CN112079494B

CN112079494B - Method for treating emulsion wastewater

Info

Publication number: CN112079494B
Application number: CN202010841288.0A
Authority: CN
Inventors: 张峰; 崔建国; 武世煊; 李红艳; 崔佳丽; 王朝旭
Original assignee: Taiyuan University of Technology
Current assignee: Taiyuan University of Technology
Priority date: 2020-06-14
Filing date: 2020-08-20
Publication date: 2022-06-17
Anticipated expiration: 2040-08-20
Also published as: CN112079494A

Abstract

The invention belongs to the technical field of wastewater treatment, and provides a method for treating emulsion wastewater. Performing coagulative precipitation with potassium ferrate as an auxiliary, treating the emulsion wastewater by combining an electrochemical oxidation method, controlling the reaction temperature to be 35-40 ℃ by using PAC as a coagulant and potassium ferrate as a coagulant aid, performing coagulative precipitation pretreatment on the emulsion wastewater for 10min, and standing for 30-40 min; after the emulsion wastewater coagulating sedimentation pretreatment is finished, a BDD electrode electrochemical oxidation process is connected to carry out advanced treatment on the effluent of the coagulating sedimentation process. The potassium ferrate is used as the coagulant aid, so that the removal effect of the coagulant on organic pollutants can be improved, and the product of the potassium ferrate after hydrolysis cannot cause harm to human bodies and secondary pollution. The biodegradability of the effluent is improved. The electrochemical method can efficiently degrade pollutants in the wastewater, does not generate harmful substances, and does not cause secondary pollution. Compared to membrane processes, it is easy to frame and does not require cleaning.

Description

Method for treating emulsion wastewater

Technical Field

The invention belongs to the technical field of wastewater treatment, and particularly relates to a method for treating emulsion wastewater.

Background

At present, the key point of the treatment of the emulsion wastewater lies in effective demulsification, namely oil-water separation. In the prior art, a flocculating agent is added into coagulating sedimentation to enhance the effects of electric neutralization, adsorption bridging and the like in a solution, so that colloidal particles in the solution are destabilized and coalesced to form a large-particle flocculating body, and then a coagulant aid is added to further enhance the size and the concentration of flocculation; the coagulation and precipitation process is followed by biological process or membrane filtration process to deeply treat the effluent of the coagulation process. Thereby leading the effluent to reach the standard and then be discharged.

In order to solve the problem of serious ultrafiltration pollution blockage of an emulsion wastewater treatment system in a steel mill, the technological parameters are determined by experimental results of Wangming and the like: after emulsion in the regulating reservoir is heated, acidified and demulsified, liquid caustic soda is added to control the pH value to be 7-9, PAFC is selected as a flocculating agent, and cationic PAM is selected as a coagulant aid. The field test operation shows that: by adjusting the adding concentration of PAFC and PAM, the COD of the air floatation effluent of the emulsion system_CrThe removal rate reaches 93.7 percent, and the air-flotation effluent can be directly discharged into a dilute alkali oil wastewater system for secondary treatment, thereby solving the problem that the emulsion system cannot normally operate due to ultrafiltration fouling.

In the wastewater treatment of certain processing industry, the wastewater containing the concentrated oil and the emulsion discharged from the acid rolling production line enters a wastewater regulating tank containing the concentrated oil and the emulsion through a distribution water tank. The waste water in the regulating tank is heated and skimmed to remove floating oil, and then is conveyed to a paper tape filter by a pump to be filtered so as to remove coarse floating slag in the waste water. The effluent of the paper tape filter enters an ultrafiltration circulating tank, the effluent of the circulating tank enters an ultrafiltration system, oil-water separation is carried out by utilizing the interception effect of an ultrafiltration membrane, and part of COD is removed_CrAnd other impurities. COD of concentrated oil wastewater after ultrafiltration treatment_CrIs still higher, in order to ensure the COD of the effluent_CrAnd (4) after reaching the standard, performing biochemical treatment on the ultrafiltration effluent. And (4) adjusting the pH value of the ultrafiltration effluent to be neutral in a pH adjusting tank, and pumping the ultrafiltration effluent into a cooling tower for cooling. After cooling downThe wastewater enters the facultative tank to be hydrolyzed so as to degrade high molecular organic matters, thereby improving the biodegradability of the wastewater and being beneficial to the normal operation of a subsequent membrane bioreactor. The effluent of the facultative tank enters an aeration tank of a membrane bioreactor, and COD in the wastewater is further degraded through aerobic activity of aerobic microorganisms_CrBOD. The interception function of the membrane can intercept microorganisms in the wastewater, maintain higher sludge concentration in the aeration tank and improve the treatment efficiency of a biochemical system. The biochemical effluent of the membrane bioreactor meets the discharge requirement and is directly discharged to a final discharge water tank.

At present, the main problems of the existing emulsion wastewater treatment technology mainly exist:

the flocculating agent and the coagulant aid Polyacrylamide (PAM) are used for treating the emulsified wastewater in the coagulating sedimentation section, although an effective oil-water separation phenomenon can occur, the biodegradability of the effluent is still low; moreover, PAM is not used properly but is not beneficial to the aggregation of flocculating constituent. Meanwhile, PAM is used in an excessive amount, so that certain toxicity is generated to human bodies.

The subsequent advanced treatment is generally connected with a biological treatment method or an ultrafiltration membrane treatment method, and the biochemical treatment mainly utilizes microorganisms to degrade pollutants in the wastewater. Mainly divided into a biological filter and an activated sludge method. The biological filter is a bioreactor, inert materials are filled in the biological filter, and pollutants are degraded mainly by means of biological communities on the materials. The activated sludge process is a process of decomposing macromolecular pollutants into micromolecular organic or inorganic substances through an aerobic or anaerobic reaction process depending on metabolism of various microorganisms in sludge. The problems of the deep treatment of the emulsified wastewater by the biological method mainly comprise that: the residence time is long, and the occupied area is large; improper seepage-proofing treatment can pollute underground water, and foul smell is easily emitted in summer, so that mosquitoes and flies are grown to cause pollution.

The ultrafiltration method for treating the emulsion wastewater mainly utilizes the obvious difference of the sizes of oil-water molecules and adopts a cross flow filtration mode to filter oil and water. Water molecules are smaller than pores and penetrate through the ultrafiltration membrane, oil molecules are larger than pores and cannot penetrate through the ultrafiltration membrane, and therefore oil-water separation is achieved. The ultrafiltration method adopts more organic membranes, but the cost of the organic membranes is too high, and the organic membranes have the defects of no high temperature resistance, low mechanical strength, easy hydrolysis and the like. Meanwhile, the ultrafiltration membrane has the problems of over-quick reduction of membrane flux, easy pollution of the membrane and the like. Cleaning is performed periodically and additional economic expenditure is incurred.

Disclosure of Invention

The invention provides a method for treating emulsion wastewater, aiming at solving the technical problems in the existing emulsion wastewater treatment process.

The invention is realized by the following technical scheme: a method for treating emulsion wastewater adopts potassium ferrate to assist coagulation and precipitation and combines an electrochemical oxidation method to treat the emulsion wastewater, and comprises the following steps:

(1) a coagulating sedimentation process: adjusting the pH value of the emulsion wastewater to 9, taking polyaluminium chloride PAC as a coagulant, taking potassium ferrate as a coagulant aid, and adding the coagulant aid in an amount of 50-100mg/L and 50-75 mg/L; stirring to uniformly disperse the medicament in the solution, controlling the reaction temperature to be 35-40 ℃, carrying out coagulation and precipitation pretreatment on the emulsion wastewater for 10min, and then standing for 30-40 min;

(2) an electrochemical oxidation process: after the emulsion wastewater coagulating sedimentation pretreatment is finished, a BDD electrode electrochemical oxidation process is connected to carry out advanced treatment on the effluent of the coagulating sedimentation process, and the specific method comprises the following steps: discharging the effluent after the coagulating sedimentation pretreatment into a new reservoir, adjusting the initial pH to be 7-9 by taking a BDD electrode as an anode and a Ti electrode as a cathode, and controlling the current density to be 50-100 mA/cm²Controlling the reaction temperature within the range of 30-40 ℃, and electrolyzing the effluent after the coagulating sedimentation pretreatment for 4-5 hours.

The coagulant is any one of polyaluminium chloride PAC, polyferric sulfate PFS, aluminum sulfate or ferric sulfate. The preferred coagulant is polyaluminium chloride PAC.

PAC dosage is 50mg/L, potassium ferrate dosage is 50mg/L, reaction temperature is 40 ℃, stirring is carried out for 10min, and standing and settling are carried out for 30 min.

In the electrochemical oxidation process of the step (2), the initial pH is 9, and the current density is 75mA/cm²The reaction temperature is 40 ℃, and the electrolytic reaction is carried out for 5 hours.

The invention adopts potassium ferrate as coagulant aid, which can improve the effect of removing organic pollutants, and the product of potassium ferrate after hydrolysis can not cause harm to human body and secondary pollution. The biodegradability of the effluent is improved. The electrochemical method is an advanced oxidation method, can efficiently degrade pollutants in the wastewater, does not generate harmful substances, and does not cause secondary pollution. Compared to the membrane treatment process, it is easy to frame and does not require cleaning.

According to the invention, the emulsion wastewater is treated by adopting a technology of carrying out coagulation precipitation on PAC (Poly aluminum chloride) assisted by potassium ferrate and then carrying out electrochemical oxidation on BDD (BDD electrode), and the conventional process commonly adopts an organic flocculant PAM (Polyacrylamide) as a coagulant aid to assist an inorganic flocculant to jointly pretreat the emulsion wastewater, but the conventional process has the common problems that the components of the emulsion are complex, the flocculant cannot effectively demulsify the emulsion wastewater, the phenomena of unobvious water-oil separation and the like occur, the removal effect on organic pollutants is poor, and the PAM is added in time to increase the volume of the flocs, so that the ideal effect cannot be achieved.

The invention adopts potassium ferrate as coagulant aid, and can greatly improve the removal effect of the solution on organic pollutants by virtue of the strong oxidizing property of the potassium ferrate. Meanwhile, the hydrolysis product with positive high charge generated in the reduction process of the ferrate can improve the treatment effect of PAC on emulsified wastewater in the coagulating sedimentation process section; and the potassium ferrate can effectively change the floc structure, enhance the floc density, accelerate the sedimentation of the floc and shorten the time required by the process. Under the conditions of neutrality and alkalescence, a good effect can be achieved, the removal efficiency of COD and turbidity can reach more than 90%, and the biodegradability is improved for the subsequent process treatment.

The potassium ferrate as a green water purifying agent can not generate secondary pollution and can effectively reduce the harm of residual aluminum. The waste water treated by the coagulating sedimentation process section is connected with a BDD electrode as an anode in an electrochemical oxidation process, and the process quickly and efficiently converts organic substances into CO by means of the reaction of strong oxidant OH generated by the electrolysis of the anode surface and the organic substances in the waste water₂And H₂O or a small molecule inorganic substance, and is coated withAnd (5) removing the effect.

The process is fast and efficient and does not need to add additional oxidant to degrade pollutants. In addition, the BDD electrode is electrochemically oxidized without generating pollutants, so that secondary pollution is avoided; and the boron-doped diamond film is an inert material, has strong acid resistance and corrosion resistance, has a wide potential window and has long service life. In contrast, the membrane filtration method or ultrafiltration method is easy to cause problems such as membrane blockage or membrane pollution after being used for many times, and the filtration membrane must be cleaned in time. The price of the membrane is expensive, the required occupied area is large, and improper treatment can cause pollution and economic loss; and by utilizing biological treatment, the required field is large, the operation cost is increased, secondary pollution is easily caused, more sludge is generated, and the sludge needs to be further treated, so that additional cost requirement is caused.

In conclusion, the method of the invention can not only improve the removal efficiency of the pollution substances in the prior art, but also effectively improve the biodegradability; the problems of secondary pollution, high cost, large occupied area and the like in the prior art can be effectively avoided. Is an economical, effective and feasible process flow.

The invention adopts two-stage process of PAC (Poly aluminum chloride) coagulation sedimentation assisted by potassium ferrate and BDD (BDD) electrode electrochemical oxidation to treat emulsion wastewater, and adopts the best experimental conditions of two-stage combined process determined by single factor experiment, namely the initial pH of a flocculation sedimentation process stage is 9, the PAC addition amount is 50mg/L, the potassium ferrate addition amount is 50mg/L, the reaction temperature is 40 ℃, the stirring is carried out for 10min, and the standing sedimentation is carried out for 30 min; the initial pH of the electrolysis process section is 9, the current density is 75mA/cm2, the reaction temperature is 40 ℃, and the electrolysis reaction is carried out for 5 hours. After the combined process treatment of coagulating sedimentation and electrochemical oxidation is carried out in sequence, the effluent is colorless and tasteless and has COD_CrIs 23mg/L, c (NH)₃-N) was 0.35mg/L, TOC was 11.75mg/L, and turbidity was 2.1 NTU. The main indexes all reach the primary standard of the integrated wastewater discharge standard (GB8978-1996), and simultaneously meet the requirements of the wastewater discharge to town sewer water quality standard (GB/T31962-.

Drawings

FIG. 1 shows the effect of potassium ferrate dosage on emulsion wastewater removal in the case of PAC dosage of 50 mg/L;

FIG. 2 shows the effect of potassium ferrate dosage on emulsion wastewater removal in the case of PFS dosage of 50 mg/L;

FIG. 3 is a graph showing the effect of potassium ferrate addition on emulsion wastewater removal when aluminum sulfate addition is 100 mg/L;

FIG. 4 shows the effect of potassium ferrate dosage on emulsion wastewater removal effect when ferric sulfate dosage is 100 mg/L;

FIG. 5 is a graph showing the effect of initial pH on the effect of contaminant coagulative precipitation removal;

FIG. 6 is a graph showing the effect of reaction temperature on the effect of removing the coagulating sedimentation of contaminants;

FIG. 7 is a graph showing the effect of settling time on the effect of removing the coagulative precipitation of contaminants;

FIG. 8 shows the effect of PAC dosage on contaminant removal at a solution pH of 9, a potassium ferrate dosage of 50mg/L, and a reaction temperature of 30 ℃;

fig. 9 is a graph of the effect of electrolyte concentration on contaminant degradation, where: (1) is COD_CrThe removal effect of (2); (2) is NH₃-the removal effect of N; (3) the removal effect of TOC;

FIG. 10 is a graph of the effect of current density on contaminant degradation; in the figure: (1) for current density to COD_CrThe removal effect of (3); (2) is current density vs. NH₃-the removal effect of N;

FIG. 11 is a graph showing the effect of electrolytic pH on contaminant degradation; in the figure: (1) for different electrolysis pH to COD_CrThe removal effect of (3); (2) for different electrolysis pH vs. NH₃-the removal effect of N;

FIG. 12 is a graph showing the effect of electrolysis temperature on contaminant degradation; in the figure: (1) for different electrolysis temperatures to COD_CrThe removal effect of (3); (2) for different electrolysis temperatures to NH₃-the removal effect of N;

FIG. 13 is a graph of TOC removal rate over time.

Detailed Description

The following further describes embodiments of the present invention.

A method for treating emulsion wastewater adopts potassium ferrate to assist coagulation and precipitation and combines an electrochemical oxidation method to treat the emulsion wastewater, and comprises the following steps:

analysis of reaction mechanism: PAC as a polymeric inorganic flocculant is hydrolyzed to produce a large amount of positively charged hydrolyzate and Al (OH)₃The colloid has strong adsorption effect, so that the addition of PAC promotes the effects of electric neutralization, adsorption bridging and the like in the solution, and the destabilization and coalescence of colloid particles in the solution are enhanced; the potassium ferrate is a water treatment agent integrating oxidation, flocculation, coagulation aid and disinfection functions.

In the invention, the pH value is adjusted to 9, which is beneficial to the potassium ferrate to exert the strong oxidizing property thereof and oxidize macromolecular organic matters into micromolecular organic matters, thereby promoting the PAC to coagulate and remove organic pollutants. Meanwhile, in the process of reducing hexavalent iron ions of potassium ferrate into trivalent iron ions, an intermediate product with a positive high valence state, positive electricity and a net structure is generated, and the net capturing effect of PAC is enhanced. And potassium ferrate can effectively change the structure of flocs and promote the aggregation of the flocs, thereby accelerating the sedimentation, being beneficial to improving the efficiency of the industry and saving the cost. And Fe (OH) produced₃The colloid can react with Al (OH)₃The colloid generates coprecipitation, can further treat pollutants in the solution, and improves the biodegradability of the wastewater. Meanwhile, the temperature of the effluent in the industry is about 30 ℃, the temperature is properly increased to 35-40 ℃, and the Brownian motion among floccules in the solution is accelerated, so that the polymerization of the floccules is accelerated.

(2) An electrochemical oxidation process: emulsion liquidAfter the wastewater coagulating sedimentation pretreatment is finished, a BDD electrode electrochemical oxidation process is connected to carry out advanced treatment on the effluent of the coagulating sedimentation process, and the specific method comprises the following steps: discharging the effluent of the coagulating sedimentation process section into a new reservoir, adjusting the initial pH to be 7-9 by taking a BDD electrode as an anode and a Ti electrode as a cathode, and controlling the current density to be 50-100 mA/cm²Within the range, the reaction temperature is controlled between 30 and 40 ℃, and the effluent of the front-stage process is electrolyzed. The electrolysis time is 4-5 h.

A large amount of OH with strong oxidizing property is generated on the electrolytic surface of the BDD, so that organic pollutants in the effluent are efficiently degraded, and the organic pollutants can be directly degraded into carbon dioxide and water on the surface of the anode. Meanwhile, the reaction temperature is increased, so that the generation rate of OH can be increased, and the indirect oxidation rate of the BDD electrode can be effectively increased. Meanwhile, Brownian motion of solute in the solution is enhanced, diffusion rate of pollutants in the solution and chemical reaction rate of the surface of the electrode are improved, and electrolytic reaction is effectively promoted. Thereby greatly improving the removal of pollutants in the wastewater, improving the biodegradability of the effluent and providing a guarantee for subsequent advanced treatment.

Experimental example 1: contrast experiment of potassium ferrate compound coagulant

A. Compounding potassium ferrate with PAC: adjusting initial pH =7 with 1mol/L sulfuric acid and sodium hydroxide solution, setting the temperature at 30 ℃, and adding a coagulant aid potassium ferrate (1% solution) into the wastewater under the condition that the PAC adding amount is 50mg/L, so that the content of the potassium ferrate in the water sample is respectively 0, 20, 30, 50 and 100 mg/L.

The effect of the amount of potassium ferrate on the removal of contaminants is shown in FIG. 1. From FIG. 1, it was found that as the amount of potassium ferrate added was increased from 0 to 50mg/L, the removal rates of CODCr and turbidity of the solution rapidly increased from 48.6%, 62.1% to 84.8%, 92.07%, respectively. Table 1 shows the effect on the emulsion wastewater removal efficiency when PAC was added only, and table 2 shows the effect on the emulsion wastewater removal efficiency when potassium ferrate was added only. As can be seen from tables 1 and 2, when only PAC (50 mg/L) or potassium ferrate (50 mg/L) is added, the removal rate of CODCr is respectively 48.6% and 14.25%, and the removal rate of turbidity is respectively 62.1% and 20.56%. When the two are added in a combined mode, the removal rate of CODCr reaches 84.8%, and the turbidity removal rate reaches 92.07%, so that obvious synergistic effect is formed.

TABLE 1 Effect on emulsion wastewater removal efficiency when PAC alone was dosed

TABLE 2 influence on emulsion wastewater removal efficiency when adding only potassium ferrate

B. Compounding potassium ferrate with PFS: adjusting the initial pH =7, setting the reaction temperature at 30 ℃, and adding a coagulant aid potassium ferrate (1% solution) into the wastewater under the condition that the adding amount of PFS is 50mg/L, so that the content of the potassium ferrate in the water sample is respectively 0, 20, 30, 50 and 100 mg/L. The results of the effect of PFS addition on the emulsion wastewater removal effect are shown in Table 3. As is clear from Table 3, when the amount of PFS added was 50mg/L and no potassium ferrate was added, the removal rates of CODCr and turbidity in the emulsion wastewater were 46.75% and 57.96%, respectively.

FIG. 2 is a graph showing the effect of potassium ferrate addition on emulsion wastewater removal in the case of PFS addition of 50mg/L, and it can be seen from the observation of FIG. 2 that CODCr and turbidity removal rates of wastewater rapidly increase from 48.6%, 62.1% to 81.25%, 90.2% with potassium ferrate increasing from 0 to 50mg/L, respectively. It can be seen by combining tables 2, 3 and 2 that the removal rate of CODCr is lower when only PFS (50 mg/L) or potassium ferrate (50 mg/L) is added, respectively 46.75% and 14.25%, and when the two agents are added into the emulsified waste liquid in a compounding way, the removal rate of CODCr reaches 81.25%, and the obvious change of turbidity can be seen visually, which indicates that the coagulation sedimentation effect of PFS is strengthened by adding potassium ferrate.

TABLE 3 result of influence of PFS dosage on emulsion wastewater removal effect

C. Potassium ferrate compounded Al₂(SO₄)₃: table 4 shows the results of the effect of adding aluminum sulfate alone on the removal effect of emulsion wastewater, and it can be seen from table 4 that when aluminum sulfate alone (100 mg/L) was added, the removal rates of CODCr and turbidity in emulsion wastewater were 31.1% and 40.36%, respectively.

FIG. 3 shows the effect of potassium ferrate on the removal of emulsion wastewater when the amount of aluminum sulfate added is 100 mg/L; it was also found from FIG. 3 that as the amount of potassium ferrate added was increased from 0 to 50mg/L, the removal rates of CODCr and turbidity of the solution rapidly increased from 31.1%, 40.36% to 75.68%, 84.88%, respectively. It can be seen by combining tables 2 and 4 that when aluminum sulfate (100 mg/L) or potassium ferrate (50 mg/L) is added alone, the removal rate of CODCr is lower, namely 31.1% and 14.25%, respectively, but when ferric sulfate and potassium ferrate are added into the emulsified liquid wastewater in a compounding manner, the removal rate of CODCr can reach 75.68%, which indicates that potassium ferrate can effectively improve the removal effect of aluminum sulfate on the emulsified wastewater.

TABLE 4 results of the effect of aluminum sulfate addition alone on the emulsion wastewater removal

D. Potassium ferrate complex Fe2(SO4) 3: table 5 shows the results of the effect of ferric sulfate addition on the removal of emulsion wastewater, when the amount of ferric sulfate addition was 100mg/L and the amount of potassium ferrate addition was 0mg/L, the removal rates of CODCr and turbidity in emulsion wastewater were 27.63% and 37.76%, respectively.

FIG. 4 shows the effect of potassium ferrate dosage on emulsion wastewater removal effect when ferric sulfate dosage is 100 mg/L; as can be seen from the observation of FIG. 4, the CODCr and turbidity removal rate of wastewater rapidly increased from 27.63% and 37.76% to 71.75% and 79.5% respectively with increasing potassium ferrate dosage (from 0 to 50 mg/L). As can be seen from the analysis of tables 2 and 5, when ferric sulfate (100 mg/L) or potassium ferrate (50 mg/L) is added alone, the removal rates of CODCr and turbidity are respectively 27.63% and 14.25% and 37.76% and 20.56%, the removal effect is poor, but when two agents are used for treating the waste emulsion in a composite way, the removal rates of CODCr and turbidity can reach 71.75% and 79.5%.

TABLE 5 results of the effect of iron sulfate addition alone on the emulsion wastewater removal

When the potassium ferrate is compounded with different coagulants (PAC, PFS, aluminum sulfate and ferric sulfate) to simultaneously remove CODcr and turbidity in the emulsion wastewater, the removal effect of the CODcr and the turbidity in the wastewater can be effectively improved. Comparing the experimental results, the optimal sequence of the effect of the potassium ferrate and the four flocculating agents for the complex treatment of the emulsion wastewater is as follows: potassium ferrate + PAC > potassium ferrate + PFS > potassium ferrate + aluminum sulfate > potassium ferrate + ferric sulfate.

The removal rate of PAC (polyaluminium chloride) compounded by potassium ferrate reaches the maximum, so PAC is selected as a coagulant in subsequent experiments.

Prior studies have also demonstrated that potassium ferrate as a coagulant aid can enhance the removal of organic contaminants. The potassium ferrate is a strong oxidant with strong oxidizing power, and the oxidizing power of the potassium ferrate is stronger than that of potassium permanganate and O₃And the like. At the same time K₂FeO₄Has the advantages of high efficiency, no toxicity, no harm and the like, and is a novel high-efficiency water purifying agent which has the functions of oxidation, adsorption, coagulation assistance, flocculation and the like and can remove organic matters and heavy metal ions.^[1-3]

The potassium ferrate can effectively change the floc structure, enhance the floc density, accelerate the sedimentation of the floc and shorten the time required by the process. And under the conditions of positive neutrality and alkalescence, a good effect can be achieved, the removal efficiency of COD and turbidity can reach more than 90%, and the biodegradability is improved for the subsequent process continuous treatment.

Experimental example 2: single factor experiment in coagulating sedimentation stage: adding 100mL of emulsion wastewater into a beaker, and adding 1mol/L of H₂SO₄And NaOH solution to adjust pH. Sequentially adding a coagulant PAC (10% solution) and a coagulant aid potassium ferrate (1% solution) in specified amounts, and performing magnetic stirring at a set temperature and a fixed rotating speed. Stirring for reaction for 10min, standing for settling for 30min, collecting supernatant, and measuring COD_CrAnd a haze value. Factors examined include: initial pH (3, 5, 7, 9, 11), PAC dosage (0, 10, 20, 30, 50, 100mg/L), potassium ferrate dosage (0, 20, 30, 50, 100mg/L), reaction temperature (20, 30, 40, 50, 60 ℃), settling time.

The influence of the initial pH on the effect of removing the coagulating sedimentation of the pollutants is shown in FIG. 5, and the initial pH value is selected to be 9 in subsequent experiments according to the experimental results of FIG. 5.

1. Effect of reaction temperature on contaminant removal effect: the removal effect of the coagulative precipitation of the pollutants at reaction temperatures of 20, 30, 40, 50 and 60 ℃ was examined under the conditions that the solution pH was 9, PAC and potassium ferrate were all 50mg/L, and the results are shown in FIG. 6. As can be seen from the figure, when the reaction temperature is raised from 20 ℃ to 40 ℃, the COD of the solution is_CrAnd turbidity removal increased from 73.9%, 89.9% to 86.3%, 96.6%, respectively. Generally speaking, with the rising of the water temperature, the Brownian motion in the solution is strengthened, and the contact probability among flocculating constituents is greatly improved; however, the water temperature is too high, the hydrolysis reaction speed of PAC and potassium ferrate can be accelerated, the flocculation is loose, the sedimentation is not easy to occur, and the coagulation sedimentation is adversely affected^[4,5]. And when the water temperature is lower, the coagulant is slowly hydrolyzed, the viscosity of water is higher, the Brownian motion is weaker, and the heterodromous flocculation of destabilized colloidal particles is not facilitated. As shown in the figure, as the reaction temperature continues to rise, the COD of the solution_CrAnd the turbidity removal rate rises slowly or even decreases. According to the experimental results, 40 ℃ is selected as the optimum reaction temperature. Due to the characteristics of the processing technology, the actual temperature of the waste emulsion is approximately between 20 and 30 ℃. Considering the influence of the reaction temperature on coagulation and the application of practical engineering, the generated wastewater is recommended to be treated as soon as possible, so that the dosage of the medicine is reduced,the energy consumption of temperature rise is reduced, and the industrial cost is saved.

2. Influence of settling time on pollutant removal effect: under the conditions that the initial pH of the solution is 9, the PAC and the potassium ferrate are both 50mg/L, the reaction temperature is 40 ℃, the solution is stirred at a constant speed for 10min and then is kept stand for precipitation, and the influence of the precipitation time on the flocculation treatment effect of the composite medicament is examined as shown in figure 7. As can be seen from FIG. 7, COD increased with the settling time in the pre-settling period (between 0 and 30 min)_CrAnd the turbidity removal rate increases rapidly; the settling time is continuously prolonged, COD_CrAnd the increase in turbidity removal rate gradually slowed down.

This indicates that the settling time directly affects the flocculation effect of the flocculent on adsorbing the pollutants in the wastewater. With time, it can be observed that after the wastewater is treated by PAC (polyaluminium chloride) assisted by potassium ferrate, fine flocculating constituents formed in the solution are mutually aggregated and extruded to form a nodular structure. Under the action of gravity, the water in the lower layer is continuously extruded, and obvious layering occurs. As settling time advances, the water layer becomes thicker and clear and the flocs become more dense. After 30min, the sedimentation had substantially stabilized and no further significant change was observed.

When the settling time is less than 30min, the flocculating constituent can not sufficiently adsorb organic pollutants in the wastewater due to short settling time, and the destabilized flocculating constituent can not completely settle, so that COD (chemical oxygen demand) is ensured_CrAnd turbidity removal is low. When the settling time exceeds 30min, COD is obtained_CrAnd turbidity removal did not change significantly or even decreased to some extent, probably due to re-dissolution of some of the organics during the lengthy settling period. Comprehensively considering, in the process of treating the emulsion wastewater by using the potassium ferrate to assist PAC, the optimal settling time is determined to be 30 min.

3. Influence of PAC dosage on pollutant removal effect: under the conditions that the pH of the solution is 9, the adding amount of potassium ferrate is 50mg/L and the reaction temperature is 30 ℃, 0, 10, 20, 30, 50 and 100mg/L PAC is respectively added into the solution, the influence of the adding amount of PAC on the pollutant removal effect is examined, and the result is shown in FIG. 8. As can be seen from the figure, when the coagulant aid with the same amount is added, the adding amount of PAC has obvious influence on the flocculation precipitation effect; followed byThe COD of the wastewater is increased continuously_CrAnd the turbidity removal rate is rapidly increased.

When the dosage of the potassium ferrate is 50mg/L, the COD of the solution is increased from 10 to 50mg/L along with the increase of the dosage of PAC_CrThe removal rate of (2) was increased from 14.25% to 84.8%, and the turbidity removal rate was increased from 20.56% to 92.07%. The PAC addition amount is increased, so that more high-valence polynuclear complexes are generated by hydrolysis in the solution, and the double-electrode lamination and adsorption charge neutralization effects are promoted. When the PAC dosage reaches 100mg/L, the COD and turbidity removal rates are respectively reduced to 82.01% and 83.54%. Because excessive flocculating constituents surround the colloidal particles, the collision probability of the colloidal particles can be reduced, the adsorption and bridging effects are influenced, and the flocculation precipitation cannot achieve the ideal effect.

4. The influence of coagulant aid dosage on the pollutant removal effect: the results of examining the influence of coagulant aids added in amounts of 0, 20, 30, 50, and 100mg/L on the contaminant removal effect under the conditions of a solution pH of 9, a PAC addition of 50mg/L, and a reaction temperature of 30 ℃ are shown in FIG. 1. As the amount of potassium ferrate added increases from 0 to 50mg/L, the solution and turbidity removal rates rapidly increase from 48.6%, 62.1% to 84.8%, 92.07%, respectively. The COD can be seen by combining tables 1 and 2_CrCOD when PAC (50 mg/L) or potassium ferrate (50 mg/L) is added_CrThe removal rate of (A) is lower, namely 48.6 percent and 14.25 percent respectively, and when the two are added in a combined way, COD is obtained_CrThe removal rate of the catalyst reaches 84.8%, and obvious synergy is formed.

On the one hand, the strong oxidizing property of potassium ferrate destroys the organic protective layer on the surface of colloid in the solution, and destabilizes the wastewater through the electric neutralization. On the other hand, Fe (OH) produced₃Flocs capable of adsorbing fine colloidal particles and reacting with Al (OH)₃The colloid is adsorbed and coprecipitated, so that pollutants in the wastewater can be effectively removed. Meanwhile, potassium ferrate is added, so that the floc structure can be changed, and the floc is more compact and easy to settle. When potassium ferrate is added in a certain amount, the stability of potassium ferrate is deteriorated, decomposition is accelerated, and excessive Fe (OH)₃The waste water is recombined with the substances difficult to settle to form suspended substances, so that COD_CrThere was a slight decrease in turbidity removal. In synthesis ofAfter considering the removal effect of pollutants and the cost of medicines, the dosage of PAC and the dosage of potassium ferrate are both determined to be 50 mg/L.

Determining the optimal experimental conditions of the two-stage combined process by adopting a single-factor experiment, namely, the initial pH of a flocculation precipitation process stage is 9, the adding amount of PAC is 50mg/L, the adding amount of potassium ferrate is 50mg/L, the reaction temperature is 40 ℃, stirring is carried out for 10min, and standing and settling are carried out for 30 min; the initial pH of the electrolysis process section is 9, and the current density is 75mA/cm²The reaction temperature is 40 ℃, and the electrolytic reaction is carried out for 5 hours. After the combined process treatment of coagulating sedimentation and electrochemical oxidation is carried out in sequence, the effluent is colorless and tasteless and has COD_CrIs 23mg/L, c (NH)₃-N) was 0.35mg/L, TOC was 11.75mg/L, and turbidity was 2.1 NTU. The main indexes all reach the primary standard of the integrated wastewater discharge standard (GB8978-1996), and simultaneously meet the requirements of the wastewater discharge to town sewer water quality standard (GB/T31962-.

The removal effect of factors such as the addition amount of the flocculating agent, the addition amount of the potassium ferrate, the reaction temperature, the initial flocculation pH value, the settling time and the like on the emulsified wastewater treated by each compound combination is considered, and finally the compound of the potassium ferrate and the polyaluminium chloride is selected to be combined into the optimal combination for the emulsified wastewater treatment. According to the single-factor experiment, the optimal conditions of all the process parameters are as follows: the PAC dosage is 50mg/L, the potassium ferrate dosage is 50mg/L, the initial pH is 9, the reaction temperature is 40 ℃, and the settling time is 30 min. At this time, the quality of the effluent from the coagulation and precipitation process stage is shown in Table 6. The removal rates of CODcr and turbidity were 89.5% and 92.5%, respectively.

Table 6: quality of wastewater discharged from coagulating sedimentation process section

Experimental example 3: electrochemical oxidation phase experiment: injecting the wastewater treated under the optimal conditions of the 500mL coagulating sedimentation process section into a beaker with the effective volume of 500mL, and adding 500mg/L Na₂SO₄Electrolytes to increase solution conductivity. The BDD anode and the Ti cathode are vertically oppositely arranged in a beaker, the distance between polar plates is 10mm, and the immersion area is 10cm²And applying a set current density to perform constant-current electrochemical degradation. Placing the beaker on a constant-temperature magnetic stirrer in the reaction to ensure that the concentration of the reaction solution is uniform and the temperature is constant; samples were taken at regular intervals to determine the concentration values of CODCr, ammonia nitrogen (NH3-N) and Total Organic Carbon (TOC). Factors examined include: current density (20, 30, 50, 75, 100mA/cm2), initial pH of the electrolysis process section (3, 5, 7, 9, 11) and electrolysis reaction temperature (20, 30, 40, 50, 60 ℃).

1. Influence of electrolyte concentration on the electrochemical oxidation effect: in order to investigate the effect of the supporting electrolyte concentration on the wastewater degradation efficiency, Na2SO4 was selected as the supporting electrolyte, and the supporting electrolyte concentrations were set to 300mg/L, 500mg/L and 1000mg/L, respectively. Taking 500mL of effluent of the coagulating sedimentation process section to be placed in a beaker, and setting the current density to be 50mA/cm²Experiments were performed with the plate spacing kept at 10 mm. The degradation effect of the supporting electrolyte concentration on the effluent of the BDD electrode electrolytic oxidation coagulating sedimentation process section is shown in figure 9.

From fig. 9 (1), (2) and (3), it can be seen that the removal rates of CODCr, ammonia nitrogen and TOC of the solution are all rapidly increased as the electrolysis time is increased from 0 to 180min when the solutions are degraded under three different concentrations of supporting electrolytes. Meanwhile, it can be seen that the degradation degree of each pollutant in the wastewater is gradually increased along with the increase of the concentration of the supporting electrolyte from 300mg/L to 1000mg/L in the same electrolysis time. The reason for the analysis may be that the addition of the auxiliary electrolyte increases the ion concentration in the solution, thereby enhancing the mass transfer capability of the ions in the solution. Meanwhile, the conductivity of the solution is continuously increased, which is beneficial to the electron transfer and the electrolytic reaction. And after 180min of electrolysis, the removal rates of CODCr, ammonia nitrogen and TOC under the electrolyte concentrations of 300mg/L, 500mg/L and 1000mg/L respectively reach 58.6%, 65.28%, 66.32%, 74.58%, 88.46%, 90.89% and 58.45%, 65.64% and 70.16%. The electrolysis time is continuously prolonged, and the removal rate is kept rising slowly.

As can be seen from the figure, the CODCr, ammonia nitrogen and TOC removal effect of the solution is not significantly different when the supporting electrolyte concentration is 500mg/L and 1000mg/L, respectively. It is thus understood that when the supporting electrolyte concentration reaches a certain level, its effect on the electrolytic process gradually diminishes or even disappears. Therefore, 500mg/L Na2SO4 was selected as the optimum supporting electrolyte concentration while ensuring efficient removal effect and reducing chemical costs.

2. Effect of current density on contaminant removal: the current density is an important factor affecting the electrochemical oxidation process. COD treated by optimum process conditions of coagulating sedimentation_Cr=456mg/L、c(NH₃-N) =26mg/L of wastewater at current density of 20, 30, 50, 75, 100mA/cm²The influence of the current density on the degradation effect of the wastewater treated by the electrolysis process section is examined, and the results are shown in (1) and (2) of FIG. 10.

The BDD electrode is mainly used for oxidizing organic pollutants by oxidizing agents such as OH, hypochlorous acid and the like generated on the surface of an anode, and indirectly oxidizing and degrading the organic pollutants by the aid of the reactions shown in formulas (1) to (4).

BDD+H₂O→BDD(·OH)+H⁺+e^- （1）

BDD(·OH)+R→BDD+CO₂+H₂O （2）

2Cl^-→Cl₂+2e^- （3）

Cl₂+H₂O→HClO+Cl^-+H⁺ （4）。

As can be seen from FIG. 10, the current density was varied from 20mA/cm at the same electrolysis time²Increased to 75mA/cm²，COD_CrAnd the removal rate of ammonia nitrogen is gradually increased. This is because increasing the current density facilitates electron transfer and produces high concentration OH, thereby accelerating oxidative degradation of the anode surface; in addition, Cl is present in the wastewater after the flocculation precipitation process section treatment^-The production of HClO oxidant may be promoted as the current density increases. The current density is increased to 100mA/cm²，COD_CrAnd ammonia nitrogen removal rate, on the contrary, shows a tendency to decrease. Because the oxygen evolution side reaction of water decomposition of the anode is aggravated by the overhigh current density, a large number of micro-bubbles are attached to the surface of the electrode, and organic pollutants are prevented from approaching the surface of the electrode to be oxidized. Therefore, 75mA/cm was selected²Is the optimum anode currentDensity.

3. Effect of electrolytic pH on contaminant removal: in order to examine the influence of different initial pH values of the electrolysis process section on the pollutant removal effect, 1mol/L H is adopted₂SO₄And NaOH solution to adjust the electrolytic pH to 3, 5, 7, 9 and 11 respectively. The effect of electrolytic pH on the contaminant removal effect is shown in FIGS. 11(1) and (2). As can be seen from the figure, the degradation effect is best under the alkalescent condition; under neutral and weakly acidic conditions; the degradation effect is the worst under strong acid and strong alkali conditions. Since the BDD electrode has weak chlorine-evolving ability and generates little HClO, the main reaction mechanism of electrolytic oxidation is the. OH indirect oxidation. The electron abstraction of hydroxyl at the anode is one of the main ways to generate OH. As the electrolysis pH increases, the hydroxide concentration increases and the BDD electrolysis surface produces more OH. However, when the amount of hydroxyl in the solution is excessive, OH generation cannot be further promoted, but the anodic oxygen evolution potential is lowered, the oxygen evolution side reaction is accelerated, and the BDD electrode is not favorable for removing organic pollutants. For ammonia nitrogen, NH is carried out under neutral to weakly alkaline conditions₃Higher removal (> 80%) of-N was achieved at 3 h. Under the condition of medium and alkali, NH₃N is present mainly in the form of free ammonia, the products of which are predominantly nitrogen and water at the anode. Therefore, the optimum electrolytic pH for electrochemically degrading organic matter is 9.0.

4. Effect of electrolysis temperature on wastewater treatment: the initial temperature of the electrolytic reaction is set to 20 ℃, 30 ℃, 40 ℃, 50 ℃ and 60 ℃, and the degradation effect of BDD electrode electrolytic oxidation treatment wastewater at different electrolytic temperatures is examined, as shown in figures 12(1) and (2). As can be seen from the figure, COD in the solution increased from 20 ℃ to 40 ℃ at the initial temperature_CrAnd the removal rate of ammonia nitrogen is continuously increased. Due to the increase of the temperature, the generation rate of OH is accelerated, so that the indirect oxidation rate of the BDD electrode is effectively improved. Meanwhile, Brownian motion of solute in the solution is enhanced, the diffusion rate of the pollutant in the solution and the chemical reaction rate of the surface of the electrode are improved, and the electrolytic reaction is effectively promoted. The BDD electrode had an electrolytic efficiency of significantly less than 40 c at initial temperatures of 50 c and 60 c for the same electrolysis time. Radical aggravation mainly due to over-high temperatureThereby reducing the reaction rate and preventing the degradation of organic substances. The removal effect and the energy consumption required by temperature rise are comprehensively considered, and 40 ℃ is selected as the initial temperature. Because spontaneous heat generation can be realized in the electrolytic process, the initial temperature of the inlet water can be properly reduced in the suggested engineering application, and the initial temperature of the electrolysis can be properly reduced to reduce the energy consumption and the cost.

5. TOC removal rate: according to the above experiment, the optimal experimental conditions of the electrolysis process section are as follows: current density 75mA/cm²The initial pH value of the solution is 9, the temperature of the solution is 40 ℃, and the TOC concentration analysis of an electrolysis experiment carried out under the conditions shows that after 5 hours of electrolysis treatment, the TOC removal rate reaches 97.8 percent, which indicates that the BDD electrode treatment almost mineralizes all organic matters in the wastewater. The TOC versus time curve is shown in FIG. 13.

6. The coagulation-electrochemical combined treatment effect is as follows: the optimal experimental conditions of the two-stage combined process determined by a single-factor experiment are adopted, namely the initial pH of a flocculation precipitation process stage is 9, the adding amount of PAC is 50mg/L, the adding amount of potassium ferrate is 50mg/L, the reaction temperature is 40 ℃, the stirring is carried out for 10min, and the standing and the sedimentation are carried out for 30 min; the initial pH of the electrolysis process section is 9, and the current density is 75mA/cm²The reaction temperature is 40 ℃, and the electrolytic reaction is carried out for 5 hours. After the combined process treatment of coagulating sedimentation and electrochemical oxidation is carried out in sequence, the effluent is colorless and tasteless and has COD_CrThe content of the active carbon is 23mg/L,c(NH₃-N) was 0.35mg/L, TOC was 11.75mg/L, and turbidity was 2.1 NTU. The main indexes all reach the primary standard of the integrated wastewater discharge standard (GB8978-1996), and simultaneously meet the requirements of the wastewater discharge to town sewer water quality standard (GB/T31962-.

Reference:

1. liu wei novel water treatment agent ferrate (chinese construction industry press, 2007).

2. Malronghua, Liu, preparation of potassium ferrate and application in water treatment, 297-298.

3. Treatment of potassium ferrate with drinking water, chemical education (2005).

4. Lizama Allende, K., McCarthy, D. T. & Fletcher, T. D. The influence of media type on removal of arsenic, iron and boron from acidic wastewater in horizontal flow wetland microcosms planted with Phragmites australis. Chemical Engineering Journal 246, 217-228, doi:https://doi.org/10.1016/j.cej.2014.02.035 (2014).

5. Songhua & Wangyuan stability of potassium ferrate in neutral and acidic media, chemical report 71, 696-700 (2008).

Claims

1. A method for treating emulsion wastewater is characterized by comprising the following steps: adopting potassium ferrate to assist coagulation sedimentation and combining an electrochemical oxidation method to jointly treat emulsion wastewater, and specifically comprising the following steps:

(1) a coagulating sedimentation process: adjusting the pH value of the emulsion wastewater to 9, adding 50-75mg/L potassium ferrate as a coagulant aid, and adding 50-100mg/L coagulant; stirring to uniformly disperse the medicament in the solution, controlling the reaction temperature to be 35-40 ℃, carrying out coagulation and precipitation pretreatment on the emulsion wastewater for 10min, and then standing for 30-40 min;

(2) an electrochemical oxidation process: after the emulsion wastewater coagulating sedimentation pretreatment is finished, connecting a BDD electrode electrochemical oxidation process, and performing advanced treatment on the effluent of the coagulating sedimentation process, wherein the specific method comprises the following steps: discharging the effluent after the coagulating sedimentation pretreatment into a new reservoir, adjusting the initial pH to be 7-9 by taking a BDD electrode as an anode and a Ti electrode as a cathode, and controlling the current density to be 50-100 mA/cm²Controlling the reaction temperature within the range of 30-40 ℃, and electrolyzing the effluent after the coagulating sedimentation pretreatment for 4-5 hours.

2. The method for treating emulsion wastewater according to claim 1, wherein: the coagulant is any one of polyaluminium chloride PAC, polyferric sulfate PFS, aluminum sulfate or ferric sulfate.

3. The method for treating emulsion wastewater according to claim 2, wherein: in the coagulating sedimentation process in the step (1): the coagulant is polyaluminium chloride PAC.

4. The method for treating emulsion wastewater according to claim 3, wherein: in the coagulating sedimentation process in the step (1): the adding amount of the PAC coagulant is 50mg/L, the adding amount of the potassium ferrate is 50mg/L, the reaction temperature is 40 ℃, the stirring is carried out for 10min, and the standing and the sedimentation are carried out for 30 min.

5. The method for treating emulsion wastewater according to claim 1, wherein: in the electrochemical oxidation process of the step (2), the initial pH is 9, and the current density is 75mA/cm²The reaction temperature is 40 ℃, and the electrolytic reaction is carried out for 5 hours.