Study On Competition Strategies For The Incubation Of White Rot Fungi Under Non-sterile Conditions

The non-specific extracellular ligninolytic enzymes of white rot fungi have the ability to degrade a variety of synthetic dyes. However, full-scale application of white-rot fungi for treatment of wastewater with dyestuff has not been reported under non-sterile conditions. What factors restrict the application of white rot fungi in practical projects? The bacterial contamination of incubation systems is the key factor contributing to application of white rot fungi. Once bacteria invade into the reaction systems, they can impact the growth and enzymes biosynthesis of white rot fungi, and then reduce the degradation of dyestuff sharply. However, it is obviously impractical in the actual projects to use the sterilization facilities to overcome bacterial contamination issue, because it will increase the operating cost greatly. Therefore, the bacterial contamination is a "bottle-neck" restricting the application of white rot fungi in practical projects.In order to solve the above problem, we investigated the competition strategy for the immobilized incubation of white rot fungi under non-sterile condition using carriers. The aim is to establish the controlling strategy for immobilized white rot fungus for treatment of wastewater with dyestuff under non-sterile condition. The mechanism of suppressing bacterial growth could be studied, and the foundation for ultimately solving the bacterial contamination issue could be established. Furthermore, the application process of white rot fungi was accelerated in practical engineering, which would play a greater practical role in the field of environmental protection. The results show that:(1) The optimal competition strategy for the immobilized incubation of white rot fungi was screened out from the four selected inert carriers through orthogonal experiments, in which manganese peroxidase (MnP) was regarded as the evaluation index, the material of carrier was polyurethane foam, the size of carrier was 1.0×1.0×1.0cm~3, the weight of carrier was 1.2 g, and the shape of carrier was three prismatic.(2) Compared with suspended culture, this strategy could effectively restrain microzymes, coccies, and bacillus, etc. under non-sterile condition, raise the stability of pH, increase the rate of carbon and nitrogen consumption, bring forward the period of producing enzyme and peak enzyme, increase the enzymatic activity (MnP 683U/L), achieve higher decolorization efficiency for reactive dye K-2BP under non-sterile conditions equal to sterile conditions (the decolorization rate was 68.21% in 24 h, 93.5% in 3 d, and rose by 80% than suspended culture in 3 d), and shorten the operational periods by 3 d.(3) Under non-sterile conditions, the different dyes adding time obviously influenced the growth of the white rot fungi, the combination degree between the fungi and the carrier, the effect of suppressing bacteria, the maximal enzymatic activity, and the decreasing extent and rate.(4) Under non-sterile conditions, the effect of decolorization was influenced by the different dyes adding time significantly. When the adding time was dose to the period of peak enzyme, the 24 h decolorization rate and the maximal decolorization rate of the reaction system were both high (the 24 h decolorization rates of the injecting dyes reaction system after incubated fungus for 2d, 3d and 4d were 68.21%, 57.47% and 55.60%, and the maximal decolorization rates were 94.69%, 93.65% and 88o64%, respectively). On the contrary, the rates were both low (both the decolorization rate of the 24 h and the maximum in the system of adding dyes on the 5th day were 49.57% and 57.56%, respectively). From the variation tendency of decolorization rate with the time, we could see that, the leap of decolorization rate mainly concentrate on the period of 24 hours after adding dyes, then the decolorization rate increased slowly and reached to the maximum after 48 hours.(5) Under non-sterile conditions, the optimal suppressing bacteria immobilized culture strategy could obtain an ideal decolorization rate after adding dyes in incubated fungi for 2d or 3d, so that the operational period of the optimal suppressing bacteria immobilized culture strategy was shortened to 4-5 days from 10 days.