Study On Biological Acidifieation Precipitation Of Lignin Of Pulp Mill Wastewaters

Pulp mill wastewaters is a kind of industry wastewater with high COD,high pH and high concentration of lignin.The extraction of lignin is the key problem of pulp mill wastewaters utilization. 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 pulp mill wastewaters.Yarrowia lipolytica strain J15 was acquired by acclimating and screening in pulp mill wastewaters, which can grow and produce acids in pulp mill wastewaters. The characterization of producing acid by strain J15 was studied. The organic acids were produced in tricarboxylic acid (TCA) cycle and glyoxylate cycle. The nitrogen source was a limited factor on the acid production by strain J15. Low concentration of the nitrogen source was beneficial to organic acid production, while the high concentration inhibited organic acid production. When glucose,ethanol and fatty acid was used as the single substrate or their compounds as co-substrates, citric acid and acetic acid were the main organic acids, accompany by other acids (malic, a-ketoglutaric acid, lactic acid,et al).The pH value could be reduced from 7 to 2 in the medium.Pulp mill wastewaters can inhibit the growth of Yarrowia lipolytica strain J15. When the initial pH ranging from 7 to 8 in the medium,the strain J15 could reduce the pH value to around 3.5. Moreover,the additional trace elements could promote the acid production by strain J15, and the optimum temperature for acid production by strain J15 was 30℃.The extraction of lignin from pulp mill wastewaters by strain J15 was investigated under the optimal condition of mass concentration of waste molasses 15g/L, initial pH 8 and culture temperature 30℃. The results showed that the pH value could be reduced to 3.39, extraction of rates of lignin could be up to 76.82%, removal rates of lignin color and COD could be up to 82.21% and 60.91% respectively at 96 hour.The purity of extracted lignin could be up to 70.09%.This study demonstrate that Yarrowia lipolytica strain J15 could growth and produce organic acids effectively in pulp mill wastewaters, besides it was feasible to extract lignin and treat pulp mill wastewaters.