Continuous mineralization of concentrated phenol dissolved in an electrolyte-containing tap water by integrating biological-photocatalytic treatment with TiO₂ separation: Utilization of sunlight and reuse of TiO₂

The continuous mineralization of concentrated phenol (200 mg l-1) in an electrolyte-containing tap water was investigated using a biological- photocatalytic treatment integrated with TiO2 separation. Black light and sunlight were used as the light source, and the reuse of TiO2 was also studied. The mineralization of phenol in tap water and the reuse of TiO2 were conducted in a flow system in which a bioreactor is combined with a narrow tube photoreactor operated under single pass and circulative flows, and the sedimented TiO2 is recycled. A high circulative flow rate prevented the TiO2 particles from coagulating due to the electrolytes in the tap water. A flow-circulation-flow operation mode using the integrated biological- photocatalytic-TiO2 separation system was the optimum for treating the concentrated phenol in the electrolyte-containing tap water without interrupting the inflow of the wastewater and the discharge of the treated water. The optimum mineralization (phenol: 0.6 mg l-1 and total organic carbon: 6.5 mg l-1) was attained by recycling the biologically treated phenol solution (20.1 mg l-1) at the flow rate of 600 ml min-1 under sunlight irradiation, while maintaining the inflow and the discharge rates at 15 ml min-1. The TiO2 particles were spontaneously sedimented by coagulation in a separation tank during the operation and the TiO2 can be reused without reducing the efficiency of five repeated treatments.