【作者】 郑燕；

【导师】 蔡伟民；

【作者基本信息】 上海交通大学 ， 环境工程， 2008， 博士

【摘要】 生物处理技术作为一种行之有效、安全可靠的方法,在环境污染的治理中起到重要作用。目前生物处理技术的热点之一是微生物胞外多聚物(EPS)的研究。EPS安全无毒,可生物降解,降解产物对环境无害,是环境友好的生物功能材料,在日常生活、工农业生产及环境保护等诸多领域中具有广阔的应用前景。EPS是微生物分泌的高分子聚合物,由粘多糖、蛋白质、核酸等生物大分子组成,具有长链分子,其上含有大量官能团,与壳聚糖的分子结构相似。基于壳聚糖吸附重金属离子的性能以及絮凝性能的报道,本文提出了利用具有类似结构的EPS作为含重金属废水、低浊度废水净化剂的思路。本文主要的研究内容包括:从活性污泥和土壤样本中筛选高产EPS的菌株,通过生理生化实验以及16S rDNA系统学研究进行鉴定;分析培养条件对生产EPS的影响,确定产EPS的最佳环境条件和营养条件;提纯EPS,研究其物理性质及结构;通过EPS吸附Cu(II)和Cd(II)的特性及机理研究,考察EPS净化含重金属废水的能力;考察EPS对高岭土、活性炭和粉煤灰等悬浊液的去浊度能力。主要的研究结果如下:(1)从活性污泥中筛选得到一株具有高产EPS能力、且该性能传代稳定的细菌F19。通过生理生化实验以及16S rDNA分析,鉴定菌株F19为芽胞杆菌,并命名为Bacillus sp. F19。生长曲线与产EPS能力研究表明,菌株Bacillus sp. F19具有稳定的产EPS能力,在培养的第86小时,发酵液中的EPS浓度可以达到1.47 g/l。该菌株生产的EPS绝大多数分布在上清液内,容易分离提取,适合于工程应用。(2)研究了各种培养条件对菌株Bacillus sp. F19生产EPS的影响,确定了最佳环境条件和营养条件,建立EPS生产模型。单因子试验结果表明,半乳糖、蔗糖、果糖、葡萄糖均是适合F19生产EPS的碳源,有机氮源有利于EPS的生产,碱性环境、高通气量、15 %的接种率有利于EPS的合成与分泌。运用Plackett-Burman试验与中心组合试验设计,通过响应曲面法建立EPS的生产模型。结果表明,葡萄糖、酵母粉和K2HPO4对EPS的产量有显著影响。当葡萄糖、酵母粉、K2HPO4的浓度分别为30.26 g l-1、6.41 g l-1和6.65 g l-1时,模型预测的EPS产量最高,达到2.21 g l-1,是未优化时的3倍。验证实验得到的多糖浓度与预测值的误差在10 %以内。(3)利用乙醇沉淀,可以从F19的发酵液中提纯到EPS。EPS呈乳白色,含水率高,干燥后的粉末密度非常小,表面多孔,特性粘度为27.57。EPS从270℃开始热解,最后剩下10.33 %的灰分。EPS中总糖和蛋白含量分别占了总量的66.4 %和16.4 %,多糖中糖醛酸是主要成份,占EPS总量的37 %;中性糖其次,占总量的3.6 %,由葡萄糖和甘露糖组成,两者比例为1:1.2;EPS中另含有0.5 %的氨基糖。(4)研究EPS吸附Cu(II)和Cd(II)的特性及机理,探讨EPS净化重金属废水的能力。结果发现,EPS是高效的Cu(II)和Cd(II)吸附剂,对Cu(II)和Cd(II)的最大吸附量分别达到244 mg/g和148 mg/g,对Cu(II)的吸附能力大于Cd(II)。EPS对Cu(II)和Cd(II)的吸附速度很快,10分钟内可以达到吸附平衡。Cu(II)在EPS上的吸附量随着溶液pH值的升高而增加,pH 4.8时吸附量达到最大。Cd(II)在EPS上的吸附量先随溶液pH值的升高而增加,pH 6.2时吸附量达到最大,之后随着pH的继续增加而降低。两种离子的吸附过程与Langmuir以及Freundlich等温线拟合良好,二级动力学反应模型可以描述吸附过程。EPS吸附金属离子的机理研究表明,吸附Cu(II)过程中存在离子交换与氧化还原反应,吸附Cd(II)的过程中,络合机理起到了关键作用。(6) EPS对高岭土、活性炭和粉煤灰悬浊液具有良好的、独立的絮凝能力,无需金属离子作为助凝剂就能够有效去除浊度。絮凝活性随着pH的增加而降低。随着絮凝剂量的增加,絮凝率先提高,到一定阶段后保持稳定,再降低。金属离子的加入对EPS的絮凝能力没有明显影响。EPS在pH 4-8或90℃处理后,仍具有絮凝性。更多还原

【Abstract】 Bio-treatment technology has been employed as an effective and safe method for wastewater treatment and extracellular polymeric substance (EPS) has attracted much attention as a promising bio-treatment technology. EPS are characterized by abundant specie, safety, nontoxicity and without secondary pollution, and can be a highly effective water green treatment agent. EPS is a kind of biological macromolecule including proteins, glycoproteins, polysaccharides, lipids and glycolipids and are important to life process. Its molecule is catenarian with many function groups, which is similar with chitosan. Based on the report of chitosan with biosorption and flocculation properties, EPS may be another effective biosorbent or bio-flocculant.The present study dealt with the production of EPS as wastewater purifying agent and its use in treatment of metal and suspension wastewater. A strain, Bacillus sp. F19, screened from active sludge samples, was employed as the EPS producer. Response surface methodology was used for optimization of medium for EPS yield. The properties and composition of the EPS were analyzed. Biosorption capacities and mechanism of Cu(II) and Cd(II) by EPS were investigated and the flocculation ability was also researched. The main research results are as follows:(1) Strain F19 with EPS producing capability was initially isolated from activated sludge. According to the physiological, biochemical and 16S rDNA sequence characterization, it was identified as Bacillus sp. EPS was mainly secreted to the culture medium. Experiments from growth curve indicated that this strain had stable ability of producing EPS and the EPS concentration get to 1.47 g/l at 86 hour. EPS was mainly secreted to the culture medium which was beneficial to application.(2) Single factor experiment illuminated that high inoculum density and shaking rate and alkaline cultural medium were favored by the producing of EPS. Glucose, yeast extract and K2HPO4 were identified as significant factors. When the concentration of glucose, yeast extract and K2HPO4 were 30.26 g l-1,6.41 g l-1 and 6.65 g l-1, respectively, the maximum polysaccharide concentration is get and predicated to be 2.21 g l-1, which is 3 time of un-optimized.(3) EPS, showing ivory white and porous surface, was precipitated by adding of ethanol to the culture medium. EPS had high moisture content and the density of dry EPS was low. The intrinsic viscosity of EPS was 27.57. EPS was mainly a polysaccharide with total sugar and total protein content of 66.4 % and 16.4 % (w/w), respectively. The contents of neutral sugar, uronic acid and amino sugars were 3.6 %, 37.0 % and 0.5 % and the molar ratio of mannose to glucose was approximate 1.2:1.(4) The adsorption of Cu(II) and Cd(II) from aqueous solution on EPS were investigated in the respective of pH, incubation time, concentration of initial metal ions and EPS dose. The results indicated that EPS was an effective adsorbent for Cu(II) and Cd(II). The maximum adsorption amount of Cu(II) and Cd(II) were 244 mg g-1和148 mg g-1, respectively. The adsorption capacity of Cu(II) was higher than Cd(II) at the same pH. Biosorption equilibrium was established in approximately 10 min. Biosorption of Cu(II) is highly pH dependent and the maximum uptake of Cu(II) was obtained at pH 4.8. Adsorption ability of Cd(II) increased with the increasing of pH until the maximum adsorption mount was reached at pH 6.2. The adsorption process was in accordance with both Langmuir and Freundlich isotherms. The second order model was applied to examine the kinetics of the adsorption and was found to be in harmony with the kinetic data well. EPS was able to adsorb Cu(II) to the surface with the release of K+. The presence of Cu2O and Cu on EPS after sorption showed that the Cu(II) was reduced by EPS。The complex mechanism is critical in Cd(II) adsorption process. (5) EPS was effective for flocculation of kaolin, activated carbon and fly coal suspension even without presence of cations. The flocculating activities of all the three suspensions dropped with increasing pH. The relationship between the concentration of the bioflocculant and its flocculating activity showed the typical flocculation curve of the biopolymer.更多还原