Study On The Characteristic Of Alkaline Black Liquor Treatmented With A Acid-producing Aspergillus Niger

Black liquor is a kind of industry wastewater with high COD, high concentration of lignin and high pH. The removal of lignin is the bottleneck problem of black liquor treatment. This paper aims to study the method of biological acidation precipitation in which organic acid is produced by acid-producing bacteria from cheap carbon resources to extract lignin from black liquor.We have already acquired an Aspergillus niger strain M1, screening from 50 fungus, that has the characteristic of producing acid by decomposing starch and cellulose in straw. The characterization of cellulase and glucoamylase produced by strain M1 and relations between enzyme and producing acid were studied. Cellulase and glucoamylase production were carried out with strain M1. The results showed that cellulose and starch were degraded and transformed to organic acid through cellulase and glucoamylase. The enzymes produced by strain M1 exhibited high enzyme activities, and the highest cellulose activity as well as glucoamylase of the supernatant of the culture amounted to 0.36IU/ml and 0.42IU/ml respectively on the second and the 10th day. The study on the effect of lignin on producing cellulase and amylase by strain M1 showed that lignin from black liquor was beneficial to cellulase production by strain M1, but it had the slow-release effect of producing amylase by strain M1.The enzymatic properties of strain M1 were studied. The optimum temperatures of cellulase and glucoamylase were 40℃and 60℃,and the optimum pH values were 6 and 4 respectively.The study on the acid production characteristic of strain M1 in black liquor process showed that the highest pH value and the highest COD which the fungi could endure were 11 and 75000mg/l. There were enough nitrogen sources for strain M1 to grow and produce acid in black liquor. Moreover, the additional nitrogen source showed no promoting effect on the acid production by strain M1 in black liquor process. The optimum temperature for acid production by strain M1 was 34℃. The removal rates of chroma and COD were above 90% and 70% after continually treating black liquor for 4 times respectively under the condition of culture temperature 34℃,initial pH 9, initial load 48000mg/l and mass concentration of straw 15g/L or that of starch 5g/L.Altogether, Aspergillus niger strain M1 could produce organic acid effectively, and it was feasible to treat black liquor by strain M1.This might be a new and economical method for black liquor treatment.