【作者】 龙向宇；

【导师】 龙腾锐；

【作者基本信息】 重庆大学 ， 市政工程， 2008， 博士

【摘要】 在活性污泥处理系统中,固液分离效果是系统运行中的关键问题之一,直接影响出水水质与回流污泥的浓度。胞外聚合物(Extracellular Polymeric Substances ,简称EPS)是活性污泥絮体的重要组分,广泛分布于絮体的内部与外层,对活性污泥的表面性质与絮凝沉降性能有重要的影响。然而,EPS对活性污泥絮凝性能与沉降性能影响的确切作用目前尚不清楚。以往的研究者主要从EPS的总数量、组分以及絮体的表面性质方面探讨EPS对活性污泥絮凝沉降性能的影响,没有考虑EPS自身的表面电荷与疏水性对污泥絮凝沉降性能的影响;并且大部分研究者将EPS作为一个整体进行研究,忽略了絮体内外层EPS组成与性质上的差异。论文以实验室培养的好氧活性污泥为研究对象,采用超声波法和阳离子交换树脂法,分别提取同细菌细胞疏松结合的EPS(Loosely bound EPS,简称LEPS)与紧密结合的EPS(Tightly bound EPS,简称TEPS),考察不同污泥龄(Sludge retention time,简称SRT)下它们组分和表面性质的变化,研究了EPS及其表面性质对活性污泥絮凝性能与沉降性能的影响;同时,将高SRT(15d)与低SRT(3d)活性污泥的LEPS与TEPS分别絮凝污泥悬浮液,考察LEPS与TEPS的絮凝特性与所形成生物絮体的沉降性能;最后,论文根据絮体内外层LEPS与TEPS表面性质的差异,从大分子作用力的角度出发,提出了活性污泥絮体结构模型。论文取得的主要研究成果如下:①论文采用葡萄糖-6-磷酸脱氢酶(Glucose-6-phosphate Dehydrogenase,简称G6PD)活性衡量细胞破损,较为系统地考察了超声波与阳离子交换树脂提取活性污泥EPS的方法与程序。结果表明,超声波提取过程宜采用硼酸玻璃材质的容器在冰水浴中进行,且不需要外加搅拌作用;同时,21kHz为超声波提取EPS的最佳作用频率,综合考虑提取效率与提取过程产生的细胞破损两方面的因素,超声波的作用时间不宜大于3min,作用功率适宜范围为32W～40W。国产凝胶型阳离子交换树脂001×7适于提取活性污泥中的EPS,在pH值为5.8～7.8的液相环境中,可获得比较稳定的EPS提取效果。树脂投加量80g/g VSS,搅拌速率500rmp,提取时间1h～3h为比较合适的提取程序;该条件下,EPS的提取量能达到85.2～139.9mg/gVSS,细菌细胞的破损率可控制在10%以内。在超声波与阳离子交换树脂联合使用提取活性污泥EPS的组合方式中,超声波—树脂法为最优的组合方式;该法与加热法、EDTA法、甲醛—NaOH法相比,具有提取效率高、化学污染小、细胞破损量小且操作方便的优点;对不同来源的污泥,超声波—树脂法提取得到的EPS总量可占污泥挥发份的8%～13%。②论文采用超声波与阳离子交换树脂分别提取活性污泥絮体中的LEPS与TEPS。结果表明,SRT对LEPS与TEPS的数量与表面性质有重要的影响。LEPS的数量随SRT的变化较大,当SRT由3d增加到15d时,其含量由62.7mg/g VSS降至25.6mg/g VSS,而TEPS的数量随SRT的变化不大,为80mg/g VSS左右。SRT由3d增大到20d,LEPS表面负电荷的数值先降低后略微升高,由∣-1.59meq/g EPS∣降低到∣-0.77meq/g EPS∣,SRT为15d时,LEPS有最低的表面电荷与最强的疏水性;而TEPS表面负电荷的数值随SRT的增大而变化的幅度较小,从∣-1.26meq/g EPS∣降低到∣-0.98meq/g EPS∣。对于不同SRT的活性污泥絮体,TEPS均较LEPS表现出更强的疏水性。③论文从EPS表面性质的角度探讨EPS对活性污泥的表面性质、絮凝性能与沉降性能的影响。结果表明,污泥的表面电荷主要受絮体外层LEPS的影响,LEPS的数量与表面负电荷的增大导致污泥表面负电荷增加;TEPS的疏水性较LEPS的疏水性与污泥的疏水性有更强的相关性,但其数量与污泥的疏水性关系不大。LEPS的数量与表面负电荷的增加会导致出水悬浮固体(简称ESS)升高,而TEPS的数量和表面负电荷与活性污泥絮凝性能关系不大;两种EPS疏水性的增大均有利于生物絮凝,促进絮体中颗粒物的凝聚,对应着低的ESS与高的重新絮凝能力(简称FA)。LEPS的数量及其表面性质是影响活性污泥沉降性能的重要因素,LEPS的数量与表面负电荷的增加及其疏水性的降低,对应着污泥指数(简称SVI)的升高与区域沉降速率(简称ZSV)的降低。TEPS的数量同SVI与ZSV关系不大,而其疏水性同SVI与ZSV有强的相关性,疏水性的增大对应着低的SVI与高的ZSV。④论文采用高SRT(15d)与低SRT(3d)活性污泥的LEPS与TEPS分别絮凝污泥悬浮液,探讨LEPS与TEPS的絮凝特性,考察LEPS或TEPS絮凝污泥悬浮液所形成生物絮体的沉降性能。结果表明,TEPS与LEPS在生物絮凝过程中表现出不同的絮凝特性,TEPS促进颗粒物之间的聚集,LEPS不利于生物絮凝;四种EPS所形成生物絮体的SVI值随EPS投加量的增大而增大的趋势由小至大排序依次为:15dTEPS<3dTEPS<15dLEPS<3dLEPS;同时,验证了在LEPS与TEPS的数量与表面性质对活性污泥絮凝沉降性能的影响研究中得到的大部分结论。⑤论文根据活性污泥絮体以及LEPS与TEPS分别絮凝污泥颗粒形成的生物絮体的结构图片,从大分子作用力的角度出发,提出了活性污泥絮体结构模型。模型认为高价阳离子,特别是三价阳离子(如Al3+、Fe3+),是活性污泥絮体形成的关键物质;LEPS和TEPS的数量与表面性质的变化是引起活性污泥絮体结构改变的重要因素。更多还原

【Abstract】 Solid-liuid separation is the key problem in running of activated sludge system, which influences the quality of effluent and the concentration of returned sludge. Extracellular Polymeric Substances (EPS) is an important part of activated sludge, which locates in interior and exterior of sludge flocs, and has important effect on flocculation and settlement of activated sludge. However, the exactly influence of EPS to flocculation and settlement is not clear. In the past research, the effect of EPS on flocculation and settlement of activated sludge was studied only from the total amount and components of EPS and the surface characters of the flocs, but not from the surface characters of EPS. Furthermore, most researchers took the EPS as a whole, ignoring the difference between interior EPS and exterior EPS. In the dissertation, the activated sludge in test scale system was taken as the subject investigated. At first, loosely bound EPS (LEPS) and tightly bound EPS (TEPS) were extracted by ultrasonic and cation exchange resin in turn. Subsequently, the components, amount and surface characters of LEPS and TEPS from different SRT activated sludge was tested, and the effect of them on flocculation and settlement of activated sludge flocs were discussed. Whereafter, LEPS and TEPS from low or high sludge retention time(SRT) activated sludge was used to reflocculate the suspended sludge liquid respectively to testify most part of the conclusions which includes the effects of amount and surface characters of LEPS and TEPS on flocculation and settlement of activated sludge. In the end, the structural model of activated sludge flocs was proposed from the viewpoint of macromolecular force, according to the discrepancy of the LEPS and TEPS surface characters. The main conclusions are as follows:①Adopting G6PD activity to value the degree of bacteria lyses in the course of extraction,the EPS extraction method by ultrasonic and cation exchange resin was systematically discussed. Borate terrariums were suggested to be used in the process of EPS extraction by ultrasonic, and the process had better be put in the ice bath without stirring. Moreover, the best ultrasonic frequency for extracting EPS was 21 kHz. Considering the extraction efficiency and the degree of bacteria lyses in the course of EPS extraction, the ultrasonic time should be lower than 3minutes, and the suitable scope of the power should be from 32W to 40W. 001×7 cation exchange resin as the extactant was suited to extract EPS. While value of pH was from 5.8 to 7.8, the extracted amount of the EPS was stable. The appropriate process of the extraction by cation exchange resin was 80g/g VSS of the addition amount of resin, 500rmp of the stir speed and 1h～3h of stirring time. By this means, the extraction amount of EPS could achieve 85.2～139.9mg/gVSS, and the bacteria lyses percentage could be controlled under 10%. Ultrasonic plus resin extraction method was proposed, which is more efficient, less chemical pollution and bacteria lyses and easier to process than heating method, EDTA method and formaldehyde-NaOH method. From different types of sludge, the amount of EPS extracted by ultrasonic followed by resin extraction method was about 8% to 13% of the volatile constituent of sludge.②LEPS and TEPS were extracted by ultrasonic and cation exchange resin in turn for the first time. The results showed that SRT had an important influence on the amount and surface characters of LEPS and TEPS. The amount of LEPS changed greatly with the change of SRT, which decreased from 62.7mg/g VSS of 3d SRT activated sludge to 25.6 mg/g VSS of 15d SRT activated sludge, while the amount of TEPS changed a little with the change of SRT.,which was about 80mg/g VSS. While the SRT increased from 3d to 20d, the value of surface negetive charge of LEPS decreased in the beginning, then increased a little latterly, which was from∣-1.59meq/g EPS∣ to∣-0.77meq/g EPS∣. When SRT was 15d, LEPS had lowest surface negative charge value and highest hydrophobicity. By contrast, the value of surface negative charge of TEPS changed a little with the increase of SRT from 3d to 15d, which was from∣-1.26 meq/g EPS∣ to∣-0.98meq/g EPS∣. Furthermore, TEPS was more hydrophobic than LEPS for different SRT activated sludge.③The influence of EPS and it’s surface characters to the surface characters, flocculation ability and seattleability of activated sludge was discussed for the first time. Surface negative charge of activated sludge was mainly affected by the amount and surface negetive charge of LEPS, increasing with the increase of them. The hydrophobicity of sludge was more significantly related to the hydrophobicity of TEPS than that of LEPS, but less to the amount of TEPS. With the increase of the amount and surface negative charge of LEPS, ESS increased, but those of TEPS had less influence on flocculation ability of activated sludge. Furthermore, lower ESS and higher FA were significantly relateded to the increase of hydrophobicity of LEPS and TEPS. While the total amount and surface negative charge of LEPS increased or its hydrophobicity dropped, SVI increased and ZSV decreased. SVI and ZSV were not significantly related to the amount of TEPS, while hydrophobicity of TEPS had strong effect on SVI and ZSV. That was to say, higher hydrophobicity of TEPS was related to lower SVI and higher ZSV.④Suspended sludge liquid was reflocculated by LEPS and TEPS of low or high SRT activated sludge respectively, and the flocculation performance of LEPS and TEPS and settleability of the reflocculated flocs were disscused. The results showed that TEPS and LEPS had different floccultion performance, the former promote flocculation,and the latter was harmful to flocculation. With the incrcease of addition amount of four types of EPS, the upwards trend of reflocculated flocs SVI was 15dTEPS<3dTEPS<15dLEPS<3dLEPS. At the same time, the most conclusions of the influence of the amount and surface characters of LEPS and TEPS on the flocculation ability and settleability of activate sludge was verified.⑤According to the microstructure photos of activated sludge flocs and flocs reflocculated by LEPS and TEPS, and macromolecular force in interior and exterior of flocs, the structural model of activated sludge flocs was proposed. In the model, high valence cation, especially tri-valence cation, was the key component in the course of flocs forming, and surface characters of LEPS and TEPS were key factors affecting activated sludge flocs structure.更多还原