A biofilm carrier suitable for low-temperature wastewater treatment, its preparation method and application

Abstract

This invention discloses a biofilm carrier suitable for low-temperature wastewater treatment, its preparation method, and its application. The biofilm carrier uses SiC ceramic as the biofilm framework. A photothermal agent is coated on the upper part of the SiC ceramic to form a photothermal conversion functional zone, while the lower part of the SiC ceramic is a microbial adhesion functional zone. Simultaneously, temperature-responsive nanocapsules are loaded on the upper part of the SiC ceramic, enabling efficient photothermal conversion, adsorption and enrichment of functional bacteria, and increased biomass, thus achieving enhanced bacterial activity under low-temperature conditions. The preparation method of this biofilm carrier is simple, and its application in microbial wastewater treatment results in a high ammonia nitrogen removal rate.

Description

Technical Field

[0001] This invention relates to the field of environmental pollutant treatment, specifically to a biofilm carrier suitable for low-temperature wastewater treatment, its preparation method, and its application. Background Technology

[0002] In global water resource management, microbial water treatment technology, as a key component of wastewater treatment and water purification, faces the increasingly prominent challenge of achieving efficient nitrogen removal under low-temperature environments, becoming one of the most pressing technical bottlenecks in the current water treatment field. Under low-temperature conditions (typically below 15°C), the metabolic rate of microorganisms slows significantly, especially for key microorganisms in nitrification and denitrification processes, such as nitrifying bacteria and anaerobic ammonia-oxidizing bacteria. This reduced activity of these microorganisms at low temperatures directly affects the nitrogen conversion process, thereby decreasing nitrogen removal efficiency.

[0003] Low temperatures not only affect the activity of free-floating microorganisms but also the formation and stability of biofilms. Biofilms play a crucial role in water treatment; low temperatures slow down the maturation process, affect biofilm structure, and consequently impact the attachment and growth of denitrifying microorganisms, reducing the stability and efficiency of the denitrification process. Under low-temperature conditions, the operating conditions of the water treatment system (such as dissolved oxygen, pH, and nutrient ratios) are more sensitive to the effects on microbial activity. Precisely controlling these conditions to meet the needs of microorganisms in low-temperature environments is key to achieving stable denitrification, but it also increases the operational complexity.

[0004] The application of biofilm technology under low-temperature conditions can leverage the high adaptability of biofilms to environmental changes, improving denitrification efficiency and system stability by optimizing biofilm cultivation and maintenance conditions. However, these regulatory methods cannot alter the microenvironment temperature, thus limiting the performance improvement of low-temperature microbial water treatment. CN202310758686.X discloses a method for preparing and applying a Schottky junction-doped composite polyvinylidene fluoride hybrid membrane with excellent photothermal conversion capabilities. This method primarily uses simple doping and phase conversion to incorporate photocatalytic materials into photothermal materials, forming a composite membrane material for the photo-oxidation / reduction of organic pollutants, thereby achieving photodegradation of organic dyes and antibacterial effects.

[0005] Photothermal conversion is a process that concentrates solar radiation energy through reflection and absorption, converting it into heat to raise the temperature. It is a low-cost and efficient energy conversion method. An ideal photothermal conversion microbial water treatment carrier should possess highly efficient and robust photothermal conversion performance. Since sunlight is weaker in winter, the photothermal carrier needs to have a high spectral absorption rate across the entire solar spectrum to effectively raise the microenvironment temperature of the carrier in low-light conditions. Simultaneously, because the ultraviolet region of sunlight has a strong inhibitory effect on microbial activity, the carrier needs a light-free microenvironment. Introducing light into the wastewater system can cause a large-scale proliferation of photosynthetic algae. These algae produce oxygen in a light-exposed environment, which significantly inhibits the activity of anaerobic bacteria, and some algal toxins can kill bacteria. Bacteria often possess photosensitive proteins, and the activity of some bacteria is inhibited by light. Therefore, the photothermal carrier must have functional regions that protect microorganisms sensitive to ultraviolet light or other wavelengths of sunlight under full-spectrum illumination. Finally, as a microbial carrier, the photothermal carrier needs to have strong microbial adhesion attraction and excellent biocompatibility, so that microorganisms can achieve efficient adsorption on the carrier surface and efficient biochemical reactions in a low-temperature environment.

[0006] In order to overcome the problem of easy loss of low-temperature microorganisms and improve the water treatment performance of low-temperature microorganisms, the inventors of this invention obtained this invention through long-term research and experimentation using the technical conditions of this laboratory. Summary of the Invention

[0007] In view of the shortcomings of the prior art, the present invention aims to provide a biofilm carrier, preparation method and application suitable for low temperature wastewater treatment, so as to solve the problems mentioned in the background art.

[0008] The technical solution adopted by the present invention to achieve the above objectives is as follows:

[0009] A low-temperature wastewater treatment biofilm carrier uses SiC ceramic as the biofilm framework, with a photothermal agent coated on the upper part of the SiC ceramic to form a photothermal conversion functional zone, and the lower part of the SiC ceramic as a microbial adhesion functional zone.

[0010] Preferably, the photothermal agent is composed of PDMS, polyhexane, and α-Fe2O3@PANI.

[0011] Preferably, temperature-responsive nanocapsules are also loaded on the upper part of the SiC ceramic.

[0012] Preferably, the temperature-responsive nanocapsule consists of a temperature-sensitive poly(N-isopropylacrylamide) shell and a slow-release microbial growth promoter core. When the temperature of the carrier microenvironment increases (>25°C), the PNIPAM shell contracts and releases the microbial growth promoter in the core.

[0013] Preferably, the microbial growth promoter includes one or more of cobalamin, menadione, and biotin.

[0014] A method for preparing a low-temperature wastewater treatment biofilm carrier specifically includes the following steps:

[0015] Step 1: Preparation of α-Fe₂O₃ nanoparticles: Sodium nitrate was added to a prepared FeCl₃ solution to adjust the pH. The solution was then poured into a polytetrafluoroethylene-lined reaction vessel and reacted at 95°C for 4 hours. After cooling to room temperature, the yellow solid was collected by centrifugation and washing. Finally, the yellow solid was calcined in a furnace at 550°C for 2 hours to obtain α-Fe₂O₃ nanoparticles.

[0016] Step 2: Preparation of α-Fe2O3@PANI: Aniline was mixed with deionized water and placed in an ice-water bath. Hydrochloric acid was slowly added to adjust the pH to 0.8-1.0. After adding the α-Fe2O3 nanoparticles obtained in Step 1, the mixture was sonicated. Ammonium persulfate solution was then slowly added to promote the polymerization of aniline. The reaction was carried out while stirring. The mixture was allowed to stand at -4℃ for 24 hours to achieve full precipitation and polymerization. Finally, the mixture was washed with deionized water and ethanol to obtain α-Fe2O3@PANI.

[0017] Step 3: Preparation of photothermal agent: PDMS precursor and crosslinking agent are mixed in a ratio of 10:1 to obtain PDMS, which is then added to polyhexane. After thorough stirring, α-Fe2O3@PANI obtained in step 2 is added to the mixture and stirred until homogeneous to obtain the photothermal agent.

[0018] Step 4: Preparation of low-temperature wastewater treatment biofilm carrier: The photothermal agent obtained in step 3 is coated on the SiC ceramic skeleton and dried at 70°C for 5 hours.

[0019] Preferably, the pH is adjusted to 1.5 in step one.

[0020] Preferably, in step two, the molar ratio of aniline to α-Fe2O3 nanoparticles is 4:1-3.

[0021] Preferably, the mass fraction ratio of PDMS, polyhexane and α-Fe2O3@PANI in the mixture of step three is 10%:10%:80%.

[0022] Preferably, the porosity of the SiC ceramic in step four is 10 ppi.

[0023] The present invention also provides the application of the low-temperature wastewater treatment biofilm carrier prepared above in low-temperature microbial water treatment.

[0024] The present invention has the following beneficial effects:

[0025] 1. The low-temperature wastewater treatment biofilm carrier prepared by this invention can achieve rapid reactor start-up in a low-temperature environment (below 15°C) and quickly attract microorganisms to form a film and attach.

[0026] 2. The surface of this low-temperature wastewater treatment biofilm carrier is divided into a photothermal conversion functional zone and a microbial adhesion functional zone, which can realize photothermal conversion and promote the attachment of microorganisms. In addition, the carrier can adsorb DNA in the environment, regulate the structure of the biofilm, promote the maturation and mass transfer of porous biofilms, slowly release iron ions, promote bacterial chemotaxis to form a film, and increase the abundance of functional bacteria. The carrier can also efficiently retain water treatment functional bacteria with slow growth rates, such as anaerobic ammonia oxidizing bacteria, and ensure good effluent quality.

[0027] 3. The interlaced honeycomb structure design of this low-temperature wastewater treatment biofilm carrier enables the formation of a light-free area in the lower layer of the carrier during the photothermal conversion process. This avoids direct exposure of microorganisms to ultraviolet rays in sunlight, effectively preventing the killing effect of ultraviolet light on microorganisms and providing a suitable growth environment for microorganisms.

[0028] 4. The surface of this low-temperature wastewater treatment biofilm carrier can also be loaded with pH-responsive nanocapsules to achieve intelligent regulation. The released biological factors enrich functional bacteria through chemotaxis, while activating the coenzyme synthesis and energy metabolism of microorganisms at low temperatures, forming a positive feedback loop of "photothermal heating-factor release-metabolic activation", thereby achieving dynamic enhancement of microbial activity in low-temperature environments. Attached Figure Description

[0029] Figure 1 This is a schematic diagram of the device.

[0030] Figure 2 This refers to the changes in ammonia nitrogen, nitrite nitrogen, and nitrate nitrogen content in the reactor's influent and effluent;

[0031] Figure 3 It refers to the changes in the reactor microbiota of two reactors (where R... p The experimental group reactor microbial community structure was set up with a biofilm carrier. c This is the microbial community structure of the control group reactor. Detailed Implementation

[0032] To further understand the present invention, preferred embodiments of the present invention are described below in conjunction with examples. However, it should be understood that these descriptions are only for further illustrating the features and advantages of the present invention, and not for limiting the scope of the claims.

[0033] It should be noted that the source of the activated sludge used in this invention is not limited; any water treatment microorganisms whose function is severely affected by low temperatures are suitable for the method of this patent. The photothermal carrier used in this invention is modified to have good microbial adsorption film formation and microbial loading capacity, which helps in the immobilization of microorganisms. Example

[0034] Step 1: Preparation of α-Fe₂O₃ nanoparticles: Dissolve 0.81 g FeCl₃·6H₂O in 20 mL of deionized water, then add 1.70 g NaNO₃. Adjust the pH of the solution to 1.5 dropwise by adding hydrochloric acid. Transfer the solution to a reaction vessel lined with 25 mL of polytetrafluoroethylene and react at 95 °C for 4 h. After cooling to room temperature, collect the yellow solid by centrifugation and washing. Finally, calcine the yellow solid in a furnace at 550 °C for 2 h to obtain α-Fe₂O₃.

[0035] Step 2: Preparation of α-Fe₂O₃@PANI: 9 mL (0.1 mol) aniline was mixed with 200 mL deionized water and placed in an ice-water bath. The pH was controlled at 1.0 by slowly adding hydrochloric acid to the aniline. Then, 8 g (0.05 mol) of synthesized α-Fe₂O₃ nanoparticles were added to the above solution and sonicated. 6.1 g ammonium persulfate was dissolved in 100 mL deionized water. The ammonium persulfate solution was slowly added to the suspension to promote the polymerization process of aniline. The solution was stored at -4℃ and allowed to stand for 24 h to allow for sufficient precipitation and polymerization. Finally, α-Fe₂O₃@PANI was obtained after washing with deionized water and ethanol.

[0036] Several different α-Fe₂O₃@PANI composite materials were prepared by varying the amount of α-Fe₂O₃ in the reaction system (0 mol, 0.025 mmol, 0.05 mmol, 0.075 mmol), labeled as α-Fe₂O₃ / PANI-n (n=0, 1, 2, 3). Through batch experiments, n=2 was selected for carrier preparation as the preferred method.

[0037] Step 3: Preparation of photothermal agent: Mix the PDMS precursor (initial reactant in the PDMS synthesis process) and crosslinking agent (to cause crosslinking reaction between PDMS precursor molecules) in a ratio of 10:1 and add them to polyhexane. After thorough stirring, add α-Fe2O3@PANI to the mixture to maintain the mass fraction of PDMS at 10%, polyhexane at 10%, and α-Fe2O3@PANI at 80%.

[0038] Step 4: Preparation of low-temperature wastewater treatment biofilm carrier: The above mixture (10% PDMS, 10% polyhexane, and 80% α-Fe2O3@PANI) was coated on a SiC ceramic skeleton (porosity 10 ppi) and dried at 70°C for 5 h to obtain the prepared low-temperature wastewater treatment biofilm carrier.

[0039] Temperature-responsive nanocapsules were loaded onto a low-temperature wastewater treatment biofilm carrier. The nanocapsules comprised a temperature-sensitive poly(N-isopropylacrylamide) (PNIPAM) shell and a slow-release microbial growth promoter core. When the carrier's microenvironment temperature exceeded 25°C, the PNIPAM shell contracted, releasing the microbial growth promoters from the core, including but not limited to cobalamin, menadione, and biotin, thus achieving photothermal synergistic intelligent regulation of microbial metabolic activity. In this experiment, cobalamin was used as the microbial growth promoter core. Example

[0040] Testing the water treatment effect of low-temperature wastewater treatment biofilm carrier

[0041] The microbial water treatment device was operated using a self-made photothermal reactor from our laboratory. Figure 1 The device consists of five parts: an inlet system, an aeration system, a photothermal carrier system, an outlet system, and a water bath system.

[0042] The water intake system includes a water intake bottle (1) and a water intake peristaltic pump (2). The water intake bottle (1) is sealed with a rubber stopper. Two holes need to be drilled in the rubber stopper, and two glass tubes are inserted into it. One of the tubes is connected to a 10L air bag (to prevent negative pressure from being generated in the wide-mouth bottle after water intake, which would affect the water intake speed or cause the bottle wall to break). The other tube is connected to the plastic tube of the water intake peristaltic pump (2). The other end of the plastic tube is connected to the water inlet (3) of the membrane bioreactor (4). The rotation speed of the peristaltic pump (2) can be set to an appropriate value to adapt to different hydraulic residence times.

[0043] The aeration system consists of an aeration head (7), an aeration pipe (8), and a gas flow meter (13). One end of the aeration pipe (8) is connected to the aeration head (7), and the other end is connected to the gas flow meter (13). The aeration head (7) is placed inside the membrane bioreactor (4). During aeration, the gas flow meter (13) is connected to the aeration gas cylinder to control the aeration flow rate.

[0044] The membrane bioreactor (4) is cylindrical in shape. It has an inlet (3) at the bottom and a water bath heating jacket (5) on the outer layer to simulate the low-temperature environment of the membrane bioreactor (4). The membrane bioreactor (4) is magnetically stirred, which facilitates the transfer of the internal matrix and uniform reaction. The stirring speed is set to 100-150 rpm during operation. The biofilm carrier (9) is placed inside the membrane bioreactor (4), with a height approximately half that of the membrane bioreactor (4). The outlet is connected to the effluent pipe of the membrane bioreactor (4). The membrane bioreactor (4) operates with continuous influent and continuous effluent, and the hydraulic residence time varies with the performance of the membrane bioreactor (4).

[0045] The water outlet system includes a peristaltic pump (15) and an outlet bottle (16). One end of the plastic tube of the peristaltic pump (15) is connected to the outlet pipe of the membrane bioreactor (4), and the other end is connected to the outlet bottle (16).

[0046] A water bath circulation system is used to simulate ambient temperature. Constant-temperature water flows through a chiller (12) and forms a closed loop with the membrane bioreactor's water bath heating jacket (5), ensuring a constant temperature within the membrane bioreactor (4). Constant-temperature chilled water generated by the chiller (12) is introduced into the water bath inlet (14). The reactor's water bath inlet (14) and water bath outlet (18) are connected to the water bath heating jacket (5), and the water bath outlet (18) is connected to the chiller (12), allowing the constant-temperature water to flow back into the chiller (12). In other words, the constant-temperature chilled water in the chiller (12) flows through the water bath inlet (14) to the water bath jacket (5), then from the water bath jacket (5) to the reactor's water bath outlet (18) and back into the chiller (12), forming a circulating water bath system.

[0047] A xenon lamp (10) was used to simulate sunlight, with the sunlight intensity set to 0.6 KW / m². 2 .

[0048] The example of using this reactor to operate anaerobic ammonium oxidation further illustrates the point:

[0049] First, the biofilm carrier was immobilized inside the reactor, and anaerobic ammonia oxidation sludge (derived from anaerobic ammonia oxidizing bacteria cultured in an anaerobic fermenter, with the proportion of anaerobic ammonia oxidizing bacteria between 50% and 80%) was added, and the reactor was started. The reactor was inoculated with anaerobic ammonia oxidation sludge at a concentration of 0.05 g VSS / L, and the initial HRT was set to 24 h. The anaerobic environment of the reactor influent was maintained through a gas mixture of N2 / CO2 (95 / 5%). NH3 in the influent and effluent was measured every two days. 4+ -N、NO 2– -N and NO 3–The concentration of -N was monitored to assess reactor performance. An anaerobic environment was maintained within the reactor, with a water bath simulating a low-temperature environment of 15°C. The influent pH was maintained between 7.3 and 7.8. A xenon lamp was used to simulate sunlight, with the sunlight intensity set at 0.6 KW / m². 2 After irradiation for 4 hours under these conditions, the temperature of the carrier rose to 30.5 degrees Celsius, while a dark area formed in the lower layer of the carrier.

[0050] To investigate the impact of the biofilm carrier on reactor performance in this invention, an anaerobic ammonia oxidation process was used as an example. Two reactors were started and operated in parallel simultaneously. One was the anaerobic ammonia oxidation reactor R mentioned above with the added biofilm carrier. P Another reactor R c Unmodified conventional SiC ceramic support was added. During reactor operation, the support in this study achieved functional zoning on the porous ceramic, with the upper layer realizing photothermal conversion, the lower layer realizing microbial attachment and increasing the abundance of functional bacteria, and the upper layer containing a small amount of algae providing end-of-pipe treatment for the wastewater of the entire reactor.

[0051] The changes in ammonia nitrogen, nitrite nitrogen, and nitrate nitrogen content in the influent and effluent of the two reactors were measured. Figure 2 It can be seen that R p and R c All systems successfully started up after 100 days of operation, including R. P The reactor starts up faster, R P The denitrification performance of the reactor is R c Four times that of the reactor; changes in the microbial community in the reactor as follows Figure 3 As shown, the abundance of anaerobic ammonia oxidizing bacteria increased by 21%, R P The biomass of the reactor compared to R c The reactor's efficiency increased by 2.2 times. This indicates that the biofilm carrier prepared in this study can achieve rapid reactor start-up in a low-temperature environment, and that the carrier can perform efficient photothermal conversion, while also adsorbing and enriching functional bacteria and increasing biomass.

Claims

1. A low-temperature wastewater treatment biofilm carrier, characterized in that, The biofilm carrier uses SiC ceramic as the biofilm framework, with a photothermal agent coated on the upper part of the SiC ceramic to form a photothermal conversion functional region, and the lower part of the SiC ceramic as a microbial adhesion functional region. The photothermal agent is composed of PDMS, polyhexane, and α-Fe2O3@PANI; The SiC ceramic is also loaded with temperature-responsive nanocapsules. The temperature-responsive nanocapsule consists of a poly(N-isopropylacrylamide) shell and a microbial growth promoter core.

2. The low-temperature wastewater treatment biofilm carrier according to claim 1, characterized in that, The microbial growth promoters include one or more of cobalamin, menadione, and biotin.

3. The low-temperature wastewater treatment biofilm carrier according to claim 1, characterized in that, The preparation method of the biofilm carrier includes the following steps: S101. Sodium nitrate was added to the prepared FeCl3 solution to adjust the pH. The solution was then poured into a reaction vessel lined with polytetrafluoroethylene and reacted at 95°C for 4 hours. After cooling to room temperature, the yellow solid was collected by centrifugation and washing. Finally, the yellow solid was calcined in a furnace at 550°C for 2 hours to obtain α-Fe2O3 nanoparticles. S102. Aniline and deionized water were mixed and placed in an ice-water bath. Hydrochloric acid was slowly added to adjust the pH to 0.8-1.

0. The α-Fe2O3 nanoparticles prepared in step S101 were added and ultrasonically treated. Ammonium persulfate solution was added slowly while stirring and reacting. After standing at -4℃ for 24 hours, the mixture was washed with deionized water and ethanol to obtain α-Fe2O3@PANI. S103. PDMS is prepared by mixing PDMS precursor and crosslinking agent in a ratio of 10:1 and adding it to polyhexane. After thorough stirring, α-Fe2O3@PANI obtained in step S102 is added to the mixture and stirred until homogeneous to obtain photothermal agent. S104. The photothermal agent obtained in step S103 is coated onto the SiC ceramic skeleton and dried at 70°C for 5 hours to obtain a low-temperature wastewater treatment biofilm carrier.

4. The low-temperature wastewater treatment biofilm carrier according to claim 3, characterized in that, In step S101, the pH is adjusted to 1.

5.

5. The low-temperature wastewater treatment biofilm carrier according to claim 3, characterized in that, In step S102, the molar ratio of aniline to α-Fe2O3 nanoparticles is 4:1-3.

6. The low-temperature wastewater treatment biofilm carrier according to claim 3, characterized in that, The mass fraction ratio of PDMS, polyhexane, and α-Fe2O3@PANI in the mixture of step S103 is 10%:10%:80%.

7. The application of the low-temperature wastewater treatment biofilm carrier as described in any one of claims 1-6 in low-temperature microbial water treatment.

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