Biological and photocatalytic treatment integrated with separation and reuse of titanium dioxide on the removal of chlorophenols in tap water

Abstract

We investigated biological, photocatalytic, and combination of biological and photocatalytic treatments in order to remove a mixture of 2-chlorophenol, 2,4-dichlorophenol, 2,4,5-trichlorophenol, and pentachlorophenol in tap water (total: 100 mg L −1, each: 25 mg L −1). The removal of chlorinated phenols was conducted with a flow biological treatment and a circulative flow photocatalytic treatment under black light and sunlight irradiations integrated with titanium dioxide separation and reuse. The combined biological–photocatalytic treatment significantly shortened the degradation and mineralization time of both the biological treatment and the photocatalytic treatment. The removed chlorophenols per hour by the combined biological–photocatalytic treatment was 25.8 mg h −1, whereas by the combined photocatalytic–biological treatment was 10.5 mg h −1. After a large portion of biodegradable 2-chlorophenol and 2,4-dichlorophenol, and around half amount of slightly biodegradable 2,4,5-trichlorophenol were removed by the biological treatment, the remained three chlorophenols, biorecalcitrant pentachlorophenol, and biodegradation products were completely removed by the subsequent photocatalytic treatment. Since titanium dioxide particles in tap water spontaneously sedimented on standing after the photocatalytic treatment, the combined treatment can be operated by integrating with the titanium dioxide separation and reuse. The TiO 2 particles were recovered and reused at least three times without significantly decreasing the removal efficiency.