Degradation-resistant wastewater degradation treatment system and method based on photoelectrocatalysis

Abstract

The invention discloses a treatment system and method for photoelectrocatalytic degradation of degradation-resistant organic matter wastewater, and belongs to the field of environmental electrochemical engineering. The system comprises a pretreatment unit, a photoelectric catalytic reaction core unit and a post-treatment unit. A core unit innovatively adopts a three-dimensional porous composite photo-anode and a gas diffusion cathode, so that the problems that a catalyst is easy to lose and inactivate due to pollution and the utilization efficiency of the catalyst and light is low are effectively solved. According to the treatment method, after the pH value of the wastewater is regulated and controlled, under illumination or additional bias voltage, hydroxyl radicals are generated by cooperating with photoelectric oxidation, and a Fenton-like reaction is initiated by in-situ production of hydrogen peroxide by a cathode, so that high-efficiency removal of refractory organic matters is realized. The process technology is simple, the system operation is stable, the energy consumption is low, the secondary pollution is less, and the method is suitable for pretreatment or advanced treatment of Baijiu with different concentrations and different turbidity or other wastewater.

Description

Technical Field

[0001] This invention belongs to the technical field of industrial wastewater treatment and environmental functional materials, specifically relating to an advanced oxidation wastewater treatment system and method, and more particularly to a system and its application method for efficiently degrading high-concentration, recalcitrant organic wastewater using photoelectro-photovoltaic synergistic catalysis technology. Background Technology

[0002] Recalcitrant wastewater typically contains high concentrations of highly toxic and structurally stable organic pollutants, which cannot be effectively removed within a reasonable timeframe using conventional biological treatment methods (such as activated sludge processes). In particular, the production of Baijiu, a traditional Chinese distilled spirit, generates large quantities of complex and highly polluting recalcitrant wastewater during its brewing process. This wastewater primarily originates from the soaking, washing, fermentation, distillation, and equipment rinsing of brewing raw materials. Its typical characteristics include: extremely high chemical oxygen demand (COD), typically reaching 20,000-100,000 mg / L or even higher; acidic pH; and high concentrations of suspended solids (SS), starch, proteins, alcohols, organic acids, esters, aldehydes, and other complex organic matter, as well as nutrients such as nitrogen and phosphorus. A significant amount of lignin, tannins, humic acid, and some synthetic additives are large, recalcitrant organic molecules with low biodegradability (BOD5 / COD), posing a significant challenge to traditional biological treatment methods.

[0003] Currently, the treatment of baijiu (Chinese liquor) brewing wastewater typically employs a combined process of "pretreatment + biological treatment + advanced treatment." Pretreatment often uses methods such as screening, sedimentation, pH adjustment, and flocculation to remove most suspended solids and some colloidal substances. The core biological treatment stage includes anaerobic and aerobic treatment. Advanced treatment is used to address effluent that is difficult to meet standards, and commonly used methods include Fenton oxidation, ozone oxidation, and activated carbon adsorption. However, existing technologies have significant drawbacks: High energy consumption: While anaerobic digestion can produce energy, the aerobic aeration process is extremely energy-intensive; advanced oxidation methods such as the Fenton process require continuous addition of hydrogen peroxide and ferrous salts, and ozone oxidation requires high energy consumption to produce ozone, resulting in high operating costs. Secondary pollution risks: The Fenton process generates a large amount of iron-containing sludge, which is difficult to dispose of; the ozone process may produce toxic byproducts such as bromate; and there are issues with the regeneration or disposal of saturated activated carbon after adsorption. Incomplete treatment: Traditional biological and partial oxidation methods struggle to completely mineralize stable aromatic compounds, heterocyclic compounds, and certain esters in wastewater, often resulting in effluent COD and color failing to consistently meet increasingly stringent discharge standards (such as the "Emission Standard of Water Pollutants for Fermented Alcohol and Baijiu Industry" (GB 27631-2011)). Complex processes and weak resistance to shock loads: Long-process biological systems are sensitive to fluctuations in water quality and quantity, with long start-up and recovery cycles.

[0004] Photoelectrocatalysis (PEC) is an advanced oxidation technology that combines photocatalysis and electrochemistry. Its basic principle is as follows: under light irradiation, a semiconductor catalyst is excited to generate electron-hole pairs; simultaneously, an applied bias voltage forces the photogenerated electrons to migrate to the counter electrode, thereby greatly suppressing electron-hole recombination and allowing more holes to remain on the catalyst surface to participate in the oxidation reaction. These holes and the hydroxyl radicals (·OH) and other strongly oxidizing species they induce can non-selectively and completely oxidize and decompose organic matter into CO2, H2O, and inorganic salts. PEC technology has advantages such as mild reaction conditions, strong oxidation capacity, low secondary pollution, and the ability to utilize solar energy, showing great potential in the treatment of recalcitrant organic wastewater.

[0005] However, although PEC technology has been widely studied in laboratory simulations of wastewater treatment, its direct application to actual liquor industrial wastewater with extremely complex composition, high concentration, and high turbidity still faces significant technical bottlenecks: (1) Catalyst deactivation and contamination: SS, grease, colloids, and macromolecular organic matter present in large quantities in liquor brewing wastewater are easily adsorbed and covered on the catalyst surface, blocking its active sites and pores, leading to rapid catalyst deactivation (i.e., "poisoning"). (2) Mass transfer limitation: The rate at which high-concentration organic pollutants diffuse from the wastewater to the catalyst active sites fixed on the electrode surface often becomes the controlling step of the entire reaction rate. (3) Lack of targeted system design: Existing PEC reactors are mostly designed for low-concentration, clear model pollutants, lacking an integrated system solution that can effectively cope with high-turbidity, easily scaled, multi-component actual industrial wastewater and can operate stably for a long time.

[0006] To date, there have been no reports on the degradation of baijiu brewing wastewater using photoelectrocatalysis. Therefore, developing a photoelectrocatalytic treatment system and method that can overcome the aforementioned bottlenecks, is specifically designed for the characteristics of baijiu brewing wastewater, and is highly efficient, stable, and has relatively low energy consumption is of urgent practical need and significant industrial value. Summary of the Invention

[0007] The primary objective of this invention is to address the shortcomings of existing baijiu wastewater treatment technologies, such as high energy consumption, easy generation of secondary pollution, and incomplete removal of recalcitrant organic matter, by providing a baijiu wastewater degradation treatment system based on photoelectrocatalysis.

[0008] Another objective of this invention is to provide a method for treating liquor wastewater using the above-mentioned system. This method can effectively adapt to the high concentration, high turbidity, and complex composition characteristics of liquor wastewater, achieve efficient degradation and partial mineralization of organic pollutants, improve the biodegradability of wastewater, reduce the subsequent treatment load and overall energy consumption, and ensure stable system operation without generating secondary pollution.

[0009] To achieve the above objectives, the present invention adopts the following technical solution: In the first aspect, the present invention provides a system for the degradation and treatment of liquor wastewater based on photoelectrocatalysis.

[0010] The system mainly includes a pretreatment unit, a core unit for the photoelectrocatalytic reaction, a power supply and control system, a post-treatment unit, and a catalyst regeneration unit. Its core innovation lies in the special design of the core unit for the photoelectrocatalytic reaction, which consists of the following parts: Three-dimensional ordered porous anode module: As the working electrode, its core is a multi-level composite photoanode supported on a conductive substrate (such as titanium mesh or carbon fiber cloth). This photoanode has a multi-level structure of "macroscopic conductive framework - mesoporous TiO2 layer - nano-oxide particle modification". Among them, the macroscopic conductive framework provides mechanical strength and fast electron transport channels; the mesoporous TiO2 layer provides high specific surface area and main catalytic activity; the surface modification components can extend the visible light response range, synergistically promote charge separation and transport, and greatly improve quantum efficiency.

[0011] High-efficiency cathode module: It adopts a gas diffusion electrode (GDE) as the counter electrode, which is composed of hydrophobic carbon cloth, activated carbon catalyst layer and PTFE binder layer. This design not only provides reduction reaction sites, but more importantly, it can efficiently reduce oxygen in the air (or directly introduce oxygen) to H2O2 in situ on the electrode surface, thus constructing an in-situ, mild Fenton-like reaction system.

[0012] Light source module: It adopts a combination of "ultraviolet LED array + visible light LED array + simulated sunlight xenon lamp" light source, which is embedded in the reactor wall or a specially made quartz sleeve. The light source layout has been optimized through optical simulation to ensure uniform light intensity distribution inside the reactor.

[0013] Integrated control module: Includes programmable DC power supply, light intensity sensor, pH meter, oxidation-reduction potential (ORP) probe, and online COD monitor. The system can intelligently adjust the applied bias voltage (0.5-2.5 V), light source intensity, and light ratio according to the influent COD and ORP values ​​to achieve adaptive optimized operation.

[0014] Secondly, the present invention provides a method for degrading liquor wastewater using the above-mentioned system.

[0015] The specific steps of this method are as follows:

[0016] (1) Pretreatment: The collected raw water is passed through a screen to remove large particulate impurities, and then enters a coagulation sedimentation tank. Polyaluminum chloride (PAC) and polyacrylamide (PAM) are added for flocculation and sedimentation to remove most of the suspended solids (SS) and colloidal substances. The supernatant enters an equalization tank, where it is homogenized and the pH is adjusted to a weakly acidic range of 3.0-6.0 (optimal 4.0-5.0) with dilute acid or alkali to facilitate subsequent photoelectrocatalysis and in-situ H2O2 production at the cathode.

[0017] (2) Photoelectrocatalytic degradation: The pretreated wastewater is pumped into the core unit of the photoelectrocatalytic reaction. The composite light source system is turned on. An external bias voltage of 0.8-2.5 V (vs. SCE) is applied. Air or oxygen is continuously introduced into the cathode chamber. The wastewater is circulated in the intelligent flow field, and the hydraulic retention time (HRT) is set to 1-12 hours (optimal 1-4 hours) according to the initial COD concentration.

[0018] During this process, the following synergistic reactions occur: Photoelectro-oxidation: Under illumination and bias voltage, the photoanode generates a large number of holes (h⁺) and ·OH, which directly oxidize and degrade organic matter. In-situ H₂O₂ production and Fenton-like reaction at the cathode: The cathode GDE efficiently reduces O₂ to H₂O₂. Some of the H₂O₂ diffuses into the bulk solution and reacts with a small amount of Fe²⁺ migrating from the photoanode (which may be present in the wastewater itself or introduced in trace amounts) or under ultraviolet light irradiation, undergoing a Fenton-like reaction to produce additional ·OH.

[0019] (3) Post-treatment and water quality adjustment: The effluent after photoelectrocatalytic treatment enters the neutralization sedimentation tank, where the pH is adjusted to 7-8 to precipitate any trace metal ions that may dissolve. Then it enters the rapid sand filter to remove fine flocs. At this point, the COD removal rate of the wastewater can reach 70%-90%, the BOD5 / COD ratio is significantly improved, and the biodegradability is greatly improved.

[0020] (4) Final disposal: The water treated above can be directly discharged into the subsequent standard biological treatment system (such as an aerobic aeration tank) for final treatment to ensure compliance with standards, or further deep treatment (such as ultrafiltration and reverse osmosis) can be carried out according to the reuse standards.

[0021] Compared with the prior art, the present invention has the following beneficial effects:

[0022] (1) High efficiency and thoroughness: The synergistic design of multi-level structure composite photoanode and GDE cathode, combined with photoelectrocatalysis and in-situ Fenton-like reaction, generates an oxidation capacity far exceeding that of single technology (multiple oxide species such as h⁺, ·OH, H2O2, etc.), which can effectively attack and break the complex aromatic rings, heterocycles and long-chain molecules in liquor wastewater, achieving deep oxidation and partial mineralization, and high COD removal rate.

[0023] (2) High energy efficiency and low secondary pollution: The system makes full use of light energy (especially by expanding the use of visible light), requires low external bias voltage, and uses air to produce H2O2 at the cathode, which reduces the cost of adding and transporting chemicals (such as H2O2 and Fe²⁺). The whole process does not produce a large amount of chemical sludge, making it environmentally friendly.

[0024] (3) Improve biodegradability and reduce overall energy consumption: This invention can be used as a highly efficient pretreatment or deep treatment unit. When used as a pretreatment, it can significantly increase the BOD5 / COD value of difficult-to-biodegrade wastewater, creating favorable conditions for subsequent biochemical treatment, thereby reducing the energy consumption and land area of ​​the entire wastewater treatment system. Attached Figure Description

[0025] To more clearly illustrate the technical solutions of the embodiments of this application, the drawings used in the description of the embodiments of this application will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0026] Figure 1 This is a schematic diagram illustrating the mechanism of wastewater degradation in the core unit of the photoelectrocatalytic reaction in this invention.

[0027] Figure 2 This is a scanning electron microscope image of the microstructure of the three-dimensional ordered porous composite photoanode in Example 1.

[0028] Figure 3 This is a comparison chart showing the COD removal rate of the effluent after treating the comprehensive wastewater of a liquor factory using Examples 1-3 and Comparative Examples 1-2. Detailed Implementation

[0029] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of this application. All other embodiments obtained by those skilled in the art based on the embodiments of this application without creative effort are within the scope of protection of this application.

[0030] This embodiment provides a wastewater treatment system based on photoelectrocatalysis and its application in the degradation of liquor wastewater, including the following steps: Example 1: Treatment of rinsing wastewater from high-concentration liquor brewing workshops

[0031] Wastewater characteristics: The sample was taken from a mixture of floor and equipment flushing water from the brewing workshop of a liquor factory. The initial COD concentration was 58,000 mg / L, pH=4.1, dark brown in color, with high suspended solids content and a strong sour odor.

[0032] Pretreatment: After passing through a grid and PAC / PAM coagulation sedimentation, the COD of the supernatant was reduced to 42,000 mg / L and the pH was adjusted to 4.5.

[0033] Photoelectrocatalytic unit: Inlet water flow rate: 2 L / h; Effective reactor volume: 2 L (HRT=4 h); The area of ​​the composite TiO2 photoanode is 16 cm², the area of ​​the gas diffusion cathode is 16 cm², and oxygen is continuously introduced into the cathode chamber; External bias setting: 1.8 V; Light source: Ultraviolet (365 nm, light intensity 50 mW / cm²) + visible light (450 nm, light intensity 50 mW / cm²) combination.

[0034] Treatment results: The COD of the treated effluent decreased to 5,250 mg / L, with a removal rate of 87.5%. The wastewater color turned light yellow, and the odor was basically eliminated. The BOD5 / COD ratio increased from 0.25 in the influent to 0.52, and the biodegradability was fundamentally improved.

[0035] Stability test: The system ran continuously for 120 hours (with the catalyst automatically regenerated every 36 hours during this period), and the COD removal rate of the effluent remained between 83% and 86%, indicating that the system has excellent operational stability. Example 2: Treatment of mixed wastewater from a medium-concentration liquor factory

[0036] Wastewater characteristics: Wastewater (containing a mixture of yellow water, bottom water, and domestic sewage) was taken from the integrated regulating tank of a liquor factory. The initial COD concentration was 12,500 mg / L, pH=5.2, and the color was brownish-yellow.

[0037] Pretreatment: COD was 9,800 mg / L after coagulation and sedimentation, and pH was adjusted to 5.0.

[0038] Photocatalytic unit: HRT shortened to 2 h. Applied bias voltage reduced to 1.2 V. Light intensity correspondingly lowered (40 mW / cm² for UV, 40 mW / cm² for visible light). Other parameters are the same as in Example 1.

[0039] Treatment results: The COD of the treated effluent decreased to 1,550 mg / L, with a removal rate of 84.2%. The effluent was clear and transparent.

[0040] Energy consumption analysis: The power consumption (including light source, water pump, and power supply) per ton of water treated in this embodiment is approximately 18-22 kWh. Compared to the traditional Fenton oxidation method (costing approximately 80-120 RMB per ton of reagents, and translating to higher power consumption) required to reduce the COD of wastewater from 9,800 mg / L to 1,550 mg / L, this method is economically competitive and eliminates the sludge disposal problem. Example 3: Treatment of biological wastewater as an advanced treatment unit

[0041] Wastewater characteristics: The wastewater was taken from the secondary sedimentation tank of a liquor wastewater treatment plant using the "UASB+A / O" process. The COD was 380 mg / L (close to the discharge standard limit but with large fluctuations), the color was 70 times higher, and it contained humic acid substances that are difficult to degrade.

[0042] System operating parameter adjustment: Pretreatment: Only the fine biological flocs need to be removed by the security filter, the pH is about 4.2, and no adjustment is required.

[0043] Photoelectrocatalytic unit: HRT set to 1 h. A low external bias voltage of 0.8 V is used. The main source is the visible light source (100 mW / cm²), utilizing the largest portion of the solar spectrum to save energy.

[0044] Treatment results: The COD of the treated effluent remained stable below 85 mg / L (meeting direct discharge standards), with a removal rate of 77.6%. Color was reduced to less than 5 times the standard. The power consumption per ton of water treated was only 6-8 kWh, demonstrating its extremely high efficiency and economy in the field of advanced water treatment. Comparative Example 1: Using the same photoanode as in Example 1, but without applying an external bias voltage (i.e., pure photocatalytic mode).

[0045] Using the exact same system configuration and batch of pretreated wastewater as in Example 1, but without applying an external bias voltage, the same batch of pretreated wastewater (COD 42,000 mg / L) was treated. After 4 hours of HRT, the effluent COD was 25,600 mg / L, with a removal rate of only 39.0%. Furthermore, after only 2 hours of operation, the photoanode surface was severely covered with dark contaminants, and the efficiency dropped sharply. This comparison demonstrates that an applied bias voltage is crucial for suppressing charge recombination and maintaining catalyst activity. Comparative Example 2: Using the system of Example 1, but with all light sources turned off (i.e., pure electrocatalytic mode).

[0046] Using the exact same system configuration and batch of pretreated wastewater as in Example 1, but with all UV and visible light sources turned off, the COD of the treated effluent was 29,500 mg / L, with a removal rate of approximately 29.8%. This result indicates that, under light-free conditions, the system's ability to oxidize and degrade high-concentration liquor wastewater by relying solely on electrochemical oxidation is significantly weakened. This demonstrates that photoexcitation is indispensable for generating sufficient photogenerated holes and hydroxyl radicals to achieve efficient degradation, and also highlights the necessity and superiority of the photoelectric synergistic effect of this invention.

[0047] The above embodiments and comparative examples fully demonstrate that the system and method provided by the present invention can effectively adapt to different concentrations of liquor wastewater, and have comprehensive advantages in efficient COD degradation, improved biodegradability, stable operation and reduced secondary pollution, providing an innovative and feasible technical path for solving the problem of high-concentration organic wastewater treatment in the liquor industry.

Claims

1. A system for treating recalcitrant organic wastewater based on photoelectrocatalysis, characterized in that, include: The pretreatment unit, the photoelectrocatalytic reaction core unit, and the posttreatment unit are connected in sequence, along with a power supply and control system that supplies power to the core unit.

2. A photoelectrocatalytic degradation system for treating recalcitrant organic wastewater, characterized in that, The core unit of the photoelectrocatalytic reaction includes: A three-dimensional porous anode module, located inside the reactor, includes a conductive substrate and a composite photoanode material loaded thereon; The cathode module, disposed opposite to the anode module, is a gas diffusion electrode; The light source module includes an array of sunlight, visible light, or ultraviolet light sources, which can uniformly illuminate the anode module.

3. The system according to claims 1 and 2, characterized in that, The composite photoanode material has a three-dimensional porous structure with a high specific surface area; the gas diffusion electrode has a multi-layer structure including a hydrophobic layer, a catalytic layer and a current collection layer, and its catalytic layer contains carbon and a catalyst.

4. The system according to claim 1, characterized in that, The power supply and control system includes a programmable DC power supply and a power management system that dynamically adjusts the power supply based on the magnitude of the photocurrent.

5. A method for degrading recalcitrant organic wastewater using the system described in any one of claims 1 to 4, characterized in that, Includes the following steps: Step 1, Pretreatment: The wastewater containing recalcitrant organic matter is passed through a screen for interception and coagulation sedimentation to remove suspended solids and colloids, and the pH is adjusted to a slightly acidic range of 3.0-6.0; Step 2, photoelectrocatalytic degradation: The pretreated wastewater is pumped into the core unit of the photoelectrocatalytic reaction, an external bias voltage is applied between the anode module and the cathode module, and oxygen-containing gas is introduced into the cathode module; Step 3, post-treatment: The effluent after photoelectrocatalytic treatment is neutralized and subjected to solid-liquid separation to obtain effluent with improved biodegradability.

6. The method according to claim 5, characterized in that, In step two, the applied bias voltage is 0.8-2.5V; the oxygen-containing gas is air or oxygen.

7. The method according to claim 5, characterized in that, In step two, the anode module generates hydroxyl radicals through in-situ photoelectric oxidation, and the cathode module generates atomic oxygen through in-situ electroreduction to induce a Fenton-like reaction.

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