A method for enhancing the anaerobic degradation of chlorinated organophosphates in sludge by using thiosulfate

Abstract

The present invention provides a method for enhancing the anaerobic degradation of chlorinated organophosphates in sludge by using thiosulfate, which comprises the following steps: placing the concentrated sludge containing chlorinated organophosphates in a fermentation tank, adding a thiosulfate solution, sealing it for pretreatment, adding inoculated sludge, purging oxygen by nitrogen bubbling, and sealing the fermentation tank for anaerobic reaction. The thiosulfate accelerates the anaerobic reductive dechlorination process of chlorinated organophosphates in the sludge, promotes the degradation and removal of chlorinated organophosphate pollutants in the sludge, and provides a technical reference for the safe treatment of sludge.

Description

Technical Field

[0001] The present invention relates to the technical field of controlling chlorinated organophosphate pollutants, and particularly relates to a method for enhancing the anaerobic degradation of chlorinated organophosphates in sludge by using thiosulfate. Background Art

[0002] With the traditional brominated flame retardants being included in the Stockholm Convention and their production and use being restricted, the global production of organophosphorus flame retardants (such as organophosphates) has been continuously increasing. Organophosphates can be divided into chlorinated organophosphates, alkyl phosphate organophosphates, and aryl phosphate organophosphates. Among them, compared with non-halogenated organophosphates, chlorinated organophosphates have high environmental persistence and long-range transport potential, showing neurotoxicity, reproductive toxicity, endocrine disruption, and carcinogenicity, and have become a new type of pollutant that has attracted much attention. Generally, after organophosphates enter the urban sewage treatment plant, they can be adsorbed on the sludge through electrostatic attraction, hydrogen bonding, and surface complexation. It is reported that the average concentration of organophosphates in the current urban sewage treatment plant sludge reaches 43.9 - 2160 μg / kg dry weight, and even the content of organophosphates in some municipal sludge can reach 1000 - 20000 μg / kg, which brings new challenges to the safe disposal of municipal sludge. Therefore, the research and development of an efficient and economical chlorinated organophosphate removal technology has become the focus and key point of current research. Summary of the Invention

[0003] The present invention provides a method for enhancing the anaerobic degradation of chlorinated organophosphates in sludge by using thiosulfate. The anaerobic reductive dechlorination process of chlorinated organophosphates in the sludge is accelerated by thiosulfate, promoting the degradation and removal of chlorinated organophosphate pollutants in the sludge, and providing technical reference for the safe treatment of sludge containing chlorinated organophosphate pollutants.

[0004] In order to solve the above technical problems, the technical solution of the present invention is as follows:

[0005] A method for enhancing the anaerobic degradation of chlorinated organophosphates in sludge by using thiosulfate, comprising the following steps: placing the concentrated sludge containing chlorinated organophosphates in a fermentation tank, adding a thiosulfate solution, sealing for pretreatment, adding inoculated sludge, purging oxygen with nitrogen, and sealing the fermentation tank for anaerobic reaction.

[0006] Specifically, the concentration of the concentrated sludge is 24 - 30 g / L, and the concentration of chlorinated organophosphates represented by tris(2-chloroethyl) phosphate is 4.28 - 5.51 mg / L. Further, the concentrated sludge is obtained by naturally settling the sludge formed by the pollution of the production wastewater of a certain flame retardant industry and discarding the supernatant; the natural settling temperature is 2 - 6 °C, and the settling time is 20 - 36 h.

[0007] Specifically, the volume ratio of the concentrated sludge to the thiosulfate solution is (60 - 600):1.

[0008] Specifically, the dosage of the thiosulfate solution, calculated by the mass of sulfur element, has a ratio range to the dry weight of the concentrated sludge of (0.0216 - 0.086):1; preferably (0.043 - 0.065):1; when the ratio is 0.043:1, the removal rate of the chlorinated organophosphates is the highest, and further increasing the dosage of thiosulfate cannot further enhance the removal of chlorinated organophosphates.

[0009] Specifically, the reaction temperature of the pretreatment is 25 - 28 °C, the stirring rate is 80 - 120 rpm, and the pretreatment time is 6 - 12 h; preferably 8 - 10 h.

[0010] Specifically, the dry weight ratio of the inoculated sludge to the concentrated sludge is (0.05 - 0.4):1, preferably (0.1 - 0.2):1; the pH of the supernatant in the fermenter after adding the inoculated sludge is 6.8 - 7.3.

[0011] Specifically, the nitrogen purging and oxygen removal time lasts for 10 - 15 min.

[0012] Specifically, the temperature of the anaerobic reaction is 25 - 37 °C, preferably 35 - 37 °C; the time of the anaerobic reaction is 2 - 20 d, preferably 15 - 20 d; the temperature and time of the anaerobic reaction affect the removal efficiency of chlorinated organophosphates.

[0013] Specifically, the inoculated sludge is taken from an anaerobic reactor that has been continuously operated in the laboratory for 3 months. The total solid content of the inoculated sludge is 24 - 26 g / L, the volatile solid content is 11 - 13 g / L, the pH value is 7.8 - 8.0, and the functional bacteria at the phylum level include p_ Pseudomonadota 、p_ Bacteroidota 、p_ Chloroflexota 、p_ Actinomycetota and p_ Bacillota ; the functional bacteria at the genus level mainly include g_ Anaerolinea 、g_ Ferruginibacter 、g_ Longilinea 、g_ Candidatus _ Promineifilum 、g_ Caldilinea 、g_ Petrimonas 、g_ Nitrospira 、g_ Ilumatobacter 、g_ Hyphomicrobium 、g_ Bradyrhizobium 、g_ Brevefilum 、g_ Ignavibacterium 、g_ Clostridium 、g_ Proteiniphilum 、g_ Treponema and g_ Desulfovibrio 。

[0014] Further, the method for culturing the inoculation sludge is as follows:

[0015] (1) Add the excess sludge taken from the secondary sedimentation tank of a municipal sewage treatment plant (total solid concentration is 24 - 30 g / L) into the anaerobic reactor, and then add a thiosulfate solution to make the concentration of thiosulfate in the anaerobic reactor reach 600 mg / L in terms of the mass of sulfur element; place the anaerobic reactor on a magnetic stirrer and fully react in a constant temperature environment (the reaction temperature is 20 ± 2 °C, rotation speed is 60 rpm);

[0016] (2) After the reaction ends, add the anaerobic sludge taken from the anaerobic zone of the A2O process in the sewage treatment plant (total solid concentration is 22 - 28 g / L) into the anaerobic reactor. The volume ratio of the added anaerobic sludge taken from the anaerobic zone of the A2O process in the sewage treatment plant to the excess sludge taken from the secondary sedimentation tank of the municipal sewage treatment plant in step (1) is 1:2; after purging oxygen with nitrogen, transfer the reactor to a constant temperature incubator (temperature is 35 ± 1 °C, rotation speed is 80 rpm) for anaerobic culture. During the culture period, a certain amount of sludge suspension is discharged from the reactor at a fixed time every day, and then an equal amount of fresh excess sludge pretreated in step (1) is supplemented; the above culture process lasts for 3 months to obtain the inoculation sludge.

[0017] During the anaerobic reaction, the pH of the supernatant in the fermentation tank is 7.2 - 8.5. The pH affects the removal efficiency of chlorinated organophosphates by influencing the growth rate, metabolic activity, and functional enzyme activity of the functional bacteria in the inoculation sludge.

[0018] The redox potential during the anaerobic reaction is -300 ~ -420 mV. The redox potential affects the removal efficiency of chlorinated organophosphates by influencing the metabolic activity of the functional bacteria in the inoculation sludge.

[0019] During the anaerobic reaction, the concentration of thiosulfate in the supernatant of the fermentation tank is 0 - 965 mg / L in terms of the mass of sulfur element, the sulfate concentration is 2 - 760 mg / L, and the sulfide concentration is 0.5 - 148 mg / L. These sulfur species affect the community structure and interaction relationship of the functional bacteria in the inoculation sludge.

[0020] During the anaerobic reaction, the acetic acid concentration in the supernatant of the fermentation tank is 20 - 1000 mg / L. Acetic acid provides a carbon source and an electron donor for the functional bacteria in the inoculation sludge, thereby strengthening the removal of chlorinated organophosphates.

[0021] Compared with the prior art, the beneficial effects of the present invention are as follows: In the present invention, thiosulfate is added to the sludge containing chlorinated organophosphorus ester pollutants. Thiosulfate promotes the anaerobic fermentation of organic matter in the sludge to generate small molecule organic acids represented by acetic acid, providing a carbon source and an electron donor for dehalogenating bacteria and improving the reaction activity of dehalogenating bacteria. At the same time, thiosulfate can improve the anaerobic reduction environment, promote the secretion of cytochrome P450 and phosphatase (which play a key role in the reduction and degradation of chlorinated organophosphorus esters), and increase the abundance of typical functional bacteria in the inoculated sludge, thereby promoting the reductive dechlorination of chlorinated organophosphorus esters. Thiosulfate accelerates the anaerobic reductive dechlorination process of chlorinated organophosphorus esters in the sludge, promotes the degradation and removal of chlorinated organophosphorus ester pollutants in the sludge, and provides a technical reference for the safe treatment of sludge containing chlorinated organophosphorus ester pollutants. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 is a graph showing the change in the removal rate of chlorinated organophosphorus esters in the comparative example and the example during the anaerobic reaction of the present invention.

[0023] Figure 2 is a relative abundance map of functional bacteria in the inoculated sludge, the control group (without adding thiosulfate) and the thiosulfate group (1000 mg / L) after the anaerobic reaction of the present invention;

[0024] Figure 3 is a graph showing the expression levels of functional genes in the control group and the thiosulfate group (1000 mg / L) after the anaerobic reaction of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0025] The present invention will be further described below with reference to specific examples and comparative examples.

[0026] In the following examples and comparative examples, the inoculated sludge was taken from an anaerobic reactor that had been continuously operating in the laboratory for 3 months. The total solid content of the inoculated sludge was 24 - 26 g / L, the volatile solid content was 11 - 13 g / L, the pH value was 7.8 - 8.0, and the functional bacteria at the phylum level included p_ Pseudomonadota 、p_ Bacteroidota 、p_ Chloroflexota 、p_ Actinomycetota and p_ Bacillota ; The functional bacteria at the genus level mainly included g_ Anaerolinea 、g_ Ferruginibacter 、g_ Longilinea 、g_ Candidatus _ Promineifilum 、g_ Caldilinea 、g_ Petrimonas 、g_ Nitrospira 、g_ Ilumatobacter 、g_ Hyphomicrobium 、g_ Bradyrhizobium 、g_Brevefilum , g_ Ignavibacterium , g_ Clostridium , g_ Proteiniphilum , g_ Treponema and g_ Desulfovibrio .

[0027] The cultivation method of the inoculum sludge is as follows: Add 500 mL of excess sludge taken from the secondary sedimentation tank of a municipal sewage treatment plant (total solid concentration is 24 - 30 g / L) into the anaerobic reactor, and then add 50 mL of thiosulfate solution to make the concentration of thiosulfate in the anaerobic reactor reach 600 mg / L (calculated by the mass of sulfur element). Place the reactor on a magnetic stirrer (rotation speed 60 rpm) and react fully for 24 h in a constant temperature air-conditioned room (20 ± 2 °C). After the reaction, add 250 mL of anaerobic sludge taken from the anaerobic zone of the A2O process of the sewage treatment plant (total solid concentration is 22 - 28 g / L) into the reactor. After purging oxygen with nitrogen, transfer the reactor to a constant temperature incubator (35 ± 1 °C; rotation speed 80 rpm) for anaerobic cultivation. During the cultivation, 100 mL of sludge suspension is discharged from the reactor at a fixed time every day, and then an equal amount of fresh excess sludge pretreated with 600 mg / L thiosulfate (calculated by the mass of sulfur element) (total solid concentration is 24 - 30 g / L) is supplemented. The above cultivation process lasts for 3 months to obtain the inoculum sludge with various functional bacteria. Example 1

[0028] Take the sludge formed by the pollution of the production wastewater in a flame retardant industry (the concentration of chlorinated organophosphates represented by tris(2-chloroethyl) phosphate is 5.11 mg / L). Let the sludge settle statically at 4 °C for 20 h to obtain concentrated sludge, and then take 600 mL of concentrated sludge (water content is 97.5%, pH value is 6.8) and add it into the fermentation tank. Add 10.0 mL of Na2S2O3·5H2O solution (0.3055 g calculated by the mass of sulfur element) into the fermentation tank. Place the fermentation tank on a magnetic stirrer and seal and react for 10 h at a stirring rate of 100 rpm and a constant temperature environment (28 °C). After the reaction, the pH value of the supernatant of the fermentation tank is 6.6. Then add 60 mL of inoculum sludge (water content is 97.5%, pH value is 7.9) into the fermentation tank, purge nitrogen for 10 min to expel oxygen, seal the fermentation tank, and place it in a constant temperature incubator (37 ± 1 °C) for anaerobic reaction. During this process, sodium thiosulfate promoted the conversion of organic matter in the sludge into acetic acid, providing a carbon source and an electron donor for the functional bacteria in the inoculum sludge. After reacting for 20 d, the pH of the supernatant of the fermentation tank is 7.3, the oxidation-reduction potential is -400 mV, the concentration of sodium thiosulfate is 4.0 mg / L (calculated by the mass of sulfur element), the concentration of acetic acid is 52.8 mg / L, and the removal rate of chlorinated organophosphates (i.e., tris(2-chloroethyl) phosphate) reaches 43.0%, which is 61.1% higher than that of the blank group. Example 2

[0029] Take the sludge formed by the pollution of the production wastewater in a certain flame retardant industry (the concentration of chlorinated organophosphates represented by tris(2-chloroethyl) phosphate is 5.11 mg / L). Let the sludge settle statically at 4°C for 20 h to obtain concentrated sludge. Then, take 600 mL of the concentrated sludge (with a water content of 97.5% and a pH value of 6.8) and add it to the fermentation tank. Add 10.0 mL of Na2S2O3·5H2O solution (0.611 g in terms of the mass of sulfur element) to the fermentation tank. Place the fermentation tank on a magnetic stirrer and seal it for reaction at a stirring rate of 100 rpm and a constant temperature environment (28°C) for 10 h. After the reaction, the pH value of the supernatant in the fermentation tank is 6.6. Then, add 60 mL of inoculated sludge (with a water content of 97.5% and a pH value of 7.9) to the fermentation tank, fill it with nitrogen for 10 min to expel oxygen, seal the fermentation tank, and place it in a constant temperature incubator (37 ± 1°C) for anaerobic reaction. During this process, sodium thiosulfate promoted the conversion of organic matter in the sludge into acetic acid, providing a carbon source and an electron donor for the functional bacteria in the inoculated sludge. After 20 d of reaction, the pH of the supernatant in the fermentation tank is 7.5, the oxidation-reduction potential is -407 mV, the concentration of sodium thiosulfate is 6.3 mg / L (in terms of the mass of sulfur element), the concentration of acetic acid is 845 mg / L, and the removal rate of chlorinated organophosphates (i.e., tris(2-chloroethyl) phosphate) reaches 59.6%, which is 123.0% higher than that of the blank group. Example 3

[0030] Take the sludge formed by the pollution of the production wastewater in a flame retardant industry (the concentration of chlorinated organophosphates represented by tris(2-chloroethyl) phosphate is 5.11 mg / L). Let the sludge settle statically at 4 °C for 20 h to obtain concentrated sludge. Subsequently, take 600 mL of concentrated sludge (with a moisture content of 97.5% and a pH value of 6.8) and place it in a fermentation tank. Add 10.0 mL of Na2S2O3·5H2O solution (1.222 g in terms of the mass of sulfur element) to the fermentation tank. Place the fermentation tank on a magnetic stirrer and seal it for reaction for 10 h at a stirring rate of 100 rpm and a constant temperature environment (28 °C). After the reaction, the pH value of the supernatant in the fermentation tank is 6.7. Subsequently, add 60 mL of inoculated sludge (with a moisture content of 97.5% and a pH value of 7.9) to the fermentation tank, purge oxygen by nitrogen for 10 min, seal the fermentation tank, and place it in a constant temperature incubator (37 ± 1 °C) for anaerobic reaction. During this process, sodium thiosulfate promoted the conversion of organic matter in the sludge into acetic acid, providing a carbon source and an electron donor for the functional bacteria in the inoculated sludge. After 20 d of reaction, the pH of the supernatant in the fermentation tank is 7.4, the oxidation-reduction potential is -412 mV, the concentration of sodium thiosulfate, in terms of the mass of sulfur element, is 28.6 mg / L, the concentration of acetic acid is 872 mg / L, and the removal rate of chlorinated organophosphates (i.e., tris(2-chloroethyl) phosphate) reaches 56.2%, which is 110.4% higher than that of the blank group.

[0031] Comparative Example 1

[0032] Take the sludge formed by the pollution of the production wastewater in a flame retardant industry (the concentration of chlorinated organophosphates represented by tris(2-chloroethyl) phosphate is 5.11 mg / L). Let the sludge settle statically at 4 °C for 20 h to obtain concentrated sludge. Subsequently, take 600 mL of concentrated sludge (with a moisture content of 97.5% and a pH value of 6.8) and place it in a fermentation tank. Place the fermentation tank on a magnetic stirrer and seal it for reaction for 10 h at a stirring rate of 100 rpm and a constant temperature environment (28 °C). After the reaction, the pH value of the supernatant in the fermentation tank is 6.7. Subsequently, add 60 mL of inoculated sludge (with a moisture content of 97.5% and a pH value of 7.9) to the fermentation tank, purge oxygen by nitrogen for 10 min, seal the fermentation tank, and place it in a constant temperature incubator (37 ± 1 °C) for anaerobic reaction for 20 d. At this time, the pH of the supernatant in the fermentation tank is 7.7, the oxidation-reduction potential is -367 mV, the concentration of acetic acid is 34.8 mg / L, and the removal rate of chlorinated organophosphates (i.e., tris(2-chloroethyl) phosphate) is 26.7%.

[0033] The change curve graphs of the removal rates of chlorinated organophosphates in Examples 1-3 and the comparative examples are as Figure 1 shown. It can be seen from the results that thiosulfate can strengthen the anaerobic degradation of chlorinated organophosphates in the sludge, thereby promoting the removal of chlorinated organophosphates in the sludge.

[0034] The functional bacteria of the prepared inoculated sludge, the control group (without thiosulfate) and the thiosulfate group (1000 mg / L) after anaerobic reaction were tested, and the results are as Figure 2 shown. It can be seen from the figure that thiosulfate pretreatment increased the abundance of typical functional bacteria in the inoculated sludge. For example, the relative abundances of the fermentation functional bacteria g_ Petrimonas and g_ Proteiniphilum involved in acetic acid production in the thiosulfate group increased by 203.4% and 251.1% respectively compared with the control group. The relative abundances of the functional bacteria g_ Clostridium and g_ Desulfovibrio responsible for reductive dechlorination increased by 177.0% and 596.1% respectively.

[0035] The expression levels of the functional genes of the control group (without thiosulfate) and the thiosulfate group (1000 mg / L) after anaerobic reaction were tested, and the results are as Figure 3 shown. It can be seen from the figure that after thiosulfate pretreatment, the expression level of the acetic acid kinase activity responsible for acetic acid production increased by 36.1%. At the same time, the expression levels of the functional genes involved in the reductive degradation of chlorinated organophosphates, such as cytochrome P450, reductive dehalogenase and phosphodiesterase, increased by 7.3 - 48.4%, thus accelerating the anaerobic reductive dechlorination process of chlorinated organophosphates.

[0036] The acetic acid concentrations of the control group (without thiosulfate) and the thiosulfate group (1000 mg / L) after anaerobic reaction were measured. The acetic acid concentration produced by fermentation increased by 1.24 - 2.54 times compared with the control group. Thiosulfate promoted the anaerobic conversion of organic matter in the sludge, providing more carbon sources and electron donors for anaerobic reductive dechlorination.

[0037] The above factors jointly contributed to the enhanced anaerobic degradation of chlorinated organophosphates by thiosulfate.

Claims

1. A method for enhancing the anaerobic degradation of chlorinated organophosphates in sludge by using thiosulfate, characterized in that It includes the following steps: The concentrated sludge containing chlorinated organophosphate is placed in a fermentation tank, thiosulfate solution is added and sealed for pretreatment, inoculated sludge is added, nitrogen is blown to drive oxygen, and the fermentation tank is sealed for anaerobic reaction; the inoculated sludge is taken from an anaerobic reactor that has been running continuously for 3 months in the laboratory, the total solid content of the inoculated sludge is 24-26g / L, the volatile solid content is 11-13g / L, the pH value is 7.8-8.0, and the functional bacteria at the phylum level include p_ Pseudomonadota 、p_ Bacteroidota 、p_ Chloroflexota 、p_ Actinomycetota and p_ Bacillota ; The functional bacteria at the genus level are mainly g_ Anaerolinea 、g_ Ferruginibacter 、g_ Longilinea 、g_ Candidatus _ Promineifilum 、g_ Caldilinea 、g_ Petrimonas 、g_ Nitrospira 、g_ Ilumatobacter 、g_ Hyphomicrobium 、g_ Bradyrhizobium 、g_ Brevefilum 、g_ Ignavibacterium 、g_ Clostridium 、g_ Proteiniphilum 、g_ Treponema and g_ Desulfovibrio ; The cultivation method of the inoculation sludge is as follows: (1) Add the excess sludge taken from the secondary sedimentation tank of the municipal sewage treatment plant to the anaerobic reactor, and then add a thiosulfate solution to make the concentration of thiosulfate in the anaerobic reactor reach 600 mg / L in terms of the mass of sulfur element; place the anaerobic reactor on a magnetic stirrer and react fully in a constant temperature environment; (2) After the reaction, add the anaerobic sludge taken from the anaerobic zone of the A2 / O process of the sewage treatment plant to the anaerobic reactor. After purging oxygen with nitrogen, transfer the reactor to a constant temperature incubator for anaerobic cultivation. During the cultivation period, a certain amount of sludge suspension is discharged from the reactor at a fixed time every day, and then an equal amount of fresh excess sludge pretreated in step (1) is supplemented; the above cultivation process lasts for 3 months to obtain the inoculation sludge.

2. The method for enhancing the anaerobic degradation of chlorinated organophosphates in sludge by using thiosulfate according to claim 1, wherein: The concentration of the thickened sludge is 24 - 30 g / L, and the concentration of chlorinated organophosphates is 4.28 - 5.51 mg / L.

3. The method for enhancing the anaerobic degradation of chlorinated organophosphates in sludge by using thiosulfate according to claim 1, characterized in that: The dosage of the thiosulfate solution, in terms of the mass of sulfur element, has a ratio range to the dry weight of the thickened sludge of (0.0216 - 0.086):

1.

4. The method for enhancing the anaerobic degradation of chlorinated organophosphates in sludge by using thiosulfate according to claim 1, characterized in that: The reaction temperature of the pretreatment is 25 - 28 °C, the stirring rate is 80 - 120 rpm, and the pretreatment time is 6 - 12 h.

5. The method for enhancing the anaerobic degradation of chlorinated organophosphates in sludge by using thiosulfate according to claim 1, characterized in that: The dry weight ratio of the inoculation sludge to the thickened sludge is (0.05 - 0.4):

1.

6. The method for enhancing the anaerobic degradation of chlorinated organophosphates in sludge by using thiosulfate according to claim 1, wherein: The temperature of the anaerobic reaction is 25 - 37 °C, and the time is 2 - 20 d.

7. The method for enhancing the anaerobic degradation of chlorinated organophosphates in sludge by using thiosulfate according to claim 1, wherein: The total solid concentration of the excess sludge taken from the secondary sedimentation tank of the municipal sewage treatment plant in step (1) is 24 - 30 g / L; the total solid concentration of the anaerobic sludge taken from the anaerobic zone of the A2 / O process of the sewage treatment plant in step (2) is 22 - 28 g / L; the volume ratio of the anaerobic sludge taken from the anaerobic zone of the A2 / O process of the sewage treatment plant added in step (2) to the excess sludge taken from the secondary sedimentation tank of the municipal sewage treatment plant in step (1) is 1:

2.

8. The method for enhancing the anaerobic degradation of chlorinated organophosphates in sludge by using thiosulfate according to claim 1, wherein: The reaction temperature in step (1) is 20 ± 2 °C, the rotation speed is 60 rpm, and the reaction time is 24 h; the temperature in the constant temperature incubator in step (2) is 35 ± 1 °C, and the rotation speed is 80 rpm.

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