环境污染与控制中英文对照过控.doc

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英文文献
Modeling of organic pollutant destruction in a stirred2tank reactor by ozonation
CHENGJiang1 , YANG Zhuo2ru1 , CHEN Huan2qin1 , KUO C. H. 2 , ZAPPI E.M. 2
Abstract :Destruction of organic contaminants in water by ozonation is a gas2liquid process which involves ozone mass transfer and fast irreversible chemical reactions. Ozonation reactor design and process optimizing require the modeling of the gas2liquid interactions within the reactor. In this paper a theoretical model combining the fluid dynamic and reaction kinetic parameters is proposed for predicting the destruction rates of organic pollutants in a semi2batch stirred-tank reactor by ozonation. A simple expression for the enhancement factor as our previous work has been applied to evaluate the chemical mass transfer coefficient in ozone absorption. 2 ,42dichlorophenol (2 ,42DCP) and 2 ,62DCP or their mixture are chosen as the model compounds for simulating , and the predicted DCP concentrations are compared with some measured data.
Keywords : dichlorophenol destruction ; ozonation ; stirred2tank reactor ; enhancement factor
Introduction
Because of the high oxidation potential of ozone (O3 ) , ozonation has been regarded as a promising method for drinking and waste water treatment. A wide range of organic pollutants in water can be degraded by O3 , O3 combined with H2O2 or UV
light , which are known as Advanced Chemical Oxidation Processes (AOPs) . Compared to the traditional treatment technologies , such as activated carbon adsorption or biodegradation , chemical oxidation with ozone offers the advantages of
greater rate and extent of contaminant destruction. Although there are numerous reports (Hoigne , 1983 ; David , 1991) on the ozonation kinetics research regarding reaction rate constant , stoichiometric ratio and the identification of intermediates , application of these reaction kinetics to yield essential information for successful reactor and process design has not been received sufficient attention ( Yue , 1992) . This may be partly due to the lack of the chemical mass transfer coefficient of ozone in a specific reactor. It is well known that the mass transfer rate of a gaseous solute in absorption is enhanced by chemical reactions. The extent of this influence is expressed in terms of the enhancement factor , E , which is defined as the ratio of the mass transfer coefficient of the chemical absorption to that of physical absorption. In general , it is hard to determine the chemical mass transfer coefficient by experiment especially in absorption processes accompanied by complex reactions while the physical mass transfer coefficient may easily be obtained experimentally or from semi-empirical approaches. Based on the film theory Kuo (Kuo ,1982) proposed an iteration method for predicting the enhancement factor of mass transfer by ozone self2decomposition and ozonation reactions. Because the derived enhancement factor is an implicit expression , it is inconvenient in application to simulating the degradation rates of organic pollutants in an ozonation reactor.
In this paper a simple explicit expression of the enhancement factor (Cheng , 2000) relating to the Danckwerts surface renewal model in ozone absorption with a first order ozone self2decomposition and a second order ozonation or a series of parallel ozonation reactions ( ajA + Bj →pj Pj , j = 1 ,2 ⋯n) has been applied to predict the DCP destruction rate by ozonation in a semi2batch stirred tank reactor.
1 　Mathematical model
1. 1 　Destruction of one single organic pollutant in aqueous solution by ozonation
When ozone is bubbled into a semi-batch stirred tank containing one organic pollutant solution , both gas and liquid phases can be assumed well mixed. The mass balance for ozone in the gas phase can be expressed as (Qiu , 1999) :

where cA , G , cA , G,0 , cA , i and cA ,L represent the concentration of ozone in the gas bulk , in the influent stream of the reactor ,at the gas2liquid interface and in the liquid bulk respectively. H , uG , εG are the liquid height in the reactor , the velocity of
gas phase and the gas holdup fraction , respectively , and t is the absorption time. kL as is the overall volumetric ozone physical mass transfer coefficient ( kL is the physical mass transfer coefficient , as is the specific interfacial area ) , E is the enhancement factor , and their product , kL as E , denotes the chemical mass transfer coefficient as discussed above.
Because no dissolved ozone was detected in most experiments ( Kuo , 1982 ; Qiu , 1999) , i. e. cA ,L ≈0 , all the fast ozonation reactions can be assumed to complete within the liquid film. Then the depletion rate of the organic component in the liquid phase can be written as (Sotelo , 1990) :

where cB ,L refers to the concentration of organic compound B in the liquid bulk , and a is the stoichiometric ratio of the ozonation reaction. In the above two equations the interfacial concentration of ozone cA , i can be expressed as cA , i = cA , G ×Sr. The solubility ratio of ozone Sr is 0. 21 —0. 28 in the pH range of 5 —9 (Qiu , 1999) and an average value 0. 24 is adopted here.
A simple explicit expression of the enhancement factor in ozone absorption with ozone self2decomposition and a second order ozonation reaction was derived in our previous work (Cheng , 2000) based on the surface renewal model as

where DA and DB are the diffusivity of ozone and organic B respectively. k is the second order reaction constant , kd is the first order ozone self2decomposition reaction constant. It should be noted that Eq. (2) is valid only if the following condition holds M = Md + M1 [1 - ( E - 1) /Q] > 4.
1. 2 　Destruction of the mixture of organic pollutants in aqueous solution by ozonation
When two or more contaminants are present initially in the liquid , the absorption of ozone is accompanied by parallel ozonation reactions. If the competition between these reactions is considered to be dependent only on the reaction constants ,the depletion rate of organic component Bj in the liquid phase can be derived as

The mass balance for ozone A in the gas phase is the same as Eq. (1) .
For the enhancement factor in ozone absorption with parallel ozonation reactions , an approximate expression can also be deduced relating to the surface renewal model as (Cheng , 2000)

where Ej represents the supposed enhancement factor in ozone absorption accompanied by a first order ozone self2 decomposition reaction and a second order ozonation reaction of a single reactant Bj .
2 　Simulating and experimental results
2 ,42DCP and 2 ,62DCP isomers were chosen as the model compounds for simulatingwhich are the least and most reactive species with ozone in the DCP isomers respectively. Dichlorophenols have been widely used in the production of pesticides , dyes and other industrial chemicals. They are listed among the 65 priority pollutants by the EPA in the Clean Water Act of 1977. The water quality criteria recommended by the EPA for DCP is 0. 04 to 0. 5μgL - 1 . For ozone absorption in a single DCP solution , the enhancement factor E , the concentrations of DCP in the liquid bulk and ozone in the gas phase , cB ,L , cA , G , can be predicted theoretically as shown in Fig. 1 and Fig. 2. by combining Eqs. (1) , (2) and (3) and applying the numeric method of MATLAB ODE program. Some experimental results by Qiu (Qiu ,1999) are also presented in Fig. 1a and Fig. 2a. The stirred2tank reactor used in the experiment , as sketched in Fig. 3 , is composed of a glass cylinder with inner diameter of 15 cm held between the top and bottom circular stainless steel plates by eight screw rods. A four-bladed baffle of stainless steel is inserted into the reactor to increase the turbulence of the gas and liquid phases. The stirrer is a turbine impeller with 6 blades. The gas sparger , a fritted disc with a porosity of 40 to 60μm ,is connected to a glass tube through which the ozone gas is bubbled into the tank. The initial volume of the solution is 3 liters in each experiment. Under the experimental condition the stirring Reynolds number of the solution is evaluated greater than 10000 , indicating perfect mixing has been achieved.

Fig. 1 　Prediction of enhancement factor and concentration of ozone absorption in 2 ,42DCP solution
(Stir speed : 200 r/min , cA , G,0 = 0. 0002 mol/L , cB ,L ,0 = 0. 0005 mol/L , a = 2 , Sr = 0. 24)

Curve No.
Key *
pH
q , L/min
k1,L/(mol·s)
kd , s - 1
kL a , s - 1
kL ×104mPs
εG
1
■
5
1
1.2 ×106
0.0003
0. 01134
3. 8
0. 01
2
●
7
1
1. 1 ×108
0.001
0. 01134
3. 8
0. 01
3
+
9
1
7. 5 ×108
0.2
0. 01134
3. 8
0. 01
4
▲
7
1.5
1. 1 ×108
0.001
0.01605
4.76
0. 013

* experimental

Fig. 2 　Prediction of enhancement factor and concentration of ozone absorption in 2 ,62DCP solution
(Stir speed : 200 r/min , cA , G,0 = 0. 0002 mol/L , cB ,L ,0 = 0. 0005 mol/L , a = 2 , Sr = 0. 24)
Curve No.
Key *
pH
q , L/min
k1, L/(mol·s)
kd , s - 1
kL a , s - 1
kL ×104 , mPs
εG
1
■
5
1
4.0×107
0. 0003
0. 01134
3.8
0.01
2
●
7
1
1.5×109
0. 001
0. 01134
3.8
0.01
* experimental
It can be seen from Fig. 1a and Fig. 2a that the predicted concentrations agree well with the experimental results at the early period of absorption (up to 90 % consumption of DCPs) in the pH range of 5 —9. But at pH 5 , significant deviation appears with ozone absorption in 2 ,42DCP solution. This is because at pH 5 the ozonation reaction constant of 2 ,42DCP decreases and the criteria of M < 4 may be not satisfied anymore , which means ozonation reactions have not completed within the liquid film and may extend to the liquid bulk. On the other hand , the mathematical model failed to simulate the concentration behavior when DCPs decrease to a certain low level , i. e. lower than 10 %of initial concentration , and predicts a shorter treatment time required for DCP removal than that measured in experiments. This is reasonable because the model neglects the side reactions between ozone and the uncertain intermediates when oxidation of DCPs nearly completes. Part of ozone may be consumed by these intermediates and result in the longer treatment time in a real absorption process. Both experimental and prediction results in Fig. 1a indicate that as the pH increases from 7 to 9 , there are little changes in the destruction rate of 2 ,42dichlorophenol because of the limitation of ozone mass transfer. However when the gas flow rate qincreases from 1 to 1. 5 LPmin at a fixed stir speed of 200 rPmin , the oxidation rate increases greatly due to the higher ozone mass transfer rate and ozone dosage.

附录2 英文文献译文
在由臭氧搅拌反应器中有机污染物的破坏模型
摘要：由臭氧引起的水中有机污染物的破坏是一种由气体到液体的过程，这种过程涉及到臭氧群的转化和快速的不可逆的反应。臭氧反应器的设计和进程优化要求在反应器里面有气体和液体相互转换的模型。在这篇论文中一个理论上的将流体动力学和反应动力学参数相结合的模型被推荐，为了预测在一个半批次臭氧搅拌反应器中有机污染物的破坏速率。一个对我们之前工作中的增强因数的简单的表述被应用在估计在臭氧吸收中化学团转化率。2,42二氯苯酚（2,42DCP）和2,62DCP或者是他们的混合物被选择作为模拟的模型化合物，而且预计DCP聚合物是和一些可测量的数据区别开的。
关键词：二氯苯酚的破坏；臭氧；搅拌翻译器；增强因子
引言
由于臭氧的强氧化点位，臭氧被当做一个对饮用水和废水处理很有前途的方法。水中有机物污染的宽范围能够用臭氧减轻，臭氧与过氧化氢或者紫外线光相结合，这就是熟知的高级化学氧化工艺（AOPs）。相比于传统的处理技术，这样的活性碳吸附或者生物降解，臭氧化学氧化有着更快的速度和更广的污染物破坏面积的优势。虽然对臭氧氧化动力学研究方面的反应速率常数，化学计量比研究和中间体鉴定有很多的报道（Hoigne , 1983 ; David , 1991），这些反应动力学的应用成功率和反应器工艺设计基本信息没有得到足够的重视（Yue , 1992）。这个在一定程度上可能是由于在一个特定的反应器中臭氧的化学转化率的缺乏。众所周知吸收了大量气体的溶质的转化速率在化学反应中被加强。这种影响程度用增强因数E来描述，E被定义为传质的化学吸收系数与其物理吸收系数的比值。一般来说，通过实验确定化学传质系数是很难得，特别是吸收过程中伴随着混合反应，而物理传质速率可能很容易根据实验确定或者从半经验的方法中获得。
薄膜理论的基础上Kuo (Kuo ,1982)提出了一个通过臭氧自身分解和氧化来预测增强因数的迭代法。因为导出来的增强因数是一个隐含的表达式，它在臭氧氧化反应器模拟有机污染物的降解率的应用方面不方便。在这篇论文中简单明确的表达了增强因数（Cheng，2000）涉及到的在臭氧一次自我分解和二次臭氧氧化或者一系列的平行氧化反应 ( ajA + Bj →pj Pj , j = 1 ,2 ⋯n)中臭氧吸收的danckwerts 表面更新模型被应用于预测在半批次搅拌器中臭氧氧化是DCP损坏率。

数学模型
1一个单一的有机污染物在水溶液中被臭氧氧化的破坏
当臭氧变成冒搅拌釜包含一个有机污染物的解决方案,无论是气态和液态阶段可以设想充分混合，这个质量平衡为臭氧气体阶段可以表示为如下(秋,1999年)。

这里的cA , G , cA , G,0 , cA , i and cA ,L代表臭氧在大部分的气体渗流流的反应器的浓度,分别是在气液接口和液体体积，H , uG , εG是反应器,液体的高度和速度。分别是速度的气相及气率,t是吸收时间。吉隆坡的整体容积臭氧物质传热传质系数(这个是物理质系数、具体的面积),是增强因子,以及他们的产品,如E表示,这个化学质系数如上所述。
因为没有溶解臭氧是大多数实验检测(1982年),美国(郭秋冬,民国80年),即钙、L≈0,所有的快速臭氧氧化反应也可以假定的液膜内完成。然后堆积速率的有机组成部分,液相可以写成(Sotelo,1990)。

那里,L是指申请审验及认证的有机化合物的浓度的液体散货,B,是计量比臭氧氧化反应。在上述两个方程的臭氧浓度的界面,我可以表达为cA.溶解度比臭氧Sr是0。21英尺0.28的pH范围1999(5),这里是采用平均值为0.24.
增强臭氧本身在臭氧吸收分解和二阶臭氧氧化反应原理,是一个简单的显式表达式,推导出在我们先前的工作(程,2000),基于表面更新模型

那里DA和DB分别为臭氧扩散性能和有机B。 k是二次反应常数， kd是第一个命令臭氧自已分解反应常数。 值得注意的是， Eq。 只有当以下情况举行， (2)是合法的 M = Md + M1 [1 - ( E - 1) /Q] > 4.
1.2 通过臭氧氧化破坏水中有机污染物的混合溶液
　最初在液体中有两个或更多的污染,吸收臭氧是伴随着平行臭氧氧化反应。如果这些反应之间的竞争被认为是只依赖于反应速率常数,由于有机成分Bj的液相可得到

在气象中臭氧A的质量平衡是同方程（1）是一样的
　　为增强臭氧吸收与平行臭氧氧化反应，近似表达式可以推导出与表面更新模型有关,如(2000)。

其中杰代表在陪同第一的顺序臭氧 自分解 反应与 Bj 的单身反应的一个第二顺序臭氧化反应的臭氧吸收的所谓的增强因子。
2模拟和实验结果
在DCP的同分异构体中，2，42DCP和2，62DCP同分异构体被选作为分别与臭氧反应用量最少且活性最大的用于模拟的模型化合物。二氯芬已被广泛用于生产农药，染料等工业化学品。它们在1977年的清洁水法案中被美国环保署列为65个最大污染物。美国环保署推荐的水质标准是每升含DCP0. 04到0.5μg。
对于单一DCP溶液中的臭氧吸收，通过结合等式（1），（2）和（3）以及应用MATLAB ODE程序的数字化方法，增强因子E，在大多数气相和液相臭氧中DCP的浓度，cB ,L , cA , G 能够从理论上预知，如图1和2所示。邱（邱，1999）的一些实验结果也列在图 1a和图 2a中。该实验所用的stirred2tank反应堆如图3：它是由一个其内顶部和底部之间用8个螺丝杆支撑直径15厘米的圆形不锈钢板的玻璃圆筒组成的。不锈钢挡板插入反应堆，以增加气相和液相的湍流。该搅拌器是一个6刀片的涡轮叶轮。气体喷雾器，一个拥有40孔隙度为60μm熔块光盘，通过臭氧气体进入罐连接到一个玻璃管。该解决方案每个实验的初始体积为3公升。在实验条件下溶液的搅拌雷诺数评估结果为大于10000，表示已经达到完美的混合。

图1,在2，42DCP解决方案中对增强因子和臭氧吸收的预测
(搅拌转速 : 200 r/min , cA , G,0 = 0. 0002 mol/L , cB ,L ,0 = 0. 0005 mol/L , a = 2 , Sr = 0. 24)

Curve No.
Key *
pH
q , L/min
k1,L/(mol·s)
kd , s - 1
kL a , s - 1
kL ×104mPs
εG
1
■
5
1
1.2 ×106
0.0003
0. 01134
3. 8
0. 01
2
●
7
1
1. 1 ×108
0.001
0. 01134
3. 8
0. 01
3
+
9
1
7. 5 ×108
0.2
0. 01134
3. 8
0. 01
4
▲
7
1.5
1. 1 ×108
0.001
0.01605
4.76
0. 013

实验

图2,在 2 ,62DCP解决方案中对增强因子和臭氧吸收的预测
(搅拌转速: 200 r/min , cA , G,0 = 0. 0002 mol/L , cB ,L ,0 = 0. 0005 mol/L , a = 2 , Sr = 0. 24)
Curve No.
Key *
pH
q , L/min
k1, L/(mol·s)
kd , s - 1
kL a , s - 1
kL ×104 , mPs
εG
1
■
5
1
4.0×107
0. 0003
0. 01134
3.8
0.01
2
●
7
1
1.5×109
0. 001
0. 01134
3.8
0.01

实验
从图1a和2a中可以看出在5 -9 pH值范围内预测浓度与早期吸收周期的实验结果（高达90％的DCP消耗量）吻合。但在pH值5时，在2，42DCP溶液中臭氧吸收出现重大偏差。这是因为在pH 5的2，42DCP的臭氧反应常数降低，不再满足M <4标准了，这意味着臭氧反应没有在液膜内完成，并可能延伸到液态散装。另一方面，当DCP浓度下降到一定水平如初始浓度的10%以下，数学模型就不能成功模拟浓缩行为，并由此可知DCP移动的处理时间比实验测量的时间短。这是合理的，因为该模型忽略了当DCP的氧化接近完成时臭氧与不确定中间体的反应。部分臭氧被中间体消耗，这导致在真正的吸收过程中处理时间更长。无论是在图1a中预测的结果还是实验结果，都表明随着 pH值从7到9的的增加，2,42DCP的破坏率变化很小，这是由于臭氧传质速率的限制。然而，当搅拌速度固定为每分钟200 转，气体流速从每分钟1升增大到1. 5升，氧化率将大大提高，这是因为臭氧传质速率和臭氧剂量较大。