活性污泥产酸发酵研究进展

有机物的厌氧生物处理一般经过三个阶段:水解阶段、产酸发酵阶段和产甲烷阶段;研究证明,产酸相不同发酵类型的形成对产甲烷相乃至整个工艺的稳定运行具有至关重要的作用,此外,污泥厌氧消化过程所产生的大量的挥发性脂肪酸(VFAs),如乙酸、丙酸、丁酸及戊酸等,还可作为化工原料用于发酵工业生产各种高附加值产品.近年来,产酸发酵受到越来越多的关注,该文主要对污泥产酸阶段的产酸发酵类型、产酸发酵细菌的生态学、产酸过程的影响因素和生态因子以及产酸发酵的液相末端产物VFAs的测定方法进行了论述.     

酸碱调控污泥厌氧发酵实现乙酸累积及微生物种群变化

摘要：【目的】通过对污泥厌氧发酵pH调控,研究挥发性脂肪酸的累积、产酸微生物种群变化及产氢产乙酸菌群对乙酸产生的贡献。【方法】测定不同pH条件下污泥厌氧发酵过程中挥发性脂肪酸的累积;分别应用末端限制性片段长度多态性（T-RFLP）和荧光原位杂交技术（FISH）分析产酸系统中微生物种群结构的变化及产氢产乙酸菌的数量。【结果】 pH为10.0时,有机酸和乙酸的产率在发酵结束时分别达到652.6 mg COD/g-VS和322.4 mg COD/g-VS,显著高于其它pH条件。T-RFLP结果表明,pH值为12     

初始pH值对产氢产乙酸/耗氢产乙酸两段耦合工艺定向生产乙酸的影响

以葡萄糖为底物,以经加热预处理并活化过的厌氧污泥为种泥,研究了初始pH值对产氢产乙酸/耗氢产乙酸两段耦合工艺厌氧发酵定向生产乙酸的影响。实验考察了7个初始pH值(5、6、7、8、9、10、11)条件下的底物降解、产物产生和发酵过程pH值的变化。结果表明:产氢产乙酸段初始pH值的变化不仅影响本阶段产酸,而且影响耗氢产乙酸段产酸。初始pH=5时主要进行乙醇型发酵;pH=6和7时主要进行丁酸型发酵;pH=8时混合酸型发酵类型逐渐占优势,pH=8~11时均以乙酸为主要产物,耦合系统生产乙酸最优初始pH值为10。在初始pH=8~11范围内,产氢产乙酸段初期的乙醇浓度一般较高,但到后期因乙醇被微生物进一步代谢转化成乙酸而使其含量下降。     

污泥厌氧消化产酸发酵过程中乙酸累积机制

[目的]研究污泥厌氧消化产挥发性脂肪酸(VFA)过程中的有机物碳流的转化机制,阐明乙酸累积机理。[方法]研究溴乙烷磺酸盐(BES)和氯仿(CHCl3)抑制模型下中间代谢产物和气体的累积,检测各产乙酸功能菌群数量,推断污泥产酸发酵过程中的有机物碳流方向和乙酸累积机理。[结果]BES模型乙酸浓度达27 mmol/L,fhs基因拷贝数比对照组高2-3倍,产氢产乙酸菌略有下降。CHCl3模型乙酸浓度达22 mmol/L,fhs基因拷贝数比BES组低一个数量级,产氢产乙酸菌下降明显。[结论]BES特异性较高,除产甲烷菌外对其他厌氧产酸细菌没有影响,乙酸浓度增加并且其主要来源于水解发酵产酸以及同型产乙酸过程。氯仿除抑制产甲烷菌外,对同型乙酸菌和产氢产乙酸菌也有强烈的抑制作用。     

酒色着色菌利用产酸克雷伯氏菌发酵废液产氢

研究了酒色着色菌(Chromatiumvinosum DSM185)利用产酸克雷伯氏菌(Klebsiellaoxytoca HP1)发酵产氢废液进行光发酵和暗发酵产氢的可行性,以达到对产氢底物的充分利用和对产氢废液的进一步处理。研究结果表明C.vinosum可以利用K.oxytoca的发酵废液进行光发酵产氢和暗发酵产氢。C.vinosum发酵产氢后废液中残余还原糖和主要有机酸(丁酸)的含量明显降低,发酵产氢的最佳pH为6.5,添加0.1%(W/W)NH4Cl能促进产氢。在光照条件下丁酸利用率可达54.38%,产氢量达36.97mL/mg;在黑暗条件下丁酸利用率可达36.01%,产氢量达37.50mL/mg。     

嗜热子囊菌利用短链有机酸生产角质酶

以嗜热子囊菌(Thermobifida fusca WSH03-11)发酵生产角质酶为模型,研究微生物利用市政污泥厌氧酸化所产短链有机酸为碳源发酵生产高附加值产品的可能。发现：(1)以丁酸、丙酸和乙酸为碳源时,有机酸和氮元素浓度分别为8.0 g/L和1.5 g/L有利于角质酶的生产;而以乳酸为碳源时,最适有机酸和氮源浓度分别为3.0 g/L和1.0 g/L;(2)改变诱导物角质的浓度,以丁酸、丙酸、乙酸和乳酸为碳源,分别比优化前提高了31.0%、13.3%、43.8%和73.2%;(3)在四种有机酸中,T. fusca WSH03-11利用乙酸的速率最快,平均比消耗速率是丙酸的1.3倍,丁酸的2.0倍及乳酸的2.2倍;以丁酸为碳源时的酶活(52.4 U/mL)是乳酸的1.7倍、乙酸的2.5倍和丙酸的3.2倍;角质酶对乳酸的得率(12.70 u/mg)分别是丁酸的1.4倍、丙酸的3.0倍和乙酸的3.8倍;(4)以混合酸为碳源生产角质酶,T. fusca WSH03-11优先利用乙酸,而对丁酸的利用受到抑制。进一步研究发现,混合酸中0.5 g/L的乙酸将导致丁酸的消耗量降低66.7%。这是首次利用混合酸作碳源发酵生产角质酶的研究报道。这一研究结果进一步确证了利用市政污泥厌氧酸化所产有机酸为碳源发酵生产高附加值产品的可行性,为以廉价碳源生产角质酶奠定了良好的基础。     

嗜热子囊菌利用短链有机酸生产角质酶

以嗜热子囊菌(Thermobifida fusca WSH03-11)发酵生产角质酶为模型,研究微生物利用市政污泥厌氧酸化所产短链有机酸为碳源发酵生产高附加值产品的可能。发现：(1)以丁酸、丙酸和乙酸为碳源时,有机酸和氮元素浓度分别为8.0 g/L和1.5 g/L有利于角质酶的生产;而以乳酸为碳源时,最适有机酸和氮源浓度分别为3.0 g/L和1.0 g/L;(2)改变诱导物角质的浓度,以丁酸、丙酸、乙酸和乳酸为碳源,分别比优化前提高了31.0%、13.3%、43.8%和73.2%;(3)在四种有机酸中,T. fusca WSH03-11利用乙酸的速率最快,平均比消耗速率是丙酸的1.3倍,丁酸的2.0倍及乳酸的2.2倍;以丁酸为碳源时的酶活(52.4 U/mL)是乳酸的1.7倍、乙酸的2.5倍和丙酸的3.2倍;角质酶对乳酸的得率(12.70 u/mg)分别是丁酸的1.4倍、丙酸的3.0倍和乙酸的3.8倍;(4)以混合酸为碳源生产角质酶,T. fusca WSH03-11优先利用乙酸,而对丁酸的利用受到抑制。进一步研究发现,混合酸中0.5 g/L的乙酸将导致丁酸的消耗量降低66.7%。这是首次利用混合酸作碳源发酵生产角质酶的研究报道。这一研究结果进一步确证了利用市政污泥厌氧酸化所产有机酸为碳源发酵生产高附加值产品的可行性,为以廉价碳源生产角质酶奠定了良好的基础。     

初始底物浓度及pH对丁酸梭菌T4发酵木糖产氢的影响

本研究采用间歇培养方式对丁酸梭菌T4发酵木糖进行产氢研究,考察初始pH和初始底物浓度对其产氢特性的影响。结果表明,菌株T4在初始pH5.0～8.5及初始底物浓度5～40g/L时均可以产氢,其累积产氢量和最大比产氢速率随着pH及底物浓度的增加均呈现先增加后减少的趋势。在pH6.5和底物浓度20g/L时,比产氢速率和累积产氢量达到最大,分别为4.26L/L和18.86mmol-H2/hg-DCW,而后随着pH或者底物浓度的增加二者均呈现减少的趋势;在pH6.5和底物浓度15g/L时,得到最大值比产氢量为2.17mol/mol-木糖。而在不同的pH下,发酵产生的液态产物主要是乙酸和丁酸,其中在pH小于6.0时,有少量的丙酸生成,而在pH大于6.0时,则有乙醇生成。     

酒色着色菌利用产酸克雷伯氏菌发酵废液产氢

研究了酒色着色菌(Chromatium vinosum DSM185)利用产酸克雷伯氏菌（Klebsiella oxytoca HP1）发酵产氢废液进行光发酵和暗发酵产氢的可行性,以达到对产氢底物的充分利用和对产氢废液的进一步处理。研究结果表明C.vinosum可以利用K.oxytoca的发酵废液进行光发酵产氢和暗发酵产氢。C.vinosum发酵产氢后废液中残余还原糖和主要有机酸（丁酸）的含量明显降低,发酵产氢的最佳pH为6.5,添加0.1%(W/W)NH₄Cl能促进产氢。在光照条件下丁酸利用率可达54.38%,产氢量达36.97 mL/mg;在黑暗条件下丁酸利用率可达36.01%,产氢量达37.50mL/mg。     

产气抑制剂对污泥和食品废弃物混合发酵产酸过程的应用研究

为了提高有机酸的浓度,探讨污泥产酸工业化的可行性,考察了三种产气抑制剂对污泥和食 品废弃物混合发酵的VFA浓度及其组成、底物转化率、产气量及产甲烷势的影响.结果表明 ,采用BES、氯仿和碱(pH10)三种手段可以有效抑制发酵后期产气作用,提高底物产酸转化率,并且对有机酸组成也有一定影响.     

Production of ethanol,organic acids and hydrogen: an opportunity for mixed culture biotechnology?

Anaerobic fermentation of biodegradable organic materials is usually carried out to obtain the final product, methane, a valuable energy source. However, it is also well known that various intermediates are produced in this process, e.g. ethanol, volatile organic acids and hydrogen. All these species have applications and value as fuels or chemicals. This paper shows a critical analysis of the potential of using anaerobic fermentation by mixed cultures to produce intermediates, e.g. ethanol, acetic, lactic and butyric acid and hydrogen, rather than methane. This paper discusses the current processes to produce these chemicals and compares them with the alternative approach of using open mixed cultures to produce them simultaneously via fermentation from renewable resources. None of these chemicals is currently produced via mixed culture fermentation: ethanol and lactic acid are usually produced in pure culture fermentation using food crops, e.g. corn or sugar cane, as starting materials; hydrogen, acetic and butyric acids are mainly produced via chemical synthesis from fossil fuel derived starting materials. A possible flow-sheet for the production of these chemicals from organic waste using mixed culture fermentation is proposed and the advantages and disadvantages of this process compared to current processes are critically discussed. The paper also discusses the research challenges which need to be addressed to make this process feasible.     

Influence of Ni(2+) concentration on biohydrogen production

In this paper, the effect of Ni(2+) concentration ranging from 0 to 50mg/L on fermentative hydrogen production by mixed cultures was investigated in batch test. The results showed that at 35 degrees C and initial pH 7.0, Ni(2+) was able to enhance the hydrogen production rate with increasing Ni(2+) concentration from 0 to 0.2mg/L, and enhance the hydrogen production potential and hydrogen yield with increasing Ni(2+) concentration from 0 to 0.1mg/L. The maximum hydrogen production potential of 288.6mL and the maximum hydrogen yield of 296.1mL/g glucose were obtained at the Ni(2+) concentration of 0.1mg/L. In all tests, the major soluble metabolites produced by mixed cultures were ethanol, acetic acid and butyric acid, without propionic acid. Ni(2+) had little effect on the substrate degradation efficiency with increasing concentration from 0 to 50mg/L. Ni(2+) was able to enhance the biomass production yield with increasing Ni(2+) concentration from 0 to 0.1mg/L. The maximum biomass production yield of 232.5mg/g glucose was obtained at the Ni(2+) concentration of 0.1mg/L. In all tests, the final pH after fermentative hydrogen production was lower than the initial pH.     

Product patterns of non-axenic sucrose fermentation as a function of pH

Summary The product patterns were analyzed for sucrose, fermented by non-axenic continuous cultures, at different pH-values. At pH 4.0–4.5, ethanol was the dominant metabolite. Butyric acid dominated between pH 4.5 and 5.0 while a mixed volatile acid pattern occured at higher pH-values. Hydrogen gas production appeared to be associated with butyric acid and never represented more then 6.5 % of the reducing equivalents of the feed.     

Effect of Aloe vera whole leaf extract on short chain fatty acids production by Bacteroides fragilis, Bifidobacterium infantis and Eubacterium limosum

Aims: To investigate the effect of Aloe vera whole leaf extract on pure and mixed human gut bacterial cultures by assessing the bacterial growth and changes in the production of short chain fatty acids. Methods and Results: Bacteroides fragilis, Bifidobacterium infantis, and Eubacterium limosum were incubated with Aloe vera extracts [0%, 0·5%, 1%, 1·5% and 2%; (w/v)] for 24 and 48 h. Short chain fatty acids production was measured by gas chromatography/mass spectrometry analyses. A significant linear increase in growth response to Aloe vera supplementation was observed at 24 h for each of the bacterial cultures; however, only B. infantis and a mixed bacterial culture showed a significant positive linear dose response in growth at 48 h. In pure bacteria cultures, a significantly enhanced dose response to Aloe vera supplementation was observed in the production of acetic acid by B. infantis at 24 h and of butyric acid by E. limosum at 24 and 48 h. In the mixed bacterial culture, the production of propionic acid was reduced significantly at 24 and 48 h in a dose‐dependent fashion, whereas butyric acid production showed a significant linear increase. Conclusions: The results indicated that Aloe vera possessed bacteriogenic activity in vitro and altered the production of acetic, butyric and propionic acids by micro‐organisms selected for the study. Significance and Impact of the Study: The results of the study suggest that consumption of a dietary supplement, Aloe vera, may alter the production of short chain fatty acids by human intestinal microflora.     

Evaluation of methods for preparing hydrogen-producing seed inocula under thermophilic condition by process performance and microbial community analysis

Five methods for preparation of hydrogen-producing seeds (base, acid, 2-bromoethanesulfonic acid (BESA), load-shock and heat shock treatments) as well as an untreated anaerobic digested sludge were compared for their hydrogen production performance and responsible microbial community structures under thermophilic condition (60 degrees C). The results showed that the load-shock treatment method was the best for enriching thermophilic hydrogen-producing seeds from mixed anaerobic cultures as it completely repressed methanogenic activity and gave the a maximum hydrogen production yield of 1.96 mol H(2) mol(-1) hexose with an hydrogen production rate of 11.2 mmol H(2) l(-1)h(-1). Load-shock and heat-shock treatments resulted in a dominance of Thermoanaerobacterium thermosaccharolyticum with acetic acid and butyric acid type of fermentation while base- and acid-treated seeds were dominated by Clostridium sp. and BESA-treated seeds were dominated by Bacillus sp. The comparative experimental results from hydrogen production performance and microbial community analysis showed that the load-shock treatment method was better than the other four methods for enriching thermophilic hydrogen-producing seeds from anaerobic digested sludge. Load-shock treated sludge was implemented in palm oil mill effluent (POME) fermentation and was found to give maximum hydrogen production rates of 13.34 mmol H(2) l(-1)h(-1) and resulted in a dominance of Thermoanaerobacterium spp. Load-shock treatment is an easy and practical method for enriching thermophilic hydrogen-producing bacteria from anaerobic digested sludge.     

Isolation of an anaerobic cellulolytic mixed culture

Summary Isolation and enrichment cultures were made for anaerobic cellulose utilizing micro-organisms from non-ruminant sources. Stable mixed cultures were developed which degraded pure cellulose (wet-milled filter paper) in a defined mineral salts medium. Components of the mixed cultures lost viability in monoculture when grown on cellulose. Growth on cellulose was stimulated at low oxygen concentrations, when increased cellulase activity and increased volatile fatty acid production occurred.Low concentrations (0.1–3 mM) of cellobiose, and to a lesser extent, glucose stimulated solubilization of cellulose by the cultures, but higher concentrations had an inhibitory effect.Growth on cellulose was accompanied by production of acetic, propionic and butyric acids. The production and profile of the acids was stable and characteristic of the culture. When an open nonaseptic fermentation was employed, the fatty acid profile was variable and also included valeric acid.     

微胶囊固定化混合菌群发酵产氢——构建一种虚拟“细胞工厂”的尝试

采用硫酸纤维素钠(NaCS)/聚二甲基二烯丙基氯化铵(PDMDAAC)微胶囊体系,固定混合产氢菌群,构建成一个能高效产氢的虚拟"细胞工厂"。经过菌群活化预处理,激活了产氢活力,进一步通过NaCS/PDMDAAC微胶囊固定化,形成适宜的内部微环境,有效增强了菌群对温度的适应能力,提高了底物浓度,氢气产量比游离细胞增长30%以上,菌体浓度提高2倍到3.2g/L。连续15批培养,囊内菌体浓度显著提高,发酵时间缩短,氢气产率保持在1.73～1.81molH2/molglucose,平均产氢速率提高了198.6%。同时还发现发酵产物中有较高比例的丁酸和乙酸,由此可以使该虚拟"细胞工厂"成为一个多产物联产体系。     

Inhibitory effects of H2 on growth of Clostridium cellobioparum.

Hydrogen inhibits the growth of hydrogen-producing Clostridium cellobioparum, but not of Escherichia coli or Bacteroides ruminicola. The inhibition is reversible. When hydrogen was removed either by palladium black or by gassing out the tube, glucose utilization increased as did optical density and hydrogen production of C. cellobioparum. Removal of the H2 by methanogenic bacteria favors the growth of C. cellobioparum. Grown with Methanobacterium ruminantium in various concentrations of glucose, the Clostridium reaches a higher optical density and produces more H2 and a higher viable cell count. The cell yield is also higher than in pure culture. In mixed culture, C. cellobioparum produces more acetic acid and less lactic acid, ethanol, and butyric acid than in pure culture. The significance of this metabolic shift and hydrogen utilization in methanogenesis is discussed.