CN107935269B - Water treatment process capable of recycling coagulant and photocatalytic material and realizing zero discharge of muddy water - Google Patents

Water treatment process capable of recycling coagulant and photocatalytic material and realizing zero discharge of muddy water Download PDF

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CN107935269B
CN107935269B CN201711396044.0A CN201711396044A CN107935269B CN 107935269 B CN107935269 B CN 107935269B CN 201711396044 A CN201711396044 A CN 201711396044A CN 107935269 B CN107935269 B CN 107935269B
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CN107935269A (en
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裴海燕
金岩
徐杭州
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Shandong University
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    • C—CHEMISTRY; METALLURGY
    • C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F1/00—Treatment of water, waste water, or sewage
    • C02F1/30—Treatment of water, waste water, or sewage by irradiation
    • C—CHEMISTRY; METALLURGY
    • C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F1/00—Treatment of water, waste water, or sewage
    • C02F1/52—Treatment of water, waste water, or sewage by flocculation or precipitation of suspended impurities
    • C02F1/5236—Treatment of water, waste water, or sewage by flocculation or precipitation of suspended impurities using inorganic agents
    • C02F1/5245—Treatment of water, waste water, or sewage by flocculation or precipitation of suspended impurities using inorganic agents using basic salts, e.g. of aluminium and iron
    • C—CHEMISTRY; METALLURGY
    • C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F1/00—Treatment of water, waste water, or sewage
    • C02F2001/007—Processes including a sedimentation step
    • C—CHEMISTRY; METALLURGY
    • C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F2305/00—Use of specific compounds during water treatment
    • C02F2305/10—Photocatalysts

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Abstract

The invention discloses a water treatment process with zero discharge of muddy water capable of recycling a coagulant and a photocatalytic material, wherein a water treatment method comprises the following steps: 1) adding a nano photocatalyst and a coagulant into raw water to be treated, and stirring to finish coagulation, wherein the nano photocatalyst is nitrogen-doped titanium dioxide (N-TiO)2) The coagulant is polyaluminum ferric chloride (PAFC); 2) standing and precipitating the coagulation system in the step 1), allowing the supernatant to enter the next treatment procedure, and irradiating the precipitated bottom mud under visible light while continuously stirring; 3) directly adding the irradiated bottom mud in the step 2) into raw water to be treated, adding a proper amount of coagulant to complete a new round of coagulation and photocatalytic degradation, and reusing the bottom mud after photocatalytic degradation for treating the raw water.

Description

Water treatment process capable of recycling coagulant and photocatalytic material and realizing zero discharge of muddy water
Technical Field
The invention relates to the field of water treatment, in particular to a water treatment process with zero discharge of muddy water capable of recycling a coagulant and a photocatalytic material.
Background
In the water treatment process of a municipal water supply plant, a large amount of bottom mud is generated in the coagulation-precipitation stage. These sediments account for about 5% of the purified water produced by waterworks. At present, most of water supply plants in China simply dehydrate the generated bottom mud and then discharge the dehydrated bottom mud into lakes and rivers, some water supply plants discharge the dehydrated bottom mud directly even without treatment, and only a small part of the bottom mud is treated in a standard way. The pollutants contained in the bottom mud are likely to cause secondary pollution after being discarded, and further influence the production and life of people. In addition, the abandonment of the bottom mud of the water supply plant can also cause the waste of water resources and aggravate the current situation of water resource shortage in China.
At present, researches on harmless treatment and resource utilization of bottom mud of water supply plants are carried out. However, the method is limited to the problems of high treatment cost, unstable effect, secondary pollution and the like. For example, the acid treatment method widely studied to recycle coagulant in the bottom sludge of water supply plant may change the pH value of raw water and affect the water quality when the treated bottom sludge is added into the raw water; the bottom mud is utilized to fire the hollow brick, so that the treatment cost is high, and the instability of the properties of the bottom mud can influence the calcining quality and success rate. Therefore, the problem to be solved is to find a feasible method for harmless and recycling the bottom sludge of the water supply plant.
Disclosure of Invention
Aiming at the technical problems in the prior art, the invention aims to provide a water treatment process with zero discharge of muddy water, which can recycle coagulant and photocatalytic material. The water treatment method can make the bottom sludge harmless and reach the recycling standard, the recycling of the bottom sludge can be realized without the dehydration treatment of the bottom sludge by the recycled bottom sludge, the bottom sludge treatment cost is reduced, the recycling of the bottom sludge can realize the recovery of the photocatalyst and the coagulant, and the harm of harmful substances in the bottom sludge to the environment is avoided.
In order to solve the technical problems, the technical scheme of the invention is as follows:
a water treatment process with zero discharge of muddy water capable of recycling a coagulant and a photocatalytic material comprises the following steps:
1) adding a nano photocatalyst and a coagulant into raw water to be treated, and stirring to finish coagulation, wherein the nano photocatalyst is nitrogen-doped titanium dioxide (N-TiO)2) The coagulant is polyaluminum ferric chloride (PAFC);
2) standing and precipitating the coagulation system in the step 1), allowing the supernatant to enter the next treatment procedure, and irradiating the precipitated bottom mud under visible light while continuously stirring;
3) directly adding the irradiated bottom mud in the step 2) into raw water to be treated, adding a proper amount of coagulant to complete a new round of coagulation and photocatalytic degradation, and reusing the bottom mud after photocatalytic degradation for treating the raw water.
The nitrogen-doped titanium dioxide photocatalyst is prepared into a photocatalytic floc by adopting polyaluminum ferric chloride as a coagulant and is settled along with bottom mud. Because the nitrogen-doped titanium dioxide photocatalyst is uniformly distributed in the raw water to be treated, the formed photocatalytic flocs are uniformly distributed in the precipitated bottom mud. Under the irradiation of visible light, pollutants which can be catalytically degraded, such as humic acid and the like in the bottom mud can be degraded more thoroughly under the catalytic action of photocatalytic flocs, and the harmless treatment of the bottom mud is realized.
Because the nitrogen-doped titanium dioxide nano photocatalyst and the coagulant exist in the bottom sediment in the form of flocs, when the bottom sediment is recycled, the recycling of the photocatalyst and the coagulant is realized, on one hand, the situation that the treated water contains a large amount of photocatalyst and coagulant is avoided, and the subsequent treatment procedures are increased, on the other hand, the using amount of the photocatalyst and the coagulant can be saved, and the treatment cost of raw water is reduced.
In addition, the bottom mud after the photocatalysis treatment can be directly recycled, the bottom mud does not need to be dehydrated, the treatment cost of the bottom mud is reduced, and the pollution to the environment caused by the direct discharge of the bottom mud is avoided.
Preferably, in the step 1), the mass ratio of the nano nitrogen-doped titanium dioxide to the polyaluminium ferric chloride is 20-100:1-5, and preferably 20-30: 1.
Preferably, in the step 2), the standing time is 5-60 min. A large amount of large alum flocs are deposited in the sedimentation stage, the upper layer water is clear water, and the remaining alum flocs with small particle size and small density continuously collide with each other and agglomerate while slowly descending until the sodium humate flocs are completely settled in the later stage.
Preferably, in step 2), the volume of the supernatant entering the next treatment procedure is 93-96% of the total volume.
Preferably, in the step 2), the illumination intensity of visible light is 3000-15000Lux, and the stirring speed is 200-1000 rpm.
Preferably, in the step 3), the mass ratio of the added coagulant to the initial adding amount is 1: 1-5.
Preferably, in step 1), the preparation method of the nano nitrogen-doped titanium dioxide comprises the following steps: 12-18 parts of butyl titanate, 18-22 parts of absolute ethyl alcohol, 0.05-0.5 part of urea and 28-35 parts of dilute nitric acid solution by weight are mixed, heated for 3-5 hours at 80-100 ℃, and then calcined for 3-5 hours at 400-500 ℃ to obtain white powder, namely the nano nitrogen-doped titanium dioxide.
Further preferably, the preparation method of the nano nitrogen-doped titanium dioxide comprises the following steps:
1) mixing butyl titanate and absolute ethyl alcohol to obtain a solution A, and dissolving urea in a dilute nitric acid solution to obtain a solution B;
2) and slowly adding the solution A into the solution B under the stirring condition, adjusting the pH value of the solution to be neutral, heating for reaction, and then calcining to obtain the nano nitrogen-doped titanium dioxide.
Still more preferably, the concentration of the dilute nitric acid is 1 mol/L.
More preferably, the weight ratio of the butyl titanate, the absolute ethyl alcohol, the urea and the dilute nitric acid is 15:20:0.05-0.5: 30.
More preferably, in the step 2), the heating reaction temperature is 75-85 ℃, and the reaction time is 2.5-3.5 hours.
More preferably, in the step 2), the calcining temperature is 400-500 ℃, and the calcining time is 2-4 hours.
The water treatment process is applied to the preparation of purified water and the treatment of industrial wastewater.
The invention has the following beneficial effects:
in the invention, in the coagulation stage, the floccule is formed by N-TiO2The powder is used as a core, and the carrier coagulation technology is utilized, so that the capability of forming flocs in a system is improved, and the consumption of a coagulant is reduced. In the photocatalytic degradation stage, pollutants (sodium humate) in the bottom mud are completely degraded under visible light. Within 40 hours, the bottom sludge TCODMnDegrading to within 20mg/L to reach the III-class water standard, so that the bottom sludge is harmless and reaches the recycling standard. The treated bottom mud can be directly added into raw water, a new round of bottom mud treatment process can be carried out only by adding a small amount of coagulant, and the degradation performance of the recycled photocatalyst is close to that of the photocatalyst used for the first time. In the process, the photocatalytic material, water resource and partial coagulant in the bottom sludge can be recycled, the process is simple, and the bottom sludge does not need to be dehydrated, so that the bottom sludge treatment cost is greatly reduced, and the feasibility of the process is improved.
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The accompanying drawings, which are incorporated in and constitute a part of this application, illustrate embodiments of the application and, together with the description, serve to explain the application and are not intended to limit the application.
FIG. 1 shows the addition of N-TiO2The powder has the enhancement effect on the coagulation effect of the sodium humate solution;
FIG. 2 shows a graph containing N-TiO2The sodium humate bottom mud can perform photocatalytic degradation under light;
FIG. 3 shows a graph containing N-TiO2And (4) evaluating the recycling of the sodium humate bottom mud.
Detailed Description
It should be noted that the following detailed description is exemplary and is intended to provide further explanation of the disclosure. Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs.
It is noted that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of exemplary embodiments according to the invention. As used herein, the singular forms "a", "an" and "the" are intended to include the plural forms as well, and it should be understood that when the terms "comprises" and/or "comprising" are used in this specification, they specify the presence of the stated features, steps, operations, and/or combinations thereof, unless the context clearly indicates otherwise.
The materials, reagents and the like used in the present invention are commercially available unless otherwise specified.
In the invention, the calculation formulas of the coagulation efficiency and the photocatalytic degradation efficiency are as follows:
coagulation efficiency (%) (raw water turbidity-turbidity of supernatant after coagulation) × 100%/raw water turbidity;
photocatalytic degradation efficiency (%) (raw water COD)MnCOD of the solution at the time point measuredMn) X 100%/raw water CODMn；
As introduced by the background art, the harmless treatment of the bottom mud in the drinking water process has certain defects, and simultaneously, the water and coagulant in the bottom mud can not be recycled to cause the waste of resources, in order to solve the technical problems, the invention provides a method for simultaneously carrying out harmless treatment and recycling on the bottom mud of a water supply plant, which comprises the following steps:
step (1): adding photocatalyst powder and coagulant into raw water, and stirring to complete coagulation.
Wherein the raw water is water solution prepared from sodium humate, and the photocatalyst is nanometer nitrogen-doped titanium dioxide (N-TiO)2) The powder and coagulant are polyaluminium ferric chloride (PAFC).
Step (2): standing for precipitation, precipitating the flocs containing the sodium humate to the bottom, and removing the sodium humate in the supernatant;
and (3): and (4) discarding the supernatant, reserving the bottom mud containing the sodium humate at the bottom, placing the bottom mud under visible light for irradiation and stirring, and degrading the sodium humate in the bottom mud after a certain time.
And (4): and directly adding the degraded bottom mud into raw water containing sodium humate, and supplementing a small amount of PAFC to perform a new round of coagulation and photocatalytic degradation, so that water, photocatalytic materials and partial coagulants in the treated bottom mud can be recycled.
In the step (1), in the preferred technical scheme of the invention, the nano N-TiO is adopted2100 to 500 parts by weight of powder and 5 to 20 parts by weight of polyaluminum ferric chloride.
In the most preferred technical scheme of the invention, the nano N-TiO 2200 parts of powder and 10 parts of polyaluminum ferric chloride.
Wherein the N-TiO is2The powder is prepared by the following method: heating 12-18 parts by weight of butyl titanate, 18-22 parts by weight of absolute ethyl alcohol, 0.05-0.5 part by weight of urea and 28-35 parts by weight of dilute nitric acid solution at 80-100 ℃ for 3-5 hours, and calcining at 400-500 ℃ for 3-5 hours to obtain white powder, namely N-TiO2。
In the preferred technical scheme of the invention, from the viewpoint of improving the effect of photocatalytic degradation, the N-TiO2The powder is prepared by the following method:
adding 15 parts by weight of butyl titanate into 20 parts by weight of absolute ethyl alcohol, and stirring to obtain a solution A;
adding 0.05-0.5 part by weight of urea into 30 parts by weight of dilute nitric acid solution, and mixing to form a solution B;
slowly adding the solution A into the solution B under the stirring condition, adjusting the pH to 7 by using a sodium hydroxide solution, and heating for 3 hours at 80 ℃;
then centrifuging the system, removing the supernatant, washing the precipitate for 3 times, calcining the precipitate for 3 hours at 400-500 ℃ to obtain white powder, namely N-TiO2。
Wherein in the step (1), the stirring condition is 150-250 rpm for 1-2 min, and 30-60 rpm for 10-20 min.
Mixing PAFC with N-TiO2The method is characterized in that the method is put into water and quickly stirred to quickly disperse the fine alum flocs to form fine alum flocs, the water body becomes more turbid at the moment, water flow can generate violent turbulence, the flocculation stage is a process that the alum flocs grow and become coarse, proper turbulence degree and enough retention time (10-20 min) are required, and a large amount of alum flocs can be observed to gather and slowly sink depending on gravity at the later stage.
In the step (2), the standing time is 5-60 min. A large amount of large alum flocs are deposited in the sedimentation stage, the upper layer water is clear water, and the remaining alum flocs with small particle size and small density continuously collide with each other and agglomerate while slowly descending until the sodium humate flocs are completely settled in the later stage.
In the step (3), the volume of the discarded supernatant liquid accounts for about 93-96% of the total volume.
In the step (3), the illumination intensity is 3000-15000Lux, and the stirring speed is 200-1000 rpm.
TiO2The semiconductor is the most widely used photocatalyst due to its advantages of non-toxicity, low cost, stable performance and corrosion resistance. However, titanium dioxide photocatalysts also have some limitations in terms of their photocatalytic efficiency: the forbidden band width is 3.2eV, the light absorption waveband is narrow (mainly in an ultraviolet region), and the sunlight utilization efficiency is low; high recombination rate of semiconductor carriers, low quantum efficiency, and the like. But not the introduction of the metal element N, can enlarge TiO2The light response range, thereby improving the photocatalytic activity in the visible light region. Thus, N-TiO2Can efficiently reduce the water pollutants under visible light.
In the step (4), in a preferred technical scheme of the invention, the supplemented polyaluminum ferric chloride is 3-6 parts by weight.
In the most preferred embodiment of the present invention, the amount of the additional polyaluminum ferric chloride is 5 parts by weight.
In the step (4), the N-TiO in the recycled bottom mud2The photocatalytic degradation effect on the sodium humate is close to that of the primary use.
In order to make the technical solution of the present invention more clearly understood by those skilled in the art, the technical solution of the present invention will be described in detail below with reference to specific examples and comparative examples.
Example 1
200mg of nano N-TiO2The powder was added to 1L of 10mg/L aqueous sodium humate solution, and stirred rapidly at 250rpm for 1min and slowly at 40rpm for 20min without PAFC. Standing for 20min after coagulation, detecting turbidity change of supernatant (2 cm below liquid level), and calculating coagulation efficiency of sodium humate to be 0, as shown in figure 1.
Example 2
200mg of nano N-TiO2The powder was added to 1L of 10mg/L aqueous sodium humate solution at 5mg/L PAFC concentration, stirred rapidly at 250rpm for 1min and slowly at 40rpm for 20 min. Standing for 20min after coagulation, detecting turbidity change of supernatant (2 cm below liquid level), and calculating coagulation efficiency of sodium humate to 69%, as shown in FIG. 1.
Example 3
200mg of nano N-TiO2The powder was added to 1L of 10mg/L aqueous sodium humate solution at 10mg/L PAFC concentration, and stirred rapidly at 250rpm for 1min and slowly at 40rpm for 20 min. Standing for 20min after coagulation, detecting turbidity change of supernatant (2 cm below liquid level), and calculating coagulation efficiency of sodium humate to 96.5%, as shown in figure 1.
Example 4
200mg of nano N-TiO2The powder was added to 1L of 10mg/L aqueous sodium humate solution at a PAFC concentration of 15mg/L, stirred rapidly at 250rpm for 1min and slowly at 40rpm for 20 min. Standing for 20min after coagulation, detecting turbidity change of supernatant (2 cm below liquid level), and calculating out sodium humate mixtureThe coagulation efficiency was 97.5%, see FIG. 1.
Example 5
200mg of nano N-TiO2The powder was added to 1L of 10mg/L aqueous sodium humate solution at a PAFC concentration of 20mg/L, stirred rapidly at 250rpm for 1min and slowly at 40rpm for 20 min. Standing for 20min after coagulation, detecting turbidity change of supernatant (2 cm below liquid level), and calculating coagulation efficiency of sodium humate to 97.5%, as shown in FIG. 1.
In conclusion, according to the principle that the coagulation effect is optimal and the coagulant is saved, 10mg/L PAFC is selected and added as the optimal coagulant dosage.
Example 6
200mg/L of N-TiO2Adding 10mg/L of PAFC into the sodium humate solution for coagulation, and after the coagulation is finished, discarding the supernatant, wherein the discarded supernatant accounts for about 95% of the total volume, and the rest part is the solution containing N-TiO2The sodium humate bottom mud solution. And (3) placing the bottom mud solution under 10000Lux intensity visible light, and carrying out photocatalytic degradation at the rotating speed of 500 rpm. Detection of COD of solutions at different time pointsMnThe photocatalytic degradation rate was calculated, and the results showed that after 40 hours of degradation, the COD of the solutionMnThe value reaches 18mg/L and reaches the class III water standard (<20mg/L) to render the bottom sludge harmless and meet the recycling standard, see fig. 2.
Example 7
Directly adding the harmlessly treated bottom mud into 1L of 10mg/L sodium humate aqueous solution, adding 5mg/L of PAFC, repeating the steps of coagulating and photocatalysis for two times (three times for use), and indicating that the photocatalytic degradation efficiency of the two times of recycling is close to that of the first time of recycling, and the COD can be treated within 48 hoursMnThe value is degraded to about 20mg/L, and the standard of harmlessness and recycling is achieved, as shown in figure 3.
When the sodium humate coagulation and photocatalytic degradation process is researched, different PAFC and N-TiO are found2The dosage can cause different coagulation and photocatalysis effects, and only the comparative examples 1 to 6 are taken as examples, but the research is not limited to the following comparative examples.
Comparative example 1
1L of 10mg/L sodium humate water solution is rapidly stirred at 250rpm for 1min and slowly stirred at 40rpm for 20 min. Standing for 20min after coagulation, detecting turbidity change of supernatant (2 cm below liquid level), and calculating coagulation efficiency of sodium humate to be 0, as shown in figure 1.
Comparative example 2
PAFC with the concentration of 5mg/L is added into 1L of 10mg/L sodium humate aqueous solution, the mixture is rapidly stirred at 250rpm for 1min, and the mixture is slowly stirred at 40rpm for 20 min. Standing for 20min after coagulation, detecting turbidity change of supernatant (2 cm below liquid level), and calculating coagulation efficiency of sodium humate to be 22.5%, as shown in figure 1.
Comparative example 3
PAFC with the concentration of 10mg/L is added into 1L of 10mg/L sodium humate aqueous solution, the mixture is rapidly stirred at 250rpm for 1min, and the mixture is slowly stirred at 40rpm for 20 min. Standing for 20min after coagulation, detecting turbidity change of supernatant (2 cm below liquid level), and calculating coagulation efficiency of sodium humate to 82%, as shown in FIG. 1.
Comparative example 4
PAFC with the concentration of 15mg/L is added into 1L of 10mg/L sodium humate aqueous solution, the mixture is rapidly stirred at 250rpm for 1min, and the mixture is slowly stirred at 40rpm for 20 min. Standing for 20min after coagulation, detecting turbidity change of supernatant (2 cm below liquid level), and calculating coagulation efficiency of sodium humate to 98%, as shown in FIG. 1.
Comparative example 5
PAFC with the concentration of 20mg/L is added into 1L of 10mg/L sodium humate aqueous solution, the mixture is rapidly stirred at 250rpm for 1min, and the mixture is slowly stirred at 40rpm for 20 min. Standing for 20min after coagulation, detecting turbidity change of supernatant (2 cm below liquid level), and calculating coagulation efficiency of sodium humate to 98%, as shown in FIG. 1.
Comparative example 6
Adding 15mg/L of PAFC into sodium humate solution for coagulation, and after coagulation is finished, discarding supernatant, wherein the discarded supernatant accounts for about 95% of the total volume, and the rest part is N-TiO-free2The sodium humate bottom mud solution. The bottom sediment solution is placed under 10000Lux intensity visible light, and is stirred at the rotating speed of 500 rpm. Detection of COD of solutions at different time pointsMnThe value, the result shows the COD in the processMnThe values remain substantially unchanged, see fig. 2.
As described above, PAFC and N-TiO were used2The bottom mud solution formed after coagulation can be subjected to photocatalytic degradation under visible light, so that the bottom mud solution is harmless and reaches the water quality standard of reuse. The recycling of the bottom mud can recover all water and N-TiO in the bottom mud2And partial coagulant, and the photocatalytic degradation efficiency is not obviously reduced after twice recycling. Therefore, the process can not only avoid the harm of the bottom mud to the environment, but also reuse the resources in the bottom mud, reduce the cost and increase the feasibility of the process.
The above description is only a preferred embodiment of the present application and is not intended to limit the present application, and various modifications and changes may be made by those skilled in the art. Any modification, equivalent replacement, improvement and the like made within the spirit and principle of the present application shall be included in the protection scope of the present application.

Claims (11)

1. A water treatment process with zero discharge of muddy water capable of recycling coagulant and photocatalytic material is characterized in that: the method comprises the following steps:
1) adding a nano photocatalyst and a coagulant into raw water to be treated, and stirring to finish coagulation, wherein the nano photocatalyst is nitrogen-doped titanium dioxide, and the coagulant is polyaluminium ferric chloride;
2) standing and precipitating the coagulation system in the step 1), allowing the supernatant to enter the next treatment procedure, and irradiating the precipitated bottom mud under visible light while continuously stirring;
3) directly adding the irradiated bottom mud in the step 2) into raw water to be treated, adding a proper amount of coagulant to complete a new round of coagulation and photocatalytic degradation, and reusing the bottom mud subjected to photocatalytic degradation for treating the raw water;
the raw water is an aqueous solution prepared from sodium humate.
2. The water treatment process according to claim 1, characterized in that: in the step 1), the mass ratio of the nano nitrogen-doped titanium dioxide to the polyaluminum ferric chloride is 20-100: 1-5.
3. The water treatment process according to claim 1, characterized in that: in the step 1), the mass ratio of the nano nitrogen-doped titanium dioxide to the polyaluminum ferric chloride is 20-30: 1.
4. The water treatment process according to claim 1, characterized in that: in the step 2), the volume of the supernatant entering the next treatment procedure accounts for 93-96% of the total volume.
5. The water treatment process according to claim 1, characterized in that: in the step 2), the illumination intensity of visible light is 3000-15000Lux, and the stirring speed is 200-1000 rpm.
6. The water treatment process according to claim 1, characterized in that: in the step 3), the mass ratio of the added coagulant to the initial addition is 1: 1-5.
7. The water treatment process according to claim 1, characterized in that: in the step 1), the preparation method of the nano nitrogen-doped titanium dioxide comprises the following steps: 12-18 parts of butyl titanate, 18-22 parts of absolute ethyl alcohol, 0.05-0.5 part of urea and 28-35 parts of dilute nitric acid solution by weight are mixed, heated for 3-5 hours at 80-100 ℃, and then calcined for 3-5 hours at 400-500 ℃ to obtain white powder, namely the nano nitrogen-doped titanium dioxide.
8. The water treatment process according to claim 1, characterized in that: the preparation method of the nano nitrogen-doped titanium dioxide comprises the following steps:
1) mixing butyl titanate and absolute ethyl alcohol to obtain a solution A, and dissolving urea in a dilute nitric acid solution to obtain a solution B;
2) and slowly adding the solution A into the solution B under the stirring condition, adjusting the pH value of the solution to be neutral, heating for reaction, and then calcining to obtain the nano nitrogen-doped titanium dioxide.
9. The water treatment process according to claim 7, wherein: the weight ratio of the butyl titanate, the absolute ethyl alcohol, the urea and the dilute nitric acid solution is 15:20:0.05-0.5: 30.
10. The water treatment process according to claim 8, wherein: in the step 2), the heating reaction temperature is 75-85 ℃, and the reaction time is 2.5-3.5 hours;
the calcining temperature is 400-500 ℃, and the calcining time is 2-4 hours.
11. Use of a water treatment process according to any one of claims 1 to 10 for the preparation of purified water and for the treatment of industrial waste water.
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