A Coupled Photocatalytic-Biological Process For Phenol Degradation In The White Rot Fungi-Oxalate-Fe₃O₄ Composite System

A lot of water in our country are polluted seriously by phenol wastewater, the treatment of phenol wastewater have been paid attention by domestic and foreign. It is an urgent need to process phenol wastewater efficiently with low energy consumption,due to its serious harm to enviroment. The toxicity of phenol is the largest of phenol compounds. Phenol is a typical representative of phenol compounds and it is most frequently found in polluted rivers and industrial effluents. There are many ways to treat phenol wastewater. However, it is difficult to reach the expected purpose with single method such as biological or chemical method to treat phenol wastewater,because phenol is difficult to degrade due to its toxicity and benzene ring structure.Development combined process is an effective way in wastewater treatment engineering.Fe₃O₄ nanoparticles suspension was prepared by reverse coprecipitation technique in this paper. Besides, a novel composite system, which combined biological degradation with photocatalytic degradation, was developed for phenol degradation at the presence of Fe₃O₄ nanoparticles and white rot fungi?Phanerochaete chrysosporium? together with its secretion oxalate. Phenol degradation under different conditions were analyzed. The results showed that Fe₃O₄ nanoparticles were spherical in shape and the surface of the spheres exhibited morphologically rough. The average sizes of Fe₃O₄ particles were in the range of 8²0nm. Meanwhile, it displayed a little agglomerate. In addition, Fe₃O₄ played an important role in the composite system as they could efficiently enhance phenol degradation when coexisted with oxalate under light. The optimal amount of Fe₃O₄ was 0.5 g/L under light, and the maximal peak value of phenol degradation efficiency?93.41%? was detected after 3 days. The increase of initial concentration of phenol in the composite system had a promotion to its degradation. Furthermore, the degradation efficiency of phenol by the composite system was much higher than the treatments which used other systems in the same conditions.In order to investigate the mechanism of phenol degradation in the composite system, we detected oxalate accumulation secreted by Phanerochaete chrysosporium,the activity of extracellular enzymes?lignin peroxidase LiP and manganese peroxidase Mn P?, the changes of hydroxyl radicals??OH? production and statistical analysis between different indexes under differert conditions. High levels of MnP activities and low levels of LiP activities were observed. And the contribution of MnP to phenol degradation was greater than that of LiP. Additionally, oxalate was found to be strongly dependent on Fe₃O₄ nanoparticles concentration. Besides, oxalate concentration raised rapidly with the increase of phenol concentration, and adequate oxalate could accelerate phenol degradation due to the participation of oxalate in the photocatalytic process. Furthermore, ?OH could be produced not only by ligninolytic enzymes, but also by Fe₃O₄ and oxalate via a series of reactions under light. And the presence of Fe₃O₄ coule enhance the generation of ?OH. Importantly, the degradation of phenol in the composite system was accomplished under the coupling of biodegradation and photocatalysis.