Process for synergistically removing humic acid by using electrically activated ferrous iron and application

Abstract

The invention relates to the technical field of water treatment, in particular to a process for synergistically removing humic acid through electrical activation of ferrous iron and application, and the process comprises the following steps: S1, adjusting the initial pH and temperature of a to-be-treated water body; s2, a cathode and an anode are inserted into a water body to be treated, the plate distance between the cathode and the anode is adjusted, the cathode is graphite, the anode is Ti / TiO2-IrO2-RuO2 or Ti / TiO2-Ta2O5-IrO2, and Fe < 2 + > is added into the Ti / TiO2-IrO2-RuO2 and the Ti / TiO2-Ta2O5-IrO2 respectively for a reaction; and S3, supplying direct current to the cathode and the anode through a direct-current power supply, and carrying out water treatment reaction for specified time. An oxidation-flocculation-precipitation combined electrochemical pretreatment process is constructed and is effectively matched with a traditional process, so that a humic acid (HA) precursor is efficiently removed, generation of disinfection by-products is reduced from the source, the water treatment efficiency can be remarkably improved in practical application, generation of the disinfection by-products is reduced, and then the urban and rural water quality standard-reaching rate is increased.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of water treatment, more specifically, it relates to a process for synergistically removing humic acid by electro-activated ferrous iron and application. BACKGROUND

[0002] Currently, chlorination disinfection has become the mainstream disinfection method in domestic water treatment due to its cost-effectiveness and significant sterilization effect. However, while chlorination disinfection effectively removes pathogenic microorganisms in water, it also inevitably generates disinfection by-products (DBPs), some of which are toxic and pose a potential threat to human health. In particular, under the increasingly stringent DBP control requirements of the newly introduced "Drinking Water Health Standards" (GB5749-2022) and international water quality directives, how to reduce the generation of disinfection by-products while ensuring water quality safety has become a key problem that needs to be solved in water treatment technology. Therefore, developing more green, safe, and low-energy water treatment disinfection technology not only effectively reduces the generation of disinfection by-products but also improves the overall water quality safety, which has important theoretical and practical significance for public health protection.

[0003] Electrocoagulation technology involves multiple fields such as electrochemistry, environmental chemistry, materials science, and colloid interface chemistry, and its mechanism is complex. It usually uses iron or aluminum as a sacrificial anode, and through an external electric field, the anode undergoes electrochemical oxidation to release flocculating ions such as ferrous ions or aluminum ions. These ions further hydrolyze to form hydroxides or hydroxyl complexes, which achieve effective removal of pollutants through four main mechanisms: compression of the double electric layer, adsorption and neutralization, adsorption bridging, and precipitation net capture. In practical applications, the removal of pollutants is often the result of the synergistic action of multiple mechanisms, and the specific mechanism that dominates or several mechanisms that work simultaneously depends on the actual water quality characteristics and reaction conditions.

[0004] Humic acid (HA) is a natural organic matter, and natural organic matter is an important precursor of disinfection by-products (DBPs). Its reaction with chlorine can generate by-products such as trihalomethanes (THMs) and haloacetic acids (HAAs) that have carcinogenic and mutagenic risks. Currently, most water plants in China still rely on traditional coagulation sedimentation and chlorination disinfection processes. If the raw water quality is complex or the organic matter content is high, the traditional water treatment process has limited removal of natural organic matter, making it difficult to effectively control the risk of disinfection by-products, and it is easy to cause by-product or residual chlorine to exceed the standard. Therefore, it is necessary to develop efficient technologies to control the generation of disinfection by-products. SUMMARY

[0005] In order to construct an oxidation-flocculation-precipitation combined electrochemical pretreatment process, effectively cooperate with the traditional process, efficiently remove humic acid (HA) precursors, reduce the generation of disinfection by-products from the source, can significantly improve the water treatment efficiency in practical application, reduce the generation of disinfection by-products, and then improve the urban and rural water quality compliance rate, the application provides a process and application of electro-activated ferrous iron synergistically removing humic acid.

[0006] In the first aspect, the application provides a process for removing humic acid by electro-activated ferrous iron, which adopts the following technical scheme:

[0007] A process for removing humic acid by electro-activated ferrous iron is carried out through a water treatment system, wherein the water treatment system comprises a reaction container, a cathode, an anode and a direct current power supply, the water body to be treated is located in the reaction container, the cathode and the anode are inserted into the water body to be treated, and the direct current power supply is electrically connected with the cathode and the anode.

[0008] The process for removing humic acid by electro-activated ferrous iron comprises the following steps:

[0009] S1, adjusting the initial pH and temperature of the water body to be treated;

[0010] S2, inserting the cathode and the anode into the water body to be treated, and adjusting the plate spacing between the cathode and the anode, wherein the cathode is graphite, the anode is Ti / TiO2-IrO2-RuO2 or Ti / TiO2-Ta2O5-IrO2, and Fe is added in Ti / TiO2-IrO2-RuO2 and Ti / TiO2-Ta2O5-IrO2 respectively. 2+ carrying out the reaction;

[0011] S3, passing direct current through the cathode and the anode by the direct current power supply to carry out water treatment reaction for a specified time.

[0012] Preferably, in the step S1, the initial pH of the water body to be treated is 5-9.

[0013] Preferably, in the step S1, the temperature of the water body to be treated is 5-45℃.

[0014] Preferably, in the step S2, the plate spacing between the cathode and the anode is 2-6cm.

[0015] Preferably, the plate spacing between the cathode and the anode is 2cm.

[0016] Preferably, in the step S2, the addition amount of Fe 2+ is 20mg / L-40mg / L.

[0017] Preferably, the addition amount of Fe 2+ is 30mg / L.

[0018] Preferably, in step S3, the direct current density is 1 mA / cm². 2 -5mA / cm 2 .

[0019] Preferably, in step S3, the direct current density is 3 mA / cm². 2 .

[0020] Secondly, the process of electro-activated ferrous sulfate synergistic removal of humic acid is being applied in the field of water treatment.

[0021] In summary, this application has the following beneficial effects:

[0022] This application proposes and realizes electrochemical and Fe... 2+ The combined mechanism of "oxidation-flocculation-coprecipitation" synergistic degradation of HA effectively destroys the high-molecular-weight aromatic structure of HA and utilizes the generated Fe(OH)3 flocs for efficient adsorption and sedimentation. Three-dimensional fluorescence spectroscopy and fluorescence index analysis verified the significant effect of the pretreatment process on the structural transformation of dissolved organic matter (DOM) and the control of disinfection by-product formation potential, providing data support for engineering applications. By investigating the efficiency, mechanism, and application of electroactivated ferrous iron in HA degradation in actual water bodies, the synergistic oxidation and adsorption pathway of electrochemical ferrous iron on HA was clarified, and process parameters and optimal operating ranges were determined, providing experimental data and theoretical references for the efficient removal of natural organic matter and the reduction of disinfection by-product formation. Attached Figure Description

[0023] Figure 1 This is a schematic diagram of the experimental setup provided in this application (Note: 1-Constant temperature heating magnetic stirrer; 2-DC power supply; 3-Experimental reactor; 4-Cathode; 5-Anode);

[0024] Figure 2 The effect of different electrodes on HA removal in this application (a) UV 254 (b) Permanganate index;

[0025] Figure 3 This application is Fe 2+ Effect of dosage on HA removal (a) UV 254 (b) Permanganate index;

[0026] Figure 4 This application is Fe 2+ Reaction kinetics of HA removal by dosage (a) UV 254 (b) Permanganate index;

[0027] Figure 5 The effect of current density on HA removal in this application (a) UV 254(b) permanganate index;

[0028] Figure 6 Effect of current density on HA removal in this application (a) UV 254 (b) permanganate index;

[0029] Figure 7 Effect of plate spacing on HA removal in this application (a) UV 254 (b) permanganate index;

[0030] Figure 8 Kinetics of plate spacing on HA removal in this application (a) UV 254 (b) permanganate index;

[0031] Figure 9 Effect of pH on HA removal in this application (a) UV 254 (b) permanganate index;

[0032] Figure 10 Effect of temperature on HA removal in this application (a) UV 254 (b) permanganate index;

[0033] Figure 11 Effect of different water sample pretreatment on DBP formation potential in this application (a) sodium hypochlorite disinfection; (b) chloramine disinfection (Note: 1 represents untreated water sample; 2 represents treated water sample);

[0034] Figure 12 Three-dimensional fluorescence characteristic spectrum of different water samples in this application (a) HA untreated; (b) HA treated;

[0035] Figure 13 Three-dimensional fluorescence characteristic spectrum of different water samples in this application (c) untreated Yangtze River; (d) treated Yangtze River;

[0036] Figure 14 Three-dimensional fluorescence characteristic spectrum of different water samples in this application (e) untreated Li Zi Lake; (f) treated Li Zi Lake;

[0037] Figure 15 Fluorescence integral volume of different water samples in this application (Note: 1 represents untreated water sample; 2 represents treated water sample);

[0038] Figure 16 Fluorescence index change of different water samples in this application (Note: 1 represents untreated water sample; 2 represents treated water sample). DETAILED DESCRIPTION

[0039] The application will be further described in detail below in combination with examples.

[0040] The test device, reagent and instrument used in the embodiments of the present application are as follows:

[0041] I. Test device

[0042] The experimental device is as shown in Figure 1 . All experiments are carried out in a 500 mL cylindrical glass reactor with an inner diameter of 80 mm and a height of 105 mm; a direct current power supply is used to connect the anode and the cathode, different electrodes are used as the anode, and graphite is used as the cathode; the size of the anode and the cathode is both 50 mm x 50 mm; a magnetic stirrer is used to gently stir the water sample at a constant speed of 400 rpm to maintain good mixing.

[0043] II. Experimental method

[0044] 1. Preparation of experimental solution

[0045] Preparation of humic acid solution: 0.500 g of HA is accurately weighed into 0.50 L of pure water, heated in a 60°C constant temperature water bath for 12 h, and then filtered with a 0.45 μm filter membrane to obtain a 1 g / L humic acid solution, which is stored in a brown blue cap bottle at 4°C-8°C; the required amount can be prepared according to the same method in proportion.

[0046] 2. Experimental scheme of process parameter influencing factors

[0047] (1) Selection of electrode: first, dilute the prepared HA solution to 20 mg / L solution 300 mL; second, adjust the pH to neutral condition, the effective area of electrode reaction is 20 cm -2 , control the reaction temperature to be 25°C, the current density is 3 mA / cm -2 , the electrode plate spacing is 2 cm, and 0.05 mol / L sodium sulfate is added as electrolyte; four kinds of electrodes, i.e., iron, stainless steel, ruthenium iridium titanium (Ti / TiO2-IrO2-RuO2) and iridium tantalum titanium (Ti / TiO2-Ta2O5-IrO2) are used as anodes, and graphite is used as a cathode; and 30 mg / L of Fe 2+ is added in Ti / TiO2-IrO2-RuO2 and Ti / TiO2-Ta2O5-IrO2 electrodes for reaction; finally, sampling is carried out at the set fixed time point, and the changes of UV 254 and permanganate index after reaction are detected immediately after filtering with a 0.45 μm filter membrane to investigate the influence of different electrodes on HA removal.

[0048] (1) Influence of Fe 2+ dosage: according to the conditions and results of electrode selection, Ti / TiO2-Ta2O5-IrO2 is used as the anode, and the current density is adjusted to 5 mA / cm -2The rest of the conditions remain unchanged, respectively add 0 mg / L, 20 mg / L, 25 mg / L, 30 mg / L, 35 mg / L and 40 mg / L of Fe 2+ The reaction was carried out; finally, at the set fixed time point, sampling was carried out, and immediately after filtering through a 0.45 μm filter, the UV 254 and permanganate index after reaction were detected, and the influence of different Fe 2+ dosage on HA removal was investigated.

[0049] (3) Influence of current density: According to the conditions and results of Fe 2+ dosage experiment, first adjust the Fe 2+ dosage to 30 mg / L, and secondly adjust the current density to 0 mA / cm -2 , 1 mA / cm -2 , 2 mA / cm -2 , 3 mA / cm -2 , 4 mA / cm -2 and 5 mA / cm -2 ; finally, at the set fixed time point, sampling was carried out, and immediately after filtering through a 0.45 μm filter, the UV 254 and permanganate index after reaction were detected, and the influence of different current densities on HA removal was investigated.

[0050] (4) Influence of plate spacing: According to the conditions and results of current density experiment, first adjust the current density to 3 mA / cm -2 , and secondly adjust the plate spacing to 2 cm, 3 cm, 4 cm, 5 cm and 6 cm; finally, at the set fixed time point, sampling was carried out, and immediately after filtering through a 0.45 μm filter, the UV 254 and permanganate index after reaction were detected, and the influence of different plate spacings on HA removal was investigated.

[0051] (5) Influence of initial pH of reaction: According to the conditions and results of plate spacing experiment, first adjust the plate spacing to 2 cm, and secondly adjust the initial solution reaction pH to 5, 6, 7, 8 and 9; after 30 min of reaction, sampling was carried out, and immediately after filtering through a 0.45 μm filter, the UV 254 and permanganate index after reaction were detected, and the influence of different pH on HA removal was investigated.

[0052] (6) Influence of reaction temperature: According to the conditions and results of pH experiment, first adjust the initial solution pH under neutral conditions, and secondly adjust the solution reaction temperature to 5℃, 15℃, 25℃, 35℃ and 45℃; after 30 min of reaction, sampling was carried out, and immediately after filtering through a 0.45 μm filter, the UV254 and the changes of permanganate index, the effect of different temperatures on HA removal was investigated.

[0053] III. Actual water body experimental scheme

[0054] The actual water body was taken from the Yangtze River as the river water source, and the Li Lake in the Chongqing University of Posts and Telecommunications Science City campus as the lake and reservoir water source. The specific water quality indicators are shown in Table 3. After sampling, the water sample was immediately filtered with a 0.45 μm filter membrane and stored at 4°C in the dark. The optimal process determined in the foregoing was used to treat the HA solution, the Yangtze River and the Li Lake water body, and three-dimensional fluorescence spectroscopy was used to characterize and analyze the water samples before and after treatment.

[0055] In the disinfection by-product formation potential experiment, a certain amount of Br - was added to the HA solution alone to make the Br - concentration in the solution reach 1 mg / L; a certain amount of sodium hypochlorite and chloramine was added to the HA solution, the Yangtze River and the Li Lake water sample (before and after treatment) to make the initial chlorine dosage 5 mg / L. Subsequently, all the solutions were placed in a 25°C constant temperature incubator for 24 h of light-free reaction. After the reaction was completed, sodium sulfite was added to terminate the reaction, and the concentration of THMs was detected.

[0056] Table 1 Main water quality parameters of the Yangtze River and the Li Lake

[0057]

[0058] IV. Analysis and detection method

[0059] 1. Detection method of permanganate index

[0060] The determination of permanganate index was detected by spectrophotometry according to the Standard Test Method for Drinking Water-Part 7: Organic Comprehensive Index (GB / T 5750.7-2023). The detection of water samples was performed according to the detection method of the standard curve of permanganate index.

[0061] 2. Detection method of UV 254

[0062] UV 254 was used to determine the degradation and removal of HA.

[0063] 3. Detection method of iron element

[0064] Total iron and Fe 2+ were detected according to the Spectrophotometric Method for Determination of Iron in Water (Trial) (HJ-T 345-2007).

[0065] 4. Electron paramagnetic resonance analysis

[0066] ​The production of hydroxyl radicals was verified by electron paramagnetic resonance (EPR) at room temperature, using 5,5-dimethyl-1-pyrroline-N-oxide (DMPO) as a spin trapping agent. The basic parameters include microwave power 25.18 mW, modulation amplitude 1.0 G, sweep width 700 G, sweep time setting 35 s, time constant setting 81.92 ms, and resonance frequency setting 9.77 GHz.

[0067] 5. Detection method of three-dimensional fluorescence spectrum

[0068] The three-dimensional fluorescence spectrum was scanned by a fluorescence spectrophotometer. During the determination, the voltage of the instrument photomultiplier tube was set to 700 V, the excitation and emission slit width was adjusted to 5 nm, the scanning rate was 12000 nm / min, and the scanning spectrum was automatically calibrated. The scanning excitation wavelength (Ex) range was set to 200-420 nm with an interval of 5 nm, and the emission wavelength (Em) range was set to 280-550 nm with an interval of 5 nm.

[0069] 6. Detection method of trihalomethane

[0070] According to the detection method of “Standard Test Method for Drinking Water Part 8: Organic Indicators” (GB / T 5750.8-2023), the detection was carried out by the purge and trap gas chromatography mass spectrometry method. The detection was carried out by Huachu Detection Technology Co., Ltd.

[0071] Embodiment

[0072] Embodiment 1

[0073] A process for synergistically removing humic acid by electro-activated ferrous iron, which is carried out by a water treatment system, the water treatment system comprising a reaction vessel, a cathode, an anode and a direct current power supply, the water body to be treated is located in the reaction vessel, the cathode and the anode are inserted into the water body to be treated, and the direct current power supply is electrically connected with the cathode and the anode; in the embodiment of the present application, the experiments are carried out in a 500 mL cylindrical glass reactor, the inner diameter of which is 80 mm and the height is 105 mm; a direct current power supply is used to connect the cathode and the anode, different electrodes are used as the anode, and graphite is used as the cathode, the size of the cathode and the anode is both 50 mm x 50 mm; a magnetic stirrer is used to gently stir the water sample at a constant speed of 400 rpm to maintain good mixing.

[0074] The process for synergistically removing humic acid by electro-activated ferrous iron comprises the following steps:

[0075] S1, adjusting the initial pH of the water body to be treated to neutral (pH 7) and controlling the temperature to 25℃; the water body to be treated is a prepared HA solution diluted to a solution of 20 mg / L of 300 mL;

[0076] S2, insert the cathode and anode into the water body to be treated, adjust the inter-electrode distance between the cathode and anode to 2 cm, and add 0.05 mol / L sodium sulfate as an electrolyte; the cathode is graphite, and the anode is Ti / TiO2-IrO2-RuO2, and 30 mg / L of Fe 2+ is added in the Ti / TiO2-IrO2-RuO2 respectively 2+ ;

[0077] S3, pass direct current to the cathode and anode through the direct current power supply, and perform water treatment reaction for a specified time; the current density is 3 mA / cm -2 .

[0078] Example 2, Comparative Examples 1-5

[0079] Example 2, Comparative Examples 1-5 differs from Example 1 in that different anodes are used, as shown in Table 2 below:

[0080] Table 2 Anode materials used in Example 2, Comparative Examples 1-5

[0081] Example / Comparative Example Anode Example 1 Ti / TiO2 - IrO2 - RuO2 / Fe 2+ ]]> Example 2 Ti / TiO2-Ta2O5-IrO2 / Fe 2+ ]]> Comparative Example 1 Fe 2+ ]]> Comparative Example 2 Iron anode Comparative Example 3 Stainless steel Comparative Example 4 [Ti / TiO2 - IrO2 - RuO2] Comparative Example 5 [Ti / TiO2-Ta2O5-IrO2]

[0082] Selection of electrodes

[0083] The electrode material plays a crucial role in the reaction, and different types of anode materials affect the removal rate of HA, the reaction rate, and the final degree of mineralization. The experiment investigated the effects of soluble iron anode, stainless steel anode, Ti / TiO2-IrO2-RuO2, Ti / TiO2-Ta2O5-IrO2, and their combination with Fe 2+ on the removal of HA.

[0084] Comparing Example 2 and Comparative Examples 1-5, according to Figure 2 the experimental results show that when Fe 2+ is added alone, there is almost no removal effect on HA within 30 minutes, indicating that the effect of Fe 2+ alone is difficult to effectively degrade HA. For stainless steel, Ti / TiO2-IrO2-RuO2, and Ti / TiO2-Ta2O5-IrO2 as anodes, the oxidation effect on HA is limited, mainly because the dose of strong oxidizing agent produced is small, making it difficult to effectively oxidize and degrade HA. In addition, the iron anode reaches a maximum UV 254 removal rate of 93.56% at 30 minutes, and this high removal rate is mainly due to the continuous production of Fe 2+Along with other iron substances, it essentially produces an in-situ coagulant and a small amount of ·OH, enabling HA to be rapidly adsorbed, settled, and oxidized. Although the iron anode can rapidly remove HA mainly through electrochemical coagulation, it generates a large amount of iron sludge during the reaction, and the excessive production of iron in different valence states indirectly affects the accuracy of permanganate index detection. Therefore, the permanganate index of HA removal by the iron anode was not detected. In contrast, Ti / TiO2-IrO2-RuO2 / Fe 2+ Ti / TiO2-Ta2O5-IrO2 / Fe 2+ The combined use of these technologies can simultaneously target UV radiation. 254 Both showed good removal rates for UV and permanganate index, and both showed similar removal rates at 30 minutes. 254 Both the permanganate index and the iron anode index can reach over 90%, comparable to the effect of iron anode treatment, but without producing a large amount of iron sludge, thus offering greater advantages in application. Furthermore, from the perspective of the overall reaction process, Ti / TiO2-Ta2O5-IrO2 / Fe... 2+ The treatment effect is slightly better than that of Ti / TiO2-IrO2-RuO2 / Fe. 2+ Analysis of cyclic voltammetry curves revealed that the area enclosed by the cyclic voltammetry curves of the Ti / TiO2-Ta2O5-IrO2 electrode was slightly larger than that of the Ti / TiO2-IrO2-RuO2 / Fe electrode. 2+ The area enclosed by the cyclic voltammetry curve is positively correlated with the charge capacity of the electrode surface, reflecting its catalytic activity. A larger area indicates a richer abundance of active sites on the anode surface. When Fe is added to the reaction... 2+ After that, Fe 2+ + It can catalyze the decomposition of H2O2 to generate more ·OH, significantly improving its oxidation capacity. Furthermore, during the oxidation process, Fe... 2+ Gradually oxidized to Fe 3+ This leads to the formation of ferric hydroxide (Fe(OH)3) flocs, which effectively remove HA through co-precipitation and adsorption, thereby further enhancing UV protection. 254 The removal rate of permanganate index. In summary, Ti / TiO2-Ta2O5-IrO2 / Fe 2+ The system performed best, enhancing oxidation capacity while also providing strong flocculation removal capability.

[0085] Examples 3-6, Comparative Example 6

[0086] The difference between Examples 3-6, Comparative Example 6 and Example 1 lies in Fe 2+ The dosage varies, as detailed in Table 3 below:

[0087] Table 3. Fe in Examples 3-7 and Comparative Example 6 2+ dosage

[0088] Example / Comparative Example Fe 2+ mg / L of Fe Example 3 20 Example 4 25 Example 1 30 Example 5 35 Example 6 40 Comparative Example 6 0

[0089] According to Figure 3 It can be seen that the removal rate of HA under different dosages presents a trend of rapid first and then flat with time. Without Fe 2+ , only by electrode reaction, the UV 254 and permanganate index removal rates of HA within 30 min are 23.85% and 35.98% respectively, which is limited. It shows that the efficiency of electrochemical oxidation is very low without Fe 2+ . But after adding Fe 2+ , the removal efficiency can be greatly improved. With the increase of Fe 2+ dosage, the removal rates of UV 254 and permanganate index gradually increase within the same reaction time. Under the condition of 30 min and 40 mg / L, the removal rates of UV 254 and permanganate index reach the maximum, which are 94.26% and 94.77% respectively. However, when the Fe 2+ dosage increases from 30 mg / L to 40 mg / L, the final removal rate does not improve significantly. Compared with the condition of 30 mg / L, the removal rates of UV 254 and permanganate index increase by 1.9% and 0.96% respectively, which is not obvious. But from the overall reaction process, it can be seen that the increase of Fe 2+ dosage increases the reaction rate, and the removal of HA within the first 10 minutes of the reaction is faster. Therefore, there is a saturation zone for Fe 2+ dosage. Appropriate increase of Fe 2+ dosage is beneficial to accelerate the degradation of HA, but when it is excessive, the effect tends to be flat, and there is waste of medicine and more residual Fe 2+ . Therefore, the dosage of 30 mg / L is selected for the follow-up experiment.

[0090] In order to better reflect the effect of Fe 2+ dosage on the removal rate of HA, the pseudo-first-order kinetics and pseudo-second-order kinetics fitting are carried out for different Fe 2+ dosages. According to Figure 4 and Table 4, when the dosage is more than 30 mg / L, the increase of Fe 2+ dosage gradually increases the kinetic constant; and the correlation coefficients (R 2 ) of the two kinetic models are both greater than 0.9, which is highly consistent with the experimental data. When the dosage is 30 mg / L, the R 2 of the pseudo-second-order model is slightly higher than that of the pseudo-first-order model, and the fitting is better. Therefore, under this dosage, active substances may be generated to oxidize and degrade HA; at the same time, Fe 2+ / Fe 3+Hydrolysis products can remove HA by adsorption or flocculation.

[0091] Table 4 Kinetic parameters of HA removal with different Fe2+ dosages

[0092]

[0093] In the electrochemical reaction process, the main reaction of the anode is (3.1), in which water molecules are oxidized to generate oxygen (O2); the cathode reaction is shown in (3.2), in which dissolved O2 is reduced to generate H2O2, and the additional Fe 2+ continues to react with H2O2 to generate ·OH, as shown in (3.3), to form Fenton to degrade pollutants. The ·OH generated by the Fenton reaction can extract protons from organic matter (RH) to generate organic free radicals (R·), which have high reactivity and can be further oxidized, as shown in (3.4); in addition, H2O2 can act as a quencher for ·OH, as shown in (3.5), and the reaction rate is 3.3 x 10 7 M -1 s -1 , but Fe 2+ reacts with ·OH to generate Fe 3+ , as shown in (3.6), and the reaction rate is 3.8 x 10 8 M -1 s -1 Therefore, by maintaining a high RH / H2O2 ratio, the impact of H2O2 on ·OH can be reduced. If the concentration of the reactants is not limited, the organic matter can be removed by complete conversion to CO2, water, and in the case of substituted organic matter, to inorganic salts. Previous Fenton studies have shown that an acidic level close to a pH of 3 is usually the best condition for Fenton oxidation. In the presence of RH, excess Fe 2+ and low pH, hydroxyl radicals can add to aromatic rings or heterocyclic rings and unsaturated bonds of olefins or acetylenes, and can also extract hydrogen atoms to initiate radical chain oxidation, as shown in (3.4), (3.7) and (3.8). In reaction (3.4), the organic free radicals generated may be oxidized by Fe 3+ , reduced by Fe 2 + or undergo dimerization, as shown in (3.9), (3.10) and (3.11). Between pH 3 and 7, ferrous ions react with hydroxyl ions to form iron hydroxyl complexes, as shown in (3.12), (3.13) and (3.14), which explains the flocculation ability of Fenton, in which suspended solids are captured and precipitated.

[0094] 2H2O → O2+ 4H + + 4e - (3.1)

[0095] O2+ 2H + + 2e - → H2O2 (3.2)

[0096] Fe 2+ + H2O2→ Fe 3+ + ·OH + OH - (3.3)

[0097] RH + ·OH → H2O + R· → further oxidation (3.4)

[0098] ·OH + H2O2→ H2O + HO2· (3.5)

[0099] ·OH + Fe 2+ → OH - + Fe 3+ (3.6)

[0100] R· + H2O2→ ROH + ·OH (3.7)

[0101] R· + O2→ ROO· (3.8)

[0102] R· + Fe 3+ - oxidation → R + + Fe 2+ (3.9)

[0103] R· + Fe 2+ -reduction → R - + Fe 3+ (3.10)

[0104] 2R· - dimerization → R-R (3.11)

[0105]

[0106] Fenton reagent has different treatment functions depending on the ratio of Fe 2+ / H2O2. When the amount of Fe 2+ used exceeds the amount of H2O2, the treatment tends to have the effect of chemical flocculation. Yoon et al. studied the application of Fenton reaction in the removal of organic matter in landfill leachate, using Fe 2+The H2O2 / H2O2 ratio is 1.25. In this case, the Fenton reaction can be divided into two processes. The first process is initial oxidation at a low pH of approximately 3. The second process is flocculation at a high pH of 7-8. This can be explained by the fact that the flocculation step in the Fenton reaction plays a major role in the selective removal of organic matter, although the Fenton reaction itself is not a flocculation process. This experiment mainly uses electrochemical methods to generate H2O2, with additional Fe added. 2+ Promotes the formation of ·OH, while Fe 2+ When the ratio of Fe to H2O2 is greater than 2 and the reaction occurs under neutral conditions, flocculation occurs. Simultaneously, Fe... 2+ It will also be anoly oxidized to Fe. 3+ It can further form Fe(OH)3 precipitate, which helps to remove pollutants from water.

[0107] Examples 7-10, Comparative Example 7

[0108] Examples 7-10 and Comparative Example 7 differ from Example 1 in that they have different current densities, as detailed in Table 5 below:

[0109] Table 5 Current densities in Examples 7-10 and Comparative Example 7

[0110] Example / Comparative Example Current density (mA / cm -2 ) Example 7 1 Example 8 2 Example 1 3 Example 9 4 Example 10 5 Comparative Example 7 0

[0111] Current density affects the formation rate of H2O2 and Fe during the reaction process. 2+ / Fe 3+ The redox cycle and the overall oxidation capacity of the system. Based on Figure 5 It can be seen that, in the absence of current and relying solely on Fe 2+ When removed alone, it has almost no degradation effect on HA, but the removal effect on HA is significantly improved with increasing current density. Within 30 minutes, at 5 mA / cm²... 2 At that time, for UV 254 The removal rates of permanganate index and [other components] reached their maximum, at 92.36% and 93.81%, respectively. However, when the current density increased from 3 mA / cm², the removal rates decreased further. 2 Increased to 5mA / cm 2 At that time, 30 minutes for UV 254 The removal improvements in permanganate index and permanganate index were minimal, at 0.64% and 1.19%, respectively. Therefore, at 3 mA / cm², the removal efficiency was low. 2 The reaction has already reached completion, and further increasing the current will have limited effect on the removal of the final organic matter. This needs to be considered from the overall reaction process and in conjunction with... Figure 6 As shown in Table 6, a higher current only accelerates the reaction rate. However, considering energy consumption and other side reactions such as hydrogen evolution or oxygen evolution, a current of 3 mA / cm² is chosen. 2Further experiments were conducted, and the R-squared of the quasi-second-order model was determined. 2 Slightly higher than the quasi-first-level model, it provides a better fit while avoiding energy waste.

[0112] Table 6. Fitting parameters of current density to the reaction kinetics of HA removal.

[0113]

[0114] Current density affects the formation rate of H2O2 and Fe 2+ / Fe 3+ The redox cycle affects flocculation and the generation of ·OH. H2O2 is a key precursor for the generation of ·OH in the electroactivated ferrous system, and its generation rate on the cathode surface is directly affected by the current density. According to equation (3.2), the more electrons provided by the cathode, the faster the generation rate of H2O2. However, the generation rate of H2O2 is not infinitely high. When the current density exceeds a certain threshold, hydrogen evolution may occur at the cathode, resulting in wasted electrons instead of being used for the generation of H2O2; excessive oxygen evolution on the anode surface will reduce electrode stability and increase the resistance of the system, thus reducing the overall oxidation efficiency. Therefore, under appropriate current density, the system can maintain a high Fe 3+ The concentration is controlled to maximize the electrocoagulation effect while avoiding side reactions. Simultaneously, H₂O₂ is generated at the cathode, which can be reacted with Fe. 2+ It catalyzes the generation of ·OH, thereby providing additional oxidation.

[0115] Examples 11-14

[0116] The difference between Examples 11-14 and Example 1 lies in the spacing between the motor boards, as detailed in Table 7 below:

[0117] Table 7 Motor plate spacing in Examples 11-16

[0118] Example Plate spacing (cm) Example 1 2 Example 11 3 Example 12 4 Example 13 5 Example 14 6

[0119] Effect of electrode plate spacing on humic acid removal efficiency

[0120] The electrode spacing is a key factor affecting the electric field distribution, charge migration rate, and final removal efficiency. According to... Figure 7 It can be seen that as the electrode plate spacing increases, the removal rate of HA gradually decreases. When the plate spacing is 2 cm, the UV removal rate is significantly lower. 254 The removal rates of UV and permanganate index reached their maximum, at 91.98% and 92.62%, respectively; compared to when the electrode spacing was 6 cm, UV... 254 The removal rates of permanganate index and permanganate were increased by 25.97% and 20.53%, respectively; from the overall reaction process and combined with Figure 8From the analysis of Table 8, it can be seen that the overall reaction rate gradually decreases as the electrode plate spacing increases, and the time to reach the same removal rate also gradually increases. In addition, the R 2 of the two kinetic models are all greater than 0.9, indicating good fitting; at the same time, when the plate spacing is 2 cm, the R 2 of the quasi-second-order model is slightly higher than that of the quasi-first-order model, and the fitting is better. Therefore, excessive electrode spacing will significantly reduce the removal capacity of HA, so in engineering applications, the electrode distance should be shortened as much as possible to improve the current efficiency and oxidation performance.

[0121] Table 8 Reaction kinetics fitting parameters of plate spacing on HA removal

[0122]

[0123] The reason is that as the electrode distance increases, the solution resistance increases and the cell voltage rises, and most of the electrical energy is wasted as Ohmic heat rather than producing oxidants. In addition, the active oxygen species produced on the cathode surface need to diffuse into the solution, and the farther the distance, the easier it is to be diluted or annihilated. The efficiency of Fe 3+ return to the cathode to regenerate Fe 2+ also decreases. Therefore, the effective ·OH yield and Fe 2+ cycle rate both decrease under large spacing. Smaller electrode spacing reduces Ohmic resistance, allowing a larger current to pass under the same voltage, or reducing energy loss under the same current, improving electrolysis efficiency. At the same time, H2O2 and Fe 2+ produced on the cathode can more easily diffuse to the vicinity of the anode and fully mix with humic acid, and Fe 3+ is also easy to diffuse back to the cathode to be reduced. Especially in a single-cell system without a diaphragm, small spacing is conducive to the formation of a micro-electrolytic cell, where the anode vicinity is the oxidation zone, and the cathode vicinity is the reduction zone. The two zones overlap to form an efficient Fenton cycle.

[0124] Examples 15-18

[0125] Examples 15-18 differ from Example 1 in that the initial pH of the water body to be treated is different, as shown in Table 9 below:

[0126] Table 9 Initial pH of the water body to be treated in Examples 15-18

[0127] Example Initial pH of the water body being treated Example 15 5 Example 16 6 Example 1 7 Example 17 8 Example 18 9

[0128] Effect of pH on treatment effect

[0129] According to Figure 9 , it can be seen that the change of pH from 6 to 9 has little effect on the UV 254The removal rate of permanganate index is almost not significantly affected, and the removal rate is more than 90%. During the reaction, the pH of the solution is considered as one of the key factors affecting the removal efficiency of HA. Generally, the acidic condition (pH is 3-5) is considered to be the most favorable for the catalytic degradation of H2O2 and the stable existence of Fe 2+ , thereby promoting the generation of ·OH and enhancing the electrochemical oxidation capacity. However, according to the experimental data, under the neutral to slightly alkaline condition, the removal efficiency of HA still maintains at a high level.

[0130] Under the neutral or slightly alkaline condition, Fe 2+ is oxidized to Fe 3+ , which is extremely easy to react with OH - to form Fe(OH)3floc, and such colloidal particles have extremely strong adsorption and embedding capacity, and can effectively capture HA molecules in water through the sedimentation sweeping mechanism. Studies have shown that under the condition of pH 6.5-8, the Fe(OH)3floc formation speed and stability are optimal, and the large particle precipitate formed can enhance the adsorption, so that the HA is removed from the solution together with the precipitate. In addition, the condition near the electric neutral point is more favorable for the charge neutralization and aggregation between the negatively charged HA and the positively charged Fe(OH)3, and this phenomenon makes the electrocoagulation efficiency under the neutral pH significantly enhanced. Secondly, the high removal rate under the neutral and alkaline conditions is also closely related to the self-buffering mechanism of the electrochemical system. During the electrolysis process, the OH - generated by the water decomposition reaction cooperates with the reaction of Fe 3+ to generate precipitate, so that the pH of the system tends to be stable, avoiding drastic changes, which is favorable for the sustainable circulation of Fe 2+ / Fe 3+ and the long-time reaction maintenance. Under the neutral pH condition, the system is more likely to maintain the stability of the electrode reaction, and although the H2O2 electrogeneration efficiency is slightly lower than that under the acidic condition, the flocculation effect is significantly enhanced, so that the overall removal efficiency is maintained. In addition, the structure of HA itself also changes under different pH conditions. Under the neutral pH condition, the humic acid presents more hydrophobic cluster structure, and its self-aggregation behavior is enhanced, which is more easily adsorbed and wrapped by the Fe(OH)3floc. This structural change increases the tendency of forming macromolecular clusters in water, enhances the interaction with the flocculant, and thus improves the removal efficiency. Therefore, although the ·OH generation under the acidic condition is stronger, under the neutral and slightly alkaline conditions, the removal rate is still high due to the enhancement of the flocculation capacity of Fe(OH)3precipitate, the stability of the electrochemical reaction system, and the improvement of the responsiveness of HA structure to flocculation, so that the removal rate can be still high in the range of pH 5-9.

[0131] Examples 19-22

[0132] The difference between Examples 19-22 and Example 1 lies in the temperature of the water to be treated, as detailed in Table 10 below:

[0133] Table 10 Temperature of the water to be treated in Examples 19-22

[0134] Example Temperature of the water body to be treated (°C) Example 19 5 Example 20 15 Example 1 25 Example 21 35 Example 22 45

[0135] 1.1.1 The effect of temperature on treatment effect

[0136] In the electroactivated ferrous iron reaction, temperature is considered one of the key parameters affecting the reaction rate and physicochemical behavior. According to... Figure 10 It can be seen that the HA removal rate remains at a high level under both low and high temperature conditions, with the removal rate remaining at around 90%.

[0137] The reasons for this are twofold. First, temperature significantly affects the formation and characteristics of Fe(OH)3 flocs in electrocoagulation. At low temperatures, although the reaction rate decreases, the Fe(OH)3 flocs become larger and more compact, facilitating the encapsulation of humic acid molecules through a "precipitation sweep" mechanism. This mechanism compensates for the efficiency loss caused by the decreased oxidation rate, and simultaneously, due to the reduced activity of HA molecules at lower temperatures, they are more easily adsorbed and captured. Conversely, at high temperatures, although H2O2 is prone to thermal decomposition and the ·OH lifetime is shortened, Fe... 2+ The oxidation rate increases, Fe 3+ Enhanced flocculation accelerates the precipitation of Fe(OH)3, thereby improving flocculation rate and removal capacity. Hasani et al.'s research indicates that at 40℃, Fe(OH)3 flocs form more rapidly, facilitating the rapid encapsulation of HA and compensating for decreased oxidation efficiency. Furthermore, temperature also affects the structural state of HA in solution. Barhoumi et al. pointed out that high temperatures promote easier adsorption of HA molecules by Fe(OH)3 flocs. At low temperatures, although molecular motion is restricted, the physical capture of HA by flocs is enhanced, maintaining a high removal efficiency. Further research has also found that temperature indirectly affects electrode surface reactions. For example, at low temperatures, electrode polarization weakens, but current efficiency slightly increases, resulting in slower H2O2 formation but higher utilization, thus maintaining an effective oxidation level.

[0138] In summary: Under low-temperature conditions, Fe(OH)3 flocs are larger, resulting in enhanced sedimentation and sweeping effects, which is key to maintaining a high removal rate; under high-temperature conditions, Fe... 2+ Oxidation accelerates, Fe 3+The precipitation reaction rate is enhanced, which makes up for the lack of thermal degradation of the oxidation reaction; the molecular configuration of humic acid, the buffer characteristics of the reaction solution, and the electrode polarization behavior jointly affect the temperature adaptability of the electrochemical reaction; therefore, in a wide temperature range, humic acid can still be removed with relatively high efficiency, and the core of the mechanism is the stability and compensatory enhancement mechanism of flocculation efficiency.

[0139] Pretreatment process energy consumption

[0140] According to Table 11, the influence of different current densities and electrode plate spacings on energy consumption is very significant. When the current density gradually increases, the voltage rises, resulting in an increase in the energy consumption required for the treatment of unit volume of water. This is because when the current increases, the solution ohmic loss and side reactions such as cathode hydrogen evolution and anode oxygen evolution are more intense, and a higher external voltage is required to maintain the target current, thereby increasing the energy consumption. On the other hand, the increase in the plate spacing also leads to an increase in the resistance and a decrease in the mass transfer efficiency, which further increases the potential difference between the electrodes, thereby increasing the energy consumption. In addition, the value of energy consumption also depends on multiple factors such as water quality characteristics, reaction time, and electrode material. If the water sample contains more inorganic anions (such as carbonate and phosphate), the quenching effect of free radicals will also reduce the overall oxidation efficiency, and it may be necessary to moderately increase the current or extend the residence time to meet the standards, but this will further increase the energy consumption. Therefore, reasonable design of electrode structure, optimization of spacing and stirring conditions can effectively improve the current efficiency and reduce the loss of side reactions.

[0141] Table 11 Energy consumption calculation table for degradation of humic acid

[0142]

[0143] Examples 39-41

[0144] Examples 23-24 differ from Example 1 in that different water samples to be treated are used, as shown in the following Table 12:

[0145] Table 12 Water samples to be treated in Examples 23-24 and Example 1

[0146]

[0147]

[0148] The optimized electro-activated ferrous process was applied to real water bodies to investigate its effect on NOM degradation and disinfection safety of drinking water. The THMs formation potential of different water bodies before and after treatment was determined under simulated chlorination conditions to compare and analyze the effect of the process on reducing DBPs precursors. In addition, the Yangtze River and Li Lake water were selected as representative water bodies, and the component transformation of humic substances and other dissolved organic matter before and after pretreatment was characterized by three-dimensional fluorescence spectrum and fluorescence index analysis to prove the removal ability of electro-activated ferrous process for organic matter of different sources.

[0149] Effect on disinfection by-product formation potential

[0150] According to Figure 11 It can be seen that in the HA solution, the THMs produced by sodium hypochlorite disinfection after electro-activated ferrous pretreatment decreased significantly, among which the decrease of TCM was the most significant, reaching 99.5%. Under chloramine disinfection conditions, although the overall THMs formation was low, it still showed a downward trend after treatment, among which TCM was below the detection limit and no specific value was detected, which indicated that HA precursors could be effectively removed to inhibit the formation of THMs. In the Yangtze River and Li Lake water bodies, similar trends were observed: in the Yangtze River water body, the TCM formation decreased by 42% after treatment under sodium hypochlorite disinfection conditions, and TBM was below the detection limit and no specific value was detected; in the Li Lake water body, the TBM decreased by 82% after treatment under sodium hypochlorite disinfection conditions. Overall, the THMs formation in various water bodies decreased significantly after treatment, but due to the differences in the content of dissolved organic matter and Br - Concentration and other factors in different water bodies, the specific decrease was different. When the Yangtze River and Li Lake water bodies were treated under chloramine disinfection conditions, although the overall DBPs formation was usually lower than that under sodium hypochlorite disinfection conditions, the effect was still significant after treatment. Under suitable pH conditions, the iron-based electrocoagulation technology had good removal effect on HA, FA and other DBPs precursors.

[0151] Three-dimensional fluorescence spectrum analysis and regional integration

[0152] To further explore the removal mechanism of organic pollutants (AOs) in HA and actual water bodies by electroactivated ferrous sulfate, this study employed three-dimensional fluorescence spectroscopy (EEM) to characterize HA solutions, the Yangtze River, and Lizihu Lake before and after treatment. This technique, based on the excitation-emission wavelength matrix, analyzes the compositional characteristics of DOMs in water samples and is widely used in water treatment to identify and track NOMs, humic acids, and protein components. According to the EEM spectral partitioning theory, the fluorescence response can be divided into five characteristic regions: Region I represents tyrosine-based aromatic proteins, Region II represents tryptophan-based aromatic proteins, Region III represents fulvic acid-like substances, Region IV represents soluble microbial metabolites, and Region V represents humic acid-like components. Based on this partitioning standard, this study systematically analyzed the fluorescence response characteristics of different water bodies before and after electroactivated ferrous sulfate treatment through spectral comparison and regional integration quantification.

[0153] from Figures 12-15 The three-dimensional fluorescence characteristic spectrum and standard fluorescence integral volume of each region shown indicate that the fluorescence signal of the HA solution in its untreated state is mainly concentrated in regions III and V. These two regions exhibit the highest peak intensity, reflecting the abundance of aromatic structures and conjugated electron systems in HA, with a predominance of highly hydrophobic macromolecules. In the Yangtze River and Lizi Lake waters, significant fluorescence response signals were detected in regions I, II, and IV, in addition to regions III and V. This suggests that the actual water bodies contain a more diverse range of soluble organic components, such as proteins, amino acid metabolites, and low-molecular-weight NOM, making their composition more complex than that of the HA solution. After treatment, the fluorescence intensity in regions III and V of the HA solution decreased most significantly, indicating that the macromolecular humic substances underwent strong oxidative chain scission and adsorption removal. While regions III and V in the Yangtze River and Lizi Lake water samples still showed a decrease, the decrease was less than that in the HA solution, suggesting that background components such as inorganic ions and organic complexes in the actual water bodies may affect the Fe... 3+ Hydrolysis or the generation of ·OH has a certain impact, affecting removal efficiency. In contrast, the fluorescence signals in regions I and II also decreased by 20%-50% after treatment, indicating that the electroactivated ferrous system can not only remove humic substances but also has a certain degradation or adsorption capacity for soluble proteins and amino acids in water. In the Lizihu Lake water sample, the fluorescence integral value in region IV decreased by nearly 50%, indicating that components related to microbial metabolism in the water were also significantly affected. ·OH, as a non-selective strong oxidant, can destroy the molecular structure of proteins, fatty acids, and nitrogen-containing organic matter through electron transfer or free radical addition reactions. ] Furthermore, Fe(OH)3 can generate surface complexation and bridging effects on the above-mentioned metabolites, thereby synergistically achieving removal.

[0154] Overall, from the perspective of EEM mapping analysis, electro-activated ferrous iron showed significant regional response characteristics in unadjusted near-neutral water bodies. The large decline in regions III and V proved its ability to attack humic macromolecules, while the decline in regions I, II, and IV demonstrated the broad adaptability of the process. Compared with traditional chemical flocculants, electro-activated ferrous iron not only achieves physical adsorption and chemical complexation through Fe(OH)3, but also achieves deep oxidation through endogenous ·OH, making it suitable for natural water body purification with complex components. The EEM results of the Yangtze River and Li Lake water bodies confirmed the broad applicability of the process.

[0155] Analysis of water sample fluorescence characteristic parameters

[0156] When characterizing the fluorescence characteristics of DOM in water bodies, fluorescence index (FI), humification index (HIX), and biological source index (BIX) are important tools commonly used to assist in determining the source, structural properties, and potential biological availability of DOM. FI is often represented by the ratio of the intensity at emission wavelength 450 nm to that at 520 nm at excitation wavelength 370 nm. When FI < 1.4, it is often an indication that DOM is mainly derived from terrestrial input, containing more high molecular weight and aromatic functional groups. When FI is between 1.4 and 1.9, DOM has both endogenous and exogenous characteristics. If FI > 1.9, it is generally considered that DOM is mainly contributed by endogenous or microbial sources. HIX is the ratio of the maximum fluorescence intensity at emission wavelengths 435-480 nm and 300-345 nm at excitation wavelength 254 nm, which can be used to measure the degree of humification of DOM. When HIX < 3, it indicates weak humification and recent endogenous sources, and the higher the value, the higher the degree of humification and the stronger the aromaticity. BIX is often defined as the ratio of fluorescence intensity at emission wavelengths 380 nm and 430 nm at excitation wavelength 310 nm, which is used to qualitatively or quantitatively reflect the microbial source characteristics or biological productivity of DOM. When BIX > 1.0, it indicates that there are more endogenous and microbial source organic matter in the water body. When BIX is between 0.8 and 1.0, it indicates that DOM has strong endogenous characteristics. If BIX < 0.8, it is likely that terrestrial matter is the main source.

[0157] According to Figure 16It can be seen that the FI of HA solution was 1.21 before treatment, indicating that it had typical characteristics of terrestrial humic acid, rich in macromolecular aromatic structure; the FI increased to 2.26 after treatment, indicating that the process can destroy the high molecular and aromatic core structure of HA, making the treated DOM tend to be of microbial or authigenic origin. Correspondingly, the HIX decreased from 0.97 to 0.48, indicating that the degree of humification was greatly reduced, which can effectively cut off the aromatic skeleton or promote the transformation of humus to low molecular; at the same time, the BIX increased from 0.29 to 1.03, showing that the product after treatment is mainly organic fragments that can be easily utilized by microorganisms, i.e. from highly terrestrial to obvious biological new features. The FI value of the Yangtze River water body was 2.05, indicating that it was mainly endogenous microbial or authigenic DOM; the FI increased slightly to 2.20 after treatment, indicating that part of the macromolecular or aromatic substances were effectively degraded, and the residual DOM further showed low molecular and endogenous characteristics; the HIX decreased slightly from 0.63 to 0.61, indicating that the degree of humification decreased slightly, which may be related to the removal of macromolecular humus by the synergistic effect of oxidation and flocculation; the BIX decreased from 1.08 to 0.98, indicating that the microbial source or biological new components were reduced during the treatment process, but a certain level of biological new components was still retained. The FI of Li Lake water body was 2.33, which increased to 2.75 after treatment, further indicating that the refractory components were removed or transformed, making the remaining / newly generated DOM tend to be low molecular and easily degradable, and more endogenous to microorganisms. However, the HIX increased from 0.62 to 0.78, showing a trend opposite to that of the Yangtze River water sample, which may be due to the preferential removal of low humification components by flocculation or oxidation, resulting in the relative enrichment of humus in the remaining DOM, or the generation of oxidation intermediates; in addition, the BIX decreased from 1.16 to 0.92, reflecting that a large amount of microbial source DOM was preferentially removed in this system, thus indirectly indicating that this system has a certain selective oxidation and removal effect on different types of DOM.

[0158] Based on the above analysis, it can be seen that the oxidative free radicals generated during the reaction attack the aromatic and unsaturated structures in DOM, causing the macromolecular humus to break and transform into intermediate products with lower molecular weight and simpler structure, and a part of them are further oxidized or removed by flocculation and adsorption; in addition, Fe 2+ / Fe 3+ The Fe(OH)3 colloid generated during the hydrolysis process combines with the hydrophobic groups and negatively charged functional groups in humus to produce flocculation and precipitation, which is particularly evident in systems with high humic acid content, which can significantly reduce the HIX value of the raw water; and the selective removal effect can cause certain specific components to be removed or transformed first, thereby affecting the fluorescence parameters of the remaining DOM.

[0159] Based on the above, the optimized electro-activated ferrous treatment process was applied to real water bodies, and the effects of the process on DBPs formation potential and DOM removal were comprehensively analyzed. The control effect of the treated water on THMs and other by-products formation was evaluated under simulated disinfection conditions, and the transformation of organic components in the water was characterized by three-dimensional fluorescence spectroscopy and fluorescence index methods. The specific conclusions are as follows:

[0160] (1) Effect on disinfection by-product formation potential

[0161] Under simulated conditions of sodium hypochlorite and chloramine addition, the THMs formation of the treated water samples decreased significantly. The experimental results showed that in the HA solution, the TCM reduction after pretreatment could reach 99.5%, while in the actual water bodies, the THMs formation of the Yangtze River and Li Lake water samples also had a large decrease. This phenomenon was mainly attributed to the adsorption and complexation between Fe 2+ Oxidation generated Fe(OH)3 flocs and DOM, and the generation of low molecular substances by oxidative chain scission of part of the DOM molecules, which effectively weakened the reaction ability of organic precursors with free chlorine (or chloramine), significantly reduced the generation risk of disinfection by-products.

[0162] (2) Three-dimensional fluorescence spectroscopy analysis and regional integration

[0163] Three-dimensional fluorescence spectroscopy was used to study the composition and distribution of DOM in the water samples before and after treatment. The results showed that in the untreated water samples, humic acid components dominated in regions III and V, while after treatment, the fluorescence signals in regions III and V decreased significantly, indicating that high molecular humic substances were effectively degraded and removed. In addition, the fluorescence intensity of proteins and microbial metabolites (regions I, II, and IV) in the Yangtze River and Li Lake water bodies also decreased, indicating that the process had broad-spectrum adaptability to different types of organic matter.

[0164] (3) Analysis of water sample fluorescence characteristic parameters

[0165] Through the determination of FI, HIX and BIX, the source and structural changes of DOM were further revealed. After treatment of HA solution, Yangtze River and Li Lake water bodies, the FI value generally increased, indicating that the remaining DOM tended to be low molecular and endogenous; the change of HIX reflected the degree of degradation of humic substances, and the significant decrease of HIX in some water samples indicated that high molecular humic acid was effectively destroyed; the change of BIX indicated the change of biodegradable components. The comprehensive changes of these parameters showed that this process not only reduced the content of organic matter, but also changed the molecular structure and source characteristics of DOM.

[0166] The application effect and safety assessment of the electroactivated ferrous process in actual water treatment provide data support, demonstrating the significant advantages of this technology in improving water quality, reducing organic pollutants, and controlling the generation of disinfection byproducts.

[0167] This specific embodiment is merely an explanation of this application and is not intended to limit it. After reading this specification, those skilled in the art can make modifications to this embodiment without contributing any inventive step, but such modifications are protected by patent law as long as they fall within the scope of the claims of this application.

Claims

1. A process for the synergistic removal of humic acid by electro-activated ferrous sulfate, characterized in that, The process is carried out through a water treatment system, which includes a reaction vessel, a cathode, an anode, and a DC power supply. The water to be treated is located inside the reaction vessel, and the cathode and anode are inserted into the water to be treated. The DC power supply is electrically connected to the cathode and anode. The process for the electro-activated ferrous synergistic removal of humic acid includes the following steps: S1. Adjust the initial pH and temperature of the water to be treated; S2. Insert the cathode and anode into the water to be treated, and adjust the plate spacing between the cathode and anode. The cathode is graphite, and the anode is Ti / TiO2-IrO2-RuO2 or Ti / TiO2-Ta2O5-IrO2. Fe is added to Ti / TiO2-IrO2-RuO2 and Ti / TiO2-Ta2O5-IrO2 respectively. 2+ To carry out the reaction; S3. Apply DC power to the cathode and anode through the DC power supply to perform a water treatment reaction for a specified time.

2. The process for synergistic removal of humic acid by electroactivated ferrous sulfate according to claim 1, characterized in that: In step S1, the initial pH of the water to be treated is 5-9.

3. The process for synergistic removal of humic acid by electro-activated ferrous sulfate according to claim 1, characterized in that: In step S1, the temperature of the water to be treated is 5-45°C.

4. The process for the synergistic removal of humic acid by electroactivated ferrous sulfate according to claim 1, characterized in that: In S2, the plate spacing between the cathode and the anode is 2-6 cm.

5. The process for synergistic removal of humic acid by electroactivated ferrous sulfate according to claim 4, characterized in that: The plate spacing between the cathode and the anode is 2 cm.

6. The process for the synergistic removal of humic acid by electro-activated ferrous sulfate according to claim 1, characterized in that: In S2, Fe 2+ The addition amount is 20mg / L-40mg / L.

7. The process for synergistic removal of humic acid by electroactivated ferrous sulfate according to claim 6, characterized in that: The Fe 2 + The addition amount is 30 mg / L.

8. The process for the synergistic removal of humic acid by electro-activated ferrous sulfate according to claim 1, characterized in that: In step S3, the direct current density is 1 mA / cm². 2 -5mA / cm 2 .

9. The process for the synergistic removal of humic acid by electro-activated ferrous sulfate according to claim 8, characterized in that: In step S3, the direct current density is 3 mA / cm². 2 .

10. The application of the electro-activated ferrous synergistic removal of humic acid process according to any one of claims 1-9, characterized in that, It is used in the field of water treatment.

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