Photo-Fenton treatment process for wastewater and application of photo-Fenton treatment process

Abstract

The invention discloses a photo-Fenton treatment process for wastewater and application of the photo-Fenton treatment process, and belongs to the technical field of wastewater treatment. In the photo-Fenton treatment process, different choices of the oxidant adding amount and the ultraviolet irradiation time are provided according to different COD indexes of wastewater which are initially measured. Meanwhile, in combination with exploration of an oxidant adding mode, the oxidant is added twice at the beginning of the reaction and within 2-3 min of the reaction, and the first-time adding amount is larger than or equal to the second-time adding amount, so that compared with a treatment mode that the same total amount of the oxidant is added at a time, waste of the oxidant is effectively avoided, COD and TOC in the wastewater are degraded more sufficiently, and the treatment effect is better. And energy conservation and efficiency improvement are realized to the greatest extent. The process is combined with a flocculation precipitation method to be used for treating the membrane filtration concentrated solutions of the wastewater with different COD contents, and the treated membrane filtration concentrated solutions of the wastewater meet the standard of being directly discharged into an ecological buffer area.

Description

Technical Field

[0001] The present invention belongs to the technical field of wastewater treatment, and particularly relates to a photo-Fenton treatment process for wastewater and its application. Background Art

[0002] With the rapid development of the printing and dyeing industry, the wastewater discharge is increasing continuously. Printing and dyeing wastewater is characterized by complex composition, high chroma, high organic matter concentration, high salinity, etc., and is difficult to treat. During the wastewater treatment process, the traditional "biochemical + reverse osmosis (RO) membrane" combined process can be used to realize the recycling of fresh water. However, the concentrated liquid after membrane filtration of the wastewater will contain a large amount of refractory organic matter, a large amount of metal ions and salts, with a low BOD / COD ratio and poor biodegradability, and it is difficult to be effectively treated by conventional biochemical methods.

[0003] At present, the Fenton process is often used in sewage treatment plants for the advanced treatment of membrane filtration concentrated water. The treated wastewater is discharged into the ecological buffer zone for further degradation after the COD is reduced to less than 50 mg / L to ensure that the effluent meets the discharge standards. The Fenton process can remove organic pollutants to a certain extent, but there are still the following problems:

[0004] (1) Low utilization rate of iron salts: The conversion of iron ions to ferrous ions in the Fenton process is very slow. A large amount of ferrous salts need to be added to ensure the efficient conversion of hydrogen peroxide to hydroxyl radicals for degrading organic matter. Therefore, the salt content increases, and a large amount of iron mud precipitates, increasing the subsequent treatment steps and treatment costs;

[0005] (2) Waste of oxidant: The degradation rate in the early stage of the Fenton process is relatively fast, but in the later stage, the utilization rate of hydrogen peroxide is relatively low due to the decrease in the content of ferrous ions, and the degradation in the later stage is weak, and the organic matter is not completely degraded; If the dosage of Fe 2+ salt is increased, when the Fe 2+ concentration in the initial system is too high, it will cause some H2O2 to decompose ineffectively, decomposing into O2 instead of ·OH, also causing waste of H2O2;

[0006] (3) Long treatment time: It takes several hours for the COD to be reduced to less than 50 mg / L, with a long hydraulic retention time and a large floor area of the equipment;

[0007] (4) Chroma and toxicity problems: Although the biological toxicity of the printing and dyeing wastewater membrane filtration concentrated liquid treated by the Fenton process has been reduced to a certain extent, the biodegradability has limited improvement, and the wastewater treated by the Fenton process has a high chroma and is difficult to meet the discharge standards, which will cause certain pollution to the ecological buffer zone.

[0008] In view of the above problems (1) and (2), in the prior art, for example, in the Chinese invention patent application with publication number CN110790436A and the invention name of a system and method for treating wastewater from composite organic acid cleaning of power plant boilers, a technical solution for improving the utilization rate of H2O2 in the Fenton reaction and reducing the amount of H2O2 is recorded. Specifically, the synergistic effect of ultraviolet light catalysis and Fenton reaction is utilized, and the iron ions contained in the wastewater are used as the catalyst for the Fenton reaction. Under the action of ultraviolet light sensitization and ultraviolet light catalyst, the Fe ions are effectively promoted. 3+ , reduction of iron complexes and generation of hydroxyl radicals. Improve the utilization rate of H2O2 in the Fenton reaction and effectively reduce the cost of wastewater treatment.

[0009] However, the applicant found in the actual application process that even if the photo-Fenton treatment process (the synergy of ultraviolet photocatalysis and Fenton reaction) is used, the COD in the wastewater still has the problem of fast initial degradation rate but obvious decrease in the later stage, waste of oxidant and the need to further improve the treatment effect. Summary of the invention

[0010] 1. Purpose of the Invention

[0011] One of the inventive purposes of the present application is to provide a photo-Fenton treatment process for wastewater, in which the amount of oxidant added and the ultraviolet light irradiation time are selected based on the initial COD index of the wastewater, wherein the oxidant is added in stages within 2 to 3 minutes of the initial photo-Fenton reaction. This process can further improve the utilization rate of H2O2 and the treatment effect, and is conducive to further reducing the treatment cost.

[0012] Another inventive object of the present application is to provide the application of the above-mentioned photo-Fenton treatment process for wastewater in treating the concentrated liquid after membrane filtration. The concentrated liquid after membrane filtration is difficult to be treated by conventional biochemical methods. The use of the above-mentioned photo-Fenton treatment process in combination with the flocculation sedimentation process can effectively control the COD and chromaticity of the final effluent, avoiding negative impacts on it when discharged into the ecological buffer zone.

[0013] 2. Technical solution

[0014] In order to achieve the above-mentioned invention object, the technical solution adopted in this application is as follows:

[0015] The present application provides a photo-Fenton treatment process for wastewater, which comprises the following steps:

[0016] S1: Determine the COD index of wastewater; adjust the pH of wastewater to 3.5-9; add Fe 2+ catalyst;

[0017] S2: Add the oxidant for the first time under ultraviolet light irradiation, and add the oxidant for the second time within 2 - 3 minutes after the first addition. The amount of oxidant added for the first time ≥ the amount of oxidant added for the second time. The ultraviolet light irradiation time and the total amount of oxidant added are determined according to the following conditions:

[0018] (ⅰ) When 200 < COD ≤ 250 mg / L, the total amount of oxidant added is 11 - 13 mM, and the ultraviolet light irradiation time is 4 - 6 minutes;

[0019] (ii) When 250 < COD ≤ 350 mg / L, the total amount of oxidant added is 15 - 17 mM, and the ultraviolet light irradiation time is 9 - 11 minutes;

[0020] (iii) When 350 < COD ≤ 450 mg / L, the total amount of oxidant added is 23 - 25 mM, and the ultraviolet light irradiation time is 14 - 16 minutes.

[0021] Further, in the above S1, the determination of the COD index of the wastewater includes: measuring the absorbance of the diluted wastewater at 275 nm after diluting the wastewater by 5 times, calculating the COD concentration of the diluted wastewater according to Y = 0.01207X - 0.0031, and calculating the COD concentration of the original wastewater, where Y is the absorbance of the wastewater diluted by 5 times at 275 nm, and X is the COD of the wastewater diluted by 5 times.

[0022] Further, in the above S1, adjust the pH of the wastewater to 3.5 - 7.

[0023] Further, in the above S1, adjust the pH of the wastewater to 3.5 - 5.

[0024] Further, in the above S1, adjust the pH of the wastewater to 3.5 or 5.

[0025] Further, in the above S1, add Fe 2+ The content of the catalyst is 0.43 - 1.73 mM.

[0026] Further, in the above S1, add Fe 2+ The content of the catalyst is 0.86 mM.

[0027] Further, in the above S1, Fe 2+ The catalyst includes FeSO4·7H2O, which can promote the rapid generation of ·OH by H2O2 and generate Fe 3+ .

[0028] Further, in the above Fe 2+ The dosage of the catalyst is 0.12 - 0.48 g / L.

[0029] Further, in the above Fe2+ The dosage of the catalyst is 0.24 g / L. When the dosage of the catalyst is in the range of 0 - 0.24 g / L, with the increase of the catalyst dosage, the COD degradation rate significantly accelerates. When the catalyst dosage continues to increase, the increase in the COD degradation rate is not significant. After considering the reagent cost, the preferred dosage of the catalyst in this application is 0.24 g / L.

[0030] Further, in the above S2, the oxidant includes hydrogen peroxide (hydrogen peroxide solution).

[0031] Further, in the above S2, the oxidant includes hydrogen peroxide (hydrogen peroxide solution) with a mass concentration of 30%.

[0032] Further, in the above S2, the irradiation wavelength of the ultraviolet light is 185 - 254 nm, which is provided by an ultraviolet lamp or the like.

[0033] Further, in the above S2, the irradiation wavelength of the ultraviolet light is 254 nm, which is provided by an ultraviolet lamp (low-pressure mercury lamp).

[0034] Further, in the above S2, the oxidant is added for the second time 2.5 minutes after the first addition of the oxidant.

[0035] Further, in the above S2, the dosage of the oxidant added for the first time is the same as that added for the second time.

[0036] Further, in the above S2,

[0037] When 200 < COD ≤ 250 mg / L, the total dosage of the oxidant added is 12 mM; and / or

[0038] When 250 < COD ≤ 350 mg / L, the total dosage of the oxidant added is 16 mM; and / or

[0039] When 350 < COD ≤ 450 mg / L, the total dosage of the oxidant added is 24 mM.

[0040] Further, in the above S2, the oxidant is added for the second time 2.5 minutes after the first addition of the oxidant, and the dosage of the oxidant added for the first time is the same as that added for the second time.

[0041] (i) When 200 < COD ≤ 250 mg / L, the dosage of the oxidant added for the first time is 6 mM;

[0042] (ii) When 250 < COD ≤ 350 mg / L, the dosage of the oxidant added for the first time is 8 mM;

[0043] (iii) When 350 < COD ≤ 450 mg / L, the dosage of the oxidant added for the first time is 12 mM.

[0044] Further, the wastewater circulation flow rate in the above treatment process is 0.5 - 2 L / min

[0045] Further, the above wastewater circulation flow rate is 2 L / min

[0046] The present application also provides an application of the above photo - Fenton treatment process for a kind of wastewater in treating wastewater membrane filtration concentrate

[0047] Further, the above application includes:

[0048] Using the above photo - Fenton treatment process to treat wastewater membrane filtration concentrate

[0049] Adjusting the pH of the treated effluent to be between 6.5 and 7.0. This pH range enables the precipitation of iron salts and is conducive to the best flocculation effect of the flocculant

[0050] Adding a flocculant for flocculation precipitation

[0051] Discharging the supernatant after flocculation precipitation

[0052] Further, the above pH is adjusted by sodium hydroxide solution

[0053] Further, the above flocculant is added under stirring conditions

[0054] Further, the above stirring includes rapid stirring for 110 - 130 s followed by slow stirring for 25 - 35 s

[0055] Further, the above stirring includes rapid stirring for 120 s followed by slow stirring for 30 s

[0056] Further, the rotation speed of the above rapid stirring is 100 - 300 r / min, and the rotation speed of the slow stirring is 30 - 50 r / min

[0057] Further, the above flocculant includes PAM (Polyacrylamide) agent

[0058] Further, the dosage of the above PAM agent is 0.0005% of the mass of the wastewater membrane filtration concentrate

[0059] Further, the above discharging of the supernatant after precipitation includes discharging the supernatant to an ecological buffer zone

[0060] Further, before discharging to the ecological buffer zone, it also includes: measuring the chemical oxygen demand (COD) and the sludge aerobic respiration rate (OUR, referring to the oxygen consumption per unit time of unit mass of activated sludge for respiration), according to STOD = OUR 废水 / OUR 内源呼吸Calculate the Specific Theoretical Oxygen Demand (STOD) to verify whether the treated wastewater is biodegradable and whether its toxicity has been reduced. When STOD < 1, the wastewater has strong toxicity and is not biodegradable; conversely, the toxicity is reduced and the wastewater is biodegradable. Given a certain COD of the wastewater, the higher the STOD, the higher the biodegradability.

[0061] Furthermore, the precipitate (sludge) from the above flocculation precipitation is transported out after pressure filtration.

[0062] This application also provides a method for treating the membrane filtration concentrate of wastewater, which includes:

[0063] Treat the membrane filtration concentrate of wastewater using the above photo-Fenton treatment process;

[0064] Adjust the pH of the treated effluent to be between 6.5 and 7.0. This pH range causes the iron salt to precipitate and is conducive to the best flocculation effect of the flocculant;

[0065] Add a flocculant for flocculation precipitation;

[0066] Discharge the supernatant after flocculation precipitation.

[0067] Furthermore, the above pH is adjusted using a sodium hydroxide solution.

[0068] Furthermore, the above flocculant is added under stirring conditions.

[0069] Furthermore, the above stirring includes rapid stirring for 110 - 130 s followed by slow stirring for 25 - 35 s.

[0070] Furthermore, the above stirring includes rapid stirring for 120 s followed by slow stirring for 30 s.

[0071] Furthermore, the rotation speed of the above rapid stirring is 100 - 300 r / min, and the rotation speed of the slow stirring is 30 - 50 r / min.

[0072] Furthermore, the above flocculant includes a PAM (Polyacrylamide) agent.

[0073] Furthermore, the dosage of the above PAM agent is 0.0005% of the mass of the membrane filtration concentrate of wastewater.

[0074] Furthermore, the above discharging of the supernatant after precipitation includes discharging the supernatant to an ecological buffer zone.

[0075] Furthermore, before discharging to the ecological buffer zone, it also includes: measuring the Chemical Oxygen Demand (COD) of the supernatant and the Oxygen Uptake Rate (OUR, which refers to the oxygen consumption per unit mass of activated sludge during respiration per unit time), and according to STOD = OUR 废水 / OUR 内源呼吸 Calculate the specific theoretical oxygen demand (STOD) to verify the biodegradability and reduced toxicity of the treated wastewater. When STOD < 1, the wastewater has strong toxicity and is not biodegradable; conversely, the toxicity is reduced and the wastewater is biodegradable. At a certain COD level of the wastewater, the higher the STOD, the higher the biodegradability.

[0076] Furthermore, the precipitate (sludge) from the above flocculation sedimentation is transported out after pressure filtration.

[0077] The present application also provides a wastewater treatment system, which includes an acid addition adjustment tank, a photo-Fenton oxidation tank, an alkali addition adjustment tank, a flocculation sedimentation tank, a sludge tank, and / or an ecological buffer zone connected in sequence.

[0078] Furthermore, the above photo-Fenton oxidation tank is an ultraviolet photo-Fenton oxidation tank, which is used to monitor the COD index, add a catalyst, control the dosage of the oxidant, and the ultraviolet light irradiation time.

[0079] The present application also provides the application of the above wastewater treatment system in treating wastewater membrane filtration concentrate.

[0080] 3. Beneficial effects

[0081] Compared with the prior art, the beneficial effects of the present application are as follows:

[0082] (1) For the photo-Fenton treatment process and its application of wastewater provided by the present application, by exploring the dosage and feeding method of the oxidant H2O2 in the photo-Fenton process, it is found that H2O2 is fed in two batches at the initial stage of the reaction and about 2.5 min into the reaction, and the wastewater is oxidized under ultraviolet light irradiation. The removal rate of COD is better than that of a one-time addition of the same total dose of H2O2. The present application effectively improves the utilization rate of the oxidant in the photo-Fenton process by adding H2O2 for the second time at 2.5 min into the reaction, avoiding the waste of the oxidant; at the same time, the ultraviolet light irradiation time is compressed to 15 min, saving the energy cost. After being treated by the photo-Fenton process, the COD of the wastewater is controlled within 60 mg / L, and the chromaticity is controlled within 30.

[0083] (2) For the photo-Fenton treatment process and its application of wastewater provided by the present application, the photo-Fenton process is combined with the flocculation sedimentation method. By treating different printing and dyeing wastewater membrane filtration concentrates, three treatment conditions suitable for wastewater membrane filtration concentrates with different COD contents are proposed, specifically including the dosage of the oxidant and the ultraviolet light irradiation time in the photo-Fenton process, aiming to match the best treatment plan for the treatment of various wastewater membrane filtration concentrates, ensuring that the treated wastewater meets the discharge standards, and further avoiding the waste of the oxidant and the energy consumption of the light source, achieving the maximum reduction of costs and increase of efficiency.

[0084] (3) A photo-Fenton treatment process for wastewater provided by this application and its application. When the wastewater treatment system treats the membrane filtration concentrate of wastewater with different water qualities, the ultraviolet photo-Fenton oxidation tank can automatically adjust the dosage of the oxidant and the ultraviolet light irradiation reaction time according to the monitored COD content in the wastewater. Then, after flocculation precipitation and separate treatment in the flocculation sedimentation tank, the COD of the final effluent of the system is controlled within 50 mg / L, the chromaticity is controlled within 20, and the BOD / COD is controlled above 0.35, all meeting the standards for direct discharge into the ecological buffer zone. Description of the Drawings

[0085] Figure 1 It is a linear relationship diagram of the absorbance at 275 nm and COD.

[0086] Figure 2 It is a diagram of the change in COD concentration in the membrane filtration concentrate of printing and dyeing wastewater under different initial pH values.

[0087] Figure 3 It is a diagram of the change in COD concentration in the membrane filtration concentrate of printing and dyeing wastewater with different catalyst dosages.

[0088] Figure 4 It is a diagram of the change in COD concentration in the membrane filtration concentrate of printing and dyeing wastewater with different oxidant dosages.

[0089] Figure 5 It is a diagram of the change in COD concentration in the membrane filtration concentrate of printing and dyeing wastewater with different circulation flow rates.

[0090] Figure 6 It is a diagram of the change in COD (a) and TOC (b) concentrations in the membrane filtration concentrate of printing and dyeing wastewater under different oxidant dosing methods.

[0091] Figure 7 It is a diagram of the change in COD (a) and chromaticity (b) in the membrane filtration concentrate of printing and dyeing wastewater treated by the photo-Fenton process combined with the flocculation precipitation method.

[0092] Figure 8 It is a diagram of the change in COD concentration in the membrane filtration concentrate of printing and dyeing wastewater treated by the photo-Fenton process combined with the flocculation precipitation method; (a) membrane filtration concentrate of printing and dyeing wastewater No. 1, (b) membrane filtration concentrate of printing and dyeing wastewater No. 2, (c) membrane filtration concentrate of printing and dyeing wastewater No. 3.

[0093] Figure 9 It is a diagram of the change in COD concentration in the optimization experiment of the treatment conditions for the membrane filtration concentrate of printing and dyeing wastewater No. 1.

[0094] Figure 10 It is a diagram of the change in COD concentration in the optimization experiment of the treatment conditions for the membrane filtration concentrate of printing and dyeing wastewater No. 3.

[0095] Figure 11This is the flow chart of the advanced treatment system for the membrane filtration concentrate of printing and dyeing wastewater in this application. Detailed implementation manners

[0096] The following further describes this application in combination with specific embodiments.

[0097] The detection methods for the indexes involved in this application are as follows:

[0098] COD (Chemical Oxygen Demand): The COD is determined by the dichromate method in GB 11914-1989 of the national standard.

[0099] OUR (Sludge Aerobic Rate): It is measured by the PF-8000 activated sludge respirometer of RSA in the United States, and the oxygen consumption curve is measured according to the continuous real-time determination method of the standardized activated sludge oxygen consumption certified by ISO. The inoculated sludge is taken from the aerobic incubator of Nanda Huaxing Environmental Protection Technology Co., Ltd. After retrieving the sludge, the sludge is centrifuged, washed with deionized water, and then centrifuged again, repeating 3 times. A certain amount of deionized water, printing and dyeing ROC and the wastewater treated by the advanced oxidation process are added to the centrifuged sludge respectively, and the sludge concentration is adjusted to reach 3000 mg / L, and then poured into the reaction bottle for on-machine determination.

[0100] TOC (Total Organic Carbon): After the water sample after the reaction is filtered through a 0.45 μm filter membrane, it is acidified with an appropriate amount of 2 mM hydrochloric acid solution for 30 min, and the TOC of the solution is measured by the subtraction method on the 3100 dry TOC analyzer of Jena, Germany.

[0101] BOD (Biochemical Oxygen Demand): The BOD is determined by the dilution and inoculation method in GB / T 7488-1987 of the national standard method.

[0102] Chromaticity: The chromaticity is determined by the dilution multiple method in GB / T 11903-1989 of the national standard.

[0103] Example 1

[0104] This example optimizes the adjustment of the initial pH of the wastewater in the photo-Fenton treatment process of the wastewater membrane filtration concentrate, specifically as follows:

[0105] The wastewater used is taken from the membrane filtration concentrate of printing and dyeing wastewater of an enterprise in Jiangsu. The conventional indexes of this membrane filtration concentrate are shown in Table 1:

[0106] Table 1

[0107]

[0108] The specific operation is as follows:

[0109] (1) Experimental method

[0110] Take 1.7L of printing and dyeing membrane filtration concentrate in a beaker and use dilute H2SO4 and NaOH solutions to adjust the initial pH of the wastewater to 3.5, 5, 7, and 9, respectively. Before the experiment, turn on the UV lamp for preheating for 15 minutes to ensure the stability of the UV lamp during the subsequent reaction. Then add 0.12g / L FeSO4·7H2O and 20mM H2O2 at one time, and quickly pour them into the reaction device to start timing (do not turn on the pump, that is, the circulation flow rate is 0L / min). The UV irradiation reaction time is 60min, and quantitative sampling is carried out at 0min, 2.5min, 5min, 10min, 15min, 30min, and 60min, respectively. The water samples are filtered through a 0.45μm filter membrane and stored in a 4℃ refrigerator. The COD content is determined within 24h.

[0111] (2) Results Analysis

[0112] The results are as follows Figure 2 As shown, the initial pH of the wastewater is in the range of 3.5 to 9. As the pH decreases, the degradation effect of COD is better under more acidic conditions. Therefore, the initial pH of the membrane filtration concentrate in this application is preferably adjusted to 3.5.

[0113] Example 2

[0114] This embodiment optimizes the dosage of the catalyst iron salt in the photo-Fenton treatment process of the wastewater membrane filtration concentrate.

[0115] The wastewater used in the experiment is the same as that in Example 1, and the specific operation is as follows:

[0116] (1) Experimental methods

[0117] 1.7L of the printing and dyeing membrane filtration concentrate was taken into a beaker and the initial pH of the wastewater was adjusted to 3.5 using dilute H2SO4 and NaOH solutions. Different from Example 1, 0.12g / L, 0.24g / L, 0.36g / L and 0.48g / L of FeSO4·7H2O were added to each group of wastewater at one time, respectively. Other treatment conditions, sampling time and sample detection were the same as Example 1.

[0118] (2) Results Analysis

[0119] The results are as follows Figure 3As shown, within the first 15 minutes of the reaction, each group showed good degradation effects on COD, and the higher the dosage of FeSO4·7H2O added, the faster the COD degradation rate. After the reaction reached 15 minutes, the degradation of COD in each group became slow. Except for the group with a FeSO4·7H2O addition amount of 0.12 g / L, the degradation of COD in other groups almost stagnated. Considering the comprehensive COD degradation effect, reagent cost, and ultraviolet light irradiation cost in this example, the dosage of FeSO4·7H2O in the photo-Fenton treatment process was preferably 0.24 g / L, and at the same time, the ultraviolet light irradiation reaction time was compressed to 15 minutes.

[0120] Example 3

[0121] In this example, the dosage of the oxidant H2O2 in the photo-Fenton treatment process of the wastewater membrane filtration concentrate was optimized.

[0122] The wastewater used in the experiment was the same as that in Example 1, and the specific operation was as follows:

[0123] (1) Experimental method

[0124] Take 1.7 L of the printing and dyeing membrane filtration concentrate in a beaker and adjust the initial pH of the wastewater to 3.5 using dilute H2SO4 and NaOH solutions. Different from Example 1, first add 0.24 g / L of FeSO4·7H2O to each group of wastewater at one time, and then add 8 mM, 12 mM, 16 mM, 20 mM, and 24 mM of H2O2 to the corresponding groups at one time. Compress the ultraviolet light irradiation reaction time to 15 minutes, and observe the change of the COD concentration in each group with the reaction time. Other treatment conditions are the same as those in Example 1.

[0125] (2) Result analysis

[0126] The results are as Figure 4 shown. It can be found that within the addition range of 8 - 16 mM of H2O2, with the increase of the addition amount, the better the COD degradation effect. When the reaction reached 15 minutes, there was no significant difference in the overall COD degradation rate among the groups with 16 mM, 20 mM, and 24 mM of H2O2 added. Therefore, considering the comprehensive COD degradation effect and reagent cost, the dosage of H2O2 in the photo-Fenton treatment process was preferably 16 mM.

[0127] Example 4

[0128] In this example, the wastewater circulation flow rate in the photo-Fenton treatment process of the wastewater membrane filtration concentrate was optimized.

[0129] The increase of the wastewater circulation flow rate can improve the mass transfer efficiency and strengthen the contact between ·OH and pollutants. In this example, the circulation flow rate of the water sample was adjusted by a circulating water pump to explore the COD degradation process. The wastewater used was the same as that in Example 1, and the specific operation was as follows:

[0130] (1) Experimental methods

[0131] Take 1.7L of the printing and dyeing membrane filtration concentrate in a beaker and use dilute H2SO4 and NaOH solutions to adjust the initial pH of the wastewater to 3.5. Different from Example 1, 0.24g / L of FeSO4·7H2O and 16mM H2O2 were added at one time, and then oxidation treatment was carried out for 15min at a circulation flow rate of 0.5L / min, 1L / min, 1.5L / min, and 2L / min, respectively. The change of COD concentration in each group with the circulation flow rate was observed, and the other treatment conditions were the same as Example 1.

[0132] (2) Results Analysis

[0133] The results are as follows Figure 5 As shown in the figure, in the range of circulation flow rate of 0.5 to 2 L / min, as the circulation flow rate increases, the COD degradation effect is better. In order to achieve the best COD removal effect, the wastewater circulation flow rate in the photo-Fenton treatment process is preferably 2 L / min. In addition, when the circulation flow rate is 2 L / min, the COD removal rate is faster in the first 2.5 minutes, and the COD degradation rate drops significantly after 2.5 minutes. It is calculated that the COD removal in the first 2.5 minutes accounts for 85.89% of the total removal. This situation occurs because Fe in the initial reaction system 2+ The content is sufficient, ·OH is produced quickly and in large quantities to degrade COD. After 2.5 minutes, the iron ion circulation is slow, resulting in Fe 2+ The content is insufficient, which cannot promote H2O2 to decompose more OH, resulting in a significant decrease in the subsequent COD removal rate.

[0134] Example 5

[0135] This embodiment optimizes the oxidant addition method in the photo-Fenton treatment process of wastewater membrane filtration concentrate.

[0136] This example is based on the results of Example 4. After 2.5 minutes of reaction, H2O2 cannot produce ·OH in time, resulting in poor subsequent wastewater treatment effect and waste of H2O2. Therefore, the effects of adding 16mM H2O2 at one time (control group) and adding the same total dose of H2O2 in batches (experimental group) on COD removal effect are compared. Also based on Example 4, the time of adding H2O2 in batches is selected at the beginning of the reaction and 2.5 minutes of the reaction, and a treatment group of adding 12mM first and then 4mM H2O2 (experimental group 1) and a treatment group of adding 8mM H2O2 twice (experimental group 2) are set.

[0137] (1) Experimental methods

[0138] The initial pH of the wastewater was adjusted in the same manner as in Example 4. At the beginning of the reaction, 0.24 g / L of FeSO4·7H2O was added to each group of wastewater at one time. Among them, 16 mM of H2O2 was added to the control group at one time at the beginning of the reaction; in Experimental Group 1, 12 mM of H2O2 was added at the beginning of the reaction, and 4 mM of H2O2 was added again after 2.5 min of reaction; in Experimental Group 2, 8 mM of H2O2 was added at the beginning of the reaction and at 2.5 min of reaction respectively. The circulation flow rate of the wastewater treated in each group was 2 L / min, and the ultraviolet light irradiation reaction time was 15 min. The changes in the concentrations of COD and TOC in the control group and the experimental groups were observed.

[0139] (2) Result analysis

[0140] As Figure 6 shown, within the first 2.5 min of the reaction, the control group had the highest degradation rate for COD and TOC. After 2.5 min, there was a sharp drop in the degradation rate. By adding a second batch of oxidant in a timely manner at 2.5 min in the experimental groups, the decline in the degradation rates of COD and TOC was slowed down. Among them, the degradation rate of TOC in Experimental Group 2 was even enhanced. After 15 min of reaction, the treatment effects of the 8 mM + 8 mM treatment group (Experimental Group 2) on COD and TOC were better than those of the 12 mM + 4 mM treatment group (Experimental Group 1). In summary, the dosing method of the oxidant in the photo-Fenton treatment process was preferably divided into two batches, with 8 mM of H2O2 added at the beginning of the reaction and at 2.5 min of reaction respectively. In addition, in this experiment, it was found that the COD in the 8 mM + 8 mM treatment group (Experimental Group 2) had dropped to 41.5 mg / L after 10 min of photo-Fenton reaction, meeting the treatment requirement of COD < 50 mg / L. Therefore, to save energy, the ultraviolet light irradiation reaction time was further compressed from 15 min to 10 min.

[0141] Example 6

[0142] In this example, the above photo-Fenton treatment process was combined with the flocculation precipitation method to treat wastewater.

[0143] Specifically, the chromaticity of the effluent after 10 min of photo-Fenton treatment in Example 5 above was detected, and it was found that its chromaticity was as high as 42. Therefore, the flocculation precipitation method was introduced to further treat the effluent. The specific flocculation precipitation operation was as follows:

[0144] The pH of the effluent after photo-Fenton treatment was adjusted to be between 6.5 and 7.0 using sodium hydroxide, and flocculation precipitation was carried out with a PAM reagent of 0.005 g / L. Then, the supernatant was taken after standing for detecting each index (see the effluent indexes after flocculation precipitation in Table 2), and the changes in the COD and chromaticity of the wastewater were mainly observed.

[0145] Result analysis:

[0146] As shown in Table 2 and Figure 7As shown in the figure, after flocculation precipitation, the COD in the effluent of photo-Fenton decreased further from 41.5 mg / L to 28.7 mg / L, and the chromaticity decreased from 42 to 11, indicating that the flocculation precipitation process has good removal effects on the COD and chromaticity of wastewater, especially the chromaticity. Therefore, the photo-Fenton process will be combined with the flocculation precipitation method in the following to improve the wastewater treatment effect.

[0147] Table 2

[0148]

[0149] Example 7

[0150] This example explores the treatment capacity of the photo-Fenton treatment process combined with the flocculation precipitation method for different actual printing and dyeing wastewaters.

[0151] A total of three kinds of membrane filtration concentrates of printing and dyeing wastewaters with different water qualities from an enterprise in Jiangsu were selected, numbered 1, 2, and 3 respectively. The conventional indexes are shown in Table 3.

[0152] Table 3

[0153]

[0154] The COD degradation experiment was carried out by using the photo-Fenton process and the flocculation precipitation method. The specific operations are as follows:

[0155] S1. Photo-Fenton treatment:

[0156] The pH of each membrane filtration concentrate of printing and dyeing wastewater was adjusted to 3.5 with 98% concentrated sulfuric acid, and 0.24 g / L of FeSO4·7H2O was added. 8 mM of 30% mass concentration of hydrogen peroxide was added at the initial stage of the reaction and 2.5 minutes after the reaction, and the reaction ended after 10 minutes of ultraviolet light irradiation.

[0157] S2. Flocculation precipitation:

[0158] The pH of the effluent after photo-Fenton treatment was adjusted to be between 6.5 and 7.0 with sodium hydroxide, and flocculation precipitation was carried out with 0.005 g / L of PAM reagent. Then, the supernatant was taken for detection after standing. The chemical oxygen demand COD and the aerobic rate OUR of the sludge (referring to the oxygen consumption per unit mass of activated sludge for respiration per unit time) were measured, and the relative oxygen consumption STOD (STOD = OUR wastewater / OUR endogenous respiration) was calculated to verify the biodegradability and toxicity of the treated wastewater.

[0159] Result analysis:

[0160] The results are as Figure 8 shown, among which the treatment results of the water samples numbered 1, 2, and 3 correspond to Figure 8For a, b, and c, it can be seen that for the wastewater with a relatively good water quality and a COD content of 214 mg / L (No. 1), the COD content rapidly drops to 30 mg / L after 5 minutes of reaction, which already meets the first-class A discharge standard for industrial wastewater; for the wastewater with a COD content of 324 mg / L (No. 2), the COD drops to 48.6 mg / L after 10 minutes of reaction, and further drops to 34.1 mg / L after flocculation precipitation, which also meets the discharge standard; however, for the wastewater with a relatively poor water quality and a COD content of 417 mg / L (No. 3), after 10 minutes of gradient photo-Fenton treatment and flocculation precipitation, the COD still remains at the level of 156 mg / L, far higher than the discharge standard.

[0161] In summary, if the same photo-Fenton process is used to treat the membrane filtration concentrates of printing and dyeing wastewater with different water qualities, there will be a situation of energy consumption waste when the water quality is relatively good and the treatment effect will not meet the standard when the water quality is relatively poor. Specifically, the water quality of the wastewater numbered 2 above is close to the optimized wastewater quality under photo-Fenton conditions, so it already meets the discharge standard with low energy consumption treatment, while the wastewaters numbered 1 and 3 respectively have the situations of wasted energy consumption and unqualified treatment. Therefore, in this embodiment, the treatment conditions of the wastewaters numbered 1 and 3 are further optimized. Specifically,

[0162] For the wastewater numbered 1, the dosage of the oxidant is reduced, and 6 mM of H2O2 is added at the initial stage of the reaction and at 2.5 minutes of the reaction respectively, and other treatment conditions and the detection of the supernatant remain unchanged.

[0163] The experimental results are as Figure 9 shown. After adjusting the treatment conditions, the COD content of the wastewater drops to 46 mg / L after 5 minutes of reaction, which is slightly lower than the discharge requirement. Combining with flocculation precipitation, the COD content is further reduced, and the obtained effluent meets the first-class A discharge standard for industrial wastewater. In summary, for the case of relatively good water quality, the dosage of the oxidant can be reduced and the ultraviolet light irradiation reaction time can be compressed at the same time to achieve the discharge target with low energy consumption.

[0164] For the wastewater numbered 3, the dosage of the oxidant is increased, and 12 mM of H2O2 is added at the initial stage of the reaction and at 2.5 minutes of the reaction respectively, and other treatment conditions and the detection of the supernatant remain unchanged.

[0165] The experimental results are as Figure 10 shown. After adjusting the treatment conditions, the COD content of the wastewater drops to 56.47 mg / L after 10 minutes of reaction, which is still slightly higher than the discharge requirement. However, considering that extending the ultraviolet light irradiation time will cause relatively large energy consumption and the subsequent wastewater treatment effect is not good, the COD content is further reduced to 46.2 mg / L by means of flocculation precipitation to ensure that the treated effluent meets the first-class A discharge standard for industrial wastewater. In summary, for the case of relatively poor water quality, the dosage of the oxidant is increased to achieve the discharge target with low energy consumption.

[0166] Example 8

[0167] This example provides a deep treatment method for the membrane filtration concentrate of wastewater with different COD contents and conducts actual tests.

[0168] Based on the research in Example 6, this application proposes three targeted treatment schemes for wastewater with different COD contents, which specifically include the following steps:

[0169] S1: Use a COD real-time detector to monitor the COD index of the wastewater membrane filtration concentrate.

[0170] S2: Adjust the pH of the wastewater membrane filtration concentrate to 3.5 with 98% concentrated sulfuric acid and add 0.24 g / L of FeSO4·7H2O. Select the dosage of the oxidant and the ultraviolet light irradiation reaction time according to the following conditions, where:

[0171] (i) When 200 < COD ≤ 250 mg / L, add 30% mass concentration of hydrogen peroxide in two portions at the beginning of the reaction and at 2.5 min of the reaction, with each dosage being 6 mM, and control the ultraviolet light irradiation duration to be 5 min.

[0172] (ii) When 250 < COD ≤ 350 mg / L, add 30% mass concentration of hydrogen peroxide in two portions at the beginning of the reaction and at 2.5 min of the reaction, with each dosage being 8 mM, and control the ultraviolet light irradiation duration to be 10 min.

[0173] (iii) When 350 < COD ≤ 450 mg / L, add 30% mass concentration of hydrogen peroxide in two portions at the beginning of the reaction and at 2.5 min of the reaction, with each dosage being 12 mM, and control the ultraviolet light irradiation duration to be 15 min.

[0174] S3: Conduct flocculation precipitation on the effluent from step S2. The specific steps are as follows:

[0175] (i) Adjust the pH of the effluent from step S2 to be between 6.5 and 7.0 with sodium hydroxide solution.

[0176] (ii) Add 0.005 g / L of PAM reagent while stirring, stir at 100 - 300 r / min for 120 s, then stir at 30 - 50 r / min for 30 s, conduct flocculation precipitation and then let it stand.

[0177] S4: After standing precipitation, conduct separate treatment on the precipitate and supernatant in step S3:

[0178] (i) Take the supernatant after standing in step S3 to measure the chemical oxygen demand COD of the wastewater and the aerobic rate OUR of the sludge (referring to the oxygen consumption per unit mass of activated sludge during respiration per unit time), and verify whether the treated wastewater has biodegradability and whether the toxicity has decreased by calculating the specific oxygen demand STOD (STOD = OUR wastewater / OUR endogenous respiration). Discharge the supernatant to the ecological buffer zone for further biochemical treatment.

[0179] (ii) The precipitated sludge in step S3 is transported out after pressure filtration.

[0180] Specifically, the membrane filtration concentrate of the wastewater in the above three COD ranges is actually treated, and the wastewater is the membrane filtration concentrate of printing and dyeing wastewater taken from an enterprise in Jiangsu.

[0181] 1) Wastewater A: COD = 324 mg / L, using (ii) in the above method, the specific operation is as follows:

[0182] Adjust the pH of the printing and dyeing wastewater to 3.5 with 98% concentrated sulfuric acid and add 0.24 g / L of FeSO4·7H2O. Add 8 mM of 30% mass concentration hydrogen peroxide at the beginning of the reaction and at 2.5 min of the reaction, and end the reaction after 10 min of ultraviolet light irradiation; use sodium hydroxide to adjust the pH of the wastewater to be between 6.5 and 7.0 again, and flocculate and precipitate with 0.005 g / L of PAM reagent, and then stand to take the supernatant for detection.

[0183] Result analysis: After detection, the COD is reduced to 34.1 mg / L, the TOC is reduced to 15.97 mg / L, STOD = 1.87, BOD / COD > 0.35, the chromaticity is reduced to 15, and BOD / COD is increased to 0.45, meeting the standard for discharge to the ecological buffer zone. According to laboratory experiments, the treatment cost is calculated to be 4.264 yuan / t.

[0184] 2) Wastewater B: COD = 214 mg / L, using (i) in the above method, and adding 6 mM of 30% mass concentration hydrogen peroxide respectively in different groups from wastewater A, and ending the reaction after 5 min of ultraviolet light irradiation, and other treatments are the same.

[0185] Result analysis: After detection, the COD is reduced to 44 mg / L, the TOC is reduced to 20.67 mg / L, STOD = 1.94, BOD / COD > 0.35, the chromaticity is reduced to 14, and BOD / COD is increased to 0.48, meeting the standard for discharge to the ecological buffer zone. According to laboratory experiments, the treatment cost is calculated to be 3.324 yuan / t.

[0186] 3) Wastewater C: COD = 417 mg / L. Using method (iii) above, 12 mM of 30% by mass hydrogen peroxide was added to the wastewater A group respectively, and the reaction was terminated after 15 minutes of ultraviolet light irradiation. Other treatments were the same.

[0187] Result analysis: After detection, COD was reduced to 46.2 mg / L, TOC was reduced to 23.25 mg / L, STOD = 1.76, BOD / COD was increased to 0.43, and the chromaticity was reduced to 18, meeting the standard for discharging into the ecological buffer zone. According to laboratory experiments, the treatment cost was calculated to be 5.664 yuan / t.

[0188] In summary, for the membrane filtration concentrate of wastewater with different COD contents, this application proposes an adaptation plan for the dosage of oxidant and the ultraviolet light irradiation time, which can further avoid the waste of oxidant and lamp source energy consumption, and the wastewater treated by different plans meets the standard for direct discharge into the ecological buffer zone.

[0189] Comparative Example 1

[0190] This comparative example treats the wastewater A in Example 7. The difference is that this comparative example uses the Fenton process instead of the photo-Fenton process, and other treatment methods and conditions are the same. Specifically:

[0191] The pH was adjusted to 3.5 by 98% concentrated sulfuric acid and 1.2 g / L of FeSO4·7H2O was added. 12 mM of 30% by mass hydrogen peroxide was added and the reaction was carried out for 240 minutes. The pH of the wastewater was adjusted again to be between 6.5 and 7.0 by sodium hydroxide, and flocculation precipitation was carried out with 0.005 g / L of PAM reagent, and the supernatant was taken for detection after standing.

[0192] After detection, after the wastewater A was oxidized by the Fenton process in this comparative example, COD was reduced to 80 mg / L, TOC was reduced to 40.6 mg / L, STOD = 1.34, and the chromaticity was reduced to 30, failing to meet the standard for discharging into the ecological buffer zone. And according to laboratory calculations, the treatment cost was 5.26 yuan / t.

[0193] Comparative Example 2

[0194] This comparative example also treats the wastewater A. The difference is that this comparative example uses the photo-Fenton process with a one-time addition of oxidant instead of the photo-Fenton process with a batchwise addition of oxidant, and other treatment methods and conditions are the same. Specifically:

[0195] The pH value was adjusted to 3.5 by 98% concentrated sulfuric acid and 0.24g / L FeSO4·7H2O was added. 16mM 30% mass concentration hydrogen peroxide was added once and the reaction was terminated by ultraviolet light illumination for 10min. The pH value of the wastewater was adjusted again between 6.5 and 7.0 by sodium hydroxide, and flocculation and precipitation were carried out by 0.005g / L PAM agent, and then the supernatant was taken for determination after standing.

[0196] After testing, after the wastewater was oxidized by the photo-Fenton process with a one-time addition of oxidant in this comparative example, the COD was reduced to 58 mg / L, the TOC was reduced to 25.7 mg / L, the STOD=1.64, and the chromaticity was reduced to 23, which failed to meet the standards for discharge into the ecological buffer zone. According to laboratory calculations, the treatment cost was 4.264 yuan / t.

[0197] Comparison Example 3

[0198] This comparative example also treats wastewater A, except that this comparative example uses ozone + photo-Fenton process instead of photo-Fenton process for treatment, specifically:

[0199] The pH was adjusted to 3.5 by 98% concentrated sulfuric acid and 0.24g / L FeSO4·7H2O was added, the ozone flux was 10mg / (L·min), the reaction time was 5 minutes, and then 12mM 30% mass concentration hydrogen peroxide was added, and the reaction time was 7min; after that, the pH of the wastewater was adjusted to between 6.5 and 7.0 by sodium hydroxide, and flocculation and precipitation were performed by PAM agent. The supernatant was taken for detection after standing.

[0200] After testing, after the wastewater was subjected to advanced oxidation treatment using the ozone + photo-Fenton process in this comparative example, COD was reduced to 49 mg / L, TOC was reduced to 21.3 mg / L, STOD=1.48, chromaticity was reduced to 15, and BOD / COD was increased to 0.38, meeting the standard for discharge into the ecological buffer zone. However, according to laboratory calculations, the treatment cost was 4.426 yuan / t, which was higher than the treatment cost of photo-Fenton, and the degree of improvement in the biodegradability of the wastewater was weaker than that of the photo-Fenton reaction.

[0201] Example 9

[0202] This embodiment provides a system for deep treatment of wastewater membrane filtration concentrate.

[0203] like Figure 11 As shown, the system includes an acidification regulating tank, a photo-Fenton oxidation tank, an alkali regulating tank, a flocculation sedimentation tank, a sludge tank and an ecological buffer zone connected in sequence. Among them:

[0204] a. Photo-Fenton oxidation pool, based on the COD index reflected by UV275 (see Figure 1)Automatically adjust the dosage of oxidant and the reaction time of ultraviolet light irradiation to deeply treat different wastewater membrane concentrates, with the COD of the treated wastewater controlled within 60 mg / L and the chromaticity controlled within 30;

[0205] b. Flocculation sedimentation tank: Further treat the wastewater membrane concentrate by adding PAM flocculant. On the one hand, precipitate heavy metal salts in the wastewater by adjusting the pH, and on the other hand, form flocs through flocculation to further remove organic matter and reduce chromaticity. The COD of the treated wastewater is controlled within 50 mg / L, the chromaticity is controlled within 20, and the BOD / COD is controlled above 0.35;

[0206] c. Ecological buffer zone: The ecological buffer zone adopts the combination of an ecological filter bed and an ecological river. The ecological filter bed at the front end can alleviate the impact of water quality fluctuations, and the ecological river at the end is used for further purification to stabilize the water quality. After photo-Fenton and flocculation sedimentation, the biological toxicity of the membrane filtration concentrate is reduced, and its biodegradability is greatly improved, enabling the BOD / COD to be maintained above 0.35. However, the wastewater still contains a certain amount of pollutants such as aniline, nitrogen and phosphorus, and metal ions, which can be further removed through the ecological buffer zone to stabilize the water quality.

Claims

1. A photocatalytic Fenton process for wastewater treatment, characterized in that, The process includes the following steps: S1: Measure the COD index of the wastewater; adjust the pH of the wastewater to 3.5 - 9; add Fe 2+ catalyst; S2: Add the oxidant for the first time under ultraviolet light irradiation, and add the oxidant for the second time within 2 - 3 minutes after the first addition. The amount of oxidant added for the first time ≥ the amount of oxidant added for the second time. The ultraviolet light irradiation time and the total amount of oxidant added are determined according to the following conditions: (ⅰ) When 200 < COD ≤ 250 mg / L, the total amount of oxidant added is 11 - 13 mM, and the ultraviolet light irradiation time is 4 - 6 minutes; (ii) When 250 < COD ≤ 350 mg / L, the total amount of oxidant added is 15 - 17 mM, and the ultraviolet light irradiation time is 9 - 11 minutes; (iii) When 350 < COD ≤ 450 mg / L, the total amount of oxidant added is 23 - 25 mM, and the ultraviolet light irradiation time is 14 - 16 minutes.

2. The photocatalytic Fenton treatment process for wastewater according to claim 1, characterized in that, In S1, Fe is added 2+ The content of the catalyst is 0.43 to 1.73 mM.

3. The photocatalytic Fenton treatment process for wastewater according to claim 2, characterized in that, In S2, the irradiation wavelength of the ultraviolet light irradiation is 185 - 254 nm.

4. The photocatalytic Fenton treatment process for wastewater according to claim 3, wherein, In S2, the amount of oxidant added for the first time is the same as the amount of oxidant added for the second time.

5. A photo-Fenton treatment process for wastewater according to any one of claims 1-4, characterized in that, In S2, add the oxidant for the second time 2.5 minutes after the first addition of the oxidant.

6. A photocatalytic Fenton process for treating wastewater according to any one of claims 1-4, characterized in that, In S2, When 200 < COD ≤ 250 mg / L, the total amount of oxidant added is 12 mM; and / or When 250 < COD ≤ 350 mg / L, the total amount of oxidant added is 16 mM; and / or When 350 < COD ≤ 450 mg / L, the total amount of oxidant added is 24 mM.

7. Application of the photo - Fenton treatment process for wastewater according to any one of claims 1 - 6 in treating the wastewater membrane filtration concentrate.

8. The application according to claim 7, characterized in that, The application includes: Using the photo - Fenton treatment process to treat the wastewater membrane filtration concentrate; Adjusting the pH of the treated effluent to be between 6.5 - 7.0; Adding a flocculant for flocculation precipitation; Discharging the supernatant after flocculation precipitation.

9. A treatment method for wastewater membrane filtration concentrate, characterized in that, The method includes: Using the photo - Fenton treatment process for wastewater according to any one of claims 1 - 6 to treat the wastewater membrane filtration concentrate; Adjusting the pH of the treated effluent to be between 6.5 - 7.0; Adding a flocculant for flocculation precipitation; Discharging the supernatant after flocculation precipitation.

10. A wastewater treatment system, characterized in that, The system includes an acid - adding adjustment tank, a photo - Fenton oxidation tank, an alkali - adding adjustment tank, a flocculation sedimentation tank, a sludge tank and / or an ecological buffer zone connected in sequence.

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