| Conventional ramie fiber manufacturers employ chemical degumming process with large amount of acid and alkali, under high temperature and pressure, resulting in poor-quality fiber product and high-density wastewater that is hard to be non-polluted. Accordingly, biodegumming process was proposed and earned continuous attention in re-cent years. However, current biodegumming processes have problems such as low effi-ciency, instability and high costs. To solve above problems, microbial degumming for ramie fiber production was carried out in this study, including interaction analysis of gum in ramie bast fibers and polysaccharide-degrading enzymes, strain breeding besed on strong degumming ability, large-scale cultivation of selected strain, in-situ microbial degumming of ramie bast fibers and degumming mechanism studies. The goal of this study is a development of microbial degumming technology for ramie fiber production and its scale-up, achieving cleaner production in this field. The main results are as below:(1) A bacterium with strong ability to degum was obtained. A screening strategy was developed by interaction analysis of gum in ramie bast fibers and polysaccha-ride-degrading enzymes. The strains were further screened by ultraviolet and chemical mutations, and an ideal bacterium was selected. The strain was identified and named Ba-cillus sp. HG-28.(2) The industrial-scale cultivation technology for Bacillus sp. HG-28was studied and developed. The optimal medium composition is30g/L glucose,20g/L (NH4SO230g/L soybeen meal,8g/L NaCl,0.2g/L K2HPO4and0.1g/L MgSO4. The optimal culture condition is36℃, initial pH7.5, and180r/min revolution frequency. At a condition of6%(V/V) inoculum, the optimal time for both cultivation stages were4.5and6h, and the bacterial concentration reached1.85×1010CFU/mL, eventually.(3) The industrial-scale pretreatment technology for microbial degumming was stud-ied and developed. The four main pretreatment processes for ramie bast fibers, i.e. solvent, supersonic, mechanical rolling and high-pressure-moisture menthods, were investigated. It was identified that4s×3times for mechanical rolling combined with1.2×105Pa×15min for high-pressure-moisture treatment showed best result:the bast fiber removal rate reached3.96%; all microorganisms and fiber scraps were removed; and the treated fibers were highly dispersed and ideal for in-situ microbial degumming.(4) The in-situ microbial degumming technology for ramie fibers was established. A degumming kettle with air sparger for even distribution of the microorganisms was de-veloped. Dynamic analyses of strain growth, enzyme activities, gum contents in in-situ microbial degumming process helped to reveal microbial degumming mechanism. The optimal condition for in-situ microbial degumming are10%inoculum,1:12of materi-al-to-liquor ratio,35℃, initial pH7.6,50m3/h ventilation rate.(5) The wastewater segmental treatment and recycle for in-situ microbial degumming was developed. By analysis of wastewater characteristics from each segment, wastewater from alkaline treatment segment should be recycled for twice; wastewater from beating treatment segment should be recycled for15times; wastewater from bleaching treatment segment should be recycled for3times and then pumped into alkaline and beating seg-ments for reutilization. The result was verified in a7t kettle, and the total wastewater volumn was just28.4%of that from chemical degumming process.(6) According to the results of in-situ microbial degumming in industrial scale, the residual gum content of degummed ramie fibers decreased to1.81%, the bundle breaking tenacity reached5.09cN/dtex. Additionally, the consumption of chemicals, water, energy and wastewater COD were significantly reduced to10%,35%,36%and13.2%, proving superior to chemical process and an excellent environmental friendliness, and the produc-tion costs sharply decreased. This study provides a sustainable alternative for the conven-tional chemical degumming industry. |
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