Study On The Treatment Of Black Liquor By Acid Producing Brown Rot Fungus

Black liquor of alkali papermaking is a kind of refractory wastewater with high pH value, high COD and high concentration of lignin, which is the primary source of the wastewater from paper mills, accounting for more than 90% of total wastewater. At present, there still was not an effective and economical way to treat the black liquor derived from pulping using straw pulp as the main material.In this paper, three acid-producing strains, brown rot fungus strain S, white rot fungi 509-112 and 509-118, were obtained. The pH value could be adjusted from 7 to 2 in PDY medium using the three fungi. The acid-producing characteristics of these fungi could be maintained after continuous culturing and transferring, and they could adjust the pH value to below 3. These results showed that these fungi had high acid-producing capability.The biological acidation precipitation of black liquor treated by these fungi showed that only the strain S, maintaining the acid-producing capability, could decline the pH value to about 3 and acid-producing capability of the other two fungi was restrained in sterilized black liquor system. Furthermore, the removal rates of COD and Color in black liquor system could reach up to 60% and 80% after treating by strain S, and the strain S was screened as the predominant strain to treat black liquor. The paper also showed that inoculum had less influence on acid-producing capability of strain S in black liquor system which was not sterilized. When the initial pH ranging from 7 to 9 in medium, the strain S could adjust the pH value to around 4.5, however, the media could deeply influence the stabilization of acid-producing capability of strain S when the pH was 10. In addition, the treatment cycles would be prolonged in culture media with higher pH. The strain S could not treat the black liquor in media with black liquor (1:2.5), which attributed to acid production of the strain S was deeply restrained. Nutriment with high concentration was beneficial for acid production.The continuous treatment of black liquor by strain S with microaerobic aeration in open environment at 25℃was investigated. The results showed that the acclimated strain S could treat the black liquor effectively in the special equipment and adapt high pH value and COD. Furthermore, after acclimating for 4-5 times, the stains could treat the black liquor with pH 11. However, the acid-producing capability of strain S was inhabited by high COD deeply. In the special treatment equipment for black liquor, the strain S could treat the black liquor with pH 10 and COD 45000mg/L, the pH could be adjusted to 4.5, COD decreased to 23038.36mg/L, removal rates of lignin and color could be up 55.46% and 56.28% respectively after 3 days treatment.The treatment of mixed wastewater by strain S showed that the strain S could treat wastewater with black liquor and sweet potato starch process wastewater effectively in sterilized environment, the COD removal rate was 75%, however, the strain S could not treat the black liquor and inosine wastewater and the wastewater with black liquor and sweet potato starch process wastewater could be treated in the open environment.