CN113636716A - Method for treating polyester micro-plastic polluted water body through series photocatalysis - Google Patents

Method for treating polyester micro-plastic polluted water body through series photocatalysis Download PDF

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CN113636716A
CN113636716A CN202110860189.1A CN202110860189A CN113636716A CN 113636716 A CN113636716 A CN 113636716A CN 202110860189 A CN202110860189 A CN 202110860189A CN 113636716 A CN113636716 A CN 113636716A
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reaction
photocatalytic
anaerobic
aerobic
sewage
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刘升卫
肖正涛
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Sun Yat Sen University
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Sun Yat Sen 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
    • C02F9/00—Multistage treatment of water, waste water or sewage
    • 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
    • C02F1/32—Treatment of water, waste water, or sewage by irradiation with ultraviolet light
    • 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
    • C02F1/66—Treatment of water, waste water, or sewage by neutralisation; pH adjustment
    • C—CHEMISTRY; METALLURGY
    • C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F2103/00—Nature of the water, waste water, sewage or sludge to be treated
    • C02F2103/34—Nature of the water, waste water, sewage or sludge to be treated from industrial activities not provided for in groups C02F2103/12 - C02F2103/32
    • C02F2103/36—Nature of the water, waste water, sewage or sludge to be treated from industrial activities not provided for in groups C02F2103/12 - C02F2103/32 from the manufacture of organic compounds
    • C02F2103/38—Polymers
    • C—CHEMISTRY; METALLURGY
    • C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F2203/00—Apparatus and plants for the biological treatment of water, waste water or sewage
    • C02F2203/006—Apparatus and plants for the biological treatment of water, waste water or sewage details of construction, e.g. specially adapted seals, modules, connections
    • C—CHEMISTRY; METALLURGY
    • C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F2209/00—Controlling or monitoring parameters in water treatment
    • C02F2209/06—Controlling or monitoring parameters in water treatment pH
    • C—CHEMISTRY; METALLURGY
    • C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F2209/00—Controlling or monitoring parameters in water treatment
    • C02F2209/20—Total organic carbon [TOC]
    • C—CHEMISTRY; METALLURGY
    • C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F2301/00—General aspects of water treatment
    • C02F2301/04—Flow arrangements
    • C02F2301/046—Recirculation with an external loop
    • 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
    • C—CHEMISTRY; METALLURGY
    • C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F3/00—Biological treatment of water, waste water, or sewage
    • C02F3/30—Aerobic and anaerobic processes

Abstract

The invention discloses a method for treating polluted water of polyester micro-plastic by series photocatalysis, which comprises the steps of hydrolyzing the polyester micro-plastic into acid monomers and/or alcohol monomers, then carrying out photocatalysis anaerobic reaction by using the alcohol monomers as an electron donor, and/or degrading the acid monomers into organic alcohol and acid intermediates in a photocatalysis aerobic reaction system; and then carrying out photocatalytic anaerobic-aerobic cyclic reaction or photocatalytic aerobic-anaerobic cyclic reaction, and finally completely degrading residual organic matters after the cyclic reaction into carbon dioxide and water and discharging the carbon dioxide and the water. Through the series photocatalytic reaction, the purpose of gradually degrading the polyester micro-plastic is achieved, and the efficiency of hydrogen production through water decomposition is improved. The method can realize effective degradation of polyester micro-plastic in sewage, can also realize photocatalytic efficient decomposition of water to produce hydrogen, and is simple, short in time consumption, low in cost and wide in application range.

Description

Method for treating polyester micro-plastic polluted water body through series photocatalysis
Technical Field
The invention belongs to the technical field of sewage treatment, and particularly relates to a method for treating a polyester micro-plastic polluted water body by series photocatalysis.
Background
"Microplastic" refers to tiny plastic fragments, fibers and particles with a size less than 5mm, which are a pollutant and a main carrier of pollution, thus interfering with the normal life activities of aquatic organisms and even endangering human health. Although the sewage treatment plant can remove most of larger plastic particles in the water body in the water treatment process, a plurality of plastic fibers and nano-scale micro-plastic particles are dischargedPutting into water. At present, researches on rivers, oceans and drinking water bodies all around the world show that the micro plastic particles are found, wherein in China, the researches show that the abundance of the Guangzhou Zhujiang micro plastic particles reaches 19860 particles/m3The polymer types are mainly Polyethylene (PE), polypropylene (PP) and polyethylene terephthalate (PET). Among various plastics, PET is one of the most widely used plastics at present, and is a polyester plastic, and is mainly applied to a plurality of fields such as synthetic fibers, films, product packaging, various beverages, mineral water bottles, electronic and electrical parts and the like, so PET micro plastic is also one of the most commonly detected micro plastics in China and even all over the world, and is also the most representative polyester plastic. The PLA (polylactic acid) micro plastic is a biodegradable polyester plastic which is newly developed at present, and has wide application prospect under the background of advocating energy conservation and emission reduction and developing low-carbon economy in the current country.
Although many processes have been developed for treating polyester plastics, most are directed to large plastic solids, which are depolymerized and recovered as valuable organics, these techniques are not well suited for use with polyester microplastic particles in aqueous environments. Therefore, the development of a treatment process capable of degrading the polyester micro-plastic and the monomer thereof in the water environment is needed at present, wherein the photocatalysis technology has the advantages of high oxidation capacity and mineralization capacity, no secondary pollution, broad spectrum on the degradation and mineralization of various pollutants, normal temperature technology, energy conservation, high efficiency, long service life, low operation cost and the like, and is widely researched in the field of water pollution treatment. However, the pure photocatalytic technology needs to react under the condition of sufficient oxygen, so an aeration device needs to be added in the practical application process, the energy consumption is high, the pollutants are directly oxidized into water and carbon dioxide, and no substance with high added value is generated in the middle for recovery. For example, patent CN112058251A combines a photocatalytic reaction of a photocatalyst with an ultrasonic degradation process to synergistically degrade plastic microbeads in wastewater, so that the process has excellent photocatalytic degradation efficiency, but the process directly treats the plastic microparticles, so that not only an auxiliary device (ultrasonic device) with high energy consumption needs to be added, but also the reaction time is long (25 days need to be illuminated), the operation cost is very high, and therefore, the efficiency is very low when the process is used for treating polyester microplastics capable of being hydrolyzed.
Therefore, there is an urgent need to develop a method for degrading polyester micro-plastics in wastewater with low cost and high efficiency and recovering products with added value from the degradation process so as to meet the requirement of practical application.
Disclosure of Invention
Aiming at the problems of high energy consumption, high cost and difficult product recovery or resource utilization of the conventional method for degrading the polyester micro-plastics in the sewage, the invention aims to provide a method for treating the polluted water body of the polyester micro-plastics by series photocatalysis. The method achieves the aim of gradually degrading the polyester micro-plastic and improves the efficiency of hydrogen production by water decomposition through the photocatalytic cycle reaction. The method promotes the photocatalytic decomposition of water to produce hydrogen while realizing the effective degradation of the polyester micro-plastic in the wastewater, and has the advantages of simple method, low cost and wide application range.
In order to achieve the purpose, the invention adopts the following technical scheme:
a method for treating a polyester micro-plastic polluted water body by series photocatalysis comprises the following steps:
s11 pretreatment: hydrolyzing polyester micro-plastics in the sewage into acid monomers and/or alcohol monomers, and adjusting the pH value of the treated sewage to 6-8;
s12 photocatalytic anaerobic reaction: carrying out photocatalytic decomposition on the sewage treated in the step S11 under an anaerobic condition to produce hydrogen;
s13 photocatalytic aerobic reaction: carrying out photocatalytic aerobic reaction on the sewage treated in the step S12 to degrade acid monomers into organic acid and alcohol intermediates;
s14 photocatalytic anaerobic-aerobic cyclic reaction: refluxing the sewage treated in the step S13 to an anaerobic reaction system of the step S12 for anaerobic-aerobic circulating reaction, and stopping the circulation when the hydrogen production rate in the anaerobic reaction system is not more than 1.25 times of the hydrogen production rate in pure water under the same condition;
and S15 post-processing: reacting the sewage in the S14 in an aerobic reaction system until the TOC concentration is lower than 30mg/L, and discharging;
alternatively, the method comprises the following steps:
s21 pretreatment: hydrolyzing polyester micro-plastics in the sewage into acid monomers and/or alcohol monomers, and adjusting the pH value of the treated sewage to 6-8;
s22 photocatalytic aerobic reaction: carrying out photocatalytic aerobic reaction on the sewage treated in the step S21 to degrade acid monomers into organic acid and alcohol intermediates;
s23 photocatalytic anaerobic reaction: carrying out photocatalytic decomposition on the sewage treated in the step S22 under an anaerobic condition to produce hydrogen;
s24 photocatalytic aerobic-anaerobic cycle reaction: refluxing the sewage treated in the step S23 to an S22 aerobic reaction system for aerobic-anaerobic cycle reaction, and stopping the cycle when the hydrogen production rate in the anaerobic reaction system is not more than 1.25 times of the hydrogen production rate in pure water under the same condition;
and S25 post-processing: reacting the sewage in the S24 in an aerobic reaction system until the TOC concentration is lower than 30mg/L, and discharging.
Researches show that the small molecular alcohol monomer which is easy to be oxidized can be used as an electron donor to promote the hydrogen production reaction by photocatalytic decomposition under the anaerobic condition, and the acid monomer which is difficult to be oxidized can be rapidly degraded in the photocatalytic aerobic reaction stage. Firstly, hydrolyzing polyester micro-plastic into acid monomers and/or alcohol monomers, then adjusting the pH value of a reaction system, promoting the hydrogen production reaction of photocatalytic decomposition water by using micromolecule alcohol monomers which are easy to be oxidized in an aqueous solution as electron donors under the anaerobic condition, and simultaneously oxidizing and degrading the micromolecule alcohol monomers and a cavity reaction; or the monomer which is difficult to oxidize and is not suitable for being directly used as an electron donor is rapidly degraded through photocatalytic aerobic reaction, and the monomer is not completely degraded into water and carbon dioxide but is degraded into organic acid and alcohol intermediates which have smaller molecular weight and are easy to oxidize by controlling the reaction time; then, the organic acid and alcohol intermediates are refluxed to an anaerobic system and can be used as an electron donor to promote the photocatalytic anaerobic water splitting to produce hydrogen. The photocatalytic anaerobic-aerobic cyclic reaction or photocatalytic aerobic-anaerobic cyclic reaction not only achieves the aim of gradually degrading the polyester micro-plastic, but also improves the efficiency of water decomposition and hydrogen production.
In conclusion, the method couples the photocatalytic degradation pollutants with the photocatalytic decomposition water to generate hydrogen, so that the organic matters are not required to be thoroughly oxidized and degraded in the aerobic reaction process, an aeration device is not required to be added, the problem of high energy consumption in the traditional photocatalytic degradation of pollutants is solved, and the problems of secondary pollution and high cost caused by the additional addition of an electron donor in the photocatalytic decomposition of water to generate hydrogen are solved. By adopting photocatalytic anaerobic-aerobic or aerobic-cyclic reaction, the method can realize the effective degradation of the polyester micro-plastic in the wastewater, and can also improve the efficiency of producing hydrogen by photocatalytic water decomposition, and has the advantages of simple method, low cost and wide application range.
Preferably, the polyester micro plastic in S11 or S21 is at least one of PET or PLA.
Preferably, when the polyester micro plastic in S11 or S21 is PET, the acid monomer is terephthalic acid and the alcohol monomer is ethylene glycol.
Preferably, when the polyester micro plastic in S11 or S21 is PLA, the acid monomer is lactic acid.
Preferably, the hydrolysis reaction in S11 or S21 is alkaline hydrolysis, and the alkali liquor is one or two of NaOH or KOH solution.
Preferably, the hydrolysis reaction in S11 or S21 has the reaction time of 24-72 hours and the reaction temperature of 30-50 ℃.
Preferably, the illumination intensity in the photocatalytic anaerobic reaction and the photocatalytic aerobic reaction is independently 3-6 mW/cm2。
Preferably, when the polyester micro plastic is PET in S11, the method comprises the steps of:
s11 pretreatment: hydrolyzing polyester micro-plastic in the sewage into terephthalic acid and ethylene glycol, and adjusting the pH value of the treated sewage to 6-8;
s12 photocatalytic anaerobic reaction: carrying out photocatalytic decomposition on the sewage treated in the step S11 under an anaerobic condition to produce hydrogen;
s13 photocatalytic aerobic reaction: carrying out photocatalytic aerobic reaction on the sewage treated in the step S12 to degrade the terephthalic acid into organic acid and alcohol intermediates;
s14 photocatalytic anaerobic-aerobic cyclic reaction: refluxing the sewage treated in the step S13 to an anaerobic reaction system of the step S12 for anaerobic-aerobic circulating reaction, and stopping the circulation when the hydrogen production rate in the anaerobic reaction system is not more than 1.25 times of the hydrogen production rate in pure water under the same condition;
and S15 post-treatment, namely reacting the sewage in the S14 in an aerobic reaction system until the TOC concentration is lower than 30mg/L and discharging.
Preferably, when the polyester micro plastic is PLA in S21, the method comprises the steps of:
s21 pretreatment: hydrolyzing polyester micro-plastics in the sewage into lactic acid, and adjusting the pH value of the treated sewage to 6-8;
s22 photocatalytic aerobic reaction: carrying out photocatalytic aerobic reaction on the sewage treated in the step S21 to degrade lactic acid into organic acid and alcohol intermediates;
s23 photocatalytic anaerobic reaction: carrying out photocatalytic decomposition on the sewage treated in the step S22 under an anaerobic condition to produce hydrogen;
s24 photocatalytic aerobic-anaerobic cycle reaction: refluxing the sewage treated in the step S23 to an S22 aerobic reaction system for aerobic-anaerobic cycle reaction, and stopping the cycle when the hydrogen production rate in the anaerobic reaction system is not more than 1.25 times of the hydrogen production rate in pure water under the same condition;
and S25 post-treatment, namely reacting the sewage in the S24 in an aerobic reaction system until the TOC concentration is lower than 30mg/L and discharging.
Preferably, the photocatalytic anaerobic reaction in S12 or S23 is added with a bifunctional photocatalyst capable of photolyzing water to produce hydrogen and photodegrading organic matters, and the concentration of the bifunctional photocatalyst is 0.4-0.8 g/L.
Further preferably, the bifunctional photocatalyst is 1 wt% platinum-doped titanium dioxide, and the concentration is 0.6 g/L.
Preferably, a photocatalyst capable of photo-degrading organic matters is added in the photocatalytic aerobic reaction in S13 or S22, and the concentration of the photocatalyst is 0.05-0.2 g/L.
Preferably, in the photocatalytic anaerobic-aerobic cyclic reaction in the step S14 or the photocatalytic aerobic-anaerobic cyclic reaction in the step S24, the time of a single photocatalytic anaerobic reaction is 1 to 4 hours, and the time of a single photocatalytic aerobic reaction is 0.5 to 2 hours.
Preferably, the post-treatment reaction time in S15 or S25 is 6-12 h.
Preferably, the number of times of the photocatalytic anaerobic-aerobic cyclic reaction or the photocatalytic aerobic-anaerobic cyclic reaction is 1-5.
It should be noted that the photocatalytic anaerobic-photocatalytic aerobic-photocatalytic anaerobic reaction is a primary cycle reaction process, and the photocatalytic aerobic-anaerobic cycle reaction is analogized in the same way.
Compared with the prior art, the invention has the following beneficial effects:
(1) compared with the method for directly carrying out photocatalytic degradation on micro plastic particles, the method provided by the invention aims at the hydrolysable polyester micro plastic, an aeration system and other auxiliary devices are not required to be added, the problem of high energy consumption in the traditional photocatalytic degradation of organic pollutants is solved, and the reaction process is carried out in an aqueous solution, so that the treatment time is greatly shortened.
(2) The invention adopts a photocatalytic anaerobic-aerobic cyclic reaction or a photocatalytic aerobic-anaerobic cyclic system, not only realizes the effective degradation of polyester micro-plastic in the wastewater, but also can improve the efficiency of hydrogen production by photocatalytic water decomposition, and does not need to artificially add extra chemical reagents as electron donors in the reaction process, thereby solving the problems of secondary pollution, increased carbon emission and high medicament cost caused by the extra electron donors needed by the traditional photocatalytic water hydrogen decomposition. The method is simple, low in cost and wide in application range.
Description of the drawings:
FIG. 1 is a flow chart of a method for treating polyester micro-plastic sewage by tandem photocatalysis in an embodiment;
FIG. 2 is a graph showing the change in the amount of hydrogen produced in the anaerobic-aerobic-anaerobic cycle reaction in example 1;
FIG. 3 is a graph showing the variation of TOC in example 1;
FIG. 4 is a graph showing the amount of hydrogen produced by anaerobic fermentation in example 2 after various aerobic periods;
FIG. 5 is a graph showing the amount of hydrogen produced by anaerobic fermentation in example 3 after various aerobic periods;
FIG. 6 is a graph showing the variation of TOC in example 3.
Detailed Description
In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention is described below by way of specific embodiments. However, it should be understood that the following examples are only for illustrating the technical solutions of the present invention more clearly, and the protection scope of the present invention should not be limited thereby. In the following description, descriptions of well-known structures and techniques are omitted so as to not unnecessarily obscure the concepts of the present invention.
In addition, it should be further noted that, in order to avoid obscuring the present invention due to unnecessary details, only the structures/processing steps closely related to the scheme according to the present invention are shown in the following embodiments, and other details not closely related to the present invention are omitted.
Example 1
(1) A method for treating a polyester micro-plastic polluted water body by series photocatalysis is disclosed, wherein the flow is shown in figure 1, and the method specifically comprises the following steps:
s1 pretreatment: in a pretreatment tank, PET micro plastic in sewage is depolymerized into terephthalic acid and ethylene glycol in an alkaline solution; wherein the concentration of the PET micro-plastic is 200mg/L, the alkaline solution is 1M NaOH solution, the reaction time is 24h, the reaction temperature is 40 ℃, after the reaction is finished, the particles participating in the micro-plastic are left in a pretreatment tank through precipitation and filter membrane filtration, and the clear liquid is introduced into a subsequent unit for further treatment.
Acid-base neutralization of S2: the pH value of the sewage after hydrolysis in the S1 is adjusted to 7 +/-0.2 by using limestone and sulfuric acid, and then the sewage is introduced into a photocatalytic anaerobic reaction tank.
S3 photocatalytic anaerobic reaction: the photocatalytic anaerobic reaction tank contains 1 wt% of platinum-doped titanium dioxide photocatalyst, and the concentration of the photocatalyst is 0.6 g/L; at 3mW/cm2Under the irradiation of an ultraviolet lamp, the dissolved oxygen in the aqueous solution is quickly consumed, and then an anaerobic environment is achieved; stirring for reaction for 5h, and recovering the generated hydrogen through a purification and collection device; after the reaction is finished, byPrecipitating and filtering, keeping the catalyst particles in the pool, and introducing the clear liquid into a subsequent unit for further treatment.
S4 photocatalytic aerobic reaction: the water body treated by the S3 enters a photocatalytic aerobic pool, a P25 photocatalyst is added into the reaction pool, and the concentration of the photocatalyst is 100 mg/L; at 3mW/cm2Stirring and reacting for 1h under the irradiation of an ultraviolet lamp, after the reaction is finished, keeping catalyst particles in the tank through precipitation and filtration, and refluxing clear liquid to the reaction system of the anaerobic tank.
S5 photocatalytic anaerobic-aerobic cyclic reaction: and (4) refluxing the sewage treated in the step (S4) to an anaerobic tank for reaction for 1h, allowing the water body after anaerobic treatment to flow into a photocatalytic aerobic tank, and stopping circulation when the hydrogen production rate in an anaerobic reaction system is not more than 1.25 times of the hydrogen production rate in pure water under the same condition.
And S6 post-processing: and (3) reacting the sewage in the S4 in an aerobic reaction system until the final TOC concentration is lower than 30mg/L, and discharging.
(2) And (6) detecting and analyzing data.
S1: detecting the hydrogen production amount and calculating the hydrogen production rate by a gas chromatograph (Agilent 7890B);
s2: detecting the TOC concentration (mg/L) of the sewage before and after treatment by using a TOC analyzer (Elementar variao TOC cube), and calculating the mineralization rate of organic matters in the water by using the following formula:
mineralization rate (TOC)1-TOC2)/TOC1；
Wherein, TOC1The TOC concentration (mg/L) of the wastewater before treatment2The TOC concentration (mg/L) of the treated wastewater was obtained.
According to the integrated wastewater discharge standard (GB 8978 & 1996), when the TOC concentration is less than or equal to 30mg/L, the wastewater is discharged according to the secondary wastewater discharge standard.
S3: detecting the absorbance of the sewage at 241nm before and after treatment by using a UV-VIS spectrometer (Shimadzu UV-2600), and calculating the degradation rate of the terephthalic acid in the sewage:
(A) degradation rate1–A2)/A1；
Wherein A is1For the sewage before treatment at 241nmAbsorbance of (A)2The absorbance of the treated wastewater at 241nm was shown.
Example 2
The comparative example provides a series of methods for treating a water body polluted by polyester micro-plastics through series photocatalysis, researches the influence of the time of the photocatalytic aerobic reaction on the initial hydrogen production rate when the photocatalytic aerobic-anaerobic cycle reaction is adopted, and concretely comprises the following steps:
s1 pretreatment: in a pretreatment tank, PET micro plastic in sewage is depolymerized into terephthalic acid and ethylene glycol in an alkaline solution; wherein the concentration of the PET micro-plastic is 200mg/L, the alkaline solution is 1M NaOH solution, the reaction time is 24h, the reaction temperature is 40 ℃, after the reaction is finished, the particles participating in the micro-plastic are left in a pretreatment tank through precipitation and filter membrane filtration, and the clear liquid is introduced into a subsequent unit for further treatment.
Acid-base neutralization of S2: and (3) regulating the pH value of the sewage hydrolyzed in the S1 to 7 +/-0.2 by using limestone and sulfuric acid, and then introducing the organic wastewater into a photocatalytic anaerobic reaction tank without anaerobic reaction.
S3 photocatalytic aerobic reaction: the water body treated by the S2 enters a photocatalytic aerobic pool, a P25 photocatalyst is added into the reaction pool, and the concentration of the photocatalyst is 100 mg/L; respectively at 3mW/cm2Stirring and reacting for 0, 1, 2, 4 and 8 hours under the irradiation of an ultraviolet lamp, after the reaction is finished, keeping catalyst particles in a pool through precipitation and filtration, and refluxing clear liquid to an anaerobic pool reaction system.
S4 photocatalytic anaerobic reaction: the photocatalytic anaerobic reaction tank contains 1 wt% of platinum-doped titanium dioxide photocatalyst, and the concentration of the photocatalyst is 0.6 g/L; at 3mW/cm2Under the irradiation of an ultraviolet lamp, the dissolved oxygen in the aqueous solution is quickly consumed, and then an anaerobic environment is achieved; stirring for reaction for 1h, and recovering the generated hydrogen through a purification and collection device; after the reaction is finished, catalyst particles are left in the pool through precipitation and filtration, and clear liquid is introduced into a subsequent unit for further treatment.
S5 photocatalytic anaerobic-aerobic cyclic reaction: and (3) allowing the water to flow into the photocatalytic aerobic tank for reaction for 1h, then refluxing into the anaerobic tank, and stopping circulation when the hydrogen production rate in the anaerobic reaction system is not more than 1.25 times of the hydrogen production rate in pure water under the same condition.
And S6 post-processing: and (3) reacting the sewage in the S5 in an aerobic reaction system until the final TOC concentration is lower than 30mg/L, and discharging.
Example 3
A method for treating a polyester micro-plastic polluted water body by series photocatalysis specifically comprises the following steps:
the difference from the example 1 is that the pH value of the sewage is adjusted to 10 +/-0.2 by using sodium carbonate and sulfuric acid in the step of S2, and then the sewage is reacted in a photocatalytic anaerobic reaction tank.
Example 4
The embodiment provides a method for treating PLA (polylactic acid) micro-plastic polluted water body by series photocatalysis, which specifically comprises the following steps:
s1 pretreatment: in a pretreatment pool, depolymerizing PLA (polylactic acid) micro-plastics in sewage into lactic acid monomers in alkaline solution; wherein the concentration of the PLA micro-plastic is 200mg/L, the alkaline solution is 1M NaOH solution, the reaction time is 24h, the reaction temperature is 40 ℃, after the reaction is finished, the particles participating in the micro-plastic are left in a pretreatment tank through precipitation and filter membrane filtration, and the clear liquid is introduced into a subsequent unit for further treatment.
Acid-base neutralization of S2: and (3) regulating the pH value of the sewage hydrolyzed in the S1 to 7 +/-0.2 by using limestone and sulfuric acid, and then introducing the organic wastewater into a photocatalytic anaerobic reaction tank without anaerobic reaction.
S3 photocatalytic aerobic reaction: the water body treated by the S2 enters a photocatalytic aerobic pool, a P25 photocatalyst is added into the reaction pool, and the concentration of the photocatalyst is 100 mg/L; respectively at 3mW/cm2Stirring and reacting for 0, 1, 2 and 3 hours under the irradiation of an ultraviolet lamp, after the reaction is finished, keeping catalyst particles in a pool through precipitation and filtration, and refluxing clear liquid to an anaerobic pool reaction system.
S4 photocatalytic anaerobic reaction: the photocatalytic anaerobic reaction tank contains 1 wt% of platinum-doped titanium dioxide photocatalyst, and the concentration of the photocatalyst is 0.6 g/L; at 3mW/cm2Under the irradiation of ultraviolet lamp, the dissolved oxygen in the water solution is quickly consumedThen, an anaerobic environment is achieved; stirring for reaction for 1h, and recovering the generated hydrogen through a purification and collection device; after the reaction is finished, catalyst particles are left in the pool through precipitation and filtration, and clear liquid is introduced into a subsequent unit for further treatment.
S5 photocatalytic aerobic-anaerobic cycle reaction: and (3) allowing the water to flow into the photocatalytic aerobic tank for reaction for 1h, then refluxing into the anaerobic tank, and stopping circulation when the hydrogen production rate in the anaerobic reaction system is not more than 1.25 times of the hydrogen production rate in pure water under the same condition.
And S6 post-processing: and (3) reacting the sewage in the S5 in an aerobic reaction system until the final TOC concentration is lower than 30mg/L, and discharging.
Comparative example 1
A method for treating a polyester micro-plastic polluted water body by series photocatalysis specifically comprises the following steps:
the difference from the example 1 is that the pH value of the sewage is adjusted to 4 +/-0.2 by using sodium carbonate and sulfuric acid in the step of S2, and then the sewage is reacted in a photocatalytic anaerobic reaction tank.
Comparative example 2
A method for treating a polyester micro-plastic polluted water body by series photocatalysis specifically comprises the following steps:
the difference from example 1 is that the concentration of the photocatalytic anaerobic reaction catalyst in the S3 step was 0.4 g/L.
Comparative example 3
A method for treating a polyester micro-plastic polluted water body by series photocatalysis specifically comprises the following steps:
the difference from example 1 is that the concentration of the photocatalytic anaerobic reaction catalyst in the S3 step was 1 g/L.
Analysis of results
In example 1, the hydrolysis rate of the plastic granules after 24 hours in the pretreatment tank was 42.5%.
The hydrogen production in the anaerobic reaction tank of example 1 was compared with that in pure water under the same conditions, and the results are shown in FIG. 2 (purging with nitrogen before each measurement, purging the hydrogen produced during the previous period). When the anaerobic reaction is carried out for 1hThe hydrogen yield can reach 215.03 mu mol/gcatH, 9.85 times of that of pure water; the hydrogen production is far higher than that of pure water in 5h of reaction, and the yield is gradually reduced along with the reduction of the concentration of the ethylene glycol. With the increase of the anaerobic reaction time, the content of the ethylene glycol is less and less, and the terephthalic acid cannot be directly used as an electron donor, so that the hydrogen production is gradually reduced; after 6 hours of anaerobic reaction, the solution is subjected to aerobic treatment for 1 hour and then flows back to the anaerobic tank again for reaction, and the hydrogen yield is increased again, which indicates that an intermediate product generated in the degradation process of the terephthalic acid can be effectively utilized as an electron donor in the anaerobic reaction. The TOC concentration of the sewage before treatment in the embodiment 1 is 67.4mg/L, and after serial photocatalytic treatment, the TOC concentration is 24.74 mg/L; by means of anaerobic-aerobic circulating reaction treatment, the PET micro-plastic in the sewage is effectively degraded, and the efficiency of producing hydrogen by photocatalytic water decomposition can be improved.
If the sequence of aerobic-anaerobic cycle is used for the PET micro plastic, the hydrogen production rate after 1 hour of reaction in the anaerobic tank after changing the reaction time in the aerobic tank is studied in example 2. As can be seen from fig. 4, as the reaction time of the aerobic tank increases, the hydrogen yield gradually decreases, because the concentration of ethylene glycol rapidly decreases (is degraded into water and carbon dioxide), and the intermediate products of terephthalic acid degradation cannot compensate for the loss of ethylene glycol as an electron donor, so the hydrogen yield is lower than that without aerobic treatment and gradually decreases; after aerobic reaction is carried out for 8 hours, the hydrogen flows into a photocatalytic anaerobic tank for photocatalytic hydrolysis hydrogen production, and the hydrogen production rate in the anaerobic tank after 1 hour is only about 88 mu mol/gcatH. Therefore, for PET micro plastic, because the ethylene glycol of the hydrolysate can be directly used as an electron donor, the organic matters in the solution can be effectively utilized as the electron donor to promote the water decomposition and hydrogen production by carrying out the photocatalytic anaerobic reaction before the aerobic reaction.
For PLA micro-plastics, example 4 investigated the hydrogen production rate after 1h of reaction in the anaerobic tank after changing the reaction time in the aerobic tank. As is clear from FIG. 5, the aerobic reaction was carried out for 1 hour, and the decomposition of water and the amount of hydrogen were effectively promoted, because lactic acid, which is a hydrolysis product of PLA, was producedBut also can be used as an electron donor, and can be degraded into organic intermediates with smaller molecular weight after a certain degree of photocatalytic aerobic reaction, and the intermediates are more favorable for promoting the photocatalytic water decomposition to produce hydrogen compared with lactic acid, and the hydrogen production is about 195.15 mu mol/gcatH is 1.46 times that of the case where no aerobic treatment is performed, and 8.94 times that of pure water. The TOC concentration of the sewage before treatment in example 4 is 86.94mg/L, and after the sewage is subjected to serial photocatalytic treatment, the TOC concentration is 18.28mg/L (FIG. 6); through aerobic-anaerobic circulating reaction treatment, the effective degradation of PLA micro-plastic in sewage is realized, and the efficiency of producing hydrogen by photocatalytic water decomposition can be improved.
In examples 1 and 3 and comparative example 1, the effect of different pH values on the treatment of PET-contaminated water was investigated. As can be seen from Table 1, the photocatalytic hydrogen production efficiency is slightly higher than that of a neutral environment in an alkaline environment, but is more favorable for mineralization of organic pollutants in the neutral environment; in the comparative example 1, in an acidic environment, not only is the hydrogen production efficiency of the anaerobic reaction greatly reduced, but also the terephthalic acid can be separated out from the solution to influence the degradation efficiency of the subsequent aerobic reaction, so that the operation of the whole reaction process is not facilitated under the acidic condition; therefore, the method is more beneficial to operation under neutral conditions, and secondary neutralization is not needed to adjust the pH value to the discharge standard when the water body is discharged.
TABLE 1 influence of pH on the hydrogen production and degradation rate of PET
Figure BDA0003185427090000111
In example 1 and comparative examples 2 and 3, the influence of different catalyst concentrations in the anaerobic reaction tank on the treatment effect of PET polluted water body was studied. As can be seen from Table 2, the hydrogen production rate is increased with the increase of the catalyst concentration, but when the catalyst concentration is 1g/L, the hydrogen production amount is improved little compared with 0.6g/L per hour, and the average hydrogen production rate per g of the catalyst is only 170.93 mu mol/gcatH, because the catalyst concentration is too high and the catalyst absorbs light because the catalyst is shielded from each other. Therefore, it is necessary to control the catalyst concentration appropriately to avoid causing the catalystIs wasted.
TABLE 2 Effect of catalyst concentration on the Hydrogen production of PET
Figure BDA0003185427090000112
The principles and embodiments of the present invention have been described herein using specific examples, which are provided only to help understand the method and the core concept of the present invention; meanwhile, for a person skilled in the art, according to the idea of the present invention, the specific embodiments and the application range may be changed. In view of the above, the present disclosure should not be construed as limiting the invention.

Claims (10)

1. A method for treating a polyester micro-plastic polluted water body by series photocatalysis is characterized by comprising the following steps:
s11 pretreatment: hydrolyzing polyester micro-plastics in the sewage into acid monomers and/or alcohol monomers, and adjusting the pH value of the treated sewage to 6-8;
s12 photocatalytic anaerobic reaction: carrying out photocatalytic decomposition on the sewage treated in the step S11 under an anaerobic condition to produce hydrogen;
s13 photocatalytic aerobic reaction: carrying out photocatalytic aerobic reaction on the sewage treated in the step S12 to degrade acid monomers into organic acid and alcohol intermediates;
s14 photocatalytic anaerobic-aerobic cyclic reaction: refluxing the sewage treated in the step S13 to an anaerobic reaction system of the step S12 for anaerobic-aerobic circulating reaction, and stopping the circulation when the hydrogen production rate in the anaerobic reaction system is not more than 1.25 times of the hydrogen production rate in pure water under the same condition;
and S15 post-processing: reacting the sewage in the S14 in an aerobic reaction system until the TOC concentration is lower than 30mg/L, and discharging;
alternatively, the method comprises the following steps:
s21 pretreatment: hydrolyzing polyester micro-plastics in the sewage into acid monomers and/or alcohol monomers, and adjusting the pH value of the treated sewage to 6-8;
s22 photocatalytic aerobic reaction: carrying out photocatalytic aerobic reaction on the sewage treated in the step S21 to degrade acid monomers into organic acid and alcohol intermediates;
s23 photocatalytic anaerobic reaction: carrying out photocatalytic decomposition on the sewage treated in the step S22 under an anaerobic condition to produce hydrogen;
s24 photocatalytic aerobic-anaerobic cycle reaction: refluxing the sewage treated in the step S23 to an S22 aerobic reaction system for aerobic-anaerobic cycle reaction, and stopping the cycle when the hydrogen production rate in the anaerobic reaction system is not more than 1.25 times of the hydrogen production rate in pure water under the same condition;
and S25 post-processing: reacting the sewage in the S24 in an aerobic reaction system until the TOC concentration is lower than 30mg/L, and discharging.
2. The method of claim 1, wherein the polyester micro plastic of S11 or S21 is at least one of PET or PLA.
3. The method of claim 1, wherein when the polyester micro plastic is PET in S11 or S21, the acid monomer is terephthalic acid and the alcohol monomer is ethylene glycol.
4. The method of claim 1, wherein the acid monomer is lactic acid when the polyester micro plastic is PLA in S11 or S21.
5. The method of claim 1, wherein when the polyester micro plastic is PET in S11, the method comprises S11-S15.
6. The method of claim 1, wherein when the polyester micro plastic is PLA in S21, the method comprises S21-S25.
7. The method as claimed in claim 1, wherein the photocatalytic anaerobic reaction in S12 or S23 is added with a bifunctional photocatalyst capable of photolyzing water to produce hydrogen and photodegrading organic matters, and the concentration of the bifunctional photocatalyst is 0.4-0.8 g/L.
8. The method of claim 1, wherein a photocatalyst for photo-degradation of organic substances is added to the photocatalytic aerobic reaction in S13 or S22, and the concentration of the photocatalyst is 0.05-0.2 g/L.
9. The method of claim 1, wherein in the photocatalytic anaerobic-aerobic cyclic reaction in S14 or the photocatalytic aerobic-anaerobic cyclic reaction in S24, the time for a single photocatalytic anaerobic reaction is 1-4 h, and the time for a single photocatalytic aerobic reaction is 0.5-2 h.
10. The method of claim 1, wherein the post-treatment reaction time in S15 or S25 is 6 to 12 hours.
CN202110860189.1A 2021-07-28 2021-07-28 Method for treating polyester micro-plastic polluted water body through series photocatalysis Pending CN113636716A (en)

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