A method for enhancing the carbon fixation performance of bacteria-algae system in treating sewage

Abstract

The present invention discloses a method for enhancing the carbon fixation performance of a bacteria-algae system in treating wastewater, belonging to the technical field of pollution reduction and carbon reduction in wastewater treatment. The present invention uses a hydrogen-producing composite photocatalytic material as a biological carrier for the bacteria-algae symbiotic system to treat wastewater. While ensuring the sewage treatment effect, the present invention effectively solves the problem of microalgae being photoinhibited by sunlight, thereby significantly improving the light energy conversion efficiency of the microalgae and achieving efficient carbon fixation in the bacteria-algae symbiotic system for treating wastewater. At the same time, the hydrogen generated by this method can also be recovered as an energy gas, achieving multiple benefits. The present invention helps promote pollution reduction and carbon reduction and resource utilization in wastewater treatment and has good application prospects.

Description

Technical Field

[0001] The present invention relates to the technical field of pollution reduction and carbon reduction in sewage treatment, and in particular to a method for enhancing the carbon fixation performance of a bacteria-algae system in treating sewage. Background Art

[0002] During traditional activated sludge wastewater treatment, large amounts of CO₂ produced by bacterial degradation of organic matter are directly released into the atmosphere. Furthermore, the electricity required to supply oxygen through aeration also results in significant indirect carbon emissions. Carbon emissions from the wastewater treatment industry already account for 2% of total carbon emissions, and reducing carbon emissions in wastewater treatment has received significant attention.

[0003] The bacteria-algae symbiotic system utilizes the symbiotic interaction between microalgae and bacteria in sludge to treat domestic sewage. Its mechanism is as follows: Under sunlight, microalgae photosynthesis produces oxygen, which is used by bacteria to degrade organic pollutants in the sewage, thereby reducing or even eliminating the need for aeration. Simultaneously, a large amount of organic carbon in the sewage is metabolized by bacterial respiration and converted into inorganic carbon (CO2 or its dissolved form, such as carbonate). This is absorbed by the microalgae through photosynthesis and converted into biomass, thereby reducing carbon emissions. Using the bacteria-algae symbiotic system to treat sewage is a wastewater treatment process with great potential for carbon reduction.

[0004] The photosynthesis process of microalgae is divided into a light reaction, which absorbs and converts light, and a dark reaction, which fixes CO2. The rate of the light reaction increases with increasing light intensity. When the light reaction rate is higher than the dark reaction rate, photoinhibition occurs, in which the algae activate their self-protection mechanism and no longer receive more light. Due to the low photoinhibition threshold of microalgae, photoinhibition easily occurs under natural sunlight, resulting in a significant reduction in the efficiency of light energy conversion, thereby limiting the microalgae's conversion of CO2, seriously affecting the carbon fixation efficiency of the bacteria-algae symbiotic system, and still generating a large amount of carbon emissions.

[0005] It can be seen that solving the problem of photoinhibition of microalgae under natural sunlight and achieving efficient carbon fixation in the bacteria-algae symbiotic system for treating wastewater are technical problems that urgently need to be solved in the current bacteria-algae symbiotic system for treating wastewater. Summary of the Invention

[0006] The purpose of the present invention is to provide a new method for treating sewage based on a bacteria-algae symbiotic system. This method uses a hydrogen-producing composite photocatalytic material as a biological carrier of the bacteria-algae symbiotic system. The photocatalytic material is coupled with the absorption of light by microalgae to regulate the conversion of solar energy into chemical energy and balance the light / dark reaction rate of the microalgae, effectively solving the problem of microalgae being photoinhibited under sunlight, significantly enhancing the light energy conversion efficiency of microalgae, and realizing efficient carbon fixation in the treatment of sewage by the bacteria-algae symbiotic system; the hydrogen generated by the photocatalytic material during the treatment process can also be recovered as an energy gas to achieve multiple effects. The method provided by the present invention is helpful to promote pollution reduction and carbon reduction and resource utilization in sewage treatment, and has good application prospects.

[0007] In order to achieve the above object, the technical solution adopted by the present invention is as follows:

[0008] A method for enhancing the carbon sequestration performance of a bacteria-algae symbiotic system in treating sewage, comprising the following steps:

[0009] The hydrogen-producing composite photocatalytic material is loaded into the reaction tank, inoculated with activated sludge and microalgae, and allowed to stand for biofilm formation. Sewage is then introduced under natural sunlight to treat the sewage and fix the generated inorganic carbon.

[0010] The hydrogen-producing composite photocatalytic material is prepared from biomass raw materials, a metal element activator and a g-C3N4 precursor.

[0011] In the present invention, the mass ratio of the metal element activator to the g-C3N4 precursor is 1:(1-2):(0.1-0.4), preferably 1:2:0.2.

[0012] In the present invention, the hydrogen-producing composite photocatalytic material is prepared by a method comprising the following steps:

[0013] (1) Mix the biomass raw materials, metal element activator and g-C3N4 precursor and place them in a tube furnace;

[0014] (2) introducing an inert gas into the tubular furnace and calcining in one pot;

[0015] (3) The product obtained in step (2) is rinsed and dried to obtain a composite material of metal element-doped g-C3N4 and activated carbon (AC), i.e., a hydrogen-producing composite photocatalytic material.

[0016] In the present invention, in step (1), the biomass raw material is selected from at least one of corn cobs, fruit shells and straw; and the particle size of the biomass raw material is 5 to 12 mm.

[0017] The metal element activator is selected from zinc chloride.

[0018] The g-C3N4 precursor is selected from at least one of dicyandiamide, urea, melamine and thiourea; preferably melamine.

[0019] In the present invention, in step (2), the inert gas used in the one-pot calcination is nitrogen and / or argon; the inert gas is introduced at a flow rate of 30 to 60 mL / min, specifically 40 mL / min;

[0020] The calcination process includes: first heating to 400-500°C, holding time for 2-4 hours, specifically 450°C, specifically 3 hours; then heating to 500-1000°C, holding time for 45-80 minutes, specifically 850°C, specifically 60 minutes.

[0021] In the present invention, the filling ratio of the hydrogen-producing composite photocatalytic material is (3-4):10, specifically 3:10.

[0022] In the present invention, the activated sludge is taken from the secondary sedimentation tank of the sewage treatment plant;

[0023] The microalgae are selected from at least one of Chlorella, Spirulina, Scenedesmus and diatoms;

[0024] The mass ratio of the activated sludge to the microalgae is 1:1 to 1:4, specifically 1:1.

[0025] In the present invention, the static film formation is a process in which bacteria and algae grow into a film on the hydrogen-producing composite photocatalytic material; and the static film formation time is 36 to 48 hours.

[0026] In the present invention, sewage is introduced into the reaction tank in a continuous operation mode.

[0027] In the present invention, the sewage can come from domestic sewage, initial rainwater, agricultural irrigation return water, aquaculture wastewater, etc., and the organic pollutant content is 300~500 mg / L, for example, 400 mg / L; the treatment time is initially set to 12h, which can be adjusted according to the actual treatment effect.

[0028] Compared with the prior art, the present invention has the following beneficial effects:

[0029] 1. The present invention adopts the hydrogen-producing composite photocatalytic material Zn-g-C3N4 / AC as the biological carrier of the bacteria-algae symbiotic system, and develops a new method to enhance the carbon fixation performance of the bacteria-algae symbiotic system in treating wastewater. This method can promote pollution reduction and carbon reduction and resource utilization of wastewater treatment.

[0030] Specifically, on the one hand, the present invention utilizes Zn-g-C3N4 to couple microalgae with light absorption to regulate the conversion of solar energy into chemical energy and balance the light / dark reaction rate of microalgae, thereby relieving the light inhibition of natural sunlight on microalgae, thereby improving the light energy conversion efficiency of microalgae, and further improving the conversion and fixation efficiency of microalgae to inorganic carbon; at the same time, Zn-g-C3N4 can be hydrolyzed to produce hydrogen under sunlight, which can be recycled as energy to achieve resource recovery in sewage treatment; on the other hand, the AC in the composite material provides a good attachment site for bacteria-algae microorganisms, and its porous structure can enrich CO2 in water, further improving the conversion and fixation efficiency of microalgae to inorganic carbon.

[0031] 2. In this invention, g-C3N4, the photocatalytic material in the composite material, can be prepared simultaneously with activated carbon, achieving uniform loading of g-C3N4 on the AC. Zinc chloride, an activator, not only creates pores to increase the specific surface area but also allows Zn to be doped into the g-C3N4, further enhancing its photocatalytic activity. This process greatly simplifies the composite material preparation process, reducing production costs and energy consumption. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 This is a 3D rendering of the hydrogen-producing composite photocatalytic material Zn-g-C3N4 / AC provided by the present invention.

[0033] Figure 2 This is a SEM photo of the hydrogen-producing composite photocatalytic material Zn-g-C3N4 / AC provided by the present invention.

[0034] Figure 3 This is the photoluminescence excitation spectrum of the hydrogen-producing composite photocatalytic material Zn-g-C3N4 / AC provided by the present invention.

[0035] Figure 4 This is the Tauc relationship diagram of the hydrogen-producing composite photocatalytic material Zn-g-C3N4 / AC and hv provided by the present invention.

[0036] Figure 5 The hydrogen-producing composite photocatalytic material Zn-g-C3N4 / AC provided by the present invention is used as a biological carrier to treat the COD concentration of the inlet and outlet water of sewage in a bacteria-algae symbiotic system.

[0037] Figure 6 The hydrogen-producing composite photocatalytic material Zn-g-C3N4 / AC provided by the present invention is used as a biological carrier to reduce CO2 emissions from sewage treatment in a bacteria-algae symbiotic system.

[0038] Figure 7 It is the transfer pathway of photosynthetic electrons in microalgae cells. DETAILED DESCRIPTION

[0039] The present invention will be further described below with reference to specific examples, but the present invention is not limited to the following examples.

[0040] Unless otherwise specified, the experimental methods used in the following examples are conventional methods.

[0041] Unless otherwise specified, the reagents, materials, instruments, etc. used in the following examples can be obtained from commercial sources.

[0042] Example

[0043] This embodiment specifically provides a method for enhancing carbon sequestration in a bacteria-algae symbiotic system. Taking domestic sewage as an example, the method includes the following steps:

[0044] Step 1: Preparation of bio-carrier Zn-g-C3N4 / AC. The specific steps are as follows:

[0045] (1) Wash the corn stalks, dry them at 90°C, crush them, and sieve them (3-4 mesh) to obtain 4.0-6.5 mm crumbs for later use.

[0046] (2) A certain mass of corn straw residue, zinc chloride and g-C3N4 precursor were weighed, and the corn straw residue, zinc chloride and g-C3N4 precursor were physically and mechanically mixed in a certain mass ratio. After being evenly ground, they were placed in a tube furnace. Under the protection of nitrogen (40 mL / min), the temperature was raised from room temperature to 450℃ at a rate of 10℃ / min and reacted for 3 h; then the temperature was continued to rise to 850℃ at a rate of 10℃ / min and reacted for 60 min. The temperature was cooled to room temperature at a rate of 10℃ / min to obtain Zn-g-C3N4 / AC with a particle size between 2.5 and 3.2 mm.

[0047] Step 2: Treating wastewater using a bacteria-algae symbiotic system

[0048] The Zn-g-C3N4 / AC prepared in step 1 was filled into a reaction tank (1.0 L) with an apparent filling volume of 0.3 L and an air collection bag installed on top. The inoculated activated sludge was taken from the secondary sedimentation tank of a sewage treatment plant and inoculated with Chlorella at a mass ratio of 1:1, and then allowed to soak for 40 hours. Domestic sewage with an organic matter concentration (measured in COD) of 400 mg / L was introduced from the bottom of the reaction tank via a peristaltic pump. The pump speed was adjusted to set the hydraulic retention time to 12 hours, and the sewage was placed under natural sunlight for treatment.

[0049] Effect verification

[0050] 1. Investigation of the specific surface area and Zn doping rate of biological carriers

[0051] According to the method conditions described in the above examples, the ratio of biomass raw material (A) and zinc chloride (B) was fixed, and the specific surface area and Zn doping rate of the bio-carriers prepared with different ratios of g-C3N4 precursor (C) were investigated; at the same time, the carrier prepared without adding g-C3N4 precursor was used as a control.

[0052] The details are as follows:

[0053] Sample 1: A:B:C mass ratio is 1:2:0.1;

[0054] Sample 2: The mass ratio of A:B:C is 1:2:0.2;

[0055] Sample 3: The mass ratio of A:B:C is 1:2:0.3;

[0056] Sample 4: A:B:C mass ratio is 1:2:0.4;

[0057] Sample 5: No g-C3N4 precursor was added, and the mass ratio of biomass raw material to zinc chloride was 1:2.

[0058] Investigation method: (1) The specific surface area and total pore volume of different biocarriers were obtained by nitrogen adsorption test and BET calculation; (2) The Zn content was determined by acid dissolution method, and the doping rate of Zn in g-C3N4 on different biocarriers was calculated.

[0059] The results are shown in Table 1.

[0060] Table 1 Specific surface area and Zn doping rate of bio-carriers

[0061]

[0062] As can be seen from Table 1, compared with sample 5, the biocarriers of samples 1-4 all have higher specific surface area and Zn doping rate, among which sample 2 has the highest specific surface area and Zn doping rate. This shows that when the ratio of biomass raw materials, metal element activator and g-C3N4 precursor is 1:2:0.2, the specific surface area and Zn doping rate of the prepared composite material are optimal.

[0063] At the same time, the test of sample 5 found that in the absence of g-C3N4 precursor, zinc chloride only plays the role of activation and pore formation in the carbonization process. Rinsing with water after carbonization can wash away the zinc chloride on the surface or in the pores of the activated carbon, so there is no zinc chloride residue in the final product.

[0064] 2. Structure and performance indicators of biological carriers

[0065] Taking biological carrier sample 2 as an example, the test results are as follows:

[0066] (1) Microstructure

[0067] Depend on Figure 1 、 Figure 2 It can be seen that Zn-doped g-C3N4 is relatively evenly distributed on the surface of activated carbon.

[0068] (2) Conductivity

[0069] The electrical conductivity of the biological carrier sample 2 was measured using a four-probe resistivity method and was found to be 800 μS / cm.

[0070] (3) Absorption of light

[0071] like Figure 3 、 Figure 4 As shown, the biological carrier sample 2 has an obvious absorption peak (420nm) in the visible light range, and the corresponding band gap is 2.68eV, indicating that the biological carrier sample 2 can have a good photoelectric response to visible light.

[0072] 3. Carbon fixation performance of bio-carriers in wastewater treatment using bacteria-algae symbiotic systems

[0073] The above-mentioned biological carrier samples 1-5 were subjected to carbon fixation efficiency testing of wastewater treatment in a bacteria-algae symbiotic system.

[0074] Test method: Under natural sunlight, the concentrations of various forms of carbon in the system (organic carbon TOC, inorganic carbon DIC, CO2, etc.) were used as detection indicators, and the carbon fixation efficiency of the bacteria-algae symbiotic system in treating wastewater was used to evaluate the photocatalytic activity of the prepared catalyst. The carbon fixation efficiency was calculated as follows: (total carbon in the inlet - total carbon in the outlet - CO2 emitted) / total carbon in the inlet. The results are shown in Table 2.

[0075] Table 2 Carbon fixation efficiency of wastewater treated by different biological carrier bacteria-algae systems

[0076]

[0077] As can be seen from Table 2, compared with sample 5, biological carrier samples 1-4 have higher carbon fixation efficiency and sample 2 has the highest carbon fixation efficiency. This shows that the composite material prepared by the present invention at the optimal ratio of biomass raw materials, metal element activator and g-C3N4 precursor can significantly improve the carbon fixation efficiency of the bacteria-algae symbiotic system in treating wastewater.

[0078] 4. Degradation effect of organic matter in sewage

[0079] The degradation effect of organic matter in the above sewage treatment experiment is as follows Figure 5As shown in Figure 2, using Biocarrier Sample 2 as an example, during the startup phase, as the biofilm formed, the COD concentration in the effluent of both the experimental group (Sample 2) and the control group (Sample 5) gradually decreased, and the COD removal rate continued to improve. The experimental group achieved stable operation faster (24 days) than the control group (32 days). During the stable operation phase, the effluent COD of both the experimental and control groups was less than 25-35 mg / L, meeting the National Class A Emission Standard (GB 18918-2002). This demonstrates that Biocarrier Sample 2 can improve the organic matter degradation efficiency of wastewater treated by the bacteria-algae symbiotic system.

[0080] 5. Treatment process exhaust gas and hydrogen production performance

[0081] During the test of the carbon fixation performance of the above-mentioned bacteria-algae symbiotic system in treating wastewater, the composition and content of the gas in the collection bag were monitored at the same time. Taking the biological carrier sample 2 as an example, the results of CO2 emission during the treatment process are as follows: Figure 6 As shown, the CO2 emission of the experimental group was almost undetectable, while the CO2 emission of the control group (sample 5) was 350~400 mg / d.

[0082] Taking biological carrier sample 2 as an example, it was calculated that the hydrogen generation rate of the experimental group was about 300~500μmol·L -1 ·h -1 , while no hydrogen was detected in the control group (sample 5).

[0083] 6. Carbon fixation mechanism of bacteria-algae system in wastewater treatment

[0084] Figure 7 This is the transfer path of photosynthetic electrons in microalgae cells. It can be seen that under light, the biological carrier Zn-g-C3N4 can generate photogenerated holes. These photogenerated holes can drive the excess electrons in the algae cells to flow out of the cells, reducing the generation of reactive oxygen species (ROS), thereby relieving the photoinhibition phenomenon and significantly improving the conversion efficiency of light energy; at the same time, the photoholes generated by Zn-g-C3N4 catalyze water to generate hydrogen, which can be recycled as an energy gas.

[0085] In summary, the present invention adopts the hydrogen-producing composite photocatalytic material Zn-g-C3N4 / AC as the biological carrier of the bacteria-algae symbiotic system, which can effectively enhance the carbon fixation performance of the bacteria-algae symbiotic system in the process of treating sewage and realize resource utilization.

[0086] Although the present invention has been described in detail above using general descriptions and specific embodiments, it will be apparent to those skilled in the art that modifications and improvements may be made based on the present invention. Therefore, such modifications and improvements, which do not depart from the spirit of the present invention, are intended to be within the scope of protection claimed herein.

Claims

1. A method for enhancing the carbon sequestration performance of a bacteria-algae symbiotic system in treating wastewater, characterized by: The method comprises the following steps: loading a hydrogen-producing composite photocatalytic material into a reaction tank, inoculating activated sludge and microalgae, allowing the reaction tank to stand to form biofilm, introducing sewage under natural sunlight, treating the sewage and fixing the generated inorganic carbon; The hydrogen-producing composite photocatalytic material is prepared by a method comprising the following steps: (1) Mix the biomass raw materials, metal element activator and g-C3N4 precursor and place them in a tube furnace; (2) introducing an inert gas into the tubular furnace and calcining in one pot; (3) rinsing and drying the product obtained in step (2) to obtain the hydrogen-producing composite photocatalytic material Zn-g-C3N4 / AC; in: The mass ratio of the biomass raw material, the metal element activator and the g-C3N4 precursor is 1:2:0.2; The calcination process comprises: firstly heating the temperature to 400-500°C and maintaining the temperature for 2-4 hours; then heating the temperature to 500-1000°C and maintaining the temperature for 45-80 minutes.

2. The method according to claim 1, wherein: In step (1), the biomass raw material is selected from at least one of corn cobs, fruit shells and straw; the particle size of the biomass raw material is 5 to 12 mm; The metal element activator is selected from zinc chloride; The g-C3N4 precursor is selected from at least one of dicyandiamide, urea, melamine and thiourea.

3. The method according to claim 1 or 2, characterized in that: In step (2), the inert gas used in the one-pot calcination is nitrogen and / or argon, and the flow rate is 30-60 mL / min.

4. The method according to claim 1 or 2, characterized in that: The filling ratio of the hydrogen-producing composite photocatalytic material in the reaction tank is (3-4):

10.

5. The method according to claim 1 or 2, characterized in that: The activated sludge is taken from the secondary sedimentation tank of the sewage treatment plant; The microalgae are selected from at least one of Chlorella, Spirulina, Scenedesmus and diatoms; The inoculation mass ratio of the activated sludge to the microalgae is 1:1 to 1:

4.

6. The method according to claim 1 or 2, characterized in that: The static film formation is a process in which bacteria and algae grow into a film on the hydrogen-producing composite photocatalytic material; the static film formation time is 36 to 48 hours.

7. The method according to claim 1 or 2, characterized in that: The reaction tank is fed with sewage in a continuous operation mode.

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