Study On Mechanism Of Wheat Straw Bio-CMP Pulping And Efficient Wastewater Treatment Technology

At present,the production raw materials of domestic paper-making enterprises are mainly imported fiber raw materials,and the annual import volume of primary pulp and waste paper ranks first in the world.However,the restrictions on waste paper import policies in 2017 have dramatically reduced the number of China's waste paper imports,and there was a shortage of paper-making raw materials.Enterprises that mass produce industrial product packaging will face serious threats.China is a large straw pulp country,with abundant wheat straw resources.The full and efficient use of wheat straw resources and the development of wheat straw bio-mechanical pulp production technology without?less?pollution are of great significance to the sustainable development of the pulp and paper industry.In this paper,the white rot fungus strain Trametes sp.48424 was liquid cultured to obtain seed liquid,and the wheat straw raw material was pretreated by single screw finer and then sterilized.Then the treated wheat straw was mixed with white rot fungus seed liquid and nutrient solution for biochemical cultivation.The enzyme activity of laccase produced by white rot fungus during the growth process was measured by ultraviolet?UV?method,and the changes of the chemical composition of the wheat straw before and after biological pretreatment were discussed.Scanning electron microscope?SEM?was used to observe the morphological changes of wheat straw before and after pretreatment with white rot fungi.The cellulase method was used to extract the enzymolysis lignin?CEL?of wheat straw before and after pretreatment with white rot fungi,and the structure of wheat straw CEL was characterized by ¹³C-NMR and FT-IR.The results showed that the white rot fungus Trametes sp.48424 could self-flocculate into small and dense fungus ball under vibrational culture condations.When attached to the wheat straw for static cultivation,the white rot fungus Trametes sp.48424 adheres to the surface of the wheat straw in the form of filaments.After pretreatment with white rot fungi Trametes sp.48424,the content of holocellulose,Klason lignin,acid-soluble lignin,benzene-alcohol extractives,and ash content of wheat straw were reduced to varying degrees.It could be seen from the SEM observation that the surface of the wheat straw after the white rot fungus pretreatment was rough and uneven,with some holes,pits and peeling phenomenon,indicating that white rot fungi had degraded some components on cell wall of wheat straw.According to the FT-IR spectrum analysis of wheat straw CEL,the effect of enzymatic hydrolysis after pretreatment with white rot fungi was better than that without pretreatment.The results of ¹³C-NMR spectrum analysis of wheat straw CEL showed that the quinone structure was formed during the lignin removal process when the white rot fungi pretreated the wheat straw.During the degradation of lignin,the side chain part of the lignin structure was broken,and the?-1 and?-5 structural parts of the lignin were cracked,so that the lignin macromolecule becomes a small molecule,and the lignin dissolves in the form of a small molecule.The wheat straw before and after pretreatment with white rot fungi Trametes sp.48424 was used to prepare respectively wheat straw RMP,CMP,Bio-RMP,and Bio-CMP pulp.The fiber morphology and physical properties of wheat straw pulp under different pulping conditions were analyzed and evaluated.According to the analysis of fiber morphology,it was found that compared with wheat straw RMP and CMP,wheat straw fiber treated with white rot fungi had a longer length,a smaller width,a less content of fine fibers and a greater degree of kinking.With the increase of the dosage of alkali,the length of the fiber gradually increased,the width became smaller,the content of fine fibers decreased,and the degree of kinking increased.The paper-formation properties of different pulps were tested,and the results showed that the paper stiffness,burst strength,tensile strength and ring crushing strength of Bio-RMP and Bio-CMP pulps after white rot fungi pretreatment were significantly improved.As the dosage of alkali used increases,the paper strength of wheat straw pulp gradually increases.In the case of the same dosage of alkali,the strength of the paper of the pulp sample with the white rot fungus treatment was higher than that of the without white rot fungus treatment.When the paper strength was almost the same,the wheat straw pulp pretreated with white rot fungui could reduce the dosage of NaOH by 2%?compared to the absolutely dry wheat straw?,which could save production costs and reduce wastewater load.The water quality of waste water produced by different pulping methods was tested and analyzed.The results showed that the COD_Cr value of the waste water of wheat straw Bio-RMP pretreated with white rot fungui was lower than that of the wheat straw RMP.With the increase of the dosage of alkali,the COD_Cr of waste water produced by wheat straw pulping gradually increased,and the lignin content increased.Comparing the effects of several flocculation systems on the removal of COD_Cr from pulping waste water,the results showed that the flocculation effect using a flocculation combination of Al₂?SO₄?₃+Ca?OH?₂ was best.When the dosage of Al₂?SO₄?₃ was 1000mg/L,the dosage of Ca?OH?₂ was 1250 mg/L,the stirring time was 25min,the temperature was25?,and the pH range was 7⁸,the flocculation effect was the best,and the COD_Crr removal rate reached 41%.The S-1 bacteria and the L-1 bacteria were respectively used to aerated biological treatment of Bio-CMP pulping wastewater after flocculation.The highest removal rate of the S-1 bacteria and L-1 bacteria were about 74.6%,64.5%respectively.The COD_Cr removal effect of the S-1 bacteria on waste water was obviously better than that of the L-1 bacteria.When the aeration time was 7 days,the COD_Cr removal effect was highest.The COD_Cr of the treated effluent after the S-1bacteria aeration treatment was about 200mg/L,and he recycling of pulping wastewater can be considered.