CN113413901A - Preparation method of recyclable visible-light-driven photocatalyst and application of recyclable visible-light-driven photocatalyst in excess sludge - Google Patents
Preparation method of recyclable visible-light-driven photocatalyst and application of recyclable visible-light-driven photocatalyst in excess sludge Download PDFInfo
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
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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
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- C02F11/06—Treatment of sludge; Devices therefor by oxidation
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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
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- C02F2305/10—Photocatalysts
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Abstract
The invention discloses a preparation method of a recyclable visible-light-driven photocatalyst and application of the recyclable visible-light-driven photocatalyst in excess sludge, wherein urea is heated, and then a product is taken out and ground to obtain a nano graphite-like phase carbon nitride visible-light-driven photocatalyst; placing the prepared visible-light-driven photocatalyst into ultrapure water, and carrying out ultrasonic treatment to obtain a uniform suspension; selecting foamed nickel as a substrate, uniformly coating the obtained suspension on the foamed nickel, and drying the foamed nickel in an oven after coating one layer each time, wherein the operation is marked as loading once and three times; repeatedly washing the prepared foam nickel coated with the turbid liquid with distilled water, and drying to obtain the recyclable photocatalyst. After the recoverable photocatalyst is used for treating the sludge, the total chemical oxygen demand degradation rate of the residual sludge reaches 27.5%, the sludge particle size is reduced from 50.53 micrometers to 38.19 micrometers, and the lactate dehydrogenase is increased by 300% compared with the initial value.
Description
Technical Field
The invention relates to the field of a device and a method for treating excess sludge through photocatalytic oxidation, in particular to a preparation method of a recyclable visible-light-driven photocatalyst and application of the recyclable visible-light-driven photocatalyst in excess sludge.
Background
With the rapid development of industrialization and urbanization, a large number of sewage treatment plants have been built. Among them, the biological treatment is the main technique for sewage treatment, and the excess sludge is the main by-product produced in the biological sewage treatment process, which contains a large amount of organic pollutants difficult to degrade and adsorbs a large amount of residual organic pollutants from the sewage, so the excess sludge must be treated and disposed before entering the environment. The total amount of sludge production in china has continued to increase in recent years. However, sludge management in china is also poor. More than 80% of the sludge is dumped without the necessary stabilization. The sludge treatment and disposal cost is more than 50 percent of the total operation cost of the sewage treatment plant. At present, the characteristics of large production scale, large potential environmental risk influence, high treatment cost and the like of excess sludge become the biggest problems faced by sewage plants, and the recycling, harmless and reduction of sludge become the key points of concern of governments and management departments of various countries in the world.
At present, the excess sludge is mostly treated by the traditional treatment process, which mainly comprises the following steps: incineration, composting and marine dumping etc., however, the increasing environmental concerns and the strict environmental regulations have led to the majority of these treatment methods being replaced by biological methods, namely composting, aerobic and anaerobic digestion. Among which anaerobic digestion is the most common. However, the anaerobic digestion technique takes a long time (up to tens of days), and the treatment effect is good, but the treatment efficiency is not high.
The photocatalytic oxidation method is used as an advanced oxidation technology, can realize direct conversion of solar energy into chemical energy, and can realize degradation of complex organic matters while effectively utilizing the solar energy. The traditional photocatalysis treatment of the excess sludge is to pretreat the excess sludge, so as to improve the subsequent bioavailability and the biogas yield. At present, the photocatalytic oxidation treatment of excess sludge is mostly carried out on sludge to improve the subsequent anaerobic digestion action rate and improve the biogas yield, the research on the direct degradation of sludge organic matters is less, meanwhile, the photocatalytic technology is applied to the treatment of sludge, powdery catalysts are adopted for treatment, the powdery photocatalysts are adopted for treatment, the sludge serving as a treatment object is different from other treatment objects, the powdery catalysts and floccules in the excess sludge can be mixed together and cannot be separated by means of centrifugation, filtration and the like, so that the photocatalysts cannot be recycled, the treatment efficiency is reduced, and the treatment cost is increased.
Disclosure of Invention
The invention provides a preparation method of a recyclable visible-light-driven photocatalyst and application of the recyclable visible-light-driven photocatalyst in excess sludge, and aims to solve the problem of low efficiency of excess sludge treatment by a method for treating excess sludge through photocatalytic oxidation.
In order to achieve the purpose, the technical scheme of the invention is as follows:
a preparation method of a recyclable visible light catalyst comprises the following steps:
the method comprises the following steps: heating urea at the heating rate of 1-3 ℃/min, heating at 550-600 ℃ for 1-3 h, taking out the product, and grinding to obtain the nano graphite-like carbon nitride visible-light-driven photocatalyst;
step two: placing the nano graphite-like phase carbon nitride visible-light-driven photocatalyst prepared in the first step into ultrapure water, and carrying out ultrasonic treatment for 15-30 min to obtain a visible-light-driven photocatalyst suspension;
step three: selecting pretreated foam nickel as a photocatalyst carrier, uniformly coating the visible light photocatalyst suspension obtained in the step two on the front and back surfaces of the pretreated foam nickel, drying the foam nickel at 40-80 ℃ after coating one layer on each surface in the period, recording the operation as loading once, and loading for 2-3 times in total to obtain a loaded visible light photocatalyst;
step four: and (4) washing the supported visible-light-driven photocatalyst prepared in the third step with distilled water to remove the unsupported catalyst, and drying at 40-80 ℃ to obtain the recyclable visible-light-driven photocatalyst.
Preferably, the visible light photocatalyst in the first step is powder with a void structure.
Preferably, the mass of the visible light catalyst in the second step is 1-2 g, and the volume of the ultrapure water is 20-40 mL.
Preferably, the size of the pretreated nickel foam in the third step is (3 cm-4 cm) × (5 cm-6 cm) in length × width, and the pretreated nickel foam is subjected to ultrasonic treatment for 15-30 min by sequentially using acetone, ethanol and deionized water, and is dried at 40-80 ℃ for later use.
The application of the recyclable visible-light-driven photocatalyst in excess sludge comprises the following steps:
step a: adding the excess sludge, keeping the liquid level of the excess sludge at a distance from a light source, suspending a recyclable visible light catalyst in the center of the excess sludge, and introducing cooling water for circulating condensation;
step b: turning on a light source, stirring, treating the excess sludge, and sampling and detecting the chemical oxygen demand value of the excess sludge at the same time interval.
Preferably, the concentration of the excess sludge in the step a is 550-650 mg/L, the power of the light source is 300-350W, the distance of the keeping distance is 10-13 cm, and the circulating condensation temperature is 15-18 ℃.
Preferably, the stirring reaction time in the step b is 24-36 h.
The preparation method of the recyclable visible-light-driven photocatalyst and the application of the recyclable visible-light-driven photocatalyst in excess sludge can realize the recycling of the visible-light-driven photocatalyst after treatment, and meanwhile, the low-concentration excess sludge is used as a treatment object, so that higher light transmittance is ensured, a photocatalytic material receives more light intensity, and the photocatalytic efficiency is improved to the greatest extent. The photocatalysis treatment system adopts the recyclable visible light catalyst to be suspended in the center of the reactor, so that the direct degradation of the excess sludge is realized, the defect that the powdery photocatalyst is difficult to recycle is overcome, and the limitation of the sludge degradation effect in the photocatalysis pretreatment sludge technology is broken.
Drawings
In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings needed to be used in the description of the embodiments or the prior art will be briefly introduced below, and it is obvious that the drawings in the following description are some embodiments of the present invention, and for those skilled in the art, other drawings can be obtained according to these drawings without creative efforts.
FIG. 1 is a schematic structural diagram of an experimental apparatus according to the present invention.
In the figure: 1. the device comprises a double-layer jacket reactor, 2, a suspension device, 3, a recyclable visible light catalyst, 4, a magnetic stirrer, 5, a light source, 6 and a thermostat.
Detailed Description
In order to make the objects, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are some, but not all, embodiments of the present invention. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.
A preparation method of a recyclable visible light catalyst comprises the following steps:
the method comprises the following steps: loading urea into a crucible to three quarters of the area, placing the crucible in a muffle furnace, heating at the heating rate of 1-3 ℃/min, heating at the temperature of 550-600 ℃ for 1-3 h, and grinding the product to obtain bright yellow powder with a pore structure, namely the nano graphite-like phase carbon nitride visible-light-driven photocatalyst;
step two: placing 1-2 g of the nano graphite-like carbon nitride visible-light-driven photocatalyst prepared in the first step into 20-40 mL of ultrapure water, and carrying out ultrasonic treatment for 15-30 minutes to obtain a uniform suspension;
step three: selecting pretreated foamed nickel with the length multiplied by the width of (3-4 cm) multiplied by (5-6 cm), sequentially performing ultrasonic treatment for 15-30 min by acetone, ethanol and deionized water, placing the pretreated foamed nickel at 40-80 ℃ for later use, taking the pretreated foamed nickel as a substrate, uniformly coating the visible light catalyst suspension obtained in the step two on the front side and the back side of the pretreated foamed nickel, and placing the pretreated foamed nickel at 40-80 ℃ for drying after coating one layer on each side in the period, wherein the operation is marked as loading once, and the loading is performed for 2-3 times in total to obtain the loaded visible light catalyst;
step four: and (4) repeatedly washing the foam nickel coated with the turbid liquid obtained in the third step with distilled water, and drying at 40-80 ℃ to obtain the recyclable nano graphite-like carbon nitride photocatalytic material.
The application of the recyclable visible-light-driven photocatalyst for treating the low-concentration excess sludge in the low-concentration excess sludge comprises the following steps:
step a: as shown in figure 1, 150mL of excess sludge with the concentration of 550-650 mg/L is added into a double-layer jacket reactor 1, and the liquid level of the excess sludge is kept at a distance of 10-13 cm from a light source 5; then suspending the recoverable nano graphite-like phase carbon nitride photocatalyst in the center of the sludge; introducing cooling water in the thermostat 6 into a jacket of a double-layer jacket reactor for circulating condensation, and keeping the temperature of residual sludge in the double-layer jacket reactor at 15-18 ℃;
step b: and (3) turning on a xenon lamp with the power of 300-350W for irradiation, turning on the magnetic stirrer 4 for stirring reaction, treating for 36h, and sampling and detecting the chemical oxygen demand value of the residual sludge at intervals of 12 h. And (4) judging whether the treatment of the excess sludge is finished or not through a pre-experiment, continuously prolonging the illumination time, and determining the COD (chemical oxygen demand) and SCOD (Small chemical oxygen demand) of the excess sludge. The results show that the COD stabilized at substantially the same level after 36h of light exposure, while the SCOD showed a tendency to increase and then decrease. The photocatalytic reaction breaks cells, so that intracellular organic matters are dissolved out and degraded simultaneously. The rate of release of soluble organics is faster than their degradation at the early stage, with the increase in SCOD. As the reaction proceeds, soluble organics are released to a limit where they are degraded at a faster rate than they are released, and the SCOD gradually decreases in the process. SCOD therefore shows a tendency to increase first and then decrease.
The action principle of the recyclable visible-light-driven photocatalyst for treating low-concentration excess sludge in the application system of the low-concentration excess sludge is as follows:
the invention provides a recyclable visible light catalytic system for treating low-concentration excess sludge, which is used for ensuring the stability of system temperature in the treatment process, ensuring that the microbial activity is not influenced by other external environments and simultaneously improving the treatment effect. The photocatalysis treatment system adopts a recyclable photocatalysis material to be suspended in the center of the reactor, realizes the direct degradation of excess sludge, overcomes the defect that a powdery photocatalyst is difficult to recycle, breaks through the limitation of sludge degradation effect in the photocatalysis pretreatment sludge technology, and is different from other existing excess sludge treatment technologies.
The recyclable visible light catalytic system for treating low-concentration excess sludge provided by the invention has the advantages that the photocatalytic material is suspended in the center of the sludge, and the sludge is limited in stirring and is farther away from a light source in the treatment process due to the excessively low placement of the photocatalytic material, so that the light intensity is weakened and increased by the sludge. In addition, the photocatalytic material is placed too high, so that the sludge close to the bottom layer is not in sufficient contact with the catalyst, the catalytic effect is reduced, the photocatalytic material is placed in the center of the sludge, visible light is ensured to fully irradiate on the catalyst, and the weakening effect of the sludge on light intensity is reduced. Meanwhile, the two surfaces of the sludge and the photocatalytic material can be fully contacted, and photocatalytic reaction sites are increased. And can ensure that the sludge is kept fully stirred in the treatment process, and avoid the influence of the photocatalytic material on the sludge.
The invention is used in the recoverable visible light catalytic system for treating low-concentration excess sludge, the recoverable visible light catalytic material 3 is prepared by taking foam nickel as a catalyst carrier and loading powdery graphite-like carbon nitride on the carrier, and has a three-dimensional porous structure, the structure has good light transmittance, the dispersity of the catalyst is improved, visible light can penetrate through the surface of the material to reach the interior more easily, more active sites are provided for the photocatalytic reaction, the roughness of the surface of the material is increased, the adsorption of sludge on the surface of the catalyst is enhanced, in addition, the foam nickel has good conductivity, the electron transfer on the surface of the photocatalyst is facilitated, the separation efficiency of photo-generated electrons and holes is improved, the activity of the photocatalytic reaction is improved, and meanwhile, the foam nickel has strong toughness and mechanical property and can be processed into various shapes, the hydraulic scouring machine can resist strong hydraulic scouring force and has the advantages of good stability, low cost, easy obtainment, easy scale and the like.
The invention adopts visible light to catalyze and treat low-concentration excess sludge, the excess sludge is used as a residual substance after sewage treatment by a biological method, and is an extremely complex heterogeneous body composed of organic residues, bacterial thalli, inorganic particles, colloids and the like, the main components of the heterogeneous body comprise plant nutrient components and toxic and harmful components, and most microorganisms are suspended in water in the form of activated sludge flocs instead of free existence. The activated sludge floc is formed by combining and polymerizing bacteria, Extracellular Polymeric Substances (EPS), granular organic substances, inorganic particles and other substances through special acting forces such as electrostatic acting force, van der Waals force, hydrophobic acting force and the like, and has biological activity. When the activated sludge exits the biological treatment system, it is referred to as excess activated sludge. In an activated sludge system, the chemical components of EPS are complex, and the components are different due to different sources. In general, protein and polysaccharide are main components of EPS, and account for about 70-80% of the total organic matter; and the content of nucleic acid, lipid, humic acid, uronic acid and the like is less, EPS exists in activated sludge flocs in large quantity, and is combined with cells through complex interaction to form a huge reticular structure, which plays a critical role in the formation and the structure of the flocs and determines the mechanical stability of microbial polymers. Activity deviceThe sexual sludge is mainly characterized by high organic matter content, fine sludge floc, light specific gravity, strong binding capacity with water, high water content (up to 99 percent), difficult dehydration and the like, and the active sludge can bring serious secondary pollution if not treated timely and effectively. When the complex organic matters are degraded by photocatalysis, the complex organic matters are mainly divided into two processes, namely the process of inactivating microorganisms and the process of degrading the microorganisms. Among them, the physiological mechanism of inactivation of microorganisms in sludge is far more complex than the chemical degradation of PPCPs, which are collectively called Pharmaceutical and Personal Care Products, novel organic substances of PPCPs and organic dyes and other pollutants. The reaction mechanism of photocatalytic degradation of activated sludge is mainly the following process, and the photocatalyst generates ROS with strong oxidizing property after receiving illumination, such as HO and O2-·、H2O2And h +, etc., these ROS first break down and break down various organic components in EPS, such as proteins, polysaccharides, nucleic acids, lipids, etc. (polypeptide chain fragmentation and saccharide depolymerization), nucleic acids being an important one of many potential degradation substances. After the destruction of nucleic acid, the replication and many metabolic functions of DNA are inhibited, and the double strand of DNA changes from coiled structure to loose structure and finally to straight structure, HO and H2O2Can cause the breakage of phosphodiester bonds between bases in a DNA chain, cause the single-strand double-strand break of a DNA molecule, destroy the double helix structure of the DNA, and further destroy the replication of the DNA and the metabolism of cell membranes, so that the cells are completely inactivated. The destruction of EPS is that sludge flocs are changed from large particle size to small particle size and pass through EPS to directly attack cell surface, ROS has important effect on the destruction of microbial cell membrane and intracellular plastid structure, and can almost indiscriminately carry out oxidative decomposition on organic matters, wherein H2O2Can enter into the cell, probably is the main factor of bacterial cell death, the cell wall and the cytoplasmic membrane are oxidized and destroyed successively to cause the respective semi-permeability loss, and the destruction of the cytoplasmic membrane causes the leakage of macromolecular particles in the cell, such as protein and RNA, etc., meanwhile, the photocatalyst can enter into the cell to oxidize and destroy the internal protein and inactivate the cell, in addition, in the photocatalysis process, the coenzyme A which participates in the enzymatic reaction in the cell respiration process is oxidized and generated simultaneouslyThe dimeric coenzyme A is formed, thereby inhibiting the respiration of biological cells and finally causing the inactivation of microorganisms. After the microorganisms in the sludge are inactivated, a plurality of bacterial fragments are generated, and the microbial residues are finally oxidized and decomposed into CO along with the increase of the illumination time2And H2O。
In order to avoid that the temperature of the system is continuously increased by energy emitted by a light source and ensure that the activity of sludge microorganisms is not influenced by the environment outside the system, the reaction device is additionally provided with a circulating condensation system, circulating condensed water is introduced into a double-layer jacket reactor in the reaction process, the temperature of the system is always kept at a lower level in the treatment process, and the system cannot fluctuate along with the increase of illumination time. The total chemical oxygen demand is measured by an ultrasonic pretreatment-potassium dichromate method, the particle size is measured by a laser particle size distribution instrument, and the lactate dehydrogenase is detected by a kit. After the system is illuminated for 36 hours, the degradation rate of Total Chemical Oxygen Demand (TCOD) of the sludge in the system can reach 27.5%, compared with other existing residual sludge treatment systems, the degradation effect is in a leading level, the particle size of the sludge is reduced to 38.19 μm from 50.53 μm after 36 hours of photocatalytic treatment, the Lactate Dehydrogenase (LDH) is increased by 300% compared with an initial value, meanwhile, the recovery of the photocatalyst can be realized while the treatment effect is ensured, the treatment difficulty is reduced, the treatment cost is reduced, and the treatment efficiency is increased.
Finally, it should be noted that: the above embodiments are only used to illustrate the technical solution of the present invention, and not to limit the same; while the invention has been described in detail and with reference to the foregoing embodiments, it will be understood by those skilled in the art that: the technical solutions described in the foregoing embodiments may still be modified, or some or all of the technical features may be equivalently replaced; and the modifications or the substitutions do not make the essence of the corresponding technical solutions depart from the scope of the technical solutions of the embodiments of the present invention.
Claims (8)
1. A preparation method of a recyclable visible light catalyst is characterized by comprising the following steps:
the method comprises the following steps: heating urea at the heating rate of 1-3 ℃/min, heating at 550-600 ℃ for 1-3 h, taking out the product, and grinding to obtain the nano graphite-like carbon nitride visible-light-driven photocatalyst;
step two: placing the nano graphite-like phase carbon nitride visible-light-driven photocatalyst prepared in the first step into ultrapure water, and carrying out ultrasonic treatment for 15-30 min to obtain a visible-light-driven photocatalyst suspension;
step three: selecting pretreated foam nickel as a photocatalyst carrier, uniformly coating the visible light photocatalyst suspension obtained in the step two on the front and back surfaces of the pretreated foam nickel, drying the foam nickel at 40-80 ℃ after coating one layer on each surface in the period, recording the operation as loading once, and loading for 2-3 times in total to obtain a loaded visible light photocatalyst;
step four: and (4) washing the supported visible-light-driven photocatalyst prepared in the third step with distilled water to remove the unsupported catalyst, and drying at 40-80 ℃ to obtain the recyclable visible-light-driven photocatalyst.
2. The method of claim 1, wherein the visible-light-induced photocatalyst in the first step is a powder with a void structure.
3. The method for preparing a recyclable visible light catalyst as described in claim 1, wherein the mass of the visible light catalyst in the second step is 1-2 g, and the volume of the ultrapure water is 20-40 mL.
4. The preparation method of the recyclable visible light catalyst as claimed in claim 1, wherein the pretreated nickel foam in step three has a length x width of (3 cm-4 cm) × (5 cm-6 cm), and the pretreated nickel foam is subjected to ultrasonic treatment for 15-30 min by using acetone, ethanol and deionized water in sequence, and dried at 40-80 ℃ for later use.
5. Use of the recoverable visible light catalyst according to any of claims 1 to 4 in excess sludge.
6. The application of the recyclable visible light catalyst in excess sludge according to claim 5, characterized by comprising the following steps:
step a: adding the excess sludge, keeping the liquid level of the excess sludge at a distance from a light source, suspending a recyclable visible light catalyst in the center of the excess sludge, and introducing cooling water for circulating condensation;
step b: turning on a light source, stirring, treating the excess sludge, and sampling and detecting the chemical oxygen demand value of the excess sludge at the same time interval.
7. The application of the recyclable visible light catalyst in low-concentration excess sludge as claimed in claim 6, wherein the concentration of the excess sludge in step a is 550-650 mg/L, the power of the light source is 300-350W, the distance of the keeping distance is 10-13 cm, and the circulating condensation temperature is 15-18 ℃.
8. The application of the recyclable visible light catalyst in low-concentration excess sludge according to claim 6, wherein the stirring reaction time in the step b is 24-36 h.
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