Study On The Correlation Between Lignin Characteristic Structure And COD

The pulp and paper industry is an important basic raw material industry closely related to the development of China's national economy and social undertakings.At the same time,it is also a water-intensive industry,producing a large amount of wastewater containing pollutants.Due to the complex composition of wastewater,high concentration of pollutants,treatment The difficulty and other characteristics make wastewater treatment an important factor limiting the sustainable development of the pulp and paper industry.This paper focuses on causing the lignin,an important source of pollution in the pulp and paper industry wastewater,to study the quantitative impact of lignin on wastewater pollution load COD.Firstly,a method for quickly and accurately estimating the ThOD value of organic pollution load based on the number of C,H and O atoms in the molecular formula of known chemical substances was established.The results show that there is a good linear correlation between ThOD and ln?C+H?/O of organic compounds.The higher the oxygen content,the lower the ThOD,and the aromatic compounds are harder to be oxidized than the non-aromatic compounds.The actual COD_Cr value of organic matter was determined.It was found that the measured COD_Cr was very close to ThOD,and the relative error was less than 5%.The spiked recovery experiment further proved that the number of C,H and O atoms in the molecular formula of known organic compounds can be quickly and accurately estimated.The organic pollution load COD provides an important theoretical basis for the control and design of total aromatics and lignin pollution in the wastewater of the pulp and paper industry.The effects of different sources of lignin on the COD of organic pollution load were quantitatively studied.The purified lignin was extracted from the black liquor of eucalyptus,red pine and bagasse,and the structure of lignin was characterized.It was found that Korean pine lignin had good thermal stability;eucalyptus lignin had higher reaction.active.The lignin lignin is mainly composed of S-type structural unit structure,the oxygen content is34.328%,the weight average molecular weight is about 5493 Da,and the Korean pine lignin is mainly composed of G-type structural unit.The oxygen content is 31.531%,the weight average molecular weight is about 12,062 Da,and the bagasse lignin is mainly H-type structural unit structure,the oxygen content is 31.918%,and the weight average molecular weight is about 8849 Da.1kg of eucalyptus,red pine and bagasse lignin produced 1.476kg,1.560kg and 1.541kg of COD,respectively,and lignin had a great impact on the organic pollution load of wastewater.The actual measured values of CODCr of the three lignin are slightly lower than the theoretical value,and the actual oxidation rate is about 85%,indicating that the lignin is difficult to completely oxidize,providing important basic theoretical data for the environmental evaluation of the pulp and paper industry.Finally,three different structures of lignin model and lignin were selected for chlorine dioxide bleaching to explore the changes of its characteristic structure during bleaching and its effect on COD.It was found that the lignin activity of S-type structure was higher and the bleaching efficiency was better.The COD of wastewater from different sources of lignin reacted with chlorine dioxide increased significantly.The CODCr value of the bleached wastewater of eucalyptus lignin was the highest.The reduction rate of COD of the three lignin after bleaching is only about 15%,which indicates that chlorine dioxide can not completely oxidize and degrade lignin.Most of the degradation products remain in the bleaching waste liquid,which will clean the pulp and paper industry.Provide basic data and references for production,wastewater treatment technologies and ideas.