Biodegradation Of Refractory Pollutant By White Rot Fungus In Co-substrate System With Lignocelluloses

The treatment of these pollutants becomes the bottleneck problem of environmental control, because of the refractory characteristics of some toxic pollutants distributed in many soil and groundwater. However, the removal of these pollutants usually requires complex physico-chemical treatment and is not quite effective, so exploring bio-treatment technology friendly to environment for these pollutants is attracting more and more attentions. White rot fungi are well known for their outstanding degradation ability because they could produce extracellular oxidative enzymes, which could act on different substrates. This ability has opened promising application prospects for the development of biotechnological processes aimed at the degradation of refractory pollutants. However, some disadvantages, such as insufficant of degradation efficiency, high cost and so on, always existed when white rot fungus was applied in actual bioremediation. Based on these problems, in this paper, the biodegradation process and mechanisms of refractory pollutants by white rot fungus in established co-substrate system with lignocelluloses were investigated. Studying the probability of using lignocelluloses as co-substrate and mechanisms of enhancing biodegradation efficiency of pollutants by white rot fungus would lay the foundation of industrial application of whit rot fungus. Some main research results were as follows:Using lignocelluloses as co-substrate, the degradation of typical aromatic compounds and nitrogen heterocyclic compounds by white rot fungus in established submerged and solid-state cultivation system was investigated. The results indicated that different pollutants could be efficiently degraded by selected white rot fungus. In the subemerged cultiviation system, 80% of malachite green could be removed by the fungus after 2d incubation, degradation rate of quinoline by the fungus could reach 89.48% after incubation for 15d and that of indole was about 100% for 6d. Furthermore, different acting forms appeared when different substrates co-existed. For instance, pollutant degradation showed an obvious antagonistic effect when pyridine and quinoline co-existed in the system, however, the synergetic action of pollutant degradation appeared when quinoline and indole co-existed in the same system. Additionally, the biodegradation kinetics of quinoline and indole by the fungus followed zero-order and first-order reaction kinetics respectively, and the addition of co-substrate enhances the fungal biomass and pollutant biodegradation. In solid-state cultivation system, different pollutants were also degraded efficiently by the fungus and degradation rate of these pollutants in the system was higher than that in submerged system. Degradation mechanisms of dyes with different structures were different although the triphenylmethane dyes all could be removed by the fungus, the dye degradation could be influenced significantly by cultivation environment. In addition, the fungus could remove 99% of indole in 5d, 93.47% and 97.4% of quinoline with 250mg/L and 150mg/L respectively and 61.5% of pyridine in 15d. The biodegradation kinetics of quinoline and indole by the fungus followed first-order and zero-order reaction kinetics in the system respectively.By analyzing the changes of soluble and insoluble components using FTIR, SEM, XRD and HPLC, the degradation environmental characteristics by fungus in solid state medium were studied. The results showed that the degradation process of pollutants by the fungus in solid state medium was a co-degradation process and the degradation of co-substrate by the fungus could provide nutrition for fungal growth, resulting in secreting different enzymes by fungus to degrade pollutants. On the co-degradation process, it is noteworthy that the phenolic compounds and lignin was degraded significantly by fungus, so the influence of phenolic compounds and extraction from lignin on pollutant degradation by fungus was also studied. The results showed that biodegradation rate and enzyme activities could be enhanced efficiently by the addition of phenolic compounds, and the main components having the capacity of enhancing rate and activities mainly exist on the supernatant of phenolic compounds after being precipitated by ethanol. In addition, same results could be obtained by the addition of extraction from lignin as that of phenolic compounds, but the structure of pollutant had a strong influence on the biodegradation rate. Furthermore, the quantitative structure-activity relationship showed that the degradation rate of easily degradable pollutants depended on spatial structure, while the stability of structure influenced the biodegradation of refractory pollutant.The degradation dynamics of dyes by crude enzyme and removal mechanism of dye by fungus in solid state system was also demonstrated. Regular characteristics were found when the dye was treated by crude enzyme obtained from different medium at different time. The dyes degradation by crude enzyme followed first-order reaction kinetics, while the relation between biodegradation amount and concentration as well as reaction rate and concentration all followed zero-order reaction kinetics. The addition of inhibitors could restrain obviously some dyes degradation. Furthermore, the decolorization mechanism of malachite green and bromophenol blue mainly attribute to laccase and laccase iso-enzyme. However, the crystal violet decolorization was special and depended on the presence of low molecular weight fraction. The degradation pathway of crystal violet by low molecular weight fraction was proposed and four main intermediates, such as phenol, N, N-dimethylaminobenzaldehyde, N,N,N',N"-tetramethylpararosaniline and [N,N-dimethylaminophenyl] [N-methylaminophenyl] benzophenone, were indentified.The biodegradation efficiency of pollutants could be improved when the established co-substrate system with lignocelluloses was applied in bioremediation. Based on the theory, a new biotechnology used to treat dye effluents was proposed and the technology could remain higher efficiency after recycling use for 5 times, which suggested that the technology had potential application in industry.