Visible-light-driven photocatalysis-biodegradation direct coupling system constructed based on waste industrial steel slag (SS) and construction method of visible-light-driven photocatalysis-biodegradation direct coupling system

Abstract

The invention discloses a visible-light-driven photocatalysis-biodegradation direct coupling system constructed based on waste industrial steel slag (SS) and a construction method of the visible-light-driven photocatalysis-biodegradation direct coupling system. According to the system, a visible light response photocatalyst prepared from SS is loaded by a modified three-dimensional porous carrier, a stable biological membrane is formed, under irradiation of visible light, photo-induced electrons and intermediate products can be quickly transferred to microorganisms, and efficient degradation and deep mineralization of pollutants are synergistically realized. The problems that a photocatalyst is easy to fall off, the efficiency is low and mineralization is not thorough through a single technology are solved through an interface stabilization technology, and the method has the advantages of being high in degradation efficiency, good in stability, wide in application range and the like, is especially suitable for treatment of refractory organic wastewater such as pharmacy and antibiotics, and has good engineering application prospects. Preferably, the polyurethane sponge carrier and the waste industrial steel slag BiOCl photocatalyst show high degradation rate and mineralization rate when tetracycline wastewater is treated.

Description

Technical Field

[0001] This invention belongs to the field of environmental bioengineering and wastewater treatment technology. Specifically, it discloses the construction and application of a visible light-driven photocatalytic-biodegradation direct coupling system (VPCB) based on waste industrial steel slag (SS) doping, which is suitable for the efficient degradation and mineralization of antibiotic wastewater. Background Technology

[0002] Antibiotic pollutants are widely present in wastewater from pharmaceutical, aquaculture, and livestock industries, exhibiting problems such as poor degradation, high toxicity, and significant ecological risks. Single biological processes are often inhibited under high antibiotic concentrations, resulting in unsatisfactory degradation efficiency and mineralization rates. While single photocatalysis can break down large organic molecules, its effectiveness is often limited by rapid photogenerated electron-hole recombination, insufficient visible light response, and inadequate mineralization of intermediate products. Direct photocatalysis-biodegradation coupling systems can overcome the shortcomings of single systems through the synergistic effect of "photocatalytic chain scission + biomineralization," but existing coupling systems still have deficiencies in interfacial stability, electron transfer efficiency, and long-term cycling stability.

[0003] Waste industrial steel slag (SS), as an industrial solid waste containing various functional components such as Ti, Fe, Ca, and Si, has the advantages of low cost and abundant resources. Its conductive / redox components, pores, and surface sites can be used to modify photocatalysts or as functional additives in composite systems. However, systematic demonstrations of how SS can enhance electron transfer, improve coupling efficiency, and reduce catalyst dosage in a "photocatalysis-biodegradation direct coupling system" are still lacking in publicly available technologies. Summary of the Invention

[0004] This invention aims to address the following problems existing in the prior art: single photocatalytic systems have high chain-breaking efficiency for pollutants but incomplete mineralization, and the photocatalyst is prone to detachment, resulting in poor operational stability; single biological systems have low degradation efficiency for antibiotic pollutants and are prone to the accumulation of intermediate products. Existing photocatalytic-biological combinations are mostly physically connected in series or parallel, resulting in long mass transfer pathways, insufficient interfacial stability, and difficulty in achieving long-term high-efficiency operation.

[0005] Therefore, this invention provides a visible light-driven photocatalysis-biodegradation direct coupling system based on SS doping and its construction method. This system, through the rational design of SS and visible light-responsive photocatalysts, simultaneously immobilizes the visible light-responsive photocatalyst and attaches microorganisms on the support surface, enabling photocatalytic chain scission and biomineralization to occur synergistically on the same spatial scale and the same support surface. Electrons and intermediate products generated by photocatalysis can be rapidly utilized by the biofilm, thereby achieving efficient removal and deep mineralization of pollutants. Alkaline pretreatment and sol-gel loading processes enhance the stability of the photocatalyst-support binding and promote long-term biofilm adhesion and growth, thus significantly improving the system's cycling stability and engineering application potential.

[0006] In this invention, "direct coupling" specifically refers to the formation of a stable attachment layer on the surface of a carrier loaded with photocatalyst by microorganisms, enabling photocatalysis and biodegradation to proceed synergistically on the same spatial scale and the same carrier. It also relates to the application of the coupling system in wastewater treatment, particularly for the treatment of antibiotic wastewater and other organic wastewater, which can maintain high stability under different pollutant concentrations and water quality conditions.

[0007] The beneficial effects of this invention are as follows:

[0008] 1. Direct coupling between photocatalyst and microorganism is achieved on the same carrier surface. SS significantly enhances electron transfer and inhibits photogenerated carrier recombination.

[0009] 2. Photogenerated electrons and intermediate products are efficiently utilized by microorganisms, significantly improving mineralization efficiency.

[0010] 3. Improve the long-term bonding stability of catalyst-support-biofilm through interface stabilization process.

[0011] 4. It exhibits high degradation rate, mineralization rate and excellent cycle stability in the treatment of wastewater containing antibiotics and other recalcitrant organic matter.

[0012] 5. It has strong scalability and is not limited to specific photocatalysts or supports, and has broad prospects for engineering applications. Attached Figure Description

[0013] Figure 1 Here is a picture of a polyurethane foam.

[0014] Figure 2 The graph shows the changes in TC degradation efficiency of SS / BiOCl@PU with different loading rates;

[0015] Figure 3 Image (a) shows a physical picture of activated sludge.

[0016] Figure 3 (b) is a photograph of the microbial attachment in the biofilm;

[0017] Figure 3 (c) is a comparison image before and after biofilm formation.

[0018] Figure 4 The graph shows the changes in TOC values ​​and TOC removal rate of influent and effluent during the biofilm formation period.

[0019] Figure 5 (a) shows the changes in TC concentration and removal rate in the influent and effluent during the microbial acclimatization period;

[0020] Figure 5 (b) shows the changes in TOC values ​​and removal rates of influent and effluent during the microbial acclimatization period;

[0021] Figure 6 (a) is a graph showing the changes in the degradation efficiency of TC wastewater under different degradation methods;

[0022] Figure 6 (b) shows the variation of TC waste mineralization efficiency under different degradation methods;

[0023] Figure 7 (a) shows the degradation curves of the VPCB system and the B system in cycle.

[0024] Figure 7 (b) shows the mineralization efficiency of the VPCB system and the B system cycle;

[0025] Figure 8 (a) is a comparison of EPS composition and PS content in biofilms of VPCB and B systems under different cycle periods;

[0026] Figure 8 (b) is a comparison of EPS composition and PN content in biofilms of VPCB and B systems under different cycle periods;

[0027] Figure 9 Figures showing the biofilm activity analysis of VPCB and B systems at different cycle periods;

[0028] Figure 10 This diagram illustrates the possible degradation mechanism of TC by the VPCB system. Detailed Implementation

[0029] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described below with reference to embodiments, but this is not intended to limit the scope of protection of this invention.

[0030] The present invention will be further described below with reference to embodiments. It should be noted that, in this document, terms such as "upper" and "lower" are used merely for the convenience of describing the drawings and are not intended to limit the direction in actual use, nor do they necessarily require or imply any such actual relationship or order between these entities or operations. Moreover, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus.

[0031] Example 1: A method for constructing a BiOCl (SS / BiOCl) photocatalytic-biodegradation direct coupling system based on waste steel slag (SS), characterized by the following steps: To achieve visible light-driven photocatalytic-biodegradation direct coupling, based on optimized carrier pretreatment and catalyst loading, an SS / BiOCl photocatalytic coupled microbial system was further constructed and evaluated.

[0032] 1. Carrier pretreatment process

[0033] Cubic polyurethane foam was selected as the composite carrier, such as Figure 1 As shown, the surface functional group content and hydrophilicity can be increased by alkaline, plasma, or other surface activation methods, thereby enhancing the binding ability with photocatalysts and microorganisms.

[0034] 2. Optimization of photocatalyst gradient loading

[0035] The SS / BiOCl photocatalyst was uniformly loaded onto the surface of a pretreated support using methods such as sol-gel and impregnation to form a catalyst-support composite. The loading process should ensure a stable bond between the catalyst layer and the support matrix to facilitate subsequent bio-attachment and reduce shedding during cycling.

[0036] 3. Directed cultivation process of biofilm

[0037] In a visible-light-responsive direct-coupled system, microorganisms need to be attached to the surface of the system with a 30% loading, and the attachment efficiency and bioactivity need to be evaluated. The specific steps are as follows:

[0038] (1) Microbial inoculation: Using activated sludge from urban domestic sewage as the source of microorganisms, supplementing with the synthetic domestic sewage formula, and preparing biofilm culture medium;

[0039] (2) Biofilm formation: The catalyst-carrier composite is placed in a culture medium containing activated sludge or target microbial communities, allowing microorganisms to directly attach to the catalyst-loaded carrier surface and gradually form a stable biofilm. Intermittent or continuous nutrient supply can be used during cultivation, and pollutant gradient acclimation can be employed as needed to improve the microorganisms' tolerance and degradation capacity to the target pollutants. When the effluent TOC tends to stabilize, it indicates that the biofilm has uniformly covered and stably adhered to the SS / BiOCl catalyst layer surface of the sponge matrix, forming a functionalized composite interface. Regular sampling and photography are conducted, such as... Figure 3 As shown in (a) and (b), the carrier surface became dark to the naked eye and was clearly distinguishable from the empty sponge and the control group loaded only with SS / BiOCl, as shown in (a) and (b). Figure 3 As shown in (c);

[0040] (3) TOC monitoring: Total organic carbon (TOC) in the influent and effluent was measured in real time throughout the biofilm formation process. The influent TOC remained stable, while the effluent TOC decreased after biofilm formation. The results are as follows: Figure 4 As shown, this indicates that microorganisms have stably attached to the surface of the 30% load system and have a highly efficient ability to remove organic matter.

[0041] (4) Tetracycline tolerance acclimatization: Biofilms were cultured using appropriate methods, and data were monitored as follows: Figure 5 As shown, there has been an improvement compared to the initial stage.

[0042] In summary, after the 30% loading system is attached to a biofilm and acclimated to TC, a stable and efficient photocatalytic-biodegradation coupled material is formed, denoted as 30SS / BiOCl@PU@biofilm, which can be directly applied to the efficient removal of TC from wastewater driven by visible light.

[0043] Example 2: A method for performance optimization and verification of a photocatalytic-biodegradation coupled reaction system based on the SS / BiOCl composite photocatalyst described in Example 1, characterized by comprising the following steps:

[0044] 1. Comparison Experiment of Degradation Methods

[0045] The degradation effects of different treatment methods on TC wastewater were compared at a dosage of 30SS / BiOCl@PU@biofilm, and the results are as follows: Figure 6 As shown:

[0046] (1) Photolysis (P): Without a catalyst, the photolysis efficiency of TC is negligible, confirming that TC has no self-luminous degradation properties;

[0047] (2) Adsorption (AD): Under light-protected conditions, 30SS / BiOCl@PU achieved a TC adsorption removal rate of 44.2% and a mineralization rate of 37.1%, demonstrating the contribution of the carrier adsorption.

[0048] (3) Biodegradation (B): Under light-proof and adequate aeration conditions, the biofilm showed a TC degradation rate of 48.7% and a mineralization rate of 67.6%, demonstrating the independent degradation ability of microorganisms.

[0049] (4) Photocatalysis (VPC): The photocatalytic degradation rate of 30SS / BiOCl@PU was 87.9% and the mineralization rate was 53.9%, verifying the visible light response activity of SS / BiOCl.

[0050] (5) Coupled System (VPCB): 30SS / BiOCl@PU@biofilm achieved a TC degradation rate of 95.2% and a mineralization rate of 76.6%, significantly better than the single system. In the synergistic mechanism, the surface biofilm partially peels off in the early stage of the reaction, exposing photocatalytic active sites; the internal porous biofilm efficiently utilizes photocatalytic intermediates, forming a dynamic complementary degradation pathway.

[0051] Therefore, the main characteristics of the VPCB system can be summarized as follows:

[0052] (1) The SS / BiOCl photocatalyst exhibits good response under visible light;

[0053] (2) After coupling with the biomembrane, the biomembrane on the surface of the carrier is initially peeled off, exposing the active sites and significantly improving the photocatalytic efficiency.

[0054] (3) Biofilms within pores can utilize intermediate products to further promote mineralization.

[0055] The VPCB system outperforms single adsorption, biological, biocatalytic, and photocatalytic systems in terms of degradation efficiency and mineralization rate, achieving the advantages of lower dosage and higher efficiency.

[0056] Example 3: A method for verifying the stability of a photocatalytic-biological coupling system, comprising the following steps:

[0057] 1. Cyclic stability test

[0058] In the four cycles of the experiment, the results were as follows: Figure 7 As shown, in the VPCB system, microorganisms enhance the mineralization ability of intermediate products through photogenerated electron transfer; however, due to biofilm exfoliation and TC desorption, the TC removal rate of the single biodegradation system (B) decreases. Therefore, the cycle stability can be further optimized by improving the interfacial bonding technology between the photocatalyst and the polyurethane sponge.

[0059] 2. Dynamic analysis of EPS components in biofilm

[0060] By detecting the content of polysaccharides (PS) and proteins (PN) in extracellular polymeric substances (EPS), it was found that... Figure 8 As shown:

[0061] (1) VPCB system: After four cycles, the EPS content was significantly higher than that of the B system. In the VPCB system, the PS content of the biofilm increased, but the PN content decreased. The mechanism of the increase is that the photocatalytic active species and TC synergistically stimulate the microorganisms to secrete EPS, forming a protective barrier.

[0062] (2) System B: EPS increment relies solely on TC stimulation, resulting in limited protective efficacy and insufficient stress resistance of biomembrane.

[0063] 3. Regulation of dehydrogenase activity

[0064] Activity comparisons showed that the dehydrogenase activity of the VPCB system was consistently higher than that of the B system. Figure 9As shown, after four cycles, the dehydrogenase activity in the VPCB system was higher than that in the B system, and the dehydrogenase activity in the B system decreased significantly after each cycle. The main mechanism is that the activity temporarily decreased due to high concentrations of TC and free radical damage in the early stage of photocatalysis, but as the running cycle lengthened, SS / BiOCl drove the dehydrogenase activity to recover and stabilize.

[0065] In summary, the dehydrogenase activity is positively correlated with TOC removal rate, confirming that microbial metabolic activity is the core regulatory factor for the system's mineralization efficiency. Furthermore, the VPCB system maintains high removal efficiency even after multiple cycles. The photocatalytic-biological synergy, through dynamic regulation of EPS secretion and dehydrogenase activity, enables microorganisms to adaptively metabolize photocatalytic byproducts, supporting the long-term stable operation of the system. This characteristic indicates that the VPCB system possesses practical engineering potential in antibiotic wastewater treatment.

[0066] Example 4: The 30SS / BiOCl@PU photocatalytic direct-coupled microbial system, as a novel treatment technology, exhibited excellent performance. The specific mechanism by which this system degrades TC wastewater is a complex and delicate process, such as... Figure 10 As shown, it can be divided into the following key steps:

[0067] 1. Initial stage of photocatalytic reaction: generation of active free radicals. When visible light irradiates the SS / BiOCl photocatalyst supported on the surface of polyurethane sponge, e - The electron is excited and jumps to the CB of the SS, and then undergoes a reduction reaction with the adsorbed O2 to generate O2. ·- , and h + Aggregates on the VB of BiOCl and undergoes an oxidation reaction with adsorbed H2O to generate · The OH group breaks its chemical bonds, gradually degrading it into a series of small molecule intermediates. Compared to the original TC macromolecule, these small molecule intermediates have better biodegradability and lower toxicity.

[0068] 2. Microbial Degradation Stage: Further Decomposition of Intermediate Products. A large number of microorganisms grow and attach within the porous structure of the polyurethane sponge. When small-molecule intermediate products generated by the photocatalytic reaction enter the porous structure of the polyurethane sponge, the microorganisms absorb and utilize them as nutrients. Simultaneously, through their metabolic activities, the microorganisms secrete various enzymes to catalyze the decomposition of the intermediate products. These enzymes can recognize the chemical bonds in the intermediate products and gradually break them, ultimately completely mineralizing the intermediate products into CO2 and H2O. This process not only achieves complete purification of TC wastewater but also provides the energy and material basis for the growth and reproduction of microorganisms.

[0069] 3. Synergistic Effects in the VPCB System: Throughout the VPCB system, microorganisms can utilize the small-molecule intermediates produced by photocatalytic degradation as a nutrient source for growth and reproduction. Photoelectrons generated through photoexcitation also play a crucial role in the system. These photoelectrons can be collected by the microorganisms and used to stimulate their metabolic activities. The injection of photoelectrons can regulate the redox state within microbial cells, enhancing their metabolic activity and chiral tolerance, thus enabling them to better adapt to changes in their surrounding environment.

[0070] Example 5: g-C3N4 nanosheets were used as a photocatalyst and immobilized on the surface of alkaline-treated carbon cloth using a sol-gel method. The composite carrier was placed in a culture medium containing activated sludge to form a biofilm, and then used to treat simulated antibiotic wastewater under visible light irradiation. Experimental results showed that the system achieved a tetracycline degradation rate of over 90%, a mineralization rate of approximately 72%, and maintained relatively stable performance after three cycles.

[0071] Example 6: Nitrogen-doped TiO2 was used as a photocatalyst and loaded onto a porous ceramic honeycomb carrier using an impregnation-calcination method. After surface alkali treatment, the photocatalyst was firmly bonded, and microorganisms easily attached to form a biofilm. Under visible light irradiation, this system showed good removal efficiency for wastewater containing sulfonamide antibiotics, with a degradation rate of up to 88% and a mineralization rate of approximately 70%.

[0072] Example 7: BiOCl was loaded onto the surface of activated carbon particles to prepare a BiOCl / activated carbon composite material, and a photocatalytic-biological direct coupling system was formed by attaching a membrane.

[0073] 1. Carrier pretreatment: The activated carbon particles were immersed in 1 mol / L NaOH solution for 10 h, followed by washing and drying.

[0074] 2. Photocatalyst loading: Activated carbon was impregnated in BiOCl sol solution for 12 h, removed and dried at 100 °C, and then calcined at 400 °C for 2 h to obtain BiOCl / activated carbon composite material.

[0075] 3. Biofilm formation: The composite material is placed in a culture medium containing activated sludge for 15-20 days to form a biofilm, and tetracycline is used as the target pollutant for gradient acclimatization.

[0076] 4. Performance Testing: Under visible light conditions, the system was used to treat 20 mg / L simulated pharmaceutical wastewater. Test results showed that the degradation rate reached 92%, the mineralization rate was approximately 73%, and the system maintained high removal performance after five consecutive operating cycles.

Claims

1. A visible light-driven photocatalysis-biodegradation directly coupled system based on waste industrial steel slag (SS) and a method for constructing the system: comprising a porous carrier, the surface or pores of which are fixed with a visible light-responsive photocatalyst prepared from SS, and a stable biofilm is formed on the surface of the carrier, under visible light irradiation, the photocatalyst and the biofilm are directly coupled through the interface to achieve the degradation and mineralization of organic pollutants.

2. The system according to claim 1, wherein the visible light-responsive photocatalyst is one of BiOCl, g-C3N4, doped TiO2 or a composite thereof, or a combination thereof.

3. The system according to claim 1 or 2, wherein the carrier is a three-dimensional porous polyurethane sponge, carbon cloth, activated carbon or ceramic honeycomb.

4. The system according to any one of claims 1-3, wherein the photocatalyst is loaded on the surface of the carrier by sol-gel method, impregnation method or electrodeposition method, and the loading rate is 5-40wt%.

5. The system according to any one of claims 1-4, wherein the biofilm is obtained by acclimation of activated sludge or target functional microbial community, and the synergistic effect with the photocatalyst is achieved through electron or intermediate product transfer.

6. A method of constructing a system according to any one of claims 1 to 5, characterised in that, comprising the following steps: (1) surface modification treatment of the carrier to introduce hydrophilic functional groups; (2) fixing the visible light-responsive photocatalyst on the surface or pores of the carrier; (3) placing the catalyst-carrier composite in a culture solution containing microorganisms, and under suitable conditions, forming a stable biofilm by biofilm formation and acclimation.

7. The method according to claim 6, wherein step (1) uses an alkaline solution, step (2) uses sol-gel method, and step (3) achieves tolerance acclimation by gradually increasing the concentration of target pollutants.

8. The system or method according to any one of claims 1-7, wherein when treating tetracycline wastewater under visible light irradiation, the degradation rate is not less than 90%, and the mineralization rate is not less than 70%.

9. The system or method according to any one of claims 1 to 8, wherein, The system is suitable for the treatment of pharmaceutical wastewater, antibiotic wastewater and other wastewater containing refractory organic matter.

10. Use of a system according to any one of claims 1 to 9 in the treatment of waste water, characterized in that, It is used to achieve the synergistic degradation and deep mineralization of organic pollutants, and maintain stable performance after multiple cycles.

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