Method for degrading COD of wastewater by bioactive carbon reinforced fenton reaction

Abstract

This invention discloses a wastewater COD degradation method using biological activated carbon to enhance the Fenton reaction, relating to the field of wastewater treatment combined with biological activated carbon technology. The method involves adding biological activated carbon and Fe to the wastewater to be treated. 2+ The source and H2O2 are mixed thoroughly, and the pH value of the wastewater to be treated is controlled at 3-7; the dosage of biological activated carbon is 0.3g-0.9g per liter of wastewater to be treated; Fe 2+ The amount of source added is based on Fe 2+ The dosage is calculated as 1.6 mmol to 2.7 mmol per liter of wastewater to be treated; the dosage of H2O2 (30% w / w) is 0.4 mL to 0.6 mL per liter of wastewater to be treated; and the bio-activated carbon meets the following conditions: (1) the surface carbonyl (C=O) content determined by C1s peak analysis by X-ray photoelectron spectroscopy (XPS) is not less than 11 Atomic%; (2) the intensity ratio of D peak to G peak (ID / IG) in Raman spectrum is calculated according to the formula nD=(1.8±0.5)×10²²×(ID / IG) / λL. 4 The calculated carbon defect density is not less than 2.2 × 10⁻⁶. 11 / cm², where λL is the excitation laser wavelength in nm; (3) conductivity not less than 1.8 S / cm. This can significantly improve the efficiency of the Fenton reaction.

Description

Technical Field

[0001] This invention relates to the field of wastewater treatment combined with biological activated carbon technology, specifically to a wastewater COD degradation method based on biological activated carbon-enhanced Fenton reaction. Background Technology

[0002] Currently, many wastewater treatment plants adopt a "two-stage biological treatment" approach, which includes two main stages: the primary treatment stage uses physical methods, such as bar screens to intercept large particles of impurities, grit removal in grit chambers, and sedimentation in primary sedimentation tanks to settle suspended solids; then, the core biological treatment stage is entered, where activated sludge or biofilm processes are applied to degrade organic pollutants into cellular material, carbon dioxide, and water in aerobic / anaerobic biological tanks; finally, the treated sludge is separated from the purified water in the secondary sedimentation tank. This complete process can remove most of the COD (Chemical Oxygen Demand, representing the amount of organic matter in water that can be chemically oxidized). However, for recalcitrant organic matter in industrial wastewater, the COD concentration after secondary biological treatment often fails to meet the Class A standard of the "Discharge Standard of Pollutants for Municipal Wastewater Treatment Plants (GB 18918-2002)" or the Class IV water quality standard of the "Environmental Quality Standard for Surface Water (GB 3838-2002)". Therefore, wastewater treatment plants that need to treat this type of industrial wastewater urgently need to be upgraded and transformed, that is, to add advanced treatment on the basis of the original secondary biological treatment.

[0003] Activated carbon adsorption and Fenton oxidation are the most common advanced treatment processes combined with biochemical treatment. However, both technologies have certain technical bottlenecks in practical applications. For example, activated carbon adsorption is limited by low COD removal rates (20%-40%) or high activated carbon dosages (1g / L-5g / L). Fenton oxidation has strict pH limitations and requires specific Fe content. 2+ The difficulties in regeneration and the large amount of iron sludge generated limit its practical application. Summary of the Invention

[0004] The inventors noted that bio-activated carbon has a large number of electron donors dispersed on its surface, such as oxygen-containing functional groups, persistent free radicals, and defect structures. Furthermore, biochar possesses advantages such as low preparation cost, wide availability, and eco-friendliness. These characteristics endow biochar with great potential as a co-catalyst to enhance the Fenton reaction. Inspired by this fact, the inventors investigated the feasibility of combining bio-activated carbon with Fenton technology to improve the efficiency of the Fenton reaction. Specifically, by exploring the sources of bio-activated carbon's enhanced Fenton reaction efficiency, they elucidated the co-catalytic mechanism of various bio-activated carbon parameters in the Fenton system. In addition, they investigated important operating parameters of bio-activated carbon in the Fenton system (such as bio-activated carbon dosage, H₂O₂ dosage, Fe...). 2+ The effects of dosage and pH value on COD degradation in wastewater were investigated. This led to the present invention. The purpose of this invention is to provide a wastewater COD degradation method that enhances the Fenton reaction using biological activated carbon, thus solving the technical problem of improving Fenton reaction efficiency.

[0005] This invention provides a wastewater COD degradation method using biological activated carbon to enhance the Fenton reaction. The method involves adding biological activated carbon and Fe2O3 to the wastewater to be treated. 2+ The source and H2O2 are mixed thoroughly, and the pH value of the wastewater to be treated is controlled at 3-7. The dosage of biological activated carbon is 0.3g-0.9g per liter of wastewater to be treated; Fe 2+ The amount of source added is based on Fe 2+ The concentration is calculated to be 1.6 mmol - 2.7 mmol per liter of wastewater to be treated; The dosage of H2O2 (30% w / w) is 0.4 mL to 0.6 mL per liter of wastewater to be treated; Furthermore, the bio-activated carbon meets the following conditions: (1) The surface carbonyl (C=O) content, as determined by C1s peak analysis of X-ray photoelectron spectroscopy (XPS), is not less than 11 Atomic% (2) Based on the intensity ratio of the D peak to the G peak in the Raman spectrum (ID / IG), the formula nD = (1.8 ± 0.5) × 10²² × (ID / IG) / λL is used. 4 The calculated carbon defect density is not less than 2.2 × 10⁻⁶. 11 / cm², where λL is the excitation laser wavelength in nm; (3) The electrical conductivity is not less than 1.8 S / cm.

[0006] Optionally, the dosage of biological activated carbon is 0.25g-0.35g per liter of wastewater to be treated.

[0007] Optional, Fe 2+Source addition amount according to Fe 2+ The concentration is calculated to be 2.0 mmol to 2.3 mmol per liter of wastewater to be treated.

[0008] Optionally, the dosage of H2O2 (30% w / w) is 0.35 mL to 0.45 mL per liter of wastewater to be treated.

[0009] Optionally, the wastewater to be treated is wastewater whose COD concentration after secondary biological treatment does not meet the Class A standard of "Discharge Standard of Pollutants for Urban Wastewater Treatment Plants (GB 18918-2002)" or the Class IV water quality standard of "Environmental Quality Standard for Surface Water (GB 3838-2002)".

[0010] Optional, Fe 2+ The source is FeSO4·7H2O.

[0011] Optionally, the surface carbonyl (C=O) content of the bio-activated carbon, as determined by C1s peak analysis using X-ray photoelectron spectroscopy (XPS), is no higher than 18 Atomic%, and the carbon defect density nD is no higher than 2.8 × 10⁻⁶. 11 / cm², conductivity not higher than 2.6S / cm.

[0012] Optionally, the surface carbonyl (C=O) content of the bio-activated carbon, as determined by C1s peak analysis of X-ray photoelectron spectroscopy (XPS), is 12-15 Atomic.

[0013] Optionally, the carbon defect density nD of the bio-activated carbon is 2.3 × 10⁻⁶. 11 / cm²-2.5×10 11 / cm².

[0014] Optionally, the bio-activated carbon has an electrical conductivity of 2-2.2 S / cm.

[0015] This invention cleverly combines bio-activated carbon with specific performance indicators (surface carbonyl content ≥11 Atomic%, carbon defect density ≥2.2×10¹¹ / cm², electrical conductivity ≥1.8 S / cm) with Fenton technology. Under a wide pH range of 3-7, only a low dosage is required (bio-activated carbon 0.3 g / L - 0.9 g / L, Fe...). 2+ The concentrations of 1.6 mmol / L to 2.7 mmol / L and H₂O₂ (0.4 mL / L to 0.6 mL / L) can significantly improve the efficiency of the Fenton reaction, effectively solving the problems of strict pH limitations and Fe content in the traditional Fenton method. 2+Technical bottlenecks such as regeneration difficulties and large amounts of iron sludge generated, as well as the low COD removal rate or high dosage requirements of conventional activated carbon adsorption methods, provide a new, efficient, economical, and environmentally friendly technological path for the deep treatment of industrial wastewater. This allows the effluent after secondary biological treatment to stably meet the Class A standard of the "Discharge Standard of Pollutants for Municipal Wastewater Treatment Plants (GB 18918-2002)" or even the Class IV water quality standard of the "Environmental Quality Standard for Surface Water (GB 3838-2002)".

[0016] The present invention will be further described below with reference to the accompanying drawings and specific embodiments. Additional aspects and advantages provided by the present invention will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice. Attached Figure Description

[0017] The accompanying drawings, which form part of this specification, are used to aid in understanding the invention. The contents provided in the drawings and their related descriptions in this specification can be used to explain the invention, but do not constitute an undue limitation of the invention.

[0018] Figure 1 This diagram illustrates the factors influencing COD removal in BAC-Fenton reaction-degraded wastewater. (a) represents the relationship between H₂O₂ dosage and COD removal rate; (b) represents the relationship between FeSO₄·7H₂O dosage and COD removal rate; (c) represents the relationship between BAC dosage and COD removal rate; and (d) represents the relationship between pH value and COD removal rate.

[0019] Figure 2 The correlation analysis diagrams for BAC samples and COD removal rate are shown. (a) shows the correlation between BAC sample specific surface area (SBET) and COD removal rate; (b) shows the relationship between BAC sample average pore size (D) and COD removal rate; (c) reflects the relationship between BAC surface carboxyl group (C=O) content and COD removal rate; (d) shows the correlation between BAC surface OCO bond content and COD removal rate; (e) shows the relationship between BAC surface carbon defect density (ID / IG) and COD removal rate; and (f) reflects the relationship between BAC electrical conductivity and COD removal rate.

[0020] Figure 3 Fe 2+ / Fe 3+ The concentration change graph shows that the horizontal axis represents time (min) and the vertical axis represents Fe. 3+ / Fe 3+ Concentration (mg / L). Operating parameters: pH=3, BAC=0.3g / L, H2O2 (30% w / w)=0.3ml / L, FeSO4·7H2O=0.3g / L, BAC sample BAC-6 was used. Wherein, (a) represents Fe2+ (a) represents the / H2O2 system; (b) indicates BAC / Fe 2+ / H2O2 system.

[0021] Figure 4 This graph compares the COD degradation effects of different solution systems. The horizontal axis represents time (min), and the vertical axis represents the COD removal rate.

[0022] Figure 5 For BAC / Fe 2+ A free radical quenching experiment was conducted on the / H2O2 system. The horizontal axis represents time (min), and the vertical axis represents the COD removal rate.

[0023] Figure 6 This is a comparison of ESR signal intensities in the BAC / H₂O₂ system DMPO₄·OH. The horizontal axis represents magnetic field strength, in units of 10⁻⁶. -4 Tesla (T), with the vertical axis representing the strength of the ESR signal.

[0024] Figure 7 for Figure 6 BAC / Fe 2+ Comparison of ESR signal intensities for the DMPO-·OH system in the / H2O2 system. The horizontal axis represents magnetic field strength, in units of 10⁻⁶. -4 Tesla (T), with the vertical axis representing the strength of the ESR signal.

[0025] Figure 8 Fe 2+ / H2O2 system and BAC / Fe 2+ Comparison of (a) sedimentation performance and (b) effluent of the / H2O2 system. Detailed Implementation

[0026] The present invention will now be clearly and completely described in conjunction with the accompanying drawings. Those skilled in the art will be able to implement the present invention based on these descriptions. Before describing the present invention in conjunction with the accompanying drawings, it should be particularly noted that: The technical solutions and features provided in the various sections, including the following description, can be combined with each other without conflict. Furthermore, where possible, these technical solutions, features, and related combinations can be given specific technical subject matter and protected by relevant patents.

[0027] The embodiments of the present invention described below are generally only some embodiments and not all embodiments. Based on these embodiments, all other embodiments obtained by those skilled in the art without creative effort should fall within the scope of patent protection.

[0028] The terms "comprising," "including," "having," and any variations thereof in this specification, the corresponding claims, and related sections are intended to cover non-exclusive inclusion. Other related terms and units can be reasonably interpreted based on the relevant content provided in this specification.

[0029] I. The bio-activated carbon used in the basic research of this invention The fundamental research of this invention utilizes a segmented pyrolysis activation method to prepare bio-activated carbon (BAC). Nan bamboo (Phyllostachys edulis) was selected as the raw material due to its unique chemical composition and structural characteristics: the high cellulose content (approximately 45%-55% dry weight), hemicellulose (20%-25% dry weight), and low lignin content (20%-25% dry weight) composition is conducive to forming a high-carbon skeleton; its naturally present inorganic elements such as silicon and potassium (approximately 1.5%-2.5% dry weight) act as activators during pyrolysis, promoting pore development; and the unique ordered parallel fiber structure of Nan bamboo helps form a continuous carbon network, determining the final electrical conductivity of the BAC. Combined with the characteristics of Nan bamboo's short growth cycle (4-5 years to mature), strong regeneration ability, and abundant resources, it becomes an ideal biomass precursor for preparing the high-performance bio-activated carbon applicable to this invention.

[0030] The specific preparation process is as follows: First, the bamboo blocks are thoroughly washed with distilled water and dried to remove surface impurities. Then, the pretreated bamboo blocks are placed in a carbonization furnace for initial pyrolysis carbonization at two different temperatures (500℃ and 600℃) and held for 2 hours at a heating rate of 5℃ / min to obtain preliminary carbonized products. Next, the preliminary carbonized products undergo secondary pyrolysis activation at three different temperatures (600℃, 700℃, and 800℃) while simultaneously introducing 20% ​​(by volume) water vapor. The heating rate is maintained at 5℃ / min, and the temperature is held for 3 hours. Nitrogen gas is introduced throughout the secondary pyrolysis activation stage to maintain an inert atmosphere. Finally, the obtained products are sieved through a 150-200 mesh sieve, yielding six bio-activated carbon (BAC) samples prepared under different conditions, providing bio-activated carbon for subsequent experiments. The six BAC samples are shown in Table 1.

[0031] It should be noted that the above preparation method is designed based on the inventors' judgment that bio-activated carbon contains a large number of electron donors, including oxygen-containing functional groups, persistent free radicals, and defect structures. These characteristics endow bio-activated carbon with great potential as an auxiliary catalyst to enhance the Fenton reaction. Meanwhile, the selection of bamboo as a raw material has clear structural orientation: its high cellulose content provides abundant oxygen-containing functional group precursors during pyrolysis; its unique ordered fiber structure is conducive to the formation of a carbon skeleton with good electrical conductivity; its low lignin content reduces secondary condensation reactions during pyrolysis, which is beneficial to maintaining the defect structure of the carbon skeleton; and the naturally present metal elements can serve as catalytic sites to promote the formation of carbonyl functional groups.

[0032] Furthermore, this invention's fundamental research also analyzes the impact of different primary pyrolysis carbonization temperatures and secondary pyrolysis activation temperatures on the Fenton reaction by precisely controlling parameters such as the surface carbonyl (C=O) content, carbon defect density, and conductivity of bio-activated carbon. This is a practical contribution of this invention. The primary pyrolysis carbonization temperature determines the formation state of the basic carbon skeleton, while the secondary pyrolysis activation temperature, combined with steam activation, dominates the type and quantity of surface functional groups, the formation of carbon skeleton defects, and the development of the electron conduction network. In particular, the secondary pyrolysis temperature in the high-temperature range (700-800℃) can simultaneously optimize these three performance indicators. This process design not only fully utilizes the structural and compositional advantages of bamboo biomass but also, through precise control of key structural parameters, allows for a more in-depth study of how BAC can improve the Fenton reaction efficiency under mild conditions.

[0033] Table 1: Six types of BAC samples used in the experiment BAC-1 500 600 <![CDATA[Moso bamboo blocks → washing and drying → primary pyrolysis at 500 °C (5 °C / min, 2 h) → secondary pyrolysis activation at 600 °C (5 °C / min, 3 h, 20% water vapor, N2 protection) → screening of 150 - 200 mesh]]> BAC-2 500 700 <![CDATA[Moso bamboo blocks → washing and drying → primary pyrolysis at 500 °C (5 °C / min, 2 h) → secondary pyrolysis activation at 700 °C (5 °C / min, 3 h, 20% steam, protected by N2) → screening with 150 - 200 mesh]]> BAC-3 500 800 <![CDATA[Moso bamboo blocks → washing and drying → primary pyrolysis at 500 °C (5 °C / min, 2 h) → secondary pyrolysis activation at 800 °C (5 °C / min, 3 h, 20% water vapor, N2 protection) → screening of 150 - 200 mesh]]> BAC-4 600 600 <![CDATA[Moso bamboo blocks → washing and drying → primary pyrolysis at 600 °C (5 °C / min, 2 h) → secondary pyrolysis activation at 600 °C (5 °C / min, 3 h, 20% steam, N2 protection) → screening with 150 - 200 mesh]]> BAC-5 600 700 <![CDATA[Moso bamboo blocks → washing and drying → primary pyrolysis at 600 °C (5 °C / min, 2 h) → secondary pyrolysis activation at 700 °C (5 °C / min, 3 h, 20% steam, N2 protection) → screening of 150 - 200 mesh]]> BAC-6 600 800 <![CDATA[Moso bamboo blocks → washing and drying → primary pyrolysis at 600°C (5°C / min, 2 h) → secondary pyrolysis activation at 800°C (5°C / min, 3 h, 20% steam, N2 protection) → screening of 150 - 200 mesh]]> II. Research Methods 2.1 The wastewater used in the experiment was taken from the effluent of a wastewater treatment plant in a pharmaceutical industrial park in Sichuan Province after secondary biological treatment. The characteristics of the effluent after secondary biological treatment were that the ammonia nitrogen, total nitrogen, and total phosphorus were basically up to standard, but the COD was around 130 mg / L-150 mg / L, and this part of the COD was dissolved recalcitrant organic matter.

[0034] 2.2 Experimental Procedure 2.2.1 Using sample BAC-6 and FeSO4·7H2O (as Fe...) 2+Using H2O2 (30% w / w), H2SO4, and NaOH as raw materials, the effects of H2O2 dosage, FeSO4·7H2O dosage, BAC dosage, and pH value on COD degradation efficiency were investigated. The experiments were conducted in 500 mL beakers. First, the reaction was carried out for 60 min with stirring in a six-stage coagulator (300 r / min, T=25℃). After the reaction was completed at a selected time point, the pH was adjusted to approximately 7-8 with 0.1 mol / L NaOH. Then, the supernatant was collected to determine the outlet COD concentration, and the degradation effects of different systems on COD were compared. The experimental conditions for each single factor are as follows: (1) Single-factor experiment on H2O2 dosage Fixed conditions: FeSO4·7H2O dosage 0.6 g / L (meaning 0.6 g per liter of wastewater, the same below), BAC dosage 0.5 g / L, pH value 3; Variable levels: H2O2 (30% w / w) dosage (mL / L) 0.2, 0.4, 0.6, 0.8, 1.0.

[0035] (2) Single-factor experiment on FeSO4·7H2O dosage Fixed conditions: H2O2 (30% w / w) dosage 0.4 mL / L, BAC dosage 0.5 g / L, pH value 3; Variable levels: FeSO4·7H2O dosage (g / L) 0.2, 0.4, 0.6, 0.8, 1.0.

[0036] (3) Single-factor experiment on BAC dosage Fixed conditions: H2O2 (30% w / w) dosage 0.4 mL / L (meaning 0.4 mL per liter of wastewater), FeSO4·7H2O dosage 0.6 g / L, pH value 3; Variable levels: BAC dosage (g / L) 0.1, 0.3, 0.5, 0.7, 0.9.

[0037] (4) Single-factor experiment on pH value Fixed conditions: H2O2 (30% w / w) dosage 0.4 mL / L, FeSO4·7H2O dosage 0.6 g / L, BAC dosage 0.5 g / L; Variable levels: pH 3, 4, 5, 6, 7.

[0038] The specific operating steps are as follows: (1) Measure 500 mL of the wastewater to be treated into a beaker; (2) Adjust the initial pH of the wastewater to the set value according to the experimental design; (3) Add the measured amount of BAC to the wastewater; (4) Add the pre-weighed FeSO4·7H2O; (5) Slowly add the metered H2O2 (30% w / w) while stirring; (6) Stir the mixture at 300 r / min at 25°C for 60 min on a six-unit coagulator; (7) After the reaction is complete, adjust the pH to 7-8 with 0.1 mol / L NaOH to terminate the reaction; (8) Let stand for 30 minutes to allow the precipitate to form fully; (9) After filtering the supernatant, the COD concentration was measured; (10) Calculate the COD removal rate and perform data analysis and chart plotting (e.g.) Figure 1 (As shown).

[0039] Each experiment was repeated three times, and the average value was taken. The optimal conditions for COD degradation of wastewater by the BAC-Fenton reaction were determined through single-factor experiments, providing a basis for subsequent process optimization.

[0040] Figure 1 This is a diagram showing the factors influencing COD in wastewater from the BAC-Fenton reaction degradation. (Based on...) Figure 1 As shown, with the increase of H2O2 (30% w / w) dosage, the COD degradation efficiency first increases and then decreases. This is attributed to the fact that the increased H2O2 (30% w / w) dosage generates more active free radicals, leading to faster COD degradation. However, when the concentration increases to above 0.4 mL / L, the COD removal efficiency no longer increases. This can be attributed to the fact that excess H2O2 acts as a free radical scavenger during the catalytic reaction, reducing the ·OH generated in the reaction and thus inhibiting COD degradation. Therefore, the H2O2 (30% w / w) dosage can be controlled at 0.4 mL-0.6 mL per liter of wastewater to be treated, more preferably at 0.35 mL-0.45 mL per liter of wastewater to be treated (0.4 mL is optimal).

[0041] With increasing FeSO4·7H2O dosage, COD removal efficiency first increases and then decreases. Studies suggest that the rate of •OH generation within the system increases with increasing Fe... 2+ The concentration increases, and the catalytic efficiency also improves. When Fe... 2+ When the concentration is too high, H2O2 will be rapidly decomposed into ·OH, which cannot react with organic matter in time, resulting in ineffective decomposition of H2O2. Furthermore, excessive iron ions can aggregate with BAC, leading to poorer COD degradation. Therefore, the dosage of FeSO4·7H2O should be 0.6 g / L (equivalent to Fe...). 2+ The optimal concentration is 2.16 mmol / L. This allows Fe to... 2+ The dosage of the source was set at 1.6 mmol / L - 2.7 mmol / L, i.e., Fe2+ A concentration of 1.6 mmol to 2.7 mmol per liter of wastewater is sufficient to ensure adequate catalytic activity while avoiding excessive Fe. 2+ This leads to adverse effects such as ineffective H2O2 decomposition and aggregation with BAC. More preferably, Fe... 2+ Source addition amount according to Fe 2+ The concentration of the wastewater to be treated is estimated at 2.0 mmol to 2.3 mmol per liter.

[0042] When the BAC dosage is around 0.3 g / L-0.9 g / L, COD can be reduced to below 30 mg / L, meeting the Class IV water quality standard of the "Surface Water Environmental Quality Standard (GB 3838-2002)". With increasing BAC dosage, the COD removal efficiency initially increases and then slows down. This is because with increased BAC dosage, more active sites in the system activate hydrogen peroxide to produce ·OH, and accelerate the removal of Fe... 3+ / Fe 2+ The conversion of BAC increases the catalytic reaction rate. With further increases in BAC dosage, the COD removal rate essentially balances out, possibly because excess BAC removes some free radicals, and the active sites decrease due to copolymerization. Therefore, 0.3 g / L of BAC is considered the optimal dosage combining economic efficiency and COD removal effectiveness. This can be reasonably extended to: 0.25 g - 0.35 g of biological activated carbon per liter of wastewater to be treated.

[0043] The COD removal rate can reach about 75% within a wide pH range of 3-7, proving that the system can achieve ideal catalytic degradation effect on COD in both acidic and neutral solutions, and the system has a wide applicable pH range.

[0044] 2.2.2 Based on the optimal operating parameters determined in Section 2.2.1, enhanced Fenton performance tests were conducted on the remaining five BAC samples (using the same test method as above) to obtain their respective COD removal rates (Qmax). Then, the correlation between the specific surface area (SBET), average pore size (D), carboxyl (C=O) content, OCO bond content, carbon defect density (ID / IG), and conductivity of each BAC sample and its COD removal efficiency was investigated.

[0045] Based on the optimal operating parameters determined in Section 2.2.1: (1) H2O2 (30% w / w) dosage: 0.4 mL / L; (2) FeSO4·7H2O dosage: 0.6 g / L; (3) BAC dosage: 0.3 g / L; (4) Initial pH value: 3.

[0046] The specific surface area (SBET), average pore size (D), carboxyl (C=O) content, OCO bond content, carbon defect density (ID / IG), and conductivity of the BAC samples were characterized as follows: the surface carbonyl (C=O) content was determined by C1s peak analysis using X-ray photoelectron spectroscopy (XPS); the surface OCO bond content was determined by C1s peak analysis using X-ray photoelectron spectroscopy (XPS); the conductivity of the material was determined using a conductivity meter; and the carbon defect density of the BAC surface was analyzed using Raman spectroscopy. Raman analysis was performed using a RAMHR800 Raman spectrometer in a confocal microscopy laboratory, equipped with a 532 nm laser. The carbon defect density (nD, cm⁻¹) of the BAC surface was measured. -2 The formula for calculating nD is nD = (1.8 ± 0.5) × 10²² × (ID / IG) / λL. 4 λL (nm) is the excitation laser wavelength. The characterization results of the BAC samples, including specific surface area (SBET), average pore size (D), carboxyl (C=O) content, OCO bond content, carbon defect density (ID / IG), and electrical conductivity, are shown in Table 2.

[0047] Table 2: Characteristic parameters of the six BAC samples used in the experiment BAC-1 300 4.63 5.8 9.2 1.70 1.07 54.9 BAC-2 690 4.24 9.0 11.3 2.10 1.12 61.5 BAC-3 530 4.82 10.9 16.4 2.22 2.17 75.0 BAC-4 548 2.61 6.0 10.3 2.08 1.10 57.2 BAC-5 956 4.35 10.2 12.2 2.20 1.88 64.7 BAC-6 1550 2.22 16.3 11.4 2.65 2.48 78.8 After obtaining the COD removal rate (Qmax) of each BAC sample, linear regression equations were established between the specific surface area (SBET), average pore size (D), carboxyl (C=O) content, OCO bond content, carbon defect density (ID / IG), and conductivity of the BAC samples and the COD removal rate. The coefficient of determination (R²) was analyzed to determine the correlation strength, and a correlation diagram was plotted (e.g., Figure 2 As shown in the figure, the regression equation and R² value are labeled.

[0048] Figure 2 This is a correlation analysis graph showing the relationship between BAC samples and COD removal efficiency. (Example:) Figure 2 As shown, Figure 2 (a) shows the correlation between the specific surface area (SBET) of BAC samples and the COD removal rate. As can be seen from the figure, the COD removal rate shows a slight decreasing trend with increasing specific surface area (SBET), but the correlation is very small (R² = 0.06571). This indicates that in the BAC-enhanced Fenton reaction system, the specific surface area of ​​BAC has little effect on the COD removal efficiency.

[0049] Figure 2(b) shows the relationship between the average pore size (D) of the BAC samples and the COD removal rate. The results show that the COD removal rate decreases slightly with increasing pore size (y=-1.5742x+70.5014), but the correlation is also very weak (R²=0.0373). This indicates that the average pore size (D) of BAC has little effect on the COD removal efficiency.

[0050] Figure 2 (c) This reflects the relationship between the carboxyl (C=O) content on the BAC surface and the COD removal rate. The results show a significant positive correlation between the two (R² = 0.8739), with the COD removal rate increasing significantly with increasing carboxyl content (y = 2.3133x + 42.3315). This indicates that carboxyl groups are important active sites on the BAC surface, and it is believed that C=O promotes Fe removal through π-electron withdrawal. 3+ / Fe 2+ Cyclic reactions enhance the efficiency of the Fenton reaction. Therefore, BAC-mediated Fe... 3+ / Fe 2+ Redox cycles can be achieved in Fenton-like systems via donor-acceptor coupling, thereby improving Fe... 3+ Reduction and H2O2 utilization efficiency.

[0051] Figure 2 (d) indicates the correlation between the OCO bond content on the BAC surface and the COD removal rate. The results show that the COD removal rate increases with increasing OCO content (y=2.5767x+34.3540), but the correlation is also low (R²=0.4773).

[0052] Figure 2 (e) The relationship between BAC surface carbon defect density (ID / IG) and COD removal rate is shown. The results indicate a strong positive correlation (R² = 0.8363), with COD removal rate significantly increasing with increasing defect density (y = 26.703x + 9.267). This suggests that BAC surface carbon defect density is a core structural feature determining the catalytic activity of BAC. The study suggests that the carbon defect density on the BAC surface plays a crucial role in the catalytic activity of Fe... 3+ It plays a crucial role in the restoration process.

[0053] Figure 2 (f) reflects the relationship between BAC conductivity and COD removal rate. The results show a strong positive correlation between the two (R² = 0.750), with COD removal rate significantly increasing with increasing conductivity (y = 12.118x + 43.84). This indicates that the electron transport capacity of BAC has a significant impact on catalytic performance, and BAC acts as both an electron donor and an electron shuttle in the enhanced Fenton reaction system.

[0054] In summary, the carbon defect density (ID / IG) and surface carboxyl group (C=O) content of BAC samples are the two most critical factors affecting their enhanced Fenton reaction catalytic performance (R² = 0.8363 and 0.8739, respectively), followed by electrical conductivity (R² = 0.750). Specific surface area (SBET) and average pore size (D) have relatively smaller effects on catalytic performance (R² = 0.0671 and 0.0373, respectively). These findings provide theoretical guidance for selecting highly efficient BACs, namely, focusing on increasing the carbon defect density and carboxyl group content while optimizing their electronic conductivity to achieve higher COD removal efficiency.

[0055] according to Figure 2 The correlation analysis results clearly show the key structural parameter constraints that BAC must meet. From Figure 2 (c) It can be seen that the carbonyl (C=O) content is strongly positively correlated with the COD removal rate (R²=0.8739). According to the regression equation y=2.3133x+42.3315, when the C=O content is 11 Atomic%, the COD removal rate is about 68%, which has a good treatment effect. Figure 2 (e) shows that carbon defect density has the strongest positive correlation with COD removal rate (R²=0.8363). According to the regression equation y=26.703x+9.267, when the carbon defect density is 2.2×10¹¹ / cm², the COD removal rate is approximately 68%. Figure 2 (f) shows a significant positive correlation between conductivity and COD removal rate (R² = 0.750). According to the regression equation y = 12.118x + 43.84, the COD removal rate is approximately 65% ​​when the conductivity is 1.8 S / cm. The lower limits of these three parameters ensure that BAC possesses basic catalytic activity. Further optimization limits (C=O content 12-15 Atomic%, carbon defect density 2.3 × 10¹¹ / cm² - 2.5 × 10¹¹ / cm², conductivity 2 S / cm - 2.2 S / cm) ensure that the COD removal rate remains stable above 70%. This is because within these ranges, the carboxyl functional groups on the BAC surface can effectively promote Fe... 3+ / Fe 2+ The cycle, surface carbon defects as active sites accelerate electron transfer, and the high electrical conductivity further enhances electron shuttle capability. The synergistic effect of these three factors significantly improves the efficiency of the Fenton reaction.

[0056] 2.2.3 To verify whether the addition of BAC accelerated Fe 2+ The regeneration of the Fenton system promotes COD removal and further enhances the traditional Fenton system (Fe... 2+ / H2O2 system) and biological activated carbon enhanced Fenton reaction system (BAC / Fe 2+Iron ion conversion was detected at different time periods in the / H2O2 system to reveal the reasons for the enhanced COD removal rate.

[0057] Figure 3 Fe 2+ / Fe 3+ Concentration change graph. Among them, Figure 3 (a)Fe 2+ / H2O2 system; Figure 3 (b)BAC / Fe 2+ / H2O2 system; operating parameters: pH=3, BAC=0.3g / L, H2O2 (30% w / w)=0.3ml / L, FeSO4·7H2O=0.3g / L; BAC sample BAC-6 was used. Figure 3 As shown, in Fe 2+ In the / H2O2 system, Fe 2+ The concentration of Fe decreased rapidly within 30 minutes, from 57.8 mg / L to 6.5 mg / L, indicating that the low COD degradation rate in the Fenton system was due to Fe. 2+ Rapid consumption. And in BAC / Fe 2+ In the / H2O2 system, Fe 2+ The concentration of Fe showed a trend of first decreasing and then increasing. Within 10 minutes, the concentration of Fe... 2+ Consumption decreased to 8.5 mg / L, then showed an increasing trend, with Fe reaching a peak after 30 minutes. 2+ The concentration rapidly increased to 24.3 mg / L and remained at a high level of around 24.5 mg / L throughout the reaction. These results indicate that BAC is a highly efficient promoter of Fe... 2+ Regenerated cocatalyst.

[0058] Figure 4 This is a comparison of the COD degradation effects of different solution systems. Operating parameters: pH=3, BAC=0.5 g / L, H2O2=0.4 ml / L, FeSO4·7H2O=0.6 g / L, BAC sample BAC-6 was used. Figure 4 As shown, the adsorption and removal efficiency of BAC for COD was only 16.0%; however, after adding H2O2, the COD removal rate of BAC / H2O2 rapidly increased to 40.0%, indicating that BAC can directly activate H2O2 to generate free radicals. The traditional Fenton system, i.e., Fe... 2+ / H2O2 only removes about 34.0% of COD, while the BAC / Fe2O3 removal rate after adding BAC is much higher. 2+ The COD removal rate of the H2O2 system is higher than that of Fe. 2+The / H2O2 system showed a significant improvement, achieving a COD removal rate of 78.5%. These results indicate that the addition of BAC significantly improves the efficiency of the Fenton reaction.

[0059] Figure 5 For BAC / Fe 2+ Radical quenching experiments were conducted on the / H2O2 system to investigate the strengthening mechanism of BAC on the Fenton system. The results showed that tert-butanol can act as a ·OH quencher, and p-benzoquinone can act as a ·O quencher. 2- Quenching agent. In the blank group without quenching agent, BAC / Fe 2+ The degradation rate of COD by BAC / Fe was 78.5%. After the addition of tert-butanol, the reaction rate decreased significantly, with a COD degradation rate of only about 18.3%. Benzoquinone had almost no effect on COD removal from the system. This result indicates that the degradation rate of COD by BAC / Fe was significantly reduced. 2 + In the / H2O2 system, ·OH is the main active free radical and plays a decisive role in the efficient degradation of COD.

[0060] To further verify the aforementioned free radical types, ESR technology was used to determine different systems. Specifically, an aqueous solution system was used to detect ·OH, and a methanol solution system was used to detect ·O. 2 As shown in Table 3, in an aqueous solution environment, whether it is the BAC / H2O2 system or the BAC / Fe... 2+ In the H₂O₂ system, the spin trapping agent DMPO successfully captured a characteristic signal with a peak intensity ratio of 1:2:2:1, corresponding to the characteristic peak of the hydroxyl adduct –·OH. Conversely, in methanol solution, no ·OH-- was detected in either system. 2- Regarding the characteristic peak values, this result is highly consistent with the conclusions obtained from the free radical quenching experiment, namely that the key to BAC strengthening the Fenton system lies in promoting the generation of more ·OH.

[0061] Table 3 ESR Free Radical Detection BAC — — <![CDATA[BAC / H2O2]]> Detected — <![CDATA[BAC / Fe 2+ / H2O2]]> Detected — Note: — indicates not detected. Figure 6 and Figure 7 The BAC / H2O2 system and BAC / Fe system are visually demonstrated. 2+ Comparison of ESR signal intensities of DMPO-·OH in the / H2O2 system. Clearly, BAC / Fe 2+ The peak intensity of the / H2O2 system is about 1.6 times that of the BAC / H2O2 system, which directly proves that the former can generate more free radicals.

[0062] Combining BAC with Fenton technology not only significantly improves COD removal efficiency but also effectively enhances the coagulation and settling performance of the system. For example... Figure 8 As shown, it can be seen that Fe 2+ The H2O2 system results in slow settling of iron sludge and a yellowish effluent. In contrast, the BAC / Fe system... 2+ The / H2O2 system demonstrated significant advantages. This system achieved complete sedimentation of iron sludge within just 5 minutes, drastically reducing iron sludge production and resulting in clear, transparent effluent.

[0063] The foregoing has described the relevant content of the present invention. Those skilled in the art will be able to implement the present invention based on these descriptions. All other embodiments obtained by those skilled in the art based on the foregoing content of this specification without inventive effort should fall within the scope of the present invention.

Claims

1. A wastewater COD degradation method using biological activated carbon to enhance the Fenton reaction, characterized in that: Add biological activated carbon and Fe to the wastewater to be treated 2+ The source and H2O2 are mixed thoroughly, and the pH value of the wastewater to be treated is controlled at 3-7. The dosage of biological activated carbon is 0.3g-0.9g per liter of wastewater to be treated; Fe 2+ The amount of source added is based on Fe 2+ The concentration is calculated to be 1.6 mmol - 2.7 mmol per liter of wastewater to be treated; The dosage of H2O2 (30% w / w) is 0.4 mL to 0.6 mL per liter of wastewater to be treated; Furthermore, the bio-activated carbon meets the following conditions: (1) The surface carbonyl (C=O) content, as determined by C1s peak analysis of X-ray photoelectron spectroscopy (XPS), is not less than 11 Atomic% (2) Based on the intensity ratio of the D peak to the G peak in the Raman spectrum (ID / IG), the formula nD = (1.8 ± 0.5) × 10²² × (ID / IG) / λL is used. 4 The calculated carbon defect density is no less than 2.2 × 10⁻⁶. 11 / cm², where λL is the excitation laser wavelength in nm; (3) The electrical conductivity is not less than 1.8 S / cm.

2. The wastewater COD degradation method using biological activated carbon to enhance the Fenton reaction as described in claim 1, characterized in that: The dosage of biological activated carbon is 0.25g-0.35g per liter of wastewater to be treated.

3. The wastewater COD degradation method using biological activated carbon enhanced Fenton reaction as described in claim 1, characterized in that: Fe 2+ Source addition amount according to Fe 2+ The concentration is calculated to be 2.0 mmol to 2.3 mmol per liter of wastewater to be treated.

4. The wastewater COD degradation method using biological activated carbon to enhance the Fenton reaction as described in claim 1, characterized in that: The dosage of H2O2 (30% w / w) is 0.35 mL to 0.45 mL per liter of wastewater to be treated.

5. The wastewater COD degradation method using biological activated carbon to enhance the Fenton reaction as described in claim 1, characterized in that: The wastewater to be treated is wastewater whose COD concentration, after secondary biochemical treatment, does not meet the Class A standard of "Discharge Standard of Pollutants for Urban Wastewater Treatment Plants (GB 18918-2002)" or the Class IV water quality standard of "Environmental Quality Standard for Surface Water (GB 3838-2002)".

6. The wastewater COD degradation method using biological activated carbon to enhance the Fenton reaction as described in claim 1, characterized in that: Fe 2+ The source is FeSO4·7H2O.

7. The wastewater COD degradation method using biological activated carbon enhanced Fenton reaction as described in claim 1, characterized in that: The surface carbonyl (C=O) content of the bio-activated carbon, as determined by C1s peak fractionation analysis using X-ray photoelectron spectroscopy (XPS), is no higher than 18 Atomic%, and the carbon defect density nD is no higher than 2.8 × 10⁻⁶. 11 / cm², conductivity not higher than 2.6S / cm.

8. The wastewater COD degradation method using biological activated carbon to enhance the Fenton reaction as described in claim 1, characterized in that: The surface carbonyl (C=O) content of the bio-activated carbon, as determined by C1s peak analysis using X-ray photoelectron spectroscopy (XPS), was 12-15 Atomic%.

9. The wastewater COD degradation method using biological activated carbon to enhance the Fenton reaction as described in claim 1, characterized in that: The carbon defect density nD of the bio-activated carbon is 2.3 × 10⁻⁶. 11 / cm²-2.5×10 11 / cm².

10. The wastewater COD degradation method using biological activated carbon to enhance the Fenton reaction as described in claim 1, characterized in that: The electrical conductivity of the bio-activated carbon is 2S / cm-2.2S / cm.

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