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机械类外文翻译【FY112】组装的多相生物反应器在实验室示范研究氧气在活性污泥的转化效率【PDF+WORD】【中文4800字】
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机械类外文翻译【FY112】组装的多相生物反应器在实验室示范研究氧气在活性污泥的转化效率【PDF+WORD】【中文4800字】,机械类,外文,翻译,fy112,组装,多相,生物反应器,实验室,示范,研究,钻研,氧气,活性污泥,转化,效率,效力,pdf,word,中文
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1 组装的多相生物反应器在实验室示范 :研究 氧气 在活性 污泥 的转化 效率 摘要 ： 一个凸显经济因素的简单的实验装置已经装配在真正 重要 的化学工程问题。研究了多相反应器是一种活性污泥反应器。目的是提升学生 对 多相反应器的理解 ,氧化废水、固体细菌群体所蕴含有机质和氮基板 ,在这种类型的反应堆 可转换为人类所需要的氧气。 气体弥散的一个因素的重要性在操作性能和本 ,reactorIn 覆盖每个多相工作在这里 ,学生确定这一因素的影响 ,在装配在考虑能源消耗 (经济成本 )的类型取决于使用都和操作条件下曝气器对于一个给定的曝气器提出了一个理 论模型 ,从而使得该解释结果基于如下假设 ,即气体吸收和生物化学反应的限制措施。适合做这试验数据的参数模型 ,并进行了比较 ,得到了允许每个类型的曝气器的行为 ,同时也提供一个理解的过程。 简介 ： 多相反应器的类型包括浆 ,滴流床、生物反应器 ,在这些系统中 ,反应气体与液体或气体的阶段发生在一个固体催化剂表面或表面的细菌组被称为生物絮状沉淀。多相反应器在两个或者更多的阶段是很有必要的 ,可以进行反应 。 活 性污泥工艺 (ASP)是一个典型的例子 ,对这类系统 ,它是最主要的生物过程发生在二次废水处理方法。在这个过程中 ,微生物氧 化有机碳氮 (nonoxidized 生化需氧量 )和总氮 )基体中包含 Kjeldahl 废水和用能量获得过程中形成新的微生物。同每一个多相反应器 ,在 ASP 组件之间转移 (氧转移 )注入气泡 (空气 )和固相 (生物 flocs)是至关重要的一个因素。因此 ,这个参数 ,极大地影响了工艺性能和运行费用 1,而且目前其最大化是一个研究领域的主要兴趣。 ASP 是一个 必须 的过程中使用的多相反应器的研究 gas-component因为受控条件下 (氧气 )的消耗速度是常数和数学程序 ,用于描述的过程中 ,能够简化。如前所述 ,活性污泥可以使用氧气氧化氮 有机质或 nonoxidized,包括死的微生物。这个过程叫做 “ 内源呼吸。由于微生物浓度的污泥是非常高的 ,它可以被认定在 转化率是不变的， 这个事实意味着 ,当没有 特殊的渠道， 氧速率也不变。 nts 2 氧气供给反应堆和散布到液 体 使用的曝气设备。通常使用 三种曝气步骤 : 一 )机械表面 充气器 。这些系统使用叶片的表面 ,搅拌反应器和分散空气进入液 体阶段 、生产表层和次表层的湍流 (图 1)。 二） 曝气系统。这些增氧机使用注射系统内的空气压缩机的粗、细气泡的形式 (氧气或空气 )在液体表面。这些多孔泡沫是获得使用穿孔管及其他类似的系统 (图 2)。 三） 喷射充 气器 。这些系统结合空气扩散与液体抽送。泵站系统使混合相 (废水生物flocs)+通过喷嘴总成。吸 (或 )空气压缩机介绍空气进入系统 (图 3)。 实验 该系统由一个多批曝气生物反应器的混合和不同的元素 ,这是一起使用的各种测量装置。实验的建立是显示在图 4。 这个生物反应器由一个圆柱形罐做成的 40-cm HDPE(30-cm 直径及高度 ),这是充满了活性污泥。这酒可以获得 (游离） 从任何污水处理厂。可进行试验研究两小时左右的时间运用一种活性污泥浓度 (以总悬浮固体物 )的距离接近 3000毫克 /升。的浓度污水处理厂活性污泥中典型 的范围很广 ,从 1000 5000毫克 /升 )的总悬浮固体物。因为这个原因 ,污泥用于组装可能需要被稀释 (与废水处理 )或浓了沉淀及清除的澄清区 )终于到达预期的浓度。此外 ,flocs 蕴含活性污泥很快安顿 ,为了维护中微生物的悬架 ,同时减少大气中的氧转移反应器表面 ,水下的离心泵泵头 0.6米 ,最大流量 :400 L / h)作为一种 搅拌器。 三种 表面 曝气器检验装配 一个 controlled-speed 模拟曝气器 (300到 3000股时每分钟转速 )搅拌 nts 3 (HEINDOLPH 2000年 )。得到了该风口增氧机 ,是通过将一 渔 业压缩机 (最大压力 :1.2米的水 ;最大流量 :2.5 L /分钟在标准条件下 ),一套管和 2-mm 阀 (直径 )和一些扩压器的石头上。在模拟 射 流曝气器使用液下泵连接到一根管子。 图一 表面曝气器 的增氧原理 nts 4 图二 扩压曝气器 的增氧原理 两个测量装置是用来获取实验数据进行了分析。一个氧仪表用于测量溶解氧浓度 (黄色 ),并包括一个 爆炸 YS52功率计 ,这是一种电学为测量装置能耗 ,详细描述这个装置 ,随着总是 提 出了一种支持指令物质作为一个微 PowerPoint 文 件。 图三 喷 流曝气器 的增氧原理 nts 5 图四 叶 片的实验装置 理论依据 一般来说 ,反应进行多相流反应器包括几个步骤。例如 ,在泥浆反应器在多相流动反应器(反应物气体发泡通过溶液含固体催化剂颗粒 )的存在五个步骤 2: 五个步骤 2: 1。从气 体阶段 吸附进入液 体 的 泡沫表面。 2。液相扩散的从泡面大部分的液体。 3。从散装液体扩散 的外部表面固体催化剂。 4。内部扩散反应物多孔催化剂。 5。在多孔催化剂 内部 的反应。 nts 6 每一步都可能被认为是反应整体速率一个阻力的的速度 ,所以 ,每一步都应该被人知道的为了模型反应器。多相反应器一个数学模型通常都相当复杂 ,因此要制造一个困难的一种实用的多相反应器实验室。所示的介绍中 ,一种很好的选择用于学术用途是考虑多相生物反应器。这些系统还相当类似 ,除了浆反应器固体颗粒是由微生物而不是固体催化剂颗粒。在多相生物反应 ,可能很危险认为 ,在外部物质的传输的氧 (和对固体表面工件不重要 ,因为 flocs(微生物 )的浓度非常 高。 此外 ,内部物质的传输效果是可以忽略不计的 ， 因为反应主要在 液体 表面。 根据 Henze 孙俐。 3、控制中的关键环节活性污泥工艺是氧气吸收进入的速度液相色谱与生化反应速率。为了氧气吸收的过程模型率 (资产 ),(t) 证明用于表达 : 表一 :实验进度 实验型曝气器的操作条件 1 表面曝气器转速 :1300每分钟转速 2 表面曝气器转速 :800每分钟转速 3 曝气增氧机粗气泡。 最大空气流动速度 4 曝气 增氧机细气泡。最大空气流动速度 在这个方程式中 , 传递系数质量和 价值取决于类型的曝气器和上了过程操作条件下 , 浓度在实验的条件是氧饱和度 (这个因素取决于进行浓度的污泥 ,介质的盐nts 7 度、温度、压力等 )。在这个参数实验的价值是假定常数。 这 生化反应速率 可以获得 (eq 2)加 快 耗氧速率由于微生物 (内源性衰变过程 )基板的氧化率 考虑到这一事实 ,正如前文所述 ,两者都做外部和内部质是可以忽略不计 ,整体 对一批质量平衡混合生物反应器可发展为 3中显示的情商 。 在这样 的情形不是 更多 外部基质 这个词 可以假设为零。此外 ,由于内源性衰变率也可以假定固定的时间区间应用 (3至 4小时 ),它可以假定数值的 是不变的。因此 ,eq 3即可简化的 eq 4。 该方程用于描述动态的变化研究了溶氧浓度的时候肖兰的性能。当整个曝气器是不工作 ,氧气吸收速率接近于零 ,因为 是 从大气中最小量是通过混合系统 ,其效果是考虑的术语 这 术语 将氧传质。一个用一个类似的意义参数 (尽管学生更容易理解 )是标准的氧化能力 (SOC),其定义是由 eq6。 nts 8 这个参数 ,给出了最大氧转移率 (gO2 / s)为给定类型的曝气器和操作条件。系统的效率是由一种曝气器 eq 7,在 W 是电源消耗 (在瓦 )。 操作规程 第 一 部分。测定微生物的呼吸率 。 把油箱灌满与活性污泥 (这很容易获得任何城市污水厂 )。打开压缩机和保持直到氧曝气饱和度是取得了 (7到 8毫克 /升 )。关掉压缩机混合使用和维护的液泵。氧气浓度会降低到零。 (在进行测量时间间隔 1分钟 )的溶解氧的随时间变化 ,直到要么是浓度为 1至 2毫克 /升 )达到或者最大实验时间已被用完 ,但 10分钟。这些数据将后来的研究中使用该系统。 第二部分。测定不同 充气机 的效率 。 在这一阶段的效率 ,不同 充气机 在不同的条件下 ,进行了研究。关掉任何曝气混合系统和维护使用液下泵。允许系统达到氧浓度约为 6毫克 /升。开关 充气机 (之一的操作条件其中显示于表格 1)和测量氧气在浓度随时间变化的时间间隔 (5秒 ),直到稳态条件表达式。测量功率的消耗。这些数据应该被保存以供将来使用。重复这个过程为每个曝气器系统。我们建议实验时间表表 1规定的数值被执行。 注意安全！ 活性 污泥法可以包含一些病原微生物 ;因此 ,我们建议使用乳液或其他塑料手套 ,避免卫生问题。污泥用于会众可以被处理的实验室中沉没。这些按照建议预防措施提出了建议以水环境联合会杯 4,一个著名的 作家 ,作品在国内外废水处理领域的权威 。不过 ,我们已经用了四年与这个大会超过 100名学生 ,并且在这段经历 ,我们也没有有经验的任何问题。 实验计算 nts 9 效率确定每种类型的曝气器和操作条件的影响。计算是使用微软 Excel 软件进行试算表 (如果在 7.0支撑材料 )。详细描述的使用这个电子表格的试验计算也是提供的证明材料 (微软 PowerPoint 文件 ) 在本质上 ,计算过程包括评估参数的质量平衡 (微分 eqs 4及 5)拟合实验实测得到的装配这些方程式。利用微分方程进行了求解欧拉一阶连续属性离散化方法 (见附件 ), 表 2。实验数据得到的实验 (立即给予例子 )。第 1部分 :测定微生物的呼吸率 表 3。实验数据得到的实验 (立即给予例子 )。第二部分 :测定的 Aerator1效率 nts 10 图 5。模拟实验与溶解氧数学拟合浓度之前。给出了实验数据 表 2。猜测值的 rend-dec 用于仿真是 0.001毫克 /升 s。 该算法是很容易实现在一个工作表。一个最小二乘 回归方法是用于调整价值参数。在该方法中 ,误差的平方之和 (社经地位 ,)功能 (eq 8),仿真和实验进行了比较价值观的溶解氧浓度、最小量是通过改变参数 / s 调整一下。 作为一个例子 ,表 2和 3显示一些实验数据在实验室获得一个先前的实验。 图 6。实验与 modeleled 溶解氧 concentration.数学拟合后。给出了实验数据 表 2。计算值 rend-dec 0.000714 毫克 /升 )是 s。 nts 11 在 从数据中可以计算出在表 2(哪个对应于第 1 部分的操作程序 )和均衡 5。在要实现这 一计算 ,学生必须 设 一个初始任意值 （一个值接近 0.001 是 )使用了优化算法来确定的正确的价值 (后 计算的值 0.000714毫克 /升 )得到s)。 5和 6显示数据实验结果与模拟数据随时间变化 ,两者之前之后 ,也就是由社经地位的最小化。它可以被观察到模型是非常敏感的 ,因为大这个参数当使用差异可以观察到一个错误的值的 此外 可以看出 ,正确的使用价值 导致两组数据匹配伟大的搜索性能 ,提出了一种情况 ,表明了适用性假设所用的模型中所描述的理论基础部分。 为了确定的值 和 为每个曝气器系统中 ,数据来自于表 3(对应于那些在第二部分获得的操作程序 )、 eq4,获得的价值 学生必须使用这必须值 和 系统的曝气器 (价值观的 0.01 s1和 8毫克 /升 )是代表两个 ),使用的参数 ,分别优化求解算法确定正确的价值观 (后这两个参数应用该算法 ,0.0144 s 值 1和 6.85毫克 /升 )获得随访 , 和 分别 )。数字第 7和第 8代表将实验结果与模拟数据随时间 ,两者分别之前和之后的 () 应用的优化步骤。它可以被观察到模型是非常敏感的参数值 ,所述以上时 ,使用正确的价值取向对每个参数提供了一个准确的数据匹配。再一次地 ,这个论证了该模型的适用 性假设中所讨论的理论基础部分。 nts 12 图 7 .模拟实验和数学拟合溶氧 concentration.之前。给出了实验数据见表 3。猜测用于仿真是 0.01毫克 /升 )的 s。猜测 用于仿真 :8毫克 /升 图 8 模拟实验和数学拟合后的溶解氧浓度。计算 的值是 0.0144 mg/L s. ，计算的值是 6.85 mg/L. nts 13 各种类型增氧机 图 9 .曝气器的效率在不同的系统使用的实验装置。 一旦形参的值 ,计算了该增氧机、价值 SOC 和 运用 eqs 可以计算出第 6和第 7条。 本程序为每个曝气器必须重复直到数学处理的数据是完整的 获得的价值 必须相似为所有的实验都不管增氧机使用的类型。图 9所示为例 ,所得结果对不同曝气器系统用于我们的实验装置。 结论 在这里我们描述了一个简单的装置 ,研究了天然气的色散对影响生物反应器的性能 ,已被多相聚集在我们的机构。学生的理解来解释多相反应器 ,以前的课堂教学中 ,增加是因为这些简单的实验。学生的目标是评价哪一个是最有效的在中控室内把氧气运送到系统。为了实现这个目标 ,学生必须监督溶解氧随时间 ,合适的结果数据到一个报道的数学模型。分析的结果数据将 允许的确定价值的效率 (定义为标准的氧化能力每瓦特的功率消耗 )的每一曝气器系统。 术语 溶解氧浓度在时间 t。 nts 14 氧饱和浓度 质量传递系数 氧气吸收速度 净生化反应速率 由于微生物耗氧速率的死亡 由于耗氧速率的氧化作用的 基体上 。 总和平方误差 。 氧化能力标准 V 反应器容量 W 能量功耗 曝气器系统的效率 附录 eqs 进行了分析计算的目的 ,3号和 4号必须由欧拉方程离散一阶的方法。因此 ,鑑别术语转化如下 3号和 4号 ,以便 eqs 被转换成 eqs 10号机和 11号机 nts 15 该递归方程可以很容易地输入一个表格 (见支持材料 );因此 ,学生可以解决的的微分方程 ,采用这种方法。为了尽量减少数学错误 ,整合步骤 (t) 必须非常小。我们通常推荐值设为 1,s。使用此值的误差很小给代表的成果 ,为系统行为。 1. Rodrigo, M. A.; Seco, A.; Ferrer, J.; Penya-Roja, J. M.; Valverde, J. L. Nonlinear Control of an Activated Sludge Aeration Process: Use of Fuzzy Techniques for Tuning PID Controllers. ISA Transactions, 1999, 38, 231241 2. Fogler, H.S. Elements of Chemical Reactor Engineering, 2nd ed.; Prentice-Hall: New Jersey, 1992. 3. Henze, M.; Gujer, W.; Mino, T.; Matsuo, T.; Marais G. Activated Sludge Model n2; IAWQ Scientific and Technical Report n3; IAWQ: London, 1995; ISSN 1025-0913. 4. Water Environmental Federation. Operation of Municipal Wastewater Treatment Plants. Manual of Practice No. 11, Fifth edition; Alexandria, VA, 1996 nts 毕业设计（论文） 外文翻译 题目 倒伞型曝气机有限元分析及优化设计 专业名称 机械设计制造及其自动化 班级学号 078105135 学生姓名 周梦远 指导教师 邢 普 填 表 日 期 2011 年 3 月 1 日 nts90 Chem. Educator 2002, 7, 9095 Assembly of a Multiphase Bioreactor for Laboratory Demonstrations: Study of the Oxygen-Transfer Efficiency in Activated Sludge Fernando Dorado*, Manuel Andrs Rodrigo, and Isaac Asencio Department of Chemical Engineering, University of Castilla-La Mancha, Campus Universitario s/n, 13004 Ciudad Real, Spain, fdoradoinqu-cr.uclm.es Received October 11, 2001. Accepted January 22, 2002 Abstract: A simple experimental device has been assembled with the aim of increasing students understanding of multiphase reactors and to highlight the importance of economic considerations in real chemical engineering problems. The multiphase reactor studied is an activated sludge reactor. In this type of reactor, organic matter and nitrogen substrates, which are contained in wastewater, are oxidized by solid bacterial groups that employ oxygen. Gas dispersion is a factor of critical importance in the operating performance and cost of every multiphase reactor. In the work covered here, students determine the influence of this factor on the assembly while considering that energy consumption (economic cost) depends on both the type of aerator used and the operational conditions for a given aerator. A theoretical model is proposed that allows the interpretation of the results based on the assumptions that gas absorption and biochemical reactions are the limiting steps. Experimental data are fitted to this model, and the parameters obtained allow comparison of the behavior of each type of aerator and also provide an understanding of the process. Introduction Multiphase reactors are reactors in which two or more phases are necessary to carry out the reaction. Types of multiphase reactors include slurry, trickle bed, and biological reactors and, in these systems, the reaction between the liquid and the gas phases takes place on a solid catalyst surface or on the surface of a bacterial group called biological floc. The Activated Sludge Process (ASP) is a typical example for this kind of system, and it is the main biological process occurring in secondary wastewater treatment. In this process, microorganisms oxidize organic (carbonaceous BOD) and nonoxidized nitrogen (total Kjeldahl nitrogen) substrates contained in wastewater and use the energy obtained in the process to form new microorganisms. As in every multiphase reactor, in the ASP the component transfer (oxygen transfer) between the injected gas bubble (air) and the solid phase (biological flocs) is a factor of critical importance. Thus, this parameter greatly influences the process performance and the operating cost 1, and currently its maximization is a research topic of major interest. The ASP is a good process to use in the study of multiphase reactors because under controlled conditions the gas-component (oxygen) consumption rate is constant and the mathematical procedure, which is used to describe the process, can be simplified. As stated above, activated sludge can use oxygen to oxidize organic matter or nonoxidized nitrogen, including dead microorganisms. This process is called endogenous respiration. Because the concentration of microorganisms in the sludge is very high, it can be assumed that the death rate is constant. This fact implies that when no additional substrate is added, the oxygen consumption rate is also constant. The oxygen is supplied to the reactor and dispersed into the liquid phase using aerating equipment. Three kinds of aerators are typically used: a) Mechanical surface aerators. These systems use a blade to agitate the surface of the reactor and to disperse air into the liquid phase, producing surface and subsurface turbulence (Figure 1). b) Diffuser systems. These aerator systems use compressors to inject air in the form of coarse or fine bubbles (oxygen or air) beneath the liquid surface. These porous bubbles are obtained using perforated pipes and other similar systems (Figure 2). c) Jet aerators. These systems combine air diffusion with liquid pumping. The pumping system circulates the mixed phase (wastewater + biological flocs) through a nozzle assembly. Suction (or a compressor) introduces air into the system (Figure 3). Experimental The experimental setup is shown in Figure 4. The system consists of one multiple batch bioreactor with different mixing and aerating elements, and this is used in conjunction with various measuring devices. The bioreactor consists of a cylindrical tank made of HDPE (30-cm diameter and 40-cm height), which is filled with activated sludge. This liquor can be obtained (free) from any wastewater treatment plant. The experimental study can be performed in about two hours by employing an activated sludge concentration (measured as total suspended solids) of close to 3000 mg/L. The concentration of the activated sludge in wastewater treatment plants typically ranges from 1000 to 5000 mg/L of total suspended solids. For this reason, the sludge to be used in the assembly may need to be diluted (with treated wastewater) or concentrated (by sedimentation and removal of the clarification zone) to finally reach the desired concentration. Moreover, the flocs that contain the activated sludge settle quickly and, in order to maintain the microorganisms in suspension and at the same time minimize oxygen transfer from the atmosphere into the reactor surface, a submerged centrifugal pump (pump head 0.6 m; maximum flow rate: 400 L/h ) is used as a mixer. 2002 Springer-Verlag New York, Inc., S1430-4171(02)02541-1, Published on Web 03/15/2002, 10.1007/s00897020541a, 720090fd.pdf ntsAssembly of a Multiphase Bioreactor for Laboratory Demonstrations Chem. Educator, Vol. 7, No. 2, 2002 91 Figure 1. Scheme showing the surface aerator. Figure 2. Scheme showing the diffuser aerator. Figure 3. Scheme showing the jet aerator. Three kinds of aerator are tested in this assembly. The surface aerator is simulated with a controlled-speed (300 to 3000 rpm) stirrer (HEINDOLPH 2000). The diffuser aerator is obtained by linking a fisheries compressor (maximum pressure: 1.2 m water; maximum flow rate: 2.5 L/min under standard conditions), a set of tubes and valves (2-mm diameter), and some diffuser stones. The jet aerator is simulated using a submerged pump connected to a tube. Two measuring devices are used to obtain experimental data. An oxygen meter is used to measure dissolved oxygen concentration Surface aeratorReactorMixerDiffuser aeratorPower meterJet aeratorFigure 4. Photograph of the experimental setup. (Yellow Spring YS52), and a power meter, which is an electrical device for measuring energy consumption, is also employed. A detailed description of the devices along with assembly instructions is presented in the supporting material as a Microsoft PowerPoint file. Theoretical Basis In general, reactions carried out in multiphase reactors involve several steps. For example, in slurry reactors (multiphase flow reactor in which the reactant gas is bubbled through a solution containing solid catalyst particles) there are five steps 2: 1. Absorption from the gas phase into the liquid phase at the bubble surface. 2. Diffusion in the liquid phase from the bubble surface to the bulk liquid. 3. Diffusion from the bulk liquid to the external surface of the solid catalyst. 4. Internal diffusion of the reactant in the porous catalyst. 5. Reaction within porous catalyst. Each step may be thought of as a resistance to the overall rate of reaction, so that the rate of each step should be known in order to model the reactor. A mathematical model for a multiphase reactor is usually quite complex and it is therefore difficult to fabricate one for a practical demonstration in the laboratory. As indicated in the introduction, a good alternative for academic purposes is to consider multiphase bioreactors. These systems are quite similar to slurry reactors except that the particulate matter consists of microorganisms rather than solid catalyst particles. In a multiphase bioreactor, it can be considered that the external mass transport of oxygen (and substrate) to the solid surface is not important because the concentration of flocs (micro-organisms) is very high. Moreover, the internal mass transport effect is negligible because reactions develop mainly on the surface. According to Henze et al. 3, the controlling stages in the activated sludge process are the rate of oxygen absorption into the liquid phase and the biochemical reaction rates. In order to model the oxygen absorption process rate ( )oa()rt, the following expression is used: ( )22*oa L O O() ()rt KaC C t= (1) 2002 Springer-Verlag New York, Inc., S1430-4171(02)02541-1, Published on Web 03/15/2002, 10.1007/s00897020541a, 720090fd.pdf nts92 Chem. Educator, Vol. 7, No. 2, 2002 Dorado et al. Table 1. Experiment Schedule Experiment Type of aerator Operating conditions 1 Surface aerator Rotation Speed: 1300 rpm 2 Surface aerator Rotation speed: 800 rpm 3 Diffuser aerator Coarse bubbles. Maximum air flow rate 4 Diffuser aerator Fine bubbles. Maximum air flow rate 5 Jet aerator Maximum water flow rate In this equation LK a is the mass transfer coefficient, the value of which depends on the type of aerator and on the process operating conditions, C is the oxygen concentration at time t and C is the oxygen saturation concentration at the conditions in which the experiment is performed (this factor depends on the concentration of sludge, the salinity of the medium, temperature, pressure, etc.). In the experiment the value of this parameter is assumed to be constant. 2O()t2*OThe net biochemical reaction rate ( )rr()rt can be obtained (eq 2) by adding the oxygen consumption rate due to dead microorganisms ( )end-dec()rt (endogenous decay process) to the oxidation rate of the substrate ( )substrate()rt. (2) rr end-dec substrate() () ()rt r t r t=+Taking into account the fact that, as stated above, both external and internal mass transfer are negligible, the overall mass balance for a batch mixed bioreactor can be developed as shown in eq 3. ()222O*L O O end-dec substrate()()()dC t()K aC C t r t r tdt=+ (3) In the case where external substrate is not added, the term rsubstrate(t) can be assumed to be zero. Moreover, because the endogenous decay rate can be assumed constant for the time interval used (3 to 4 hours), it can be assumed that the numerical value of is constant. Hence, eq 3 can be simplified to eq 4. end-decr()222O*L O O end-dec()(dC tKaC C t rdt=+ (4) This equation is used to describe the dynamics of the dissolved oxygen concentration when studying the performance of aerators. When the aerator is not working, the oxygen absorption rate is close to zero because mass transport from the atmosphere is minimized by the mixing system, and its effect is considered in the term. end-decr2Oend-dec()dC trdt= (5) The term LK a quantifies the oxygen mass transfer. A parameter with a similar meaning (although easier to understand for students) is the standard oxygenation capability (SOC), defined by eq 6. (6) 2*LOSOC K aVC=This parameter gives the maximum oxygen transfer rate (g of O2/s) for a given type of aerator and set of operating conditions. The efficiency of an aerator system is defined by eq 7, where W is the power consumption (in watts). SOCW = (7) Operating procedure Part 1. Determination of the Microorganism Respiration Rate. Fill the tank with activated sludge (this can be easily obtained from any municipal wastewater treatment plant). Switch on the compressor and maintain aeration until oxygen saturation is achieved (7 to 8 mg/L). Switch off the compressor and maintain mixing using the submerged pump. The oxygen concentration will decrease to zero. Take measurements (at time intervals of 1 min) of dissolved oxygen versus time, until either a concentration of 1 to 2 mg/L is reached or a maximum experimental time of 10 min has elapsed. These data will be used later in the study of the system. Part 2. Determination of the Efficiency of Different Aerators. In this stage the efficiency of different aerators, under different conditions, is studied. Switch off any aeration system and maintain mixing using the submerged pump. Allow the system to reach an oxygen concentration of approximately 6 mg/L. Switch on one of the aerators (the operating conditions of which are shown in Table 1) and measure oxygen concentration versus time (at time intervals of 5 s) until steady-state conditions are obtained. Measure the power consumption. These data should be stored for later use. Repeat this procedure for each aerator system. We suggest that the experimental schedule given in Table 1 be followed. Caution! Activated sludge can contain some pathogenic microorganisms; therefore, we recommend the use of latex or other plastic gloves to avoid sanitary problems. Sludge used in the assembly can be disposed of in the laboratory sink. These precautions are in accordance with recommendations proposed by the Water Environmental Federation 4, a well-known body that works in the field of wastewater treatment. Nevertheless, we have used this assembly for four years with more than 100 students and, in this period, we have not experienced any problems. Experimental Calculations Data obtained in the experimental section are used to determine the efficiency of each type of aerator and the influence of the operating conditions. Calculations can be performed using Microsoft Excel 7.0 spreadsheets (provided in the supporting material). A detailed description of the use of this spreadsheet for the experimental calculations is also provided in the supporting material (Microsoft PowerPoint file). In essence, the calculation procedure consists of estimating the parameters of mass balance (differential eqs 4 and 5) by fitting the experimental data obtained from the assembly to these equations. The differential equations are solved using the Euler first-order discretization method (see appendix) because 2002 Springer-Verlag New York, Inc., S1430-4171(02)02541-1, Published on Web 03/15/2002, 10.1007/s00897020541a, 720090fd.pdf ntsAssembly of a Multiphase Bioreactor for Laboratory Demonstrations Chem. Educator, Vol. 7, No. 2, 2002 93 Table 2. Experimental Data Obtained for the Experiment (Given as an Example). Part 1: Determination of The MicroOrganism Respiration Rate Time (s) Measured dissolved oxygen concentration (mg/L)0 7.24 60 7.18120 7.14180 7.10240 7.06 300 6.99360 6.94420 6.93480 6.90 540 6.89600 6.84Table 3. Experimental Data Obtained for the Experiment (Given as an Example). Part 2: Determination of The Aerator1 Efficiency Time (s) Measured Dissolved oxygen concentration (mg/L) 0 6.11 15 6.3230 6.3145 6.4460 6.53 75 6.5890 6.60105 6.63120 6.67 135 6.72150 6.74180 6.79195 6.81 6.66.76.86.977.17.27.30 200 400 600 800time (s)Dissolvedoxygenconcentration(mg/l)Experimental Data Modellized DataFigure 5. Experimental versus modeled dissolved oxygen concentration before mathematical fitting. Experimental data given in Table 2. Guess value of rend-dec used for the simulation is 0.001 mg/L s. this algorithm is very easy to implement in a spreadsheet. A least-squares regression method is used to adjust the value of the parameters. In this method, the square errors sum (SES) function (eq 8), which compares simulated and experimental values of the dissolved oxygen concentration, is minimized by changing the parameter/s to be adjusted. As an example, Tables 2 and 3 show some experimental data obtained in the laboratory for a previous experiment. The value 6.756.86.856.96.9577.057.17.157.27.257.30 200 400 600 800time (s)Dissolved oxygen concentration (mg/l)Experimental Data Modellized DataFigure 6. Experimental versus modeleled dissolved oxygen concentration. after mathematical fitting. Experimental data given in Table 2. Calculated value of rend-decis 0.000714 mg/L s. ( )222OOexperimental model1() ()ntiSES C i C i=(8) of can be calculated from data in Table 2 (which corresponds to part 1 of the operating procedure) and eq 5. In order to perform this calculation, the student must fix an initial arbitrary value of (a value close to 0.001 mgOend-decrend-decrrend-decrend-r2/Ls is representative) and use the optimization algorithm to determine the correct value of (after the calculation a value of 0.000714 mg/Ls is obtained). Figures 5 and 6 show the experimental and the simulated data versus time, both prior to and after the minimization of SES. It can be observed that the model is very sensitive to this parameter because large discrepancies can be observed when using an incorrect value of Moreover, it can be seen that the use of the correct value of leads to the two sets of data matching with great accuracy, a situation that demonstrates the applicability of the assumptions used in the model described in the Theoretical Basis section. decend-decIn order to determine the values of LK a and C for each aerator system, data from Table 3 (corresponding to those obtained in part 2 of the operating procedure), eq 4, and the obtained value of must be used. Students must fix arbitrary values of 2*Oend-decrLK a and for the aerator system (values of 0.01 s2*OC1and 8 mg/L are representative of the two parameters, respectively) and use the optimization algorithm to
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