Measurements To Suppress Bacteria Contamination In White-rot Fungal Reactors

White-rot fungi can secrete extracellular lignin-degrading enzymes to degrade a wide variety of recalcitrant compounds, which makes them very attractive for treating wastewater containing recalcitrant compounds. Nevertheless, there is a major problem in white-rot fungal reactors that is bacterial contamination. It inhibits normal function of fungi, and finally results in operation failure of the reactor. Two strategies are proposed to solve this problem in this paper. One is to develop a new carrier to immobilize fungal mycelium for enhancing the biomass of immobilizing mycelium and consequently keeping them competitive with the contaminating bacteria in reactor. The second one is to select ozone as the bactericide.A new carrier, the knotted cotton-thread, was designed and made. It was used to immobilize the mycelium of P. chrysosporium. The properties of the immobilized biomass were tested. The results showed that the consumption rate of glucose and the biomass (dry weight) in the immobilized culture was 1 and 0.9 times higher than that of the suspended culture, respectively. In addition, MnP was produced in immobilized culture 3 day ahead of that in the suspended culture. Furthermore, about 2.5 times higher yields of the MnP activity were obtained in immobilized culture (1469 U/L) compared with that in suspended culture (426 U/L).A convenient way, to homogenize the immobilized mycelia as the inoculum to resume their growth on the knotted cotton-thread carriers, was suggested and tested to increase the immobilized biomass. The average regrowth biomass on per carrier can be improved by this way to 0.0314 g that was higher than 0.01 g resulted from with conidiospores as inoculum.The feasibility of using ozone to suppress contaminating bacteria in the white-rot fungal reactors was tested. The results showed that MnP activity was not affected by ozone with ozone concentration of 0.98 mg/L. A novel white-rot fungal reactor system was designed and made which is characterized by having a separate ozone treatment unit coupled with the fungal reactor, by which the adverse effects of ozone on white-rot fungi can be prevented. Taguchi method was used to optimize the control conditions of using ozone to control the growth of contaminating bacteria in the white-rot fungal reactor system. The optimized parameters are reached. Based upon these work, the white-rot fungal reactor system was run continually to investigate the effectiveness of ozone suppressing contaminating bacteria, the production of MnP, and the decolorization of acid blue 45 in the system respectively. The results showed that the numbers of contaminating bacteria can be controlled at 1.18×105 CFU/mL by using ozone, at 8.4×104 CFU/mL by using ozone plus 1.7 g/L of the immobilizing fungal mycelium, which was lower than that of by using ozone plus non-immobilized mycelium(7.13×105 CFU/mL). The lowest numbers of contaminating bacteria in the reactor, 4.65×104 CFU/ mL, can be controlled by using ozone plus 4.3 g/L immobilizing fungal mycelium. The P. chrysosporium continuously produced MnP and decolourized acid blue 45.