| Lignin is a three-dimensional heteropolymer synthesized from phenylpropane units.It has three structrual units: 4-hydroxyphenyl unit,guaiacol unit,and syringyl unit.Lignin exist widely in plant cell walls,It can keep the integrity of plants and protect plants from attacking by pathogen.Lignin is the second most abundant biopolymers on Earth.Due to the molecular weight is very high and the structure is so complex,the biodegradation of lignin is difficult.Lignin is one of the main obstacles to the global carbon cycle.As one of the most recalcitrant liginin monomers,sinapic acid is the precursor of syringyl.To date,the study is very few aboat the biodegradation of sinapic acid.There are aboat 50% syringyl units in the hardwood lignin,so the study of sinapic acid biodegradation is significant for us to understand the degradation of lignin.Alkali lignin and the monomers of lignin is the main contaminants of paper-making wastewater.They can cause high COD,high color,high toxicity and hard biodegradation.Nowadays,the study of lignin biodegradation and its application in papermaking wastewater treatment is become more and more popular.As the by-product of pulping and paper-making industry,alkali lignin causes the high COD and color of pulping and paper-making wastewater.The study of alkali lignin biodegradation can help us to understand the treatment of pulping and paper-making wastewater and the lignin biodegradation.The fungus Aspergillus sp.F-1 with lignin-degrading ability was screened out by our team in the sludge of a paper mill in Yueyang last year.The previous study shows that dark black liquor(BL)can be treated by Aspergillus sp.F-1 effectivly.The highest COD and color removal were 58.2% and 50.2%,respectively.Based on the results,we predicted that Aspergillus sp.F-1 can be used to the advanced treatment of paper-making wastewater.(1)Sinapic acid is the most recalcitrant lignin model monomer,there is no study about sinapic acid degradation by fungus in 24 h till now.Based on the studies before,the study of sinapic degradation by Aspergillus sp.F-1 was carried out.The result shows that:(1)Aspergillus sp.F-1 can use sinapic acid as the sole carbon resource.(2)Compared with other experimental groups,the growth rate of Aspergillus sp.F-1 was the best when the concentration of sinapic acid was 200 mg / L,and the complete degradation of sinapic acid could be achieved in 24 h.(3)The UVand FTIR analysis revealed that the ten-hour period between 6h and 16 h was an important time for sinapic acid degradation by Aspergillus sp.F-1.The HPLC and(4)TOC analysis revealed that 99.44% degradation of sinapic and 99.12% degradation of TOC in 16 h.(5)Based on GC-MS analysis,2-methoxy-phenol and 2,6-dimethoxy-4-vinylphenol were identified as the main intermediates of sinapic acid degradation.(2)The optimum conditions of the lignin degradation by Aspergillus sp.F-1 were studied.The optimum conditions:the nitrogen source is NaNO3,,culture temperature is 30℃,the pH of culture medium is 7,the rotate speed is 150r/min.The enzyme activity of MnP and Lac were 60U/L and 1021U/L,MnP activity on the first day is the highest.At the early stage the activity of Mn P is higher than Lac activity but at the later stage the the activity of Lac is 30 times higher than MnP activity.(3)Based on the results above,the treatment of paper-making wastewater by Aspergillus sp.F-1 was studied.The optimal condition: glucose 10g/L,the quantity of inoculation 4g/L,pH 7.Under the optimal condition 38.24% color removal was observed.The enzyme activity analysis shows that the MnP and Lac were secreted during the process.The UV analysis shows that the lignin compounds in the wastewater was reducing during the process of treatment. |
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