Kinetic control of sodium hypochlorite electrolysis process and disinfection effect in sewage treatment
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摘要:
为提升次氯酸钠电解工艺的产氯量和满足城镇污水处理站深度处理单元出水的消毒要求，从反应动力学角度，探究次氯酸钠电解工艺的电解参数如盐水浓度、电流密度和电解温度对次氯酸钠生产过程的影响，分析深度处理单元出水水质对次氯酸钠消毒效果的影响，明晰电解参数和出水水质的影响机制。结果表明：当盐水浓度、电流密度、电解温度和电解时间分别为40 g/L、20 A/dm2、32 ℃和2.5 h时，能够有效控制温度影响、析氯电位、歧化反应和活化能，并使次氯酸钠产量提高到9.28 g/L。当次氯酸钠的投加量至少为5 mg/L和控制接触反应时间为5 min时，次氯酸钠对粪大肠杆菌群的灭菌性比其对COD和氨氮的氧化性更占竞争优势，并将水样中粪大肠杆菌群数减少至102.97个/L，达到了GB 18918—2002《城镇污水处理厂污染物排放标准》一级A排放标准中细菌学指标要求。
Abstract:In order to increase the chlorine production of sodium hypochlorite electrolysis process and meet the disinfection requirements of effluent from the advanced treatment unit in township sewage treatment station, from the perspective of reaction kinetics, the influence of electrolytic parameters such as saline concentration, current density and electrolytic temperature on the production process of sodium hypochlorite was investigated, and the influence of effluent quality of the advanced treatment unit on the disinfection effect of sodium hypochlorite was analyzed, to clarify the influence mechanism of electrolytic parameters and effluent quality. The results showed that the temperature effect, chlorine evolution potential, disproportionation reaction and activation energy could be effectively controlled by adjusting the saline concentration, current density, electrolytic temperature and time to 40 g/L, 20 A/dm2, 32 ℃ and 2.5 h, respectively, and then the yield of sodium hypochlorite could be increased to 9.28 g/L. When the dosage of sodium hypochlorite was at least 5 mg/L and the contact reaction time was 5 min, the sterilization performance of sodium hypochlorite against fecal coliform groups in denitrification filter effluent was more competitive than its oxidation performance of COD and ammonium, and could reduce the number of fecal coliform groups in water samples to 102.97 L-1, and finally meet the bacteria index requirements of A-level standard of Discharge Standard of Pollutants for Municipal Waste-water Treatment Plant (GB 18918-2002).
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图 1 次氯酸钠电解工艺示意
Figure 1. Schematic diagram of sodium hypochlorite electrolysis process
图 2 在不同盐水浓度下次氯酸钠浓度和电解槽温度与电解时间的关系
Figure 2. Interrelation between sodium hypochlorite concentration and bath temperature with electrolysis time at different saline concentrations
图 3 在高盐水浓度下氯酸钠和高氯酸钠浓度曲线
Figure 3. Concentration curve of sodium chlorate and sodium perchlorate at high saline concentrations
图 4 不同电流密度下盐水浓度的变化
Figure 4. Concentration curve of electrolyte at different current densities
图 5 次氯酸钠浓度、电流效率和电能消耗与电解时间的关系
Figure 5. Relation between sodium hypochlorite concentration, current efficiency and electronic consumption withelectrolysis time
图 6 不同电流密度下盐水浓度变化率的自然对数ln[M0/(M0−Mt)]与电解时间的关系
Figure 6. Relation between natural logarithm of saline concentration ln[M0/(M0−Mt)] and electrolysis time at different current densities
图 7 在不同电解液初始温度下电解过程中电解槽温度与次氯酸钠浓度的关系
Figure 7. Relation between bath temperature and sodium hypochlorite concentration in electrolytic process at different initial temperature of electrolyte
图 8 不同次氯酸钠投加量下粪大肠杆菌群对数(lgn)与消毒时间的关系
Figure 8. Interrelation between the logarithm of fecal coliform (lgn) and disinfection time at different dosage of sodium hypochlorite
图 9 不同次氯酸钠投加量和消毒时间下粪大肠杆菌群数对数(lgn)与出水水质的关系
Figure 9. Interrelation between the logarithm of fecal coliform (lgn) and effluent quality at different dosages and disinfection time
表 1 某城镇污水处理站的反硝化滤池出水水质
Table 1. Effluent quality of denitrification filter in a township wastewater treatment station
COD/
(mg/L)氨氮浓度/
(mg/L)pH 粪大肠杆菌群数/(个/L) (15~32)±5 (0.8~3.6)±0.1 (6.4~7.2)±0.2 (2.9×104~3.5×104)±5×102 
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表 2 不同盐水浓度下次氯酸钠浓度曲线的拟合方程
Table 2. Fitting equations of sodium hypochlorite concentration curve under different saline concentrations
序号 盐水浓度/(g/L) 曲线拟合方程 参数取值 R2 1 10
$ y = {y_{0,i}} + {a_i}t $y0,1=165.9，a1=491.4 0.973 2 20 y0,2=−30，a2=724.1 0.992 3 30 y0,3=114.9，a3=908.8 0.989 4 40
$ y = {y_{0,i}} + {a_i}t + {b_i}{t^2} $y0,4=32，a4=1716.3，b4=−252.8 0.997 5 50 y0,5=159.5，a5=2141.3，b5=−411.5 0.988 注：i表示在不同盐水浓度下次氯酸钠浓度曲线拟合方程对应的序号，依次为1、2、3、4和5。
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表 3 不同电流密度下盐水浓度变化率的自然对数ln[M0/(M0−Mt)]与电解时间（t）的拟合方程
Table 3. Fitting equations of the interrelation between natural logarithm of saline concentration ln[M0/(M0−Mt)] and electrolysis time (t) at different current densities
序号 电流密度/(A/dm2) 曲线拟合方程 k R2 1 5 ln[M0/(M0−Mt)]=kit 0.021 0.915 2 10 0.048 0.990 3 15 0.067 0.985 4 20 0.078 0.992 5 25 0.083 0.997 注：同表2。
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表 4 不同电解槽温度下电解生成次氯酸钠的反应速率常数及其表观活化能
Table 4. Reaction rate constant and its apparent activation energy of sodium hypochlorite at different bath temperatures
T/K b/h−1 ln|b| lnA Ea/(kJ/mol) R2 299 1.225 0.203 −145.4 43.6 0.92 301 1.020 0.019 303 0.305 −1.187 305 0.075 −2.590 307 −0.419 −0.871 −57.8 17.4 0.96 309 −0.250 −1.386 311 −0.219 −1.521 313 −0.131 −2.036
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