The Study On Breeding Selection Of Lignin-degrading In Phragmites Australis And Application In Pulping

This paper is aimed at exploring the efficient lignin-degrading strains as its goal, andcommon Penicillium sp., bacteria, sulfoacid-producing Penicillium sp. and Trichoderma sp.were utilized as experimental strains and Phragmites australis as experimental materials.For purpose of obtaining effective ligin-degrading stains, four different strains werecombined to degrade lignin and the degradation rate of lignin was compared, so as todetermine the optimum strain combination. Then different mixing methods of mixedstrains, various mixing ratios and solid-to-liquid ratios were optimized to obtain theoptimal combination strains. The optimal technological condition for bio-mechanical pulpwas explored through the utilization of mixed laccase and xylanase to bleach paper pulp.The main results of this thesis are as follows:1. In this experiment, one strain was screened from soil sample of rotten tree roots andit was identified as common Penicillium sp. through microscopic examination andmolecular identification.2. Common Penicillium sp. was found to produce laccase by enzymatic determinationand the yield of its enzyme was up to55U/mL through medium component optimization.And the liquid culture fermentation condition of this strain was obtained: temperature30℃, pH value6, rotating speed170rpm, and the highest yield of enzyme activity reached59.6U/mL under these conditions, with the activity increased by12.39times comparedwith that of enzyme activity without optimization.At the same time, the protein contentwas14.67μg/mL and the lignin degradation rate was35.25%.3. Through the breeding selection of four different combination strains, the ABDcombination showed the best lignin degradation rate. The lignin content was10.66%andthe degradation rate was67.27%with the mixing ratio of A:B:D to1:4:16after eight days’treatment. The reasons may be related to their enzyme yields and the synergistic effects ofdifferent enzymes, which would have a good value in reducing investment costs inindustrial manufactures. Therefore, the three strains were chosen as the dominant straincombination.4. With the bleaching liquid by chemical methods and conditions optimized, the optimal conditions for the bleaching of pulp were shown: pulp concentration4%, hydrogenperoxide5%, EDTA2%,hydrogen peroxide1%, temperature60℃and reaction time2h.The whiteness of pulp reached48.9%and was increased by8.3%ISO, compared with theformer whiteness40.6%.5. Through the pretreatment of paper pulp bleaching by laccase, xylanase andlaccase/xylanase, the pulp brightness could reach52.1%, and with the mixing ratiooptimized and the ratio of laccase: xylanase to2:1, the whiteness was59.6%. Thewhiteness was improved by7.5%ISO, compared with the paper pulp without enzymepretreatment.6. Through the detection of bleaching effluent, CODCrvalue of waste water wasreduced and at the same time pH value showed the alkalescence by the utilization ofenzyme. That is to say, the removal rate of CODCrby mixed enzymes was reduced by20.01%, compared with that of bleaching effluent which had no pretreatment of enzymes,and the pH value was lowered from10.3±0.2to8±0.2.It comes to the conclusion that the mixed strains have obvious effects on lignindegradation and their mixed enzymes show the distinct effects for pulp bleaching, whichwill have important significance in biopulping.