| With the change of forest resources in China,the contradiction between supply and demand of wood is becoming more and more prominent.Therefore,the efficient utilization of logging residues has been a hot topic in recent years.In the macro form,there is a great difference between logging residues and wood.However,in the micro morphology(i.e.wood fiber scale),there is little difference between logging residues and wood.It is an effective way to make use of logging residues for pulping and papermaking.However,pulping and papermaking is facing the problem of high energy consumption and serious pollution.The effective treatment of wastewater has been an important issue for the industry.Due to the large discharge,high concentration and complex composition of pulping wastewater,it is of great significance to reduce the content of organic pollutants and improve its biodegradability.In this thesis,the CMP alkali impregnation wastewater of poplar logging residues was taken as the study object.The anaerobic treatment effect of impregnation wastewater was studied before and after the laccase pretreatment,so as to provide theoretical support for the effective treatment of the pulping wastewater from logging residues.In this study,the pollution characteristics of CMP alkali impregnated wastewater of poplar wood logging residues were analyzed by infrared spectroscopy,ultraviolet spectroscopy,and GC-MS to qualitatively and quantitatively analyze the pollution components of wastewater.The contents of lignin and sugar substances were determined by spectrophotometry.The main pollutant indexes e.g.,BOD5,COD,carbon,nitrogen and phosphorescence,and analysis were quantitatively determined.In order to investigate the optimal conditions of laccase interaction with CMP alkali impregnated wastewater of poplar wood harvesting residue,the experimental design and analysis were performed using the lignin removal rate and B/C(BOD5/COD)as evaluation indexes.The optimal range of single parameter was obtained by single-factor experimental method.The experiment was optimized by response surface methodology with three factors and three levels.The best combination of action conditions was obtained through the establishment of regression equation model,and the significance test and optimization results were verified.Finally,the anaerobic treatment effects of two kinds of alkali impregnated wastewater in anaerobic reactor(UASB)were compared and analyzed,such as COD removal,gas production,volatile fatty acids,particle size and settling velocity of anaerobic granular sludge,so as to verify the effect of laccase pretreatment.The main conclusions are as follows:(1)The wastewater consisted of organic substances such as alkanes,phenols or alcohols,aromatic compounds,sugars,ethers,phenolic substances,and carboxylic acid substances.The sugars concentration in wastewater was 4.728x103 mg/L.The BOD5/COD value was 0.664.The C:N:P was 100.15:4.62:1.These data show that the wastewater has good biochemical properties.The content of pollutants(e.g.,sulfate,nitrate,nitrite and ammonia nitrogen,inhibiting the anaerobic treatment process),did not reach the inhibitory concentration.The concentration of lignin in wastewater was high,and thus laccase was needed to remove lignin in wastewater for anaerobic treatment.(2)The optimal conditions for laccase pretreatment were 157 U/L of laccase dosage,37.1782 ℃ of reaction temperature,and 4.56 h of reaction time.The results were obtained through the validation test.The maximum deviation from the predicted value was not more than 1.45%,and the optimization results were credible.The effects of various factors on lignin removal rate and B/C ratio were analyzed,and the order of influence degree was laccase dosage,reaction time,and reaction temperature.The laccase pretreatment is applied to the lignin removal rate and B/C.(3)After pretreatment with laccase,the COD value of the inlet and outlet water decreased,and the COD removal rate increased by about 40%.The laccase pretreatment avoided the accumulation of volatile fatty acids and kept the VFA concentration of effluent at about 1.75 g/L,which was conducive to the normal operation of anaerobic reactor.The gas production was enhanced by laccase pretreatment during anaerobic treatment process.The particle size and density of granular sludge in wastewater were also increased,which indicated that the coagulation of anaerobic granular sludge was enhanced,and the activity and state of microorganism in wastewater were improved.The laccase pretreatment can obviously improve the anaerobic treatment effect of CMP alkali impregnation wastewater of poplar logging residues,including improving the toxicity of wastewater,reducing the difficulty of anaerobic treatment,enhancing the operation efficiency of anaerobic reactor,improving the effluent quality,and increasing the gas production. |
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