CN113307421B - Electrochemical oxidation auxiliary Fenton oxidation method for aldehyde chemical wastewater treatment - Google Patents
Electrochemical oxidation auxiliary Fenton oxidation method for aldehyde chemical wastewater treatment Download PDFInfo
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- C02F1/461—Treatment of water, waste water, or sewage by electrochemical methods by electrolysis
- C02F1/467—Treatment of water, waste water, or sewage by electrochemical methods by electrolysis by electrochemical disinfection; by electrooxydation or by electroreduction
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Abstract
The invention discloses an electrochemical oxidation auxiliary Fenton oxidation method for aldehyde chemical wastewater treatment, which comprises the following steps: s1 is aimed at aldehyde chemical wastewater, firstly, electrochemical oxidation is adopted to generate complexing agent; s2 adding ferrous ion into the system after step S1, making the complexing agent complex with the ferrous ion to form a ferrous ion complex; s3 at step S2, hydrogen peroxide is added to the system to degrade the ferrous ion complex and hydrogen peroxide by Fenton oxidation. The micromolecular organic acid with complexing ability generated in situ by degrading aldehyde pollutants in electrochemical oxidation treatment is utilized, the micromolecular organic acid is difficult to continue degrading but can be complexed with ferrous ions in situ to form a ferrous ion complex, and the Fenton reaction can be carried out not only under an acidic condition but also under a neutral/alkaline condition by utilizing the micromolecular organic acid participating in the subsequent Fenton oxidation reaction.
Description
Technical Field
The invention belongs to the field of sewage treatment processes, and particularly relates to an electrochemical oxidation auxiliary Fenton oxidation method for treating aldehyde chemical wastewater.
Background
In the past decades, with the development of industry, industrial wastewater becomes one of the major water pollution types in China, the general pollution of various inorganic and organic substances causes serious problems in the world, the production wastewater from the industries of petrifaction, paint, pesticide, coal conversion and the like contains pollutants of nitrogen-containing heterocyclic compounds, oxygen-containing heterocyclic compounds and the like with higher concentration, NHCs and OHCs are harmful, difficult-to-degrade, toxic and harmful substances, and the treatment is difficult. The wastewater treatment process for producing NHCs and OHCs in fine chemistry generally adopts pretreatment processes such as precipitation, air flotation or chemical oxidation reduction to improve the biodegradability of wastewater, and then a series of biological treatment processes are carried out to discharge the conventional indexes such as water quality COD, ammonia nitrogen, total phosphorus and the like. Effluent (also called chemical tail water) produced by secondary biochemical treatment of fine chemical wastewater generated in NHCs and OHCs production generally can remain nitrogen heterocyclic refractory pollutants, and the heterocyclic compounds can be retained and displayed for a long time after being discharged from an external environment water body and have certain ecological risk and ecological hazard. The degradation of nitrogen and oxygen heterocyclic compounds and the advanced treatment of such tail water have attracted great attention in recent years.
The electrochemical oxidation technology and the Fenton oxidation technology are typical chemical wastewater physicochemical treatment technologies at present, are often utilized in chemical wastewater treatment process design, and have better treatment effects. The traditional Fenton method has the problems that the iron mud amount is large, the iron ion loss is serious, and the iron ion utilization rate is low when the sewage is treated; the requirement on the pH value of the wastewater is strict, and resources are consumed to monitor and regulate the pH value in real time. Once the pH is above 4, the fenton oxidation efficiency is greatly reduced. A large amount of ferrous ions are required to be added in the traditional Fenton oxidation process, a large amount of iron mud can be generated, the generated iron mud belongs to dangerous solid waste, the dangerous solid waste needs to be subjected to subsequent treatment, and the cost is high.
How to enable the Fenton oxidation reaction to maintain higher activity in a wider pH value range becomes a problem to be solved urgently in the field of sewage treatment by the Fenton oxidation method.
Disclosure of Invention
1. Problems to be solved
Aiming at the problem that the Fenton oxidation is limited by the pH of sewage to be treated in the prior art, the invention provides an electrochemical oxidation auxiliary Fenton oxidation method for treating aldehyde chemical wastewater.
2. Technical scheme
Advanced oxidation technologies (AOPs) have been widely used for degrading nitrogen-containing heterocyclic organic compounds that are not easily biochemically treated in water, the main mechanism of AOPs (ozone oxidation, Fenton oxidation, electrochemical oxidation, etc.) is the process of generating hydroxyl radicals (. OH) which are strong oxidizing substances, meanwhile, the AOP process mainly based on. OH cannot achieve the complete mineralization of pollutants, and small molecular weight substances which are difficult to continue to degrade are generated in the degradation process of most pollutants, and are rarely reused in research. The research of the subject group finds that when the products of the incomplete degradation of the pollutants in the chemical wastewater containing the aldehydes through electrochemical oxidation reach a certain amount, the Fenton oxidation efficiency is higher in a wider pH range. The principle of the method is analyzed, and the incomplete degradation product is complexed with the catalyst to promote further activation of hydroxyl radicals, so that Fenton oxidation can be efficiently carried out in a wider pH range.
The technical scheme adopted by the invention is as follows:
an electrochemical oxidation auxiliary Fenton oxidation method for treating aldehyde chemical wastewater comprises the following steps:
s1 is aimed at aldehyde chemical wastewater, firstly, electrochemical oxidation is adopted to generate complexing agent;
s2 adding ferrous ion into the system after step S1, making the complexing agent complex with the ferrous ion to form a ferrous ion complex;
s3 at step S2, hydrogen peroxide is added to the system to degrade the ferrous ion complex and hydrogen peroxide by Fenton oxidation.
The electrochemical oxidation degradation of the aldehyde pollutants is realized by directly oxidizing the aldehyde pollutants by hydroxyl radicals generated by an anode, and the process can not achieve the complete mineralization of the aldehyde pollutants, but can oxidize and degrade the aldehyde pollutants into small molecular organic acids. In the electrochemical oxidation process, aldehyde substances in the chemical wastewater can be oxidized into micromolecular organic acid, and the micromolecular organic acid can be in-situ complexed with ferrous ions to form a ferrous ion complex. Under the conditions of acidity, alkalescence and neutral pH, the small molecule hasThe organic acid complexing agent can be mixed with Fe2+The complexing ability is stronger than that of the original background organic matter in the chemical wastewater, so that ferrous ions exist in the form of a ferrous ion-small molecule organic acid complex, the ferrous ions are protected, the ferrous ions are prevented from becoming ferric hydroxide precipitate under a neutral condition or a weakly alkaline condition, the utilization rate of the ferrous ions under the neutral or weakly alkaline pH condition is improved, the reaction activity is ensured, and the subsequent Fenton oxidation reaction condition is not limited in an acid pH range.
Preferably, the COD provided by the aldehyde group in the aldehyde chemical wastewater accounts for more than 50% of the total COD content in the wastewater.
Preferably, the COD provided by the aldehyde group in the aldehyde chemical wastewater accounts for more than 65% of the total COD content in the wastewater. When the aldehyde group provides COD which is more than or equal to 65% of the total COD, more complexing agents can be provided for the subsequent Fenton oxidation or the electro-catalytic Fenton oxidation, and the oxidation efficiency is improved.
Preferably, the current density of the electrochemical oxidation in the step S1 is 2-30 mA/cm2The time of electrochemical oxidation is 3 min-12 h, and pH does not need to be adjusted during Fenton oxidation in step S3.
Preferably, carboxyl in the small-molecule organic acid complexing agent formed by the aldehyde group in the step S1 under the electrochemical oxidation condition is made to react with Fe added in the step S22+The molar ratio of (0.5-6): 1. Meanwhile, when the molar ratio of the complexing agent to the Fe2+ added in the step S2 is (0.2-2.5): 1, the proportion of the complexed Fe2+ is high, and the Fenton oxidation efficiency is less influenced by the pH. Even under the alkaline condition, because the aldehyde substance is easier to be oxidized, the electrochemical oxidation of the aldehyde substance under the alkaline condition can improve the oxidation efficiency and ensure that the Fenton reaction can also occur under the neutral or alkaline condition.
Preferably, greater than or equal to 50% of the ferrous ions are complexed by the small molecule organic acid.
Preferably, greater than or equal to 60% of the ferrous ions are complexed by the small molecule organic acid.
Preferably, 70% to 75% of the ferrous ions are complexed by the small molecule organic acid.
Preferably, the step S2 and the step S3 are separated by more than 5 min.
Preferably, an aeration step is added before the step S1 to ensure that the dissolved oxygen in the wastewater is 2-8 mg/L. The electrochemical oxidation effect can be greatly improved by improving the dissolved oxygen content of the wastewater, the aldehyde pollutants are oxidized and degraded into small molecular organic acid which is used as an in-situ complexing agent to be complexed with ferrous ions, the subsequent Fenton oxidation is promoted, and the pH value does not need to be adjusted; after the addition of the aeration step, the efficiency of fenton oxidation is less affected by alkaline conditions.
Preferably, the step S3 is to add H2O2And Fe added in the step S22+The ion molar ratio is (5-60): 1.
Preferably, the current density of the electrochemical oxidation in the step S1 is 5-25 mA/cm2。
Preferably, the Fenton oxidation in the step S3 is enhanced simultaneously by adopting electrochemical oxidation at the beginning of the step S3, and the current density of the electrochemical oxidation is 1-15 mA/cm2. By enhancing fenton oxidation in step S3 by electrochemical oxidation, the trivalent iron complex after fenton reaction can be further reduced to a ferrous iron complex, and the generation of iron sludge during operation can be reduced.
Preferably, the electrochemical oxidation in step S1 or step S3 uses a plate or tube electrode.
Preferably, in the electrochemical oxidation in step S1 or step S3, the anode material may be one of all electrodes with catalytic oxidation capability, such as a lead oxide electrode, a ruthenium oxide electrode, and a BDD electrode.
Preferably, in the electrochemical oxidation step of step S1 or step S3, the electrode material is plate electrode, ruthenium oxide electrode is used as anode, and stainless steel electrode is used as cathode.
3. Advantageous effects
Compared with the prior art, the invention has the beneficial effects that:
(1) aiming at the treatment of the pollutants which are difficult to degrade in the aldehyde chemical wastewater, the technical scheme of the invention adopts an electrochemical auxiliary Fenton oxidation coupling process, utilizes micromolecule organic acid with complexing ability generated in situ by degrading the aldehyde pollutants in the electrochemical oxidation treatment, the micromolecule organic acid is difficult to continue degrading but can be complexed with ferrous ions in situ to form a ferrous ion complex, and can be used for participating in the subsequent Fenton oxidation reaction, so that the Fenton reaction can be carried out not only under the acidic condition, but also under the neutral/alkaline condition (the Fenton oxidation efficiency is more than 50 percent), the pH adjustment of the wastewater is not needed, and the limitation that the Fenton oxidation can be carried out under the acidic condition is broken;
(2) because the total COD in the aldehyde chemical wastewater is determined, the required amount of ferrous ions for Fenton oxidation is certain, the proportion of COD (chemical oxygen demand) in the total COD provided by aldehyde groups can be determined by a micromolecular organic acid complexing agent for complexing the ferrous ions, and the aldehyde substances are fully oxidized by controlling the current density and time of electrochemical oxidation, so that the ferrous ions are complexed by the micromolecular organic acid as much as possible, a better Fenton oxidation effect is achieved, meanwhile, the complexing agent protects the ferrous ions, and the ferrous ions can be prevented from becoming ferric hydroxide precipitates under a neutral or alkaline condition as much as possible, the utilization rate of the ferric ions is improved, and the dosage of the ferrous ions is reduced; the experiment in the embodiment 6 shows that the pH value is 6.5, when the aldehyde group provides COD which is more than or equal to 65% of the total COD, more complexing agents can be provided for the subsequent Fenton oxidation or the electro-catalytic Fenton oxidation, the pH is not required to be adjusted to be acidic, and the Fenton oxidation efficiency can be improved to be more than 63%;
(3) the invention leads the complexing agent formed by the aldehyde group in the step S1 under the condition of electrochemical oxidation and the Fe added in the step S22+The molar ratio of (0.25-3): 1, in which case Fe2+The complexed proportion is more than 50 percent, the generation of the complex partially offsets the influence of neutral or alkaline environment on Fenton oxidation, and the Fenton reaction can also be ensured to occur under neutral or alkaline conditions; even under the alkaline condition, because the aldehyde substance is easier to be oxidized, the oxidation efficiency can be improved by carrying out electrochemical oxidation on the aldehyde substance under the alkaline condition, and the Fenton reaction can be ensured to occur under the neutral or alkaline condition;
(4) the invention controls the current density of electrochemical oxidation and the adding amount or the generating amount of ferrous ions, so that more than 50 percent of the ferrous ions are complexed by micromolecular organic acid; theoretically, the more ferrous ions that are complexed by the organic acid, the lower the dependence of the fenton oxidation reaction on pH;
(5) in the invention, the interval between the step S2 and the step S3 is more than 5min, so that ferrous ions are firstly complexed to form a complex, rather than being firstly subjected to Fenton oxidation reaction with hydrogen peroxide; then taking part in Fenton reaction in the form of ferrous complex;
(6) according to the invention, an aeration step is added before the electrochemical oxidation step, the dissolved oxygen content of the wastewater is improved, so that aldehyde pollutants are favorably oxidized and degraded into small-molecular organic acids, and the small-molecular organic acids are used as in-situ complexing agents to be complexed with ferrous ions to promote subsequent Fenton oxidation, and the dissolved oxygen content in the wastewater is controlled to be 2-8 mg/L in the embodiment 5 and the comparative example 5B of the invention, so that a better aldehyde group oxidation effect is realized.
Drawings
FIG. 1 is a diagram of the process flow and mechanism of the electrochemical assisted Fenton oxidation coupling of the present invention;
FIG. 2 is a graph showing the effect of removing pyrazole by Fenton oxidation when the electrochemical oxidation time of step S1 is 0.5, 1, 2, 3, and 4 hours, respectively, in the simulation wastewater treated by the coupled process of electrochemical oxidation and Fenton oxidation in example 1;
FIG. 3 is a graph showing the comparison of the removal rates of pyrazole by Fenton oxidation reactions when ferrous ions are complexed by oxalic acid in amounts of 50% -55%, 60% -65%, 70% -75%, 80% -85% and 90% -95% in example 2;
FIG. 4 is a graph comparing the removal effect of the coupled process of electrochemical oxidation + Fenton oxidation at initial pH values of 3, 6, 7, 10, and 11 on the nitrogenous heterocyclic compound in example 3;
FIG. 5 is a graph comparing the removal effect of the "electrochemical oxidation + electro-enhanced Fenton' oxidation" coupled process on the nitrogenous heterocyclic compound at initial pH values of 3, 6, 7, 10 and 11 in example 4;
FIG. 6 is a graph showing the comparison of the effect of removing nitrogenous heterocyclic compounds in Fenton oxidation in the case where the "electrochemical oxidation + Fenton oxidation" coupled process in example 5 is performed with aeration and the case where no aeration is performed in comparative example 5A;
FIG. 7 is a graph showing the comparison of the effects of removing nitrogenous heterocyclic compounds in Fenton oxidation when the amount of dissolved oxygen is controlled to be 2, 4, 5, 6, and 8mg/L by adding aeration to the "electrochemical oxidation + Fenton oxidation" coupled process in comparative example 5B;
fig. 8 is a graph comparing the removal effect of the nitrogen-containing heterocyclic compounds in the fenton oxidation when the aldehyde organic molecules in the wastewater contribute COD of more than 65% and less than 65% in the electrochemical oxidation + fenton oxidation coupling process in example 6.
Detailed Description
Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs; as used herein, the term "and/or" includes any and all combinations of one or more of the associated listed items.
The examples, in which specific conditions are not specified, were conducted under conventional conditions or conditions recommended by the manufacturer. The reagents or instruments used are not indicated by the manufacturer, and are all conventional products available commercially.
Concentrations, amounts, and other numerical data may be presented herein in a range format. It is to be understood that such a range format is used merely for convenience and brevity and should be interpreted flexibly to include not only the numerical values explicitly recited as the limits of the range, but also to include all the individual numerical values or sub-ranges encompassed within that range as if each numerical value and sub-range is explicitly recited. For example, a numerical range of about 1 to about 4.5 should be interpreted to include not only the explicitly recited limit values of 1 to about 4.5, but also include individual numbers (such as 2, 3, 4) and sub-ranges (such as 1 to 3, 2 to 4, etc.). The same principle applies to ranges reciting only one numerical value, such as "less than about 4.5," which should be construed to include all of the aforementioned values and ranges. Moreover, such an interpretation should apply regardless of the breadth of the range or feature being described.
An electrochemical auxiliary fenton oxidation coupling mechanism diagram for the efficient treatment of aldehyde chemical wastewater is shown in fig. 1, and a treatment device comprises an electrochemical oxidation device, a fenton oxidation device or an electrochemical oxidation enhanced fenton oxidation device.
The invention is further described with reference to specific examples.
Example 1
In the embodiment, the wastewater to be treated adopts self-prepared simulated wastewater, 500mg/L glyoxal solution is prepared, 500mL of the solution is taken as the wastewater to be treated, 50mg/L of pyrazole and 0.05mol of anhydrous sodium sulfate are added. Wherein the pyrazole is a target pollutant which is difficult to degrade.
This example uses a coupled process of electrochemical oxidation + Fenton oxidation. Preparing five parts of the same simulated wastewater, adjusting the pH value of the wastewater to 6.5, and respectively carrying out electrochemical auxiliary oxidation for 0.5, 1, 2, 3 and 4 hours, wherein plate electrodes are selected as electrode materials in an electrochemical auxiliary oxidation unit, a ruthenium dioxide coating plate electrode is used as an anode material, and a stainless steel plate electrode is used as a cathode material. The current density is controlled to be 3.5 to 6.5mA/cm at this stage2And carrying out constant current treatment on the wastewater, and turning off a power supply. Then taking tail water after electrochemical oxidation treatment as raw water, and adding Fe2+(the dosage is shown in the specification and H2O2Proportion of (1), adding H after ferrous ions are completely dissolved and complexed for about 5min2O2To make the wastewater COD and H2O2In a mass ratio of 1:0.8, iron (II) to H2O2The molar ratio of the target pollutant pyrazole is about 1:10, the Fenton oxidation method is used for reaction degradation for 2h, and samples are taken at 0min, 15 min, 30 min, 60 min, 90 min and 120min during the Fenton oxidation period to detect the residual content of the target pollutant pyrazole.
FIG. 2 shows the effect of removing pyrazole in simulated Fenton oxidation of wastewater, wherein curves a, b, c, d and e correspond to different time points of pyrazole c/c when Fenton oxidation is carried out after electrochemical oxidation time of 0.5, 1, 2, 3 and 4h in advance0(detection concentration of pyrazole/initial concentration of pyrazole), the results show that the electrochemical oxidation time is different in advance, and H is added at the beginning of the Fenton oxidation reaction (0 min)2O2The time) the concentration of the pyrazole is not obviously changed, and the removal rate is not enough 10 percent, because the pyrazole in the simulated wastewater belongs to a nitrogen heterocyclic compound which is difficult to degrade, and the easily degradable substance glyoxal in the wastewater is mainly degraded in the electrochemical oxidation process in advance to be degraded into small molecular organic acid (such as glyoxylic acid, oxalic acid and the like).
The Fenton oxidation stage utilizes in-situ generation in an electrochemical oxidation reactionThe small molecular organic acid is used as a complexing agent to be complexed with ferrous ions, and Fe is contained in the solution2+And complexes thereof with H2O2Fenton oxidation occurs to degrade pyrazole in the simulated wastewater. As can be seen from fig. 2: as the electrochemical auxiliary oxidation reaction time is increased from 0.5H to 2H (curves a-c in sequence), the removal effect of fenton oxidation on pyrazole is obviously enhanced, because the electrochemical oxidation time is increased, more glyoxal can be oxidized to generate more micromolecular organic acid complexing agents in situ, and in the subsequent reaction, more complex compounds and H are generated by complexing with ferrous ions2O2The Fenton oxidation reaction is carried out, and Fe is improved2+The utilization rate is increased, and the removal rate of pyrazole is increased from 30-35% (electrochemical oxidation for 0.5h) to 55-60% (electrochemical oxidation for 2 h); when the electrochemical auxiliary oxidation reaction time is increased from 2h to 4h (curves c-e are sequentially formed), the removal effect of the fenton oxidation on the pyrazole is not obviously enhanced, and the removal rate slowly floats within 60% -65%, because the degree of degrading organic pollutants by the electrochemical oxidation reaction is limited, the aldehyde substances in the wastewater are converted into micromolecule organic acid by the electrochemical reaction, after the reaction is carried out for 2-3 h, the content of glyoxal is reduced, the content of the micromolecule organic acid is increased, the contact probability of the glyoxal and an electrode is reduced, the micromolecule organic acid and the glyoxal are difficult to be continuously oxidized, after the reaction time is continuously increased, the electrochemical oxidation is changed into electrolytic water from an electrolytic organic substance to cause reaction stagnation, the utilization rate of a complexing agent is not increased, the utilization rate of ferrous ions is difficult to be increased again during subsequent fenton oxidation, and the removal rate of the pyrazole is not obviously enhanced.
The embodiment illustrates that, by adding the electrochemical auxiliary oxidation in-situ generated small-molecule complexing agent before the fenton oxidation reaction, under a neutral condition (pH 6.5), the more the small-molecule complexing agent generated in situ is, the better the effect of the subsequent fenton oxidation reaction on removing the degradation-resistant pollutants is, but due to the limitation of the electrochemical oxidation and the limited content of the aldehyde substances in the wastewater, the efficiency of the fenton oxidation reaction cannot be increased along with the continuous increase of the electrochemical oxidation time, and considering the operation cost, when the COD of the aldehyde substances in the solution is 350-450 mg/L, which accounts for 70% -80% of the total COD, and the wastewater treatment capacity is 500mL, the electrochemical oxidation time is 2h, 30% -40% of the aldehyde in the wastewater can be oxidized into the small-molecule acid, and the removal rate of the target pollutants by the subsequent fenton oxidation is 55% -60%.
Example 2
In this example, simulated wastewater was used to treat wastewater, five 500mL portions of 50mg/L pyrazole solution were prepared, and different amounts of oxalic acid (the amounts of oxalic acid and Fe were added)2+Proportion), stirring to dissolve, adding FeSO4·7H2O, adding H after ferrous ions are completely dissolved and complexed in about 5min2O2To simulate COD and H in the wastewater2O2In a mass ratio of 1:0.8, iron (II) to H2O2Is about 1: 10. Fe in wastewater a2+And C2H2O4The molar ratio is about 1:0.25 (Fe)2+The molar ratio of the Fe to the carboxyl is about 1:0.5), Fe in the wastewater b2+And C2H2O4The molar ratio is about 1:0.5 (Fe)2+Molar ratio of the Fe to carboxyl is about 1:1), Fe in the wastewater c2+And C2H2O4The molar ratio is about 1:1 (Fe)2+The molar ratio of the Fe to the carboxyl is about 1:2), Fe in the wastewater d2+And C2H2O4The molar ratio is about 1:1.5 (Fe)2+Molar ratio to carboxyl group is about 1:3), Fe in waste water e2+And C2H2O4The molar ratio is about 1:3 (Fe)2+The molar ratio to carboxyl groups is about 1: 6).
According to different adding amounts of oxalic acid, the ferrous ions in the wastewater a are complexed by the oxalic acid ions by about 50-55%, the ferrous ions in the wastewater b are complexed by the oxalic acid ions by about 60-65%, the ferrous ions in the wastewater c are complexed by the oxalic acid ions by about 70-75%, the ferrous ions in the wastewater d are complexed by the oxalic acid ions by about 80-85%, and the ferrous ions in the wastewater e are complexed by the oxalic acid ions by about 90-95%.
And after all the medicines are added, adjusting the pH value of all the simulated wastewater to 6.5, carrying out Fenton reaction for 120min, and respectively sampling and detecting the removal rate of the target pollutant pyrazole in the solution after the reaction is finished. The removal effect of pyrazole in simulated wastewater is shown in FIG. 3, and columns a, b, c, d and e correspond to pyrazole c/c in wastewater a, b, c, d and e, respectively0(xi diAzole detection concentration/pyrazole initial concentration), the results show that when ferrous ions are complexed by 50% to 75%, the pyrazole removal effect is increased along with the increase of the complexed amount of the ferrous ions, when the complexed amount is 70% to 75%, the removal rate reaches 55% to 60% at the highest, and compared with the electrochemical oxidation + fenton oxidation coupling process in example 1, the maximum removal rate of pyrazole in the simulated wastewater is slightly reduced, because small molecular organic acid generated in situ by the electrochemical oxidation is generally difficult to be oxidized again and cannot serve as a second pollutant to interfere with the degradation of the pyrazole in the fenton reaction, while the embodiment is a simulation experiment, the added oxalic acid not only complexes with the ferrous ions, but also serves as a pollutant to be oxidized continuously and interferes with the degradation of the pyrazole by hydroxyl radicals. When the complexing amount of ferrous ions is more than 75%, the removal rate of pyrazole is reduced along with the increase of the complexing amount, and when the complexing amount of the ferrous ions is 90-95%, the removal rate of the pyrazole is only 35-40%, because excessive oxalic acid interferes with the degradation of hydroxyl radicals to the pyrazole, and part of the ferrous ions are wrapped to influence the reaction of the ferrous ions and hydrogen peroxide, so that the removal rate of the pyrazole is reduced. In the actual industrial aldehyde-containing wastewater, the small-molecular organic acid generated in situ is difficult to be oxidized again, and the situation that the fenton oxidation efficiency is reduced along with the increase of the complexing amount of the ferrous ions in the embodiment can not occur.
This example illustrates that under neutral conditions, pH 6.5, with an added molar ratio of oxalic acid to ferrous ion of 1:1, ferrous ions are complexed by 70% to 75%, the removal rate of pyrazole in fenton oxidation reaches up to 55% to 60%, which is slightly lower than that of electrochemically in situ generated small organic acids, for reasons previously described.
Example 3
In the embodiment, the quality of the industrial tail water to be treated is the tail water discharged in the production process of a chemical fiber enterprise, the COD content is 6000-8000 mg/L, the COD contributed by aldehyde organic molecules is 55-60%, the pH value of the wastewater is 9-10, main pollutants are pollutants such as acetaldehyde, triethylene glycol, PTA, EG and the like, and the industrial tail water to be treated also comprises refractory nitrogen-containing heterocyclic compounds such as pyrrole, indole, pyrazole and the like.
This example uses a coupled process of electrochemical oxidation + Fenton oxidation.
In the embodiment, the electrode material in the electrochemical auxiliary oxidation unit is a plate electrode, the anode material is a ruthenium dioxide coating plate electrode, and the cathode material is a stainless steel plate electrode. The current density is controlled to be 3.5 to 6.5mA/cm at this stage2And (3) carrying out constant-current treatment on the wastewater, respectively adjusting the pH values of the wastewater to 3, 6, 7, 10 and 11 before the treatment, keeping the treatment time for 3h, and turning off a power supply.
The tail water after electrochemical oxidation treatment is used as raw water in the Fenton oxidation unit, the chemical fiber plant wastewater is subjected to subsequent treatment, and iron (II) is added (the addition amount is shown in the specification and H)2O2Proportion of (1), adding H after ferrous ions are completely dissolved and complexed for about 10min2O2To make the wastewater COD and H2O2In a mass ratio of 1:0.8, iron (II) to H2O2Was subjected to Fenton oxidation for 3 hours at a molar ratio of about 1: 10.
Fig. 4 shows the change in the removal rate of the nitrogen-containing heterocyclic compound in the wastewater, and curves a, b, c, d, and e correspond to the target pollutants c/c at pH 3, 6, 7, 10, and 11, respectively0(target contaminant final concentration/target contaminant initial concentration). The result shows that in the electrochemical oxidation stage (0-3 h), the nitrogen-containing heterocyclic compound in the wastewater has a complex structure and belongs to an organic pollutant which is difficult to degrade, the removal rate is not more than 10%, and in the process, the electrochemical oxidation mainly degrades the part of the organic pollutant which is easy to degrade, such as aldehydes and the like in the wastewater, so as to degrade the part into micromolecular organic acid; in the Fenton oxidation stage (3-6 h), the removal rate is slowly reduced along with the increase of pH, but when the pH is increased to 11, the removal rate is still more than 50%.
When the pH value is 3, electrochemically oxidizing small-molecule organic acid generated in situ as a complexing agent and Fe with catalytic capacity2+Complexing is carried out to stabilize ferrous ions in the system and reduce Fe2+/Fe3+Oxidation-reduction potential, but the reaction environment is acidic, and the complexing ability of ferrous ions and complexing agents is weak compared with neutral or alkaline conditions, so that Fe2+And H2O2Reaction predominance, Fe in solution2+And small amount of complexes thereofAnd H2O2The Fenton oxidation reaction is carried out to degrade the nitrogenous heterocyclic compounds in the wastewater, and the removal rate reaches 75-80%. When the pH value is 6 or 7, the Fenton reaction in the stage continuously utilizes micromolecule organic acid generated in situ by electrochemical oxidation as a complexing agent to generate a ferrous ion complex, the pH value is increased, the complexing capability is increased, and Fe in the solution2+And complexes thereof with H2O2The Fenton oxidation reaction is carried out to degrade the nitrogenous heterocyclic compounds in the wastewater, and the removal rate reaches 55-60 percent. When the pH value is 10 or 11, the complexing ability of ferrous ions and small molecular organic acid generated in situ is strongest in the stage, and ferrous ion complex and H are used in the solution2O2The reaction is dominant, and the removal rate of the nitrogen-containing heterocyclic compound is 50 to 55 percent.
This example illustrates that the method for treating aldehyde wastewater by electrochemical-assisted fenton oxidation can effectively widen the pH range of wastewater treatment, break the limitation that the conventional fenton oxidation needs to be performed under acidic conditions, and the removal rate of the organic pollutants difficult to degrade under strongly alkaline conditions (pH 11) is still above 50%.
Example 4
The wastewater treatment and other conditions in this example were consistent with those in example 3, except that:
in this embodiment, a "electrochemical oxidation + electrochemical oxidation enhanced fenton oxidation" coupling process is adopted.
In the embodiment, the electrode material in the electrochemical auxiliary oxidation unit is a plate electrode, the anode material is a ruthenium dioxide coating plate electrode, and the cathode material is a stainless steel plate electrode. The current density of the electrochemical oxidation is controlled to be 3.5 to 6.5mA/cm at this stage2And (3) carrying out constant-current treatment on the wastewater, respectively adjusting the pH values of the wastewater to 3, 6, 7, 10 and 11 before the treatment, keeping the treatment time for 3h, and turning off a power supply.
In the electrochemical oxidation enhanced Fenton oxidation unit, tail water after electrochemical oxidation treatment is used as raw water, the chemical fiber plant wastewater is subjected to subsequent treatment, a ruthenium dioxide coated plate type electrode is adopted as an anode, a stainless steel plate type electrode is adopted as a cathode, and the current density of the step is controlled to be 0.5-2.5 mA/cm2Adding iron (II) (adding)The addition amount is shown in the specification2O2Proportion of (1), about 5min after ferrous ions are completely dissolved, H is added2O2To make the wastewater COD and H2O2In a mass ratio of 1:0.8, iron (II) to H2O2Was subjected to Fenton oxidation for 3 hours at a molar ratio of about 1: 10.
Fig. 5 shows the change in the removal rate of the nitrogen-containing heterocyclic compound in the wastewater, and curves a, b, c, d, and e correspond to the target pollutants c/c at pH 3, 6, 7, 10, and 11, respectively0. The results show that in the electrochemical oxidation stage (0-3 h), the removal rate of the nitrogenous heterocyclic compound in the wastewater is not more than 10%, and the reaction process is the same as that in the example 3; in the electrochemical oxidation enhanced Fenton oxidation stage (3-6 h), most of nitrogen-containing heterocyclic compounds in the wastewater are removed within one hour, and the removal rate is slowly reduced along with the increase of pH, but when the pH is increased to 11, the removal rate is still over 55%. The Fenton oxidation reaction mechanism under acidic, neutral and alkaline conditions is similar to that of the electrochemical oxidation and Fenton oxidation coupling process, and the removal effect is better than that of the electrochemical oxidation and Fenton oxidation coupling process on the whole because the electrochemical oxidation is used for strengthening the oxidation of the anode in the electrochemical oxidation in the Fenton oxidation to continuously oxidize pollutants in wastewater, and the reduction near the cathode is used for reducing Fe in the solution3+Reduction of the-complex to Fe2 +Complexes to increase the efficiency of iron utilization.
This example illustrates that the coupled process of "electrochemical oxidation + electrochemical oxidation to enhance fenton oxidation" can also break the limitation of pH value to fenton oxidation method, and in the subsequent fenton oxidation process, by adding electrochemical oxidation at the same time, the pollutants in water can be continuously oxidized, and simultaneously Fe can be promoted3+/Fe2+Reduction, compared with Fenton oxidation, improves the utilization efficiency of iron, thereby enhancing the removal effect of the nitrogen-containing heterocyclic compound.
Example 5
The wastewater treatment and other conditions in this example were consistent with those in example 3, except that:
in the embodiment, a coupling process of blast aeration, electrochemical oxidation and Fenton oxidation is adoptedThe treatment device comprises a blower aeration device, an electrochemical oxidation device and a Fenton oxidation device. The processing capacity per unit time is 100m3/d。
In this embodiment, the wastewater is aerated and then subjected to the subsequent electrochemical oxidation and fenton oxidation. And (3) carrying out blast aeration on the wastewater for 2h by using an air blower, so that the wastewater is fully contacted with air, and the dissolved oxygen content of the wastewater is increased to 8 mg/L. The pH value is adjusted to 6.5 before aeration, so that the wastewater is subjected to subsequent treatment under a neutral condition.
The electrode material in the electrochemical auxiliary oxidation unit is a plate electrode, the anode material is a ruthenium dioxide coating plate electrode, and the cathode material is a stainless steel plate electrode. The current density is controlled to be 3.5 to 6.5mA/cm at this stage2And carrying out constant current treatment on the wastewater for 3h, and turning off a power supply.
The tail water after electrochemical oxidation treatment is used as raw water in the Fenton oxidation unit, the chemical fiber wastewater is subjected to subsequent treatment, and COD and H in the wastewater2O2In a mass ratio of 1:0.8, iron (II) to H2O2Was subjected to Fenton oxidation for 3 hours at a molar ratio of about 1: 10.
Comparative example 5A
Under the same conditions as other conditions of example 5, the chemical fiber wastewater was treated by a coupled process of electrochemical oxidation and Fenton oxidation, except that the aeration step was omitted, and compared with example 5.
The pair of effects of removing the nitrogenous heterocyclic compound is shown in figure 6: the curve a is the treatment effect of the coupled process of 'blast aeration + electrochemical oxidation + Fenton oxidation', and the curve b is the treatment effect of the coupled process of 'electrochemical oxidation + Fenton oxidation' without the aeration step, and as can be seen from the figure, the removal effect of the aeration step is better than that of the aeration step, and the removal rate can reach 80% -85%, because the aeration step is added before the electrochemical oxidation, the dissolved oxygen concentration of the sewage can be effectively improved, which is beneficial to the electrochemical oxidation of aldehyde substances in the sewage, and the aldehyde organic pollutants in the wastewater are degraded by the electrochemical oxidation in the process to be degraded into micromolecular organic acid substances; in the Fenton oxidation stage, the Fenton reaction is carried outUsing small molecular organic acid generated in situ by electrochemistry as complexing agent and Fe with catalytic capability2+Complexing is carried out to stabilize ferrous ions in the system and reduce Fe2+/Fe3+Oxidation-reduction potential of Fe2+Complexing agents more readily react with H2O2Reaction is carried out, Fe in solution2+Complexing agent and H2O2The Fenton oxidation reaction is carried out to degrade the nondegradable organic pollutants in the wastewater, the Fenton oxidation reaction is high in speed, and most of the target pollutants are removed within one hour of the reaction.
Comparative example 5B
Under the same conditions as those in example 5, the process of "forced air aeration + electrochemical oxidation + fenton oxidation" coupling was used, the pH value was adjusted to 6.5 before aeration, the aeration time was controlled so that the dissolved oxygen levels of the sewage after aeration were 2, 4, 5, 6, and 8mg/L, respectively, and the subsequent treatment was carried out to compare the removal effects of the nitrogen-containing heterocyclic compounds at different dissolved oxygen levels.
The removal effect of the target pollutants at different dissolved oxygen amounts is shown in fig. 7: curves a, b, c, d, e show the corresponding removal effects at dissolved oxygen levels of 2, 4, 5, 6, 8mg/L, respectively. According to the figure, the removal effect of the nitrogenous heterocyclic compound is better and better when the dissolved oxygen in the wastewater is increased along with the increase of the aeration time, the removal rate is 50-55% when the dissolved oxygen is 2mg/L, and the removal rate is 80-85% when the dissolved oxygen is increased to 8 mg/L. Therefore, along with the increase of the aeration time, the content of dissolved oxygen in the wastewater is higher, the electrochemical oxidation effect is better, so that more small-molecular organic acid complexing agents can be generated to promote the subsequent Fenton oxidation reaction, and the removal effect of target pollutants is improved.
Example 6
In the embodiment, the tail water discharged in the production process of a chemical fiber enterprise is adopted for treating the wastewater, the COD content is 6000-8000 mg/L, two parts of the tail water are selected, wherein the COD contributed by aldehyde organic molecules in the tail water A is 50-55%, the COD contributed by aldehyde organic molecules in the tail water B is 65-70%, and the pH value of the wastewater is 9-10.
This example uses a coupled process of electrochemical oxidation + Fenton oxidation.
In the embodiment, the electrode material in the electrochemical auxiliary oxidation unit is a plate electrode, the anode material is a ruthenium dioxide coating plate electrode, and the cathode material is a stainless steel plate electrode. The current density is controlled to be 3.5 to 6.5mA/cm at this stage2And (3) carrying out constant-current treatment on the wastewater, adjusting the pH value of the wastewater to 6.5 before treatment, keeping the treatment time for 3h, and turning off a power supply.
The tail water after electrochemical oxidation treatment is used as raw water in the Fenton oxidation unit, the chemical fiber plant wastewater is subjected to subsequent treatment, and iron (II) is added (the addition amount is shown in the specification and H)2O2Proportion of (1), adding H after ferrous ions are completely dissolved and complexed for about 10min2O2To make the wastewater COD and H2O2In a mass ratio of 1:0.8, iron (II) to H2O2Was subjected to Fenton oxidation for 3 hours at a molar ratio of about 1: 10.
The removal effect of the nitrogen-containing heterocyclic compound in the wastewater is shown in FIG. 8, wherein the curve a is the nitrogen-containing heterocyclic compound c/c in the tail water A0(final concentration/initial concentration), curve B is the nitrogen-containing heterocyclic compound c/c in tail water B0As can be seen from the figure, the percentage of COD provided by the aldehyde substances in the initial wastewater can affect the removal effect of the nitrogen-containing heterocyclic compounds to a certain extent, and when the aldehyde substances COD accounts for 50% -55% of the total COD and the initial pH is 6.5, the removal rate of the target pollutants is 40% -50%; when the aldehyde substance COD accounts for 65-70% of the total COD and the initial pH is 6.5, the removal rate of the target pollutant is increased to 63-68%, because more aldehyde organic substances can provide more micromolecular organic acids to be complexed with ferrous ions, so that the ferrous ions are protected, the subsequent Fenton oxidation rate is increased, and the removal effect of the nitrogen-containing heterocyclic compound is further enhanced.
Example 7
Selecting chemical fiber wastewater after certain biochemical treatment, wherein the COD content is 500-600 mg/L, the COD of the treated effluent needs to be less than or equal to 40mg/L, the COD needs to be treated at 460-560 mg/L, and 460-560 g of COD is removed from each ton of water.
Traditional fenton operating parameter calculation:
conventional Fenton hydrogen peroxide dosingAddition H2O2: when the COD is 2:1 (mass ratio), 27% of hydrogen peroxide 3407.4-4148.1 g is needed to be added into 1 ton of water, and the traditional Fenton H is adopted2O2：Fe2+If the molar ratio is 5:1, FeSO is added to 1 ton of water4·7H2O1504.5-1831.5 g, so conventional Fenton 1 ton water produces Fe (OH)3579-705 g, and 2895-3525 g of the sludge with water content of 80%.
Electrochemical oxidation assisted Fenton oxidation parameter calculation:
hydrogen peroxide dosage H of electrochemical oxidation + Fenton oxidation coupling process2O2: when the COD is 0.8:1 (mass ratio), 1363-1659 g of 27% hydrogen peroxide is required to be added into 1 ton of water, and the coupling process H of electrochemical oxidation and Fenton oxidation2O2：Fe2+If the molar ratio is 10:1, FeSO is added for 1 ton of water4·7H2O301-366 g, so that the coupling process produces Fe (OH) from 1 ton of water3116-141 g, and 580-705 g of sludge with water content of 80%.
Therefore, the electrochemical oxidation and Fenton oxidation coupling process for treating the same ton of water is only 20-25% of the cement produced by the traditional Fenton, and the dangerous solid waste treatment cost of the process is greatly reduced.
The above description is illustrative of the present invention and its embodiments, and the description is not limiting, and the embodiments shown in the examples are only one of the embodiments of the present invention, and the actual situation is not limited thereto. Therefore, if the person skilled in the art receives the teaching, it is within the scope of the present invention to design the similar manner and embodiments without departing from the spirit of the invention.
Claims (7)
1. An electrochemical oxidation auxiliary Fenton oxidation method for treating aldehyde chemical wastewater is used for degrading nondegradable pollutants in the aldehyde chemical wastewater, wherein COD provided by aldehyde groups in the aldehyde chemical wastewater accounts for more than 65% of the total COD in the wastewater; the method is characterized by comprising the following steps:
s1 is aimed at aldehyde chemical wastewater, firstly, electrochemical oxidation is adopted to generate complexing agent;
s2 adding ferrous ion into the system after step S1, making the complexing agent complex with the ferrous ion to form a ferrous ion complex; and more than or equal to 50 percent of ferrous ions are complexed by the small molecular organic acid;
s3, adding hydrogen peroxide into the system after step S2 to ensure that the ferrous ion complex and the hydrogen peroxide are subjected to Fenton oxidation reaction for degradation;
the interval between the step S2 and the step S3 is more than 5 min;
an aeration step is added before the step S1 to ensure that the dissolved oxygen in the wastewater is 2-8 mg/L;
in the fenton oxidation in step S3, pH adjustment is not required.
2. The electrochemical oxidation-assisted Fenton oxidation method for aldehyde chemical wastewater treatment according to claim 1, wherein the current density of the electrochemical oxidation in the step S1 is 2 to 30mA/cm2Meanwhile, the time of electrochemical oxidation is 3 min-12 h.
3. The electrochemical oxidation-assisted Fenton oxidation method for aldehyde chemical wastewater treatment according to claim 1, wherein the carboxyl group in the small molecule organic acid complexing agent formed by the aldehyde group in the step S1 under the electrochemical oxidation condition is made to react with the Fe added in the step S22+The molar ratio of (0.5-6): 1.
4. The electrochemical oxidation-assisted Fenton oxidation method for aldehyde chemical wastewater treatment according to claim 2, wherein the H added in step S32O2And Fe added in the step S22+The ion molar ratio is (5-60): 1.
5. The electrochemical oxidation-assisted Fenton oxidation method for aldehyde chemical wastewater treatment according to claim 2, wherein the current density of the electrochemical oxidation in the step S1 is 5-25 mA/cm2。
6. The method of claim 2, wherein the Fenton oxidation in step S3 is enhanced by electrochemical oxidation at the beginning of step S3, and the current density of the electrochemical oxidation is 1-15 mA/cm2。
7. The electrochemical oxidation-assisted fenton oxidation method for aldehyde chemical wastewater treatment according to claim 6, wherein in the electrochemical oxidation of step S1 or step S3, the anode material is selected from one of a lead oxide electrode, a ruthenium oxide electrode, and a BDD electrode.
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