膜生物反应器封闭循环发酵残液特性及处理技术研究
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摘要
在工业中，以玉米、小麦、薯类等含淀粉质植物及蜜糖为原料，经糖化、发酵和蒸馏的工艺制取工业乙醇，再将工业乙醇中的少量水脱除后进一步制得燃料乙醇。燃料乙醇可看成一种生物转化的太阳能，是一种取之不尽用之不竭的可再生能源。大力发展燃料乙醇能节约石油，确保国家能源安全，净化空气质量，改善环境。
燃料乙醇生物发酵生产的传统工艺，由于微生物的产物抑制特性，存在高能耗、高水耗和高污染的问题。在能源和水资源成本日益高涨、环境问题越来越受到人们关注的情况下，降低能耗、水耗和减少污染成为必须面对和解决的问题。
本研究基于自己构建的硅橡胶(PDMS)复合膜生物反应器封闭循环发酵系统，利用PDMS膜渗透汽化对乙醇的选择性分离特性，在发酵过程中实现对发酵液中产物乙醇的原位分离，减少乙醇对酵母细胞的抑制。该系统能长时间平稳运行，发酵罐中乙醇浓度、酵母浓度和乙醇产率维持稳定，乙醇产率较传统间歇发酵可提高4.5倍。但系统长期运行的周期受制于酵母细胞的老化。目前的实验连续运行记录是500小时。
本文对PDMS膜生物反应器封闭循环发酵系统发酵残液性态进行了分析研究。在系统封闭循环连续运行时，由于发酵液中作为营养物质加入的没有被完全消耗的无机盐、PDMS渗透汽化不能分离除去的发酵副产物和死细胞的长期累积，使发酵微生物的生长环境恶化，当系统运行周期结束时，发酵罐中的残液成为需要处理的发酵废弃物，其总量约为传统间歇发酵工艺的1／6，但性态差别很大。发酵残液的总固体质量为76.71g／L，固含量为7.52％，含约2％(w％)的乙醇，残液COD为1.2×10~5mg／L。发酵残液中除含有酵母细胞外，还含有蛋白质、纤维素、糖类物质、甘油、脂类、杂醇油、有机酸等很有价值的副产物。对此种残液进行后处理，有效利用废弃物并实现发酵工艺的废液零排放，成为该系统的又一主要工艺技术问题。
本文对PDMS膜生物反应器封闭循环发酵系统发酵残液的处理工艺路线和设备进行了研究。提出利用玉米酒精糟制取全蛋白饲料(DDGS)工艺作为处理PDMS膜生物反应器封闭循环乙醇发酵残液工艺的设想。残液处理回收的物质部分回到发酵罐作为培养基，部分被用于生产蛋白饲料。设想的工艺技术路线中的主要设备卧式螺旋卸料沉降离心机、多效减压浓缩蒸发器、离心喷雾干燥塔等在高浓度有机废水处理当中普遍应用，是成熟的技术设备。结合在实验室进行的实验和分析，该工艺技术设想具有一定合理性。
Ethanol could be produced with raw material which contains starch, such as corn, wheat and tapioca and molasses by saccharification, fermentation and distillation. The distillate product would be further dehydrated to become the fuel ethanol. As a substitute of fossil fuels, fuel ethanol is a perfect clean energy. It was thought as a solar energy which transformed by bioprocess. It can make sure the safety of energy sources of a country and improve air environment to some extent.
The traditional batch fermentation for ethanol production exist some disadvantages, such as high energy-consumption, high water-consumption and high waste water release. With continuously elevating energy-cost and water-cost, particularly environmental problems, we must develop an innovative fermentation technology for producing fuel ethanol.
The membrane bioreactor system for continuous fermentation was constructed based on the composite silicone rubber membrane (PDMS) with high selectivity to ethanol, which prepared in our laboratory. In this system, ethanol product was separated in situ by Pervaporation, and then inhibition of the ethanol to the yeast was reduced. The system could be steadily running for a long time. During the ferment period, ethanol and yeast concentration in the broth and the ethanol production rate were keeping steady. The ethanol production rate was 4.5 times of the conventional batch fermentation process. But the time of the continuous fermentation was limited by aging of the yeast. We could achieve a continuous ferment experiment of 500 hours.
There were cumulative inorganic salts in ferment broth, which were fed into the broth as nutriments. In addition, there were nonvolatile co-products in the broth, which could not be removed by Pervaporation. The accumulated inorganic salts, nonvolatile coproducts and dead cell were effects on the yeast cell growth. After the fermentation was ended, the residual broth must be treated with. The residual broth volume was only the one-sixth of conventional batch fermentation processes, and had much different properties. The total solid of the residual broth was 76.71g/L, corresponding to a TS concentration of 7.52%. The ethanol concentration in the residual broth was about 2% (wt), and the COD was 1.2×10~5mg/L. There were also other valuable co-products such as protein, cellulose, saccharides, glycerol, esters, fusel oil, and organic acid and so on, besides the yeast. To utilize the residual broth and achieve a zero-discharge of the waste water has become an important technical problem in the continuous fermentation system.
In this paper, the process technology for dealing with the residual broth was investigated in experiment, and the DDGS technology was imaged for the future industrial practice. The recovery byproduct from the residual was mostly used for animal feed, while the remaining was returned to the ferment system as the culture medium. We thought this technology to have considerable economic interest. This technology would need only some usual apparatus and machines, such as decanter centrifuges, multiple reduced pressure evaporators, spray dryers. These machines were proven safe and reliable in industrial practices. We could accordingly believe the imaged technology logical.
燃料乙醇生物发酵生产的传统工艺，由于微生物的产物抑制特性，存在高能耗、高水耗和高污染的问题。在能源和水资源成本日益高涨、环境问题越来越受到人们关注的情况下，降低能耗、水耗和减少污染成为必须面对和解决的问题。
本研究基于自己构建的硅橡胶(PDMS)复合膜生物反应器封闭循环发酵系统，利用PDMS膜渗透汽化对乙醇的选择性分离特性，在发酵过程中实现对发酵液中产物乙醇的原位分离，减少乙醇对酵母细胞的抑制。该系统能长时间平稳运行，发酵罐中乙醇浓度、酵母浓度和乙醇产率维持稳定，乙醇产率较传统间歇发酵可提高4.5倍。但系统长期运行的周期受制于酵母细胞的老化。目前的实验连续运行记录是500小时。
本文对PDMS膜生物反应器封闭循环发酵系统发酵残液性态进行了分析研究。在系统封闭循环连续运行时，由于发酵液中作为营养物质加入的没有被完全消耗的无机盐、PDMS渗透汽化不能分离除去的发酵副产物和死细胞的长期累积，使发酵微生物的生长环境恶化，当系统运行周期结束时，发酵罐中的残液成为需要处理的发酵废弃物，其总量约为传统间歇发酵工艺的1／6，但性态差别很大。发酵残液的总固体质量为76.71g／L，固含量为7.52％，含约2％(w％)的乙醇，残液COD为1.2×10~5mg／L。发酵残液中除含有酵母细胞外，还含有蛋白质、纤维素、糖类物质、甘油、脂类、杂醇油、有机酸等很有价值的副产物。对此种残液进行后处理，有效利用废弃物并实现发酵工艺的废液零排放，成为该系统的又一主要工艺技术问题。
本文对PDMS膜生物反应器封闭循环发酵系统发酵残液的处理工艺路线和设备进行了研究。提出利用玉米酒精糟制取全蛋白饲料(DDGS)工艺作为处理PDMS膜生物反应器封闭循环乙醇发酵残液工艺的设想。残液处理回收的物质部分回到发酵罐作为培养基，部分被用于生产蛋白饲料。设想的工艺技术路线中的主要设备卧式螺旋卸料沉降离心机、多效减压浓缩蒸发器、离心喷雾干燥塔等在高浓度有机废水处理当中普遍应用，是成熟的技术设备。结合在实验室进行的实验和分析，该工艺技术设想具有一定合理性。
Ethanol could be produced with raw material which contains starch, such as corn, wheat and tapioca and molasses by saccharification, fermentation and distillation. The distillate product would be further dehydrated to become the fuel ethanol. As a substitute of fossil fuels, fuel ethanol is a perfect clean energy. It was thought as a solar energy which transformed by bioprocess. It can make sure the safety of energy sources of a country and improve air environment to some extent.
The traditional batch fermentation for ethanol production exist some disadvantages, such as high energy-consumption, high water-consumption and high waste water release. With continuously elevating energy-cost and water-cost, particularly environmental problems, we must develop an innovative fermentation technology for producing fuel ethanol.
The membrane bioreactor system for continuous fermentation was constructed based on the composite silicone rubber membrane (PDMS) with high selectivity to ethanol, which prepared in our laboratory. In this system, ethanol product was separated in situ by Pervaporation, and then inhibition of the ethanol to the yeast was reduced. The system could be steadily running for a long time. During the ferment period, ethanol and yeast concentration in the broth and the ethanol production rate were keeping steady. The ethanol production rate was 4.5 times of the conventional batch fermentation process. But the time of the continuous fermentation was limited by aging of the yeast. We could achieve a continuous ferment experiment of 500 hours.
There were cumulative inorganic salts in ferment broth, which were fed into the broth as nutriments. In addition, there were nonvolatile co-products in the broth, which could not be removed by Pervaporation. The accumulated inorganic salts, nonvolatile coproducts and dead cell were effects on the yeast cell growth. After the fermentation was ended, the residual broth must be treated with. The residual broth volume was only the one-sixth of conventional batch fermentation processes, and had much different properties. The total solid of the residual broth was 76.71g/L, corresponding to a TS concentration of 7.52%. The ethanol concentration in the residual broth was about 2% (wt), and the COD was 1.2×10~5mg/L. There were also other valuable co-products such as protein, cellulose, saccharides, glycerol, esters, fusel oil, and organic acid and so on, besides the yeast. To utilize the residual broth and achieve a zero-discharge of the waste water has become an important technical problem in the continuous fermentation system.
In this paper, the process technology for dealing with the residual broth was investigated in experiment, and the DDGS technology was imaged for the future industrial practice. The recovery byproduct from the residual was mostly used for animal feed, while the remaining was returned to the ferment system as the culture medium. We thought this technology to have considerable economic interest. This technology would need only some usual apparatus and machines, such as decanter centrifuges, multiple reduced pressure evaporators, spray dryers. These machines were proven safe and reliable in industrial practices. We could accordingly believe the imaged technology logical.
引文
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[3] 杨崎勋．可再生能源：基于生态经济的战略思考[J]．浙江经济，2006，17：54．
[4] Ogden JM, Wiliams R H, Larson E D. Societal lifecycle costs of cars with alternative fuels/ engines [J]. Energy Policy, 2004, 32(1): 7～27.
[5] Solomon BD, Banerjee A. A global survey of hydrogen energy research development and policy [J]. Energy Policy, 2006, 34(7): 781～792.
[6] 刘海峰．乙醇燃料的发展应用现状和前景[J]．研究与探索，2004：31～33．
[7] 马赞华．酒精高效清洁生产新工艺[M]．北京：化学工业出版社，2003．1：1．
[8] 王成军，黄少杰．国外燃料乙醇工业的发展现状及其对我国的启示[J]．工业技术经济， 2005．24(5)：110～112．
[9] 许沧粟，顾洁，杜德兴．乙醇在摩托车汽油机中的试验研究[J]．内燃机工程，2003，(5)：60-62
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[13] 王凯军，秦人伟．发酵工业废水处理[M]．北京：化学工业出版社，2000，1．
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[15] Jae-Sok Kim, Byung-Gee Kim, Chung-Hak Lee et al. Development of clean technology in alcohol fermentation industry[J]. Cleaner Prod. 1997, 5(4): 263-267.
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[18] Eirsh Yu E. Revere-osmosis, Ion-exchange, and pervaporation membranes: Polyeric materials, forming methods and hydrate and transport properties[J]. A review. Russian J Appl Chem, 1993, 67 (2, part 1): 159～175.
[19] 陈翠仙，韩宾兵，朗宁·威(Ranil Wickramasinghe)．渗透蒸发与蒸气渗透[M]．北京：化学工业出版社，2004，1．
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[21] Qureshi.N, Blaschek.H.P. Butanol recovery from model solution/fermentation broth by pervaporation evaluation of membrane performance[J]. Biomass and Bioenergy, 1999, 17: 175～184.
[22] 张慧敏，肖泽仪，冯明．膜生物反应器与有机化合物的生物转化研究进展[J]．化工进展，2006，25(5)：485．
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[2] 汤士娟，付永涛．浅谈燃料乙醇生产技术进展[J]．酿酒，2002，29(5)：1．
[3] 杨崎勋．可再生能源：基于生态经济的战略思考[J]．浙江经济，2006，17：54．
[4] Ogden JM, Wiliams R H, Larson E D. Societal lifecycle costs of cars with alternative fuels/ engines [J]. Energy Policy, 2004, 32(1): 7～27.
[5] Solomon BD, Banerjee A. A global survey of hydrogen energy research development and policy [J]. Energy Policy, 2006, 34(7): 781～792.
[6] 刘海峰．乙醇燃料的发展应用现状和前景[J]．研究与探索，2004：31～33．
[7] 马赞华．酒精高效清洁生产新工艺[M]．北京：化学工业出版社，2003．1：1．
[8] 王成军，黄少杰．国外燃料乙醇工业的发展现状及其对我国的启示[J]．工业技术经济， 2005．24(5)：110～112．
[9] 许沧粟，顾洁，杜德兴．乙醇在摩托车汽油机中的试验研究[J]．内燃机工程，2003，(5)：60-62
[10] Energy Information Administration. Annual energy review 2005. DOE/EIA-0384. US Department of Energy. Washington, D C. 2006.
[11] 钱伯章．燃料乙醇的发展现状和趋势[J]．研究探讨，2006(6)：16～19．
[12] Prasad.S, Anoop Singh, Joshi.H.C. Ethanol as an alternative fuel from agricultural, industrial and urban residues[J]. Resources Conservation & Recycling 2007;50.
[13] 王凯军，秦人伟．发酵工业废水处理[M]．北京：化学工业出版社，2000，1．
[14]韩景筠，陈希海．耐高温酿酒高活性干酵母在酒精连续发酵生产中的应用[J]．酿酒科技，1998，2：71-72．
[15] Jae-Sok Kim, Byung-Gee Kim, Chung-Hak Lee et al. Development of clean technology in alcohol fermentation industry[J]. Cleaner Prod. 1997, 5(4): 263-267.
[16] 郑领英，王学松．膜技术[M]．北京：化学工业出版社，2000，2．
[17] 时钧，袁权．膜技术手册[M]．化学工业出版社，2001．
[18] Eirsh Yu E. Revere-osmosis, Ion-exchange, and pervaporation membranes: Polyeric materials, forming methods and hydrate and transport properties[J]. A review. Russian J Appl Chem, 1993, 67 (2, part 1): 159～175.
[19] 陈翠仙，韩宾兵，朗宁·威(Ranil Wickramasinghe)．渗透蒸发与蒸气渗透[M]．北京：化学工业出版社，2004，1．
[20] Lipnizki.F, Robert.W.F. Pervaporation-based hybrid process: a review of process design: applications and economics[J]. Joumal of Membrane Science, 1999, 153:183～210.
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