A tea polyphenol modified polyferric flocculant, a preparation method and application thereof

Abstract

This invention discloses a tea polyphenol-modified polyferric sulfate flocculant, its preparation method, and its application, belonging to the field of anaerobic fermentation slurry dewatering. This invention uses polyferric sulfate as the chain-like main body and tea polyphenols as the cross-linking agent. Under alkaline conditions, tea polyphenols form chelate coordination bonds with iron ions in polyferric sulfate, while hydrophilic ether oxygen bonds in polyethylene oxide combine with phenolic hydroxyl groups to form hydrogen bonds, forming a three-component polymer network. The modified polyferric sulfate flocculant prepared by this invention has enhanced charge neutralization capacity compared to conventional flocculants. Through coordination bonds and hydrogen bonds, it improves the flocculant's adsorption bridging and network replenishment / sweeping capabilities, resulting in faster floc formation, larger and stronger flocs, faster settling rates, and higher turbidity and organic matter removal rates.

Description

Technical Field

[0001] This invention belongs to the field of anaerobic fermentation biogas slurry dewatering, specifically relating to a tea polyphenol-modified polyferric flocculant, its preparation method, and its application. Background Technology

[0002] With the rapid development of my country's economy and the continuous improvement of people's living standards, the output of food waste nationwide has been increasing year by year. It is usually in a state of solid-liquid coexistence, and its composition is highly correlated with local dietary habits, but it is generally characterized by high water content. Due to its large volume, high water content, and easy decomposition, food waste has brought great challenges to the management and resource utilization of municipal solid waste, and therefore has always occupied the main market of municipal solid waste treatment.

[0003] Currently, the main methods for treating food waste both domestically and internationally include landfill, incineration, and resource recovery technologies (aerobic composting, anaerobic fermentation, feed production, and insect bioconversion). Landfilling involves combining food waste with ordinary household waste, after sorting, crushing, and compaction, and then burying it together in landfills. Landfilling is not only low-cost and has a large processing capacity, but it is also widely applicable. However, the most significant problem with landfilling is the generation of foul odors, impacting the lives of nearby residents. Furthermore, landfilled waste produces leachate containing carcinogens under the combined effects of microorganisms and high pressure. If this leachate leaks, it can cause secondary pollution to water bodies. Incineration uses high temperatures (approximately 850–1000℃) to oxidize and decompose the organic matter in the waste, thereby reducing its volume. The residue after incineration... Only about 20% of the original slag remains, and its volume is only about 10% of the original volume. The heat released during incineration can be used for power generation and heating. However, this process produces toxic and harmful substances such as dioxins, and the operation and maintenance costs are high, energy consumption is large, and the technical requirements are high. Aerobic composting, on the other hand, uses the oxidative decomposition and biosynthesis of aerobic microorganisms to convert organic matter into stable humus. Food waste, feces, and crop straw can all be treated through aerobic composting. The resulting fertilizer can improve the physical and chemical properties and microbial structure of the soil. However, composting cannot fully recover the rich nutrients in food waste, resulting in poor quality and the potential for secondary pollution. Problems such as contamination and pollution exist, and the high moisture content, high oil content, and high salt content of kitchen waste can adversely affect microbial activity, thus hindering the application of compost products on large-scale land. Feed processing can employ two methods: biological and physical. The biological method utilizes microorganisms to treat kitchen waste, accumulating useful microorganisms, enzymes, and intermediate metabolites through their growth, reproduction, and metabolism. After drying, these can be processed into protein feed. The physical method involves dehydrating the kitchen waste, then using high-temperature treatment to kill viruses, followed by crushing and processing into feed. Although high-temperature treatment can effectively kill some viruses, it cannot completely eliminate them. Ensuring the complete elimination of all viruses is crucial, but using this feed to feed animals could pose a risk of disease transmission. Therefore, biosafety concerns limit the application and development of food waste as animal feed. Insect bioconversion technology utilizes the synergistic metabolic action of specific organisms such as fly larvae, black soldier flies, mealworms, and earthworms with environmental microorganisms under controlled artificial conditions to ultimately produce fly larvae or black soldier flies. This technology is simple to operate, consumes less energy, reduces processing costs, and brings economic, environmental, and social benefits. However, due to the low level of automation in its production equipment, high environmental control costs, and product sales issues, it is difficult to achieve large-scale production.

[0004] Food waste is rich in organic matter, and its biogas production capacity is about 15 times that of livestock and poultry manure, making it extremely suitable as a substrate for anaerobic fermentation. Anaerobic fermentation of food waste can reduce its environmental impact and produce biogas, a clean and renewable energy source that can be used as fuel and for power generation. The resulting biogas slurry and residue can be used as organic fertilizer. The closed fermentation tank prevents the spread of odors. Therefore, anaerobic fermentation has become the mainstream technology for the resource utilization of food waste due to its high energy recovery potential. However, due to the high moisture content of food waste, a large amount of biogas slurry and residue are produced after anaerobic fermentation. Achieving low-cost and efficient separation of biogas slurry and residue is an important step.

[0005] The anaerobic fermentation broth from food waste has a high suspended solids content, with many negatively charged particles, making it very stable and resulting in poor dewatering. The main dewatering agent on the market is PAC (polyacrylamide), but its addition easily leads to pipe scaling and blockage, affecting centrifuge efficiency and severely impacting production. Furthermore, PAC is added as a solid-state dissolution agent, requiring a large workload and generating significant solid waste, resulting in excessively high overall costs. Additionally, the clarified liquid produced after separating the sludge and biogas slurry still contains high concentrations of COD and ammonia nitrogen, failing to meet emission standards. Therefore, further treatment is necessary to achieve emission targets. Summary of the Invention

[0006] This invention provides a tea polyphenol-modified polyferric flocculant, its preparation method, and its application. It can enhance the charge neutralization ability of the flocculant, and the prepared flocculant has a large network structure, thereby enhancing its net-catching ability. Furthermore, the formed flocs have high strength and are not easily compressed and destroyed by water flow, thus achieving good flocculation performance with a relatively small amount of flocculant added.

[0007] To achieve the above objectives, the present invention adopts the following technical solution:

[0008] A method for preparing a tea polyphenol-modified polyferric flocculant includes the following steps:

[0009] Dissolve polyethylene oxide in deionized water, and stir for 30-60 minutes after the liquid becomes clear to obtain solution A;

[0010] Add tea polyphenols to solution A and stir at a certain temperature for 20-30 minutes to carry out the hydrogen bond formation reaction;

[0011] Polyferric sulfate was dissolved in water to obtain solution B. Solution B was added to solution A after the reaction. The pH of the mixture was adjusted with NaOH solution, and the mixture was stirred at a specific temperature and then allowed to stand for aging to obtain a novel composite polyferric flocculant.

[0012] In the steps described above, the stirring time after the polyethylene oxide is dissolved in water is 30 to 60 minutes, preferably 60 minutes;

[0013] The molar ratio of tea polyphenols to polyethylene oxide is (20-30):(30-40), preferably 25:30; the stirring temperature after adding tea polyphenols to solution A is 20-30°C, preferably 25°C;

[0014] The molar ratio of polyferric sulfate to tea polyphenols is (5-15):(20-40), preferably 8:25; the pH is adjusted to 7-10 with NaOH solution; the stirring temperature after pH adjustment is 20-30℃, preferably 25℃.

[0015] The tea polyphenol-modified polyferric flocculant prepared above has a large network structure and a large number of hydrogen bonds and coordination bonds; the specific structure is as follows:

[0016]

[0017] Beneficial effects: This invention provides a tea polyphenol-modified polyferric flocculant, its preparation method, and its application, which have the following advantages compared with the prior art:

[0018] (1) Tea polyphenols have a lot of phenolic hydroxyl groups. Under alkaline conditions, they form chelate coordination bonds with iron ions in polyferric sulfate. Meanwhile, the main functional groups in polyethylene oxide are hydrophilic ether oxygen bonds, which are more likely to combine with phenolic hydroxyl groups to form hydrogen bonds. Therefore, tea polyphenols can act as crosslinking agents in the coagulation process of polyethylene oxide and polyferric sulfate, combining them to form a three-component polymer network with a large number of hydrogen bonds and coordination bonds. This gives the flocs sufficient crosslinking degree and flocculation strength.

[0019] (2) The modified polyferric flocculant prepared by the present invention has the ability to neutralize electricity, while its adsorption bridging and net filling sweeping ability is greatly improved, the floc formation rate is faster, the flocs are larger and stronger, the settling rate is faster, the turbidity and organic matter removal rate is high, and the coagulation performance is better than that of conventional flocculants on the market.

[0020] (3) The preparation process of this invention is simple to operate, requires fewer types of raw materials and is inexpensive, does not require the addition of coagulant during coagulation, and the treated water has no residual iron, tea polyphenols and polyethylene oxide monomers, which can reduce the preparation cost while ensuring the safety of the effluent water quality and no secondary pollution.

[0021] (4) The present invention increases the network structure of polyferric molecules by introducing tea polyphenols and polyethylene oxide, which greatly improves the flocculation ability of flocculants, and the amount of flocculant used is less, resulting in lower treatment costs. Attached Figure Description

[0022] Figure 1This is a reaction mechanism diagram of the preparation method in the embodiments of the present invention;

[0023] Figure 2 This is a comparison diagram of the raw biogas slurry in the embodiment of the present invention and the experimental process. Detailed Implementation

[0024] The present invention will now be described in detail with reference to the accompanying drawings and specific embodiments:

[0025] like Figure 1 As shown, polyethylene oxide contains hydrophilic ether oxygen bonds, which readily combine with the phenolic hydroxyl groups in tea polyphenols to form hydrogen bonds in the environment, thus obtaining a hydrogen-bonded product. Then, under alkaline or slightly alkaline conditions, polyferric sulfate containing ferric ions is added, which combines with the phenolic hydroxyl groups under alkaline conditions to form coordinate bonds. These coordinate bonds are very stable, and finally, a three-component polymer with tea polyphenols as a crosslinking agent is obtained.

[0026] Example 1

[0027] A method for preparing a novel polyferric flocculant modified with tea polyphenols includes the following steps:

[0028] By molar amount, 40 parts of polyethylene oxide were dissolved in deionized water, and the solution was stirred for 50 minutes after the liquid became clear to obtain a polyethylene oxide solution. 30 parts of tea polyphenols were added to the polyethylene oxide solution and magnetically stirred at 25°C to initiate the hydrogen bond formation reaction. 10 parts of polyferric sulfate were dissolved in water to obtain a polyferric solution. The polyferric solution was added to the reacted polyethylene oxide solution to obtain a mixture. The pH of the mixture was adjusted to 10 with NaOH solution, stirred at 20°C, and then allowed to stand for aging to obtain a novel composite polyferric flocculant.

[0029] Example 2

[0030] A method for preparing a novel polyferric flocculant modified with tea polyphenols includes the following steps:

[0031] By molar amount, 30 parts of polyethylene oxide were dissolved in deionized water, and the solution was stirred for 60 minutes after the liquid became clear to obtain a polyethylene oxide solution. 25 parts of tea polyphenols were added to the polyethylene oxide solution and magnetically stirred at 25°C to initiate the hydrogen bond formation reaction. 8 parts of polyferric sulfate were dissolved in water to obtain a polyferric solution. The polyferric solution was added to the reacted polyethylene oxide solution to obtain a mixture. The pH of the mixture was adjusted to 8.0 with NaOH solution, stirred at 25°C, and then allowed to stand for aging to obtain a novel composite polyferric flocculant.

[0032] The above-described embodiments and traditional PAC and PFS flocculants were used in dewatering tests of anaerobic fermentation slurry from kitchen waste. The mass ratio of the applied flocculant concentrate to the original slurry was 50,000 ppm. The water content of the anaerobic fermentation slurry from kitchen waste was 97%, the pH was 8.0, the initial COD was 8338 mg / L, the initial ammonia nitrogen was 3013.1 mg / L, the initial TN was 3384.3 mg / L, and the initial SS was 7895.5 mg / L. The comparison results are as follows (unit: mg / L):

[0033] Table 1. Comparison of flocculant and PAC flocculant in the dewatering of anaerobic fermentation slurry from kitchen waste in the examples.

[0034] Sample Name effluent COD Ammonia nitrogen in effluent Outflow TN Water SS Example 1 4654 1863 2318 557 Example 2 4372 1677 2015 473 PAC 5191.8 2122.3 2611.8 3175

[0035] Table 2 shows the removal rates of various indicators of the flocculant and PAC flocculant used in the anaerobic fermentation slurry of kitchen waste in the embodiments.

[0036] Sample Name COD removal rate ammonia nitrogen removal rate TN removal rate SS removal rate Example 1 44.2％ 38.2％ 31.5％ 92.9％ Example 2 47.6％ 44.3％ 40.5％ 94％ PAC 37.7％ 29.6％ 22.8％ 60％

[0037] Comparing the results in Tables 1 and 2 above, it can be seen that the novel polyferric flocculants prepared in Examples 1 and 2 have an absolute advantage over traditional PAC in terms of dewatering effect on anaerobic fermentation slurry from kitchen waste. Furthermore, the flocculant prepared in Example 2 is even more effective than that in Example 1, indicating that the preparation method in Example 2 is optimal. This is because the ratio of polyethylene oxide to tea polyphenols and the stirring time for hydrogen bond formation in Example 2 are superior to those in Example 1. When adjusting the pH with NaOH solution, Example 2 adjusts it to the optimal level of 8.0, which results in more coordinate bonds being formed subsequently, leading to a larger polymeric network structure and a more stable flocculated structure. Moreover, as... Figure 2 During the experiment shown, the flocs were large and dense, and the flocs settled in layers at a fast rate.

[0038] The above are merely preferred embodiments of the present invention, which are helpful for those skilled in the art to further understand the present invention, but do not limit the present invention in any way. It should be noted that for those skilled in the art, any modifications and improvements made without departing from the concept of the present invention are protected by the present invention.

Claims

1. A tea polyphenol-modified polyferric flocculant, characterized by, The flocculant is a polymer network structure combined by hydrogen bonds and coordination bonds, and the structure of the flocculant is as follows: 。 2. A method for preparing the tea polyphenol-modified polyferric flocculant as described in claim 1, characterized in that, The method comprises the following steps: Dissolve polyethylene oxide in deionized water, and stir to obtain solution A after the liquid becomes clear; Add tea polyphenol into solution A, and stir to generate hydrogen bonds; Dissolve polyferric sulfate in water to obtain solution B, add solution B into the solution A after the generation of hydrogen bonds, adjust pH, and then stir and stand to obtain modified polyferric flocculant.

3. The preparation method of the tea polyphenol-modified polyferric flocculant according to claim 2, characterized in that, The stirring time of the polyethylene oxide dissolved in water is 30-60 min.

4. The preparation method of the tea polyphenol-modified polyferric flocculant according to claim 2, characterized in that, The molar ratio of tea polyphenol to polyethylene oxide is (20-30):(30-40).

5. The method for preparing the tea polyphenol-modified polyferric flocculant according to claim 2 or 4, characterized in that, The stirring temperature of solution A after adding tea polyphenol is 20-30℃.

6. The preparation method of the tea polyphenol-modified polyferric flocculant according to claim 2, characterized in that, The molar ratio of polyferric sulfate to tea polyphenol is (5-15):(20-40).

7. The preparation method of the tea polyphenol-modified polyferric flocculant according to claim 2, characterized in that, Adjust the pH to 7-10.

8. The method for preparing tea polyphenol-modified polyferric coagulant according to claim 2 or 7, characterized in that, The stirring temperature after adjusting the pH is 20-30℃.

9. The use of the tea polyphenol modified polyferric coagulant of claim 1, characterized in that, The flocculant is used for dewatering of anaerobic fermentation of kitchen waste.

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