| White-rot fungi have the characteristics of non-specificity, high efficiency and broad spectrum. It has a better application prospect in bioremediation of refractory organics chlorophenols(CPs). White-rot fungi and laccase have shown great research value and application potential in various industrial fields, such as industrial wastewater treatment and pulp biobleaching. However, a major limitation for successful industrial application of laccase in the bioremediation processes is the high costs of laccase production and low production. Adding cheap natural substrate and metal ions, optimization of enzyme production medium to improve laccase production were studied. Optimizing the various influential factors and investigating enzyme production rule of white-rot fungi based on fermentation kinetics model were researched. Wastewater biological repair mechanism by white-rot fungi and laccase was studied based on chlorophenol compounds wastewaster. This study provides a theoretical and technical supports for the treatment of wastewater by white-rot fungi and laccase.Optimization of laccase production by Pleurotus ostreatus was made by adding natural substrates. The group of orange peel produced most laccase and its highest laccase activity was enhanced from 5U/mL to 45U/mL and the fermentation time was shortened by 1/3. The research on fermentation kinetics was carried out. Two fermentation kinetics models(the culture with orange peel and the culture of control) were proposed and compared. The results indicate orange peel extract could not only greatly improve the fungi’s ability of proliferation and producing laccase but also make the productivity and yield factors much higher than the control.The mechanism involved in bioremediation of CPs was studied. The study showed that the biosorption capacity of P. ostreatus to phenol and chlorophenols increased in the following order: 2,4,6-TCP>>2-CP>phenol>PCP. Two schemes of 2,4,6-TCP addition were tested to study the effect to fungal cultures: stepwise addition from the moment of inoculation and single addition after five days of growth. Different schemes of 2,4,6-TCP addition did not change the final biomass concentration. The CPs removal rate of the the liquid fungal cultures with stepwise addition of 2,4,6-TCP and 2-CP were higher than that of the cultures with single addition after five days of growth. The laccase activity of liquid fungal cultures with stepwise addition of 2,4,6-TCP and 2-CP were 10 times and 5 times of that of cultures with single addition after five days of growth. As a result the inhibition of CPs on laccase activity can be decreased and the CPs removal rate can be improved by change schemes of CPs addition.The adsorption ratio and degradation ratio of treatment of chlorophenols solution(the concentration of CPs between 10~30mg/L) by P. ostreatus was studied and the result showed that the degradation ratio was much higher than adsorption ratio for treatment of 2-CP; the degradation and adsorption were about the same ratio for 2,4,6-TCP; the degradation ratio was much higher than adsorption ratio for treatment of PCP and the degradation ratio decreased with the improvement of concentration.Laccase produced by P. ostreatus in submerged culture was purified by centrifugation. The optimum pH and temperature for crude laccase activity were 3 and 45oC, respectively. The CPs removal rate catalyzed by laccase could be improved by increasing laccase concentration, using buffer solution and adding mediator ABTS(2,2’-Azinobis-(3-ethylbenzthiazonline-6-sulphonate)). Laccase were inactivated to some degree during the removal reaction possibly due to the reaction intermediates formed. The reaction of degradation 2-CP, 2,4,6-TCP and PCP catalyzed by laccase followed the first-order reaction and the reaction activation energy were about 26.52, 33.52 and 48.19KJ/mol, respectively. |
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