Intimately Coupled System Of Visible-light-responsive Photocatalysis And Biodegradation For Enhancing Phenol Wastewater Treatment

Phenols are commonly present in wastewaters from various industrial processes, including coal processing, paper manufacture, pharmaceutical production, and petrochemical refining. The high toxicity of phenols contaminated wastewater seriously threatens aquatic eco-system and human health. As to effective phenol degradation, generally, high cost, low efficiency and complex operation conditions are faced by photocatalysis alone, biodegradation alone and sequential coupling of photocatalysis and biodegradation, respectively. The intimate coupling of photocatalysis and biodegradation（ICPB） is a promising method for overcoming these limitations. However, the use of UV light in current ICPB researches, which accounts for less than 4% of the entire solar spectrum limits the utilization of solar energy.In this study, we used a combination of hydrothermal method and self-assembly to develop a thin and even layer of visible-light-responsive photocatalyst(Er³⁺:YAlO₃/TiO₂) on sponge-type carriers, namely Er³⁺:YAlO₃/TiO₂-sponge. Response surface methodology（RSM） was used to optimize preparation conditions, including hydrothermal temperature, Er³⁺:YAlO₃/TiO₂ concentration and coating ratio. The obtained RSM model showed highly significant in statistics for its P value at 0.0002 and exhibited a satisfactory consistence between experimental results and predicted values. By considering the interactions between various preparation conditions, the achieved condition of Er³⁺:YAlO₃/TiO₂-sponge was at hydrothermal temperature（130 oC）, Er³⁺:YAlO₃/TiO₂ concentration（19.75 g/L） and coating ratio（20 g/L）. In addition, photocatalyst characterizations demonstrated Er³⁺:YAlO₃/TiO₂ film were even and uniform with few cracks and agglomeration, existed in anatase pattern and showed strong visible-light-responsive.Then, composite cubes were prepared with followed biofilm cultivation on the optimal Er³⁺:YAlO₃/TiO₂-sponge. When stabilization was achieved, the degradations of phenol（50 mg L–1） were compared for four protocols in novel circulating beds: adsorption（AD）, visible-light-responsive photocatalysis（VPC）, biodegradation（B）, and intimately coupled visible-light-responsive photocatalysis and biodegradation（VPCB）. The phenol and DOC removal efficiencies using VPCB in 16 h were 99.8% and 65.2%, respectively, i.e., higher than those achieved using VPC（71.6% and 50.0%） or B（99.4% and 58.2%）. Finally, combined with the detection and analysis of biomass and phenol intermediates, a visible-light-induced ICPB mechanism was proposed.