Study On Bioprocess Of Alkaline Wheat Straw Pulping Black Liquor By White Rot Fungi

Most paper making industry in China takes the herbaceous material as the pulp and thus the alkaline wheat straw pulping black liquor is the main wastewater produced by paper mills. For the moment, the best process method of black liquor-chemical recovery is unsuitable for the treatment of alkaline wheat straw pulping black liquor for the characteristics of little silicon content, low caloric value and small scale. Because the investment and run expense are too high for many paper mills, the black liquor is still the main source of environmental pollution and the main difficulty in development of papermaking industry.The thesis focused on bioprocess of alkaline wheat straw pulping black liquor and provided a new technology in its treatment.It was showed in the study of characteristics of 30 strains of white rot fungi in black liquor treatment that photodissociation did not have obvious promoting effect on black liquor treatment by white rot fungi. Different species of the strains presented distinct characteristics. Strain S1B had strong ability of pH decline and it could reduce the system pH effectively from pH 7 below pH 2. Most of the lignin in the system was acidulated and the COD removal ratio reached over 60%. Strain CD4 could adjust system pH from pH3 to neutral, and the COD removal ratio reached about 50%. Strain BP2 could secrete laccase and remove almost about 80% acid-soluble lignin from the system. Strain AX2 had certain ability of acid-soluble lignin degradation. The study of fusants showed possibly synergistic effect of different strains on lignin degradation and COD removal.The study of the characteristics of strain S1B showed that the system pH, the load of black liquor and carbon resource had prominent effect on acid generation by strain S1B.The possible conditions in black liquor treatment was as follows: original system pH between pH6-7, COD under 13000mg/L, with supplementation of 0.5% carbon resource, temperature between 25℃ to 40℃ , without any salts. The study of black liquor process by strain S1B, AX2, BP2, CD4 and their mixed culture indicated that strain S1B was the major strain in the process which declined system pH effectively. Mixed culture did not improve the ability of strain S1B in resistance of high alkali and high load, and on the contrary restrain the acid generation of strain S1B. Therefore, single culture was more suitable for strain S1B in black liquor process.Strain CD4 could reduce the system COD of the filtrate of strain S1B and increase the system pH effectively. The study of different strains cultured with strain CD4 showed that the mixed culture of strain BP2 and strain CD4 removed the acid-soluble lignin of the filtrate effectively.The final process mode of black liquor by white rot fungi was decided that strain S1B was singly cultured first, then strain BP2 and strain CD4 were mixed cultured. Finally the filtrate was with the characteristics of COD between 3000-4000mg/L, pH neutral, the content of acid-soluble lignin about 0.2g/L.After the study on the effect of different aided methods, such as UV-Fenton, ultrasonic, filtration through fungal culture, acidification by alkali-proof strain, A/O process and interior electrolytic method on black liquor treatment by white rot fungi, it showed that the combination of filtration through fungal culture and acidification by alkali-proof strain was the better pre-processing. And consequently 50% black liquor was absorbed and the system pH was declined from pH12-13 to pH6. The combination of A/O process and interior electrolytic method was the better post-processing which declined the system COD under 200mg/L.After the study of scale up of different unit operations, the process technology of black liquor was achieved: filtration through fungal culture- acidification by alkali-proof strain-acidulation by acid generation by white rot fungi-pH adjustment with - A/O process-interior electrolytic method. And after 20-day continuous process the black liquor was treated effectively.The characteristic of pH adjustment...