Effect Of Aspergillus Niger Treatment On Papermaking White Water

White water circulated and returned to system can provide the benefits of lower effluent treatment costs, energy savings and lower chemical costs. However, less fresh water enters and more of white water is recycled, various dissolved and colloidal substances (DCS) will accumulate in the mill process waters. Many DCS are detrimental to both the papermaking wet end process and the quality of the resulting paper products.The DCS main come from lipophilic extracts and carbohydrate substance, such as fatty acid, resin acid glyceride and pectins. Because these substances have anion charges, the DCS accumulation is a serious problem in papermaking with mechanical pulp.The method of treatment on whitewater is mainly by using cationic polymerization to neutralize the anion charges of DCS. However, it not only costs much money, but also increases the difficulty of the papermaking course.Enzyme has these advantages: high effectivity, reaction condition mildly, environment friendly, it is tried to use to solve the problems of bio-pulping, pitch trouble, improve the fiber properties, bio-bleach and waste water treatment.Commodity enzymes activities holded short time in the white water .Nonrenrwablity and higher cost restrict the use of commodity enzymes in the papermaking process.Aspergillus niger is an important fermentation industry microorganism. It can product different enzymes in different mediums. Whitewater, especially Mechanical pulps Whitewater can provide nutrients for Aspergillus niger. While, the enzymes produced by Aspergillus niger can catalysis and resolve the DCS, reduce the cation demand (CD) of white water, lower effect caused by whitewater closed. The study has theory and practice sense.First, the method measured the activity of pectinase ,xylanase ,celluase was used to screen the Aspergillus niger strains, the results showed, the pectinase , xylanase , celluase activities of M1 ,M2 ,M3 were higher than KC1 ,KC2, KC3. The activity of pectinase of M1, M2 and M3 was ten times higher than KC1, KC2 and KC3. While,the activity of xylanase was 15 times higher. The activity of celluase was 3 times higher.M1 is the highest of pectinase activity, 100.5IU/ mL.M2 is shortly weaker than M1, 1072.9 IU/ mL.M3 is 1050.5 IU/ mL. Thus, we choose M1 as the best strain to optimize culture medium and treatment on whitewater.Secondly, the existing medium was optimized to achieve the requirement of whitewater treatment. The culture condition was changed, temperature, pH, inoculation volume, loaded liquid volume, carbon source, nitrogen source. The results showed, the best culture medium composition was bran 10-20 g/L, glucose 20g/L, (NH4)2SO4 15.0g/L, KH2PO4 3.0 g/L, MgSO4·7H2O 1.0 g/L, pH=4.0.The best fermentation temperature is 30℃, the best inoculation volume was 5%, and loaded liquid volume 50 mL. After optimization, the pectinase activity increased 168.7 IU/mL, to 1279.2IU/mL. The xylanase activity was 722.2 IU/mL, and the celluase activity was 232.0 IU/mL.Thirdly, the Aspergillus niger was cultured in the whitewater. The enzymes activities and the changes of the whitewater characters were measured to discuss the the effects on whitewater treatment by Aspergillus Niger. The results showed, Aspergillus niger could grow in the whitewater. The enzymes activities were improved as the increase of cycle indexes. The pectinase, xylanase, celluase activities achieved the maxima in the 24-36 hours, 1219.3 IU/mL, 1218.4 IU/mL and 253.2 IU/mL separately. The CD and COD of the APMP whitewater reduced 37.1% and 37.9%. And the DCS water reduced 49.4% and 28.0%. The GC-MC analysis results indicated that M1 can product bio-enzymes.these enzymes can effectively break down lignin derivatives, pitches and pectins. The whitewater treated by M1 had more small molecules decomposition products, such as aniline, glycerol, propane, acid and sugar substances.At last, we choose different mechanical pulps whitewater to culture Aspergillus niger. In the 24-36 hours, the pectinase, xylanase, celluase activities achieved separately the maxima 1219.3 IU/mL, 1218.4 IU/mL, 253.2 IU/mL and 1080.1 IU/mL, 1166.9 IU mL, 188.8 IU/mL in the APMP and BCTMP whitewater. Treatment by the Aspergillus niger, the COD and CD of three different mechanical pulps whitewater all reduced. The COD and CD of BCTMP whitewater reduced 41.7% and 58.3%. The DCS water reduced 46.6% and 59.4%. The GC-MC analysis results indicated that the BCTMP-3 white water, resin acids were oxidized, releasing from the colloidal substances. Fatty acids and high molecular weight substances were decreased.