. Depending on the conditions employed, nearly complete decoloration (>90%) could be achieved, while mineralization never exceeded 50%. Shake-flask tests with non-acclimated activated sludge showed that both the original and photocatalyzed effluents were degradable aerobically with the biodegradation rate of the original effluent being three times greater than the oxidized one. On the other hand, photocatalytic oxidation of the original effluent was at least two orders of magnitude faster than its biological oxidation to achieve comparable levels of degradation.