A treatment process for cassava fiber and fine chemical mixed wastewater

Abstract

This invention relates to a treatment process for mixed wastewater from cassava fiber and fine chemical processes, belonging to the field of wastewater treatment technology. The treatment process includes the following steps: after adjusting the pH of the mixed wastewater, it enters an acid precipitation flotation tank for flotation separation, then enters a pH adjustment tank, and subsequently, it reacts with hydrogen peroxide from the bottom into a Fenton-like fixed-bed reaction tank for catalytic oxidation under the action of a Fenton-like catalyst. Next, it enters a neutralization and adjustment tank, followed by a secondary A / O system for anoxic and aerobic biological treatment, then a secondary sedimentation tank and a phosphorus removal tank, and finally an ozone oxidation tank where ozone is circulated and added via micro-nano bubbles for deep oxidation under the action of an ozone catalyst. Finally, the wastewater meets discharge standards. This invention improves wastewater treatment efficiency and ensures stable effluent compliance through a synergistic multi-stage treatment process.

Description

Technical Field

[0001] This invention relates to the field of wastewater treatment technology, and in particular to a treatment process for mixed wastewater from cassava fiber and fine chemicals. Background Technology

[0002] Cassava alcohol production primarily uses fresh or dried cassava as raw material, undergoing processes such as crushing, pulping, cooking, saccharification, fermentation, and distillation to obtain the product. The biggest source of pollution is the distillation wastewater discharged after distillation; for every ton of alcohol produced, 12-15 tons of distillation wastewater are generated. This wastewater is characterized by high concentrations of organic pollutants (COD typically reaching 20,000-50,000 mg / L) and high levels of suspended solids (SS reaching 2,000-5,000 mg / L), including incompletely decomposed cassava fiber. Meanwhile, fine chemical wastewater is characterized by its complexity, toxicity, and difficulty in treatment. It contains a large amount of structurally stable organic pollutants (such as benzene compounds and heterocyclic compounds), and some components are highly toxic, exhibiting extremely poor biodegradability (B / C ratio typically below 0.2).

[0003] When the two types of wastewater are mixed, their combined characteristics present complex treatment challenges. First, cassava fiber is granular or flocculent with a wide particle size distribution, easily clogging pipes, pumps, and the water distribution system of subsequent treatment units. If it directly enters advanced oxidation or biochemical units, it will deposit on the catalyst surface or microbial carriers, leading to a sharp decline in treatment efficiency. Cassava alcohol distillation wastewater has a high discharge temperature (50-70℃), while fine chemical wastewater has a variable temperature. The mixed wastewater has an unstable temperature, adversely affecting the microbial activity of the biochemical system. The mixed wastewater has a darker color, affecting the sensory indicators of the effluent, and the coloring substances are often difficult to remove using conventional methods. Second, the mixed wastewater has a high total COD and contains both easily degradable organic matter (such as sugars and organic acids) and recalcitrant organic matter (such as lignin derivatives and synthetic intermediates). The recalcitrant components have stable structures, making them difficult to mineralize using conventional biochemical methods. Fine chemical wastewater contains a large amount of resistant organic matter, resulting in an overall B / C ratio in the mixed wastewater typically below 0.2-0.3. Direct biological treatment is inefficient, necessitating pretreatment to improve its biodegradability. Fine chemical wastewater may contain toxic substances such as phenols, halogenated hydrocarbons, and nitro compounds, which inhibit sensitive microorganisms like nitrifying and denitrifying bacteria, potentially leading to the collapse of the biological system. The two types of wastewater have different pH levels, with the mixed wastewater exhibiting pH fluctuations between 2 and 12, threatening the stable operation of subsequent treatment units. Furthermore, cassava fiber wastewater has an excessively high C / N ratio while being relatively deficient in nitrogen and phosphorus, hindering normal microbial metabolism and requiring the addition of nutrients to maintain the biological system's operation.

[0004] Currently, the advanced treatment process for this type of wastewater is generally "air flotation + Fenton + AO system + secondary sedimentation tank". However, this traditional process has obvious defects in practical application: (1) Incomplete treatment: Traditional Fenton oxidation has limited mineralization capacity for high concentrations of recalcitrant organic matter, and the COD of the effluent is often difficult to stably reach the first-level discharge standard (≤100mg / L); (2) High operating cost: The dosage of Fenton reagent (ferrous salt and hydrogen peroxide) is large, generating a large amount of iron-containing chemical sludge, and the sludge treatment and disposal costs are high; (3) Weak shock resistance: The biochemical system is easily affected by water quality fluctuations and has a long recovery period; (4) Insufficient adaptability: It has not been optimized for the high suspended solids and high fiber characteristics of mixed wastewater, resulting in frequent blockage of the pretreatment unit and affecting the overall operational stability.

[0005] In summary, considering the complex characteristics of mixed wastewater from cassava fiber and fine chemicals, developing a deep treatment process that is stable in operation, highly efficient, resistant to shock, and produces high-quality effluent has significant practical implications and application value. Summary of the Invention

[0006] To address the aforementioned technical problems, this invention provides a treatment process for mixed wastewater from cassava fiber and fine chemicals. This invention improves wastewater treatment efficiency through a synergistic multi-stage treatment process, ensuring stable effluent compliance with standards.

[0007] In a first aspect, the present invention provides a treatment process for mixed wastewater from cassava fiber and fine chemicals, the treatment process comprising the following steps: (1) Acid precipitation flotation treatment: The pH of the mixed wastewater is adjusted to 3.0-4.0 and then enters the acid precipitation flotation tank for flotation separation; (2) Fenton-like fixed bed catalytic oxidation treatment: The effluent from step (1) enters the pH adjustment tank to adjust the pH to 3.0-3.5, and then enters the Fenton-like fixed bed reaction tank from the bottom with hydrogen peroxide, and carries out catalytic oxidation reaction under the action of Fenton-like catalyst; (3) Neutralization and biochemical treatment: The effluent from step (2) enters the neutralization and conditioning tank to adjust the pH to neutral, and then enters the secondary A / O system for anoxic and aerobic biological treatment; (4) Deep oxidation treatment: The effluent from step (3) is fed into a secondary sedimentation tank and a phosphorus removal tank, and then into an ozone oxidation tank. Ozone is added in a circulation manner through micro-nano bubbles, and deep oxidation is carried out under the action of ozone catalyst. Finally, the wastewater meets the discharge standards.

[0008] In the above technical solution, in step (1), the pH of the mixed wastewater is adjusted to an acidic state of 3.0-4.0, causing cassava fiber and some colloidal substances to flocculate and precipitate, which are then efficiently removed by dissolved air flotation. This step can remove most of the suspended solids and fibers, reducing the solid load of subsequent units. It can also prevent fibers from entering the subsequent catalyst bed and causing blockage, thus protecting the catalyst activity. At the same time, it removes some COD, reducing the pressure on subsequent treatment.

[0009] In step (2), the pH is precisely adjusted to a weakly acidic condition of 3.0-3.5 because Fe 2+ / Fe 3+ and Cu + / Cu 2+ The hydrogen peroxide redox couple exhibits the highest activity within this pH range, with the best decomposition efficiency for H2O2. After mixing with wastewater in the inlet pipe, hydrogen peroxide enters the reaction tank from the bottom using an upflow method, ensuring sufficient contact between the wastewater and the catalyst, extending the reaction time, and improving oxidation efficiency. Under the action of the iron-copper bimetallic catalyst, H2O2 is activated to generate hydroxyl radicals (·OH) and singlet oxygen (¹O2), oxidizing and decomposing recalcitrant organic matter into smaller molecules, significantly improving the biodegradability of the wastewater and creating favorable conditions for subsequent biological treatment.

[0010] Step (3) involves neutralization and biochemical treatment of the wastewater pretreated with advanced oxidation, followed by conventional biological treatment. The neutralization and equalization tank adjusts the wastewater pH to neutral (6.5-7.5) to create a suitable environment for microbial growth. The secondary A / O system includes an anoxic tank and an aerobic tank. In the anoxic tank, denitrifying bacteria reduce nitrates to nitrogen, achieving denitrification. In the aerobic tank, aerobic bacteria degrade organic matter and oxidize ammonia nitrogen to nitrates. Through alternating anoxic and aerobic operation, both organic matter removal and nitrogen removal can be achieved simultaneously.

[0011] The deep oxidation treatment in step (4) is crucial to ensuring that the effluent meets the standards. Wastewater first enters a secondary sedimentation tank for sludge-water separation. The supernatant then enters a phosphorus removal tank for chemical phosphorus removal to ensure total phosphorus meets the standards, and subsequently enters an ozone oxidation tank. The use of micro-nano bubbles for circulating ozone addition greatly increases the contact area between ozone gas and water, improving ozone solubility and mass transfer efficiency. Simultaneously, the bursting of micro-nano bubbles generates localized high temperature and pressure, which catalyzes the generation of more hydroxyl radicals, further enhancing oxidation efficiency. Under the action of a manganese oxide catalyst, ozone is activated to generate hydroxyl radicals and singlet oxygen, deeply mineralizing residual recalcitrant organic matter and ensuring that the effluent meets discharge standards.

[0012] Optionally, in step (2), the Fenton-like fixed-bed reactor is provided with a water distribution zone, a support layer, a catalyst bed and a buffer zone from bottom to top; the support layer includes a support beam, a grid covering, a pebble layer and a quartz sand layer.

[0013] In the aforementioned technical solution, the Fenton-like fixed-bed reactor features a layered structure. The water distribution zone is located at the bottom, ensuring even distribution of the incoming water across the entire bed cross-section, preventing short-circuiting and flow deviation. The support layer, composed of support beams, a surface grid, pebbles, and quartz sand, with particle sizes decreasing from bottom to top, serves multiple functions: supporting the catalyst, evenly distributing the water flow, and preventing catalyst loss. The catalyst bed, filled with active catalyst, is the region where the oxidation reaction occurs. The buffer zone, located at the top, provides stable space for the water flow and facilitates the installation of a sludge scraper. This layered structure ensures long-term stable operation of the reactor, preventing catalyst loss and bed clogging.

[0014] The grating plate measures 38×38×50mm and is made of pure 901 or 907 epoxy resin with a panel thickness of 3cm, featuring high strength and corrosion resistance. The cobblestones have a particle size of 6-9mm, the quartz sand 0.5-1.0mm, and the catalyst 80-240 mesh, with the particle size decreasing sequentially to form a graded support layer, effectively preventing catalyst loss with the water flow. Simultaneously, the wastewater upward flow velocity is controlled to be less than 8m / h, keeping the catalyst bed in a slightly expanded state, ensuring sufficient contact between the wastewater and the catalyst while preventing the catalyst from being washed out of the bed. A liftable rotary sawtooth scraper is installed at the top of the reaction tank to periodically clean contaminants trapped on the catalyst surface, preventing bed caking and maintaining catalyst activity.

[0015] The grating panel measures 38*38*50 mm, made of pure 901 or 907 resin, with a panel thickness of 3 cm. The cobblestones have a particle size of 6-9 mm, and the quartz sand has a particle size of 0.5-1.0 mm. The particle size decreases sequentially from cobblestones to quartz sand and then to catalyst, thus supporting the catalyst and preventing its loss. Simultaneously, the upward flow velocity of the wastewater is less than 8 m / h to ensure that the catalyst is not lost.

[0016] Optionally, the Fenton-like catalyst is an iron-copper bimetallic oxide / geopolymer microsphere catalyst, wherein the catalyst uses porous geopolymer microspheres as a support, and iron oxide nanoparticles and copper oxide nanoparticles are loaded on the surface and in the pores of the support.

[0017] In the above technical solution, the geopolymer is formed from metakaolin under alkali activation, possessing a three-dimensional network structure, high mechanical strength, and resistance to acid and alkali corrosion, making it suitable for long-term use in wastewater treatment. The microspheres prepared by the suspension solidification method have a macroporous-mesoporous hierarchical structure, with macropores ranging from 50-200 μm in diameter, allowing cassava fibers to pass through smoothly and preventing bed clogging. The surface of the geopolymer is rich in hydroxyl groups (-OH), which can form chemical bonds with metal oxides, enhancing the adhesion of active components and extending catalyst lifetime.

[0018] Fe 2+ / Fe 3+Redox pairs can directly activate H₂O₂ to generate hydroxyl radicals (·OH). The introduction of copper has a dual effect: on the one hand, Cu… + / Cu 2+ Redox reactions can catalyze the decomposition of H₂O₂ to generate free radicals, while Cu + Can accelerate Fe 3+ Reduced to Fe 2+ Fe 2+ / Fe 3+ and Cu + / Cu 2+ The electron cycling of the two redox pairs significantly improves the utilization rate of H2O2 and the reaction rate.

[0019] Optionally, the iron oxide is Fe2O3 or Fe3O4, with a loading of 5-10 wt%; the copper oxide is CuO, with a loading of 3-8 wt%; and the molar ratio of iron to copper is 2-1:1.

[0020] In the above technical solutions, an iron loading of 5-10 wt% ensures sufficient active sites; too low a loading results in insufficient activity, while too high a loading leads to nanoparticle aggregation and blockage of microsphere pores. A copper loading of 3-8 wt% can control the risk of copper ion dissolution while ensuring a synergistic effect. Within the iron-copper molar ratio range of 2-1:1, when iron is in excess (>2:1), the synergistic effect of copper is diluted; when copper is in excess (<1:1), the active sites of iron are covered, and copper dissolution increases. A bimetallic synergistic effect can be achieved within this sub-molar ratio range.

[0021] Optionally, the specific preparation steps of the Fenton-like catalyst are as follows: (1) Preparation of geopolymer microsphere carrier: Mix metakaolin and water glass at a mass ratio of 10:3-5 evenly and stir for 10-20 min to obtain geopolymer slurry. Drop the slurry evenly into hot silicone oil at 80-90℃ and stir to disperse at 200-400 rpm. After the droplets solidify in the silicone oil for 10-30 min, take them out, wash with deionized water to remove the surface silicone oil, and dry at 60-80℃ for 12-24 h to obtain porous geopolymer microspheres. (2) Iron-copper bimetallic loading: Prepare a mixed solution containing iron salt and copper salt, with a total metal ion concentration of 0.5-1.0 mol / L. Immerse the geopolymer microspheres in the mixed solution, sonicate for 25-35 min, let stand for 10-15 h, and then dry at 75-85℃ for 10-15 h. (3) Calcination activation: The dried microspheres are placed in a muffle furnace and heated to 400-500℃ at 3-5℃ / min for 3-5h. After natural cooling, the Fenton-like catalyst is obtained.

[0022] In the above technical solution, metakaolin (Al2O3·2SiO2) undergoes a depolymerization-condensation reaction under the action of water glass to form an amorphous geopolymer gel (NASH gel) with a three-dimensional network structure. Water generated during the geopolymerization process evaporates, leaving pores, and the accumulation of the gel network itself forms a mesoporous structure. This macroporous-mesoporous hierarchical structure allows cassava fibers to pass through smoothly, avoiding bed clogging. The slurry is then dropped into hot silicone oil, utilizing interfacial tension to spherize the droplets. The silicone oil, acting as a dispersion medium, is insoluble in water, ensuring the slurry droplets remain spherical. Subsequently, it is thermally cured at 80-90℃. The high temperature accelerates the geopolymerization reaction, promotes gel network formation, and allows the microspheres to solidify rapidly and maintain their shape. Stirring and dispersion prevent microsphere adhesion and control the microsphere particle size distribution.

[0023] Fe 3+ and Cu 2+ The ions exist in aqueous solution as hydrated ions. Controlling the molar ratio ensures the bimetallic synergistic effect. During impregnation, the solution enters the microsphere channels through capillary action, and the metal ions diffuse with the solution to the interior and surface of the microspheres. During ultrasonication, the ultrasound generates a cavitation effect, promoting the uniform distribution of metal ions within the microsphere channels and preventing excessively high local concentrations. After standing for 10-15 hours, the metal ions are fully adsorbed onto the surface of the microspheres and the inner walls of the channels. The adsorption mechanisms are: ① coordination with hydroxyl groups (-OH) on the carrier surface; ② adsorption onto the negatively charged carrier surface through electrostatic attraction. Drying at 75-85℃ for 10-15 hours slowly removes moisture, allowing the metal salt to be uniformly deposited within the channels, preventing rapid drying from causing salt migration to the surface.

[0024] Slow heating at a rate of 3-5℃ / min prevents microsphere cracking due to thermal stress and also ensures a gradual decomposition of nitrates, avoiding a sudden increase in pressure within the pores that could damage the structure. Calcination at 400-500℃ for 3-5 hours decomposes the nitrates: 2Fe(NO3)3 → Fe2O3 + 6NO2↑ + 1.5O2↑, 2Cu(NO3)2 → 2CuO + 4NO2↑ + O2↑, forming nano-Fe2O3 and CuO particles. Simultaneously, the metal oxides form chemical bonds with the support surface (e.g., Fe-O-Si, Cu-O-Si), enhancing the bonding strength and improving stability.

[0025] Optionally, the method of adding ozone in step (4) is as follows: the wastewater in the contact tank is pumped out by a circulation pump, mixed with ozone by a gas-liquid mixer to form micro-nano bubbles, and then returned to the bottom of the tank.

[0026] In the aforementioned technical solutions, traditional ozone aeration methods result in large bubble diameters, rapid rising speeds, short gas-liquid contact times, and low ozone utilization rates. This invention employs a circulating pump to extract wastewater from the pool, which is then forcefully mixed with ozone generated by an ozone generator in a gas-liquid mixer. This mixture utilizes shearing action to form micro / nano bubbles with a diameter of less than 50 μm, which are then returned to the bottom of the pool. Micro / nano bubbles offer the following advantages: ① Large specific surface area, resulting in high gas-liquid mass transfer efficiency; ② Slow rising speed and long residence time in water, increasing ozone dissolution time; ③ Localized high temperature and pressure generated when bubbles burst, catalyzing the generation of more hydroxyl radicals; ④ Charged surfaces of micro / nano bubbles, which can adsorb pollutants with opposite charges in the water, improving removal efficiency. This technology can achieve ozone utilization rates exceeding 95%, significantly reducing ozone consumption and operating costs.

[0027] Optionally, the ozone catalyst is a manganese oxide / geopolymer microsphere catalyst, wherein the catalyst uses porous geopolymer microspheres as a support, and manganese oxide nanoparticles are loaded on the surface and in the pores of the support.

[0028] In the above technical solution, manganese is one of the transition metals with the highest ozone catalytic activity. The abundant oxygen vacancies on the surface of MnO2 and / or Mn2O3 can effectively promote ozone decomposition to generate hydroxyl radicals (·OH) and singlet oxygen (¹O2). Using the same geopolymer microsphere support as the Fenton-like catalyst can achieve synergistic production of the two types of catalysts and reduce industrialization costs.

[0029] Optionally, the manganese oxide is MnO2 and / or Mn2O3, and the loading is 5-10% of the total mass of the ozone catalyst.

[0030] In the above technical solution, a manganese loading of 5-10% can ensure sufficient active centers. If it is too low, the catalytic activity will be insufficient, and if it is too high, the nanoparticles will easily agglomerate, reducing the specific surface area.

[0031] Optionally, the ozone catalyst is prepared using the following steps: (1) Preparation of geopolymer microsphere carrier: Mix metakaolin and water glass at a mass ratio of 10:3-5 evenly and stir for 10-20 min to obtain geopolymer slurry. Drop the slurry evenly into hot silicone oil at 80-90℃ and stir to disperse at 200-400 rpm. After the droplets solidify in the silicone oil for 10-30 min, take them out, wash with deionized water to remove the surface silicone oil, and dry at 60-80℃ for 12-24 h to obtain porous geopolymer microspheres. (2) Manganese metal loading: The porous geopolymer microspheres are immersed in a 0.1-0.3 mol / L potassium permanganate solution for 2-4 hours, and then dried at 75-85℃ for 1-3 hours. (3) Reduction and transformation: The dried microspheres are immersed in a reducing agent solution of 0.8-1.2 mol / L for 1-3 hours. After soaking, the microspheres are taken out, washed repeatedly with deionized water until neutral, and dried at 75-85℃ for 10-15 hours to obtain the ozone catalyst.

[0032] In the above technical solution, potassium permanganate is used as a precursor, KMnO4 is a strong oxidizing agent, and MnO4 is a chemical precursor. - The negatively charged ions can be adsorbed onto the positively charged sites on the surface of geopolymer microspheres through electrostatic interactions. Soaking for 2-4 hours can preserve the MnO4... - The MnO4 fully diffuses into the deep pores of the microspheres, laying the foundation for subsequent uniform loading. It is then dried at 75-85℃ for 1-3 hours to remove moisture, allowing the MnO4 to fully diffuse into the microspheres. - It is evenly deposited on the inner wall of the pore.

[0033] The reducing agent solution is at least one of citric acid, oxalic acid, or ascorbic acid. Citric acid, oxalic acid, ascorbic acid, and other organic acids are mild reducing agents and can reduce MnO4 at room temperature. - It is reduced to MnO2. MnO4 - Within the pores, the MnO2 nanoparticles are reduced and directly nucleate and grow on the support surface, exhibiting strong adhesion and resistance to detachment. The reduction reaction can be completed at room temperature with extremely low energy consumption. Washing to neutrality removes residual reducing agent and reaction byproducts, preventing interference with subsequent catalytic reactions.

[0034] In summary, the present invention has at least one of the following beneficial technical effects: 1. This invention efficiently removes cassava fiber through acid precipitation and air flotation, avoiding clogging of subsequent catalysts; the Fenton-like unit converts recalcitrant organic matter into easily biodegradable small molecules, improving biodegradability; the ozone unit deeply mineralizes residual organic matter; and through a synergistic multi-stage treatment process, treatment efficiency is improved, ensuring stable effluent compliance.

[0035] 2. The Fenton-like catalyst of this invention utilizes iron-copper bimetallic oxide / geopolymer microspheres, taking advantage of Fe... 2+ / Fe 3+ and Cu + / Cu 2+ The synergistic effect of the two redox pairs accelerates electron transfer and improves H2O2 utilization. The ozone catalyst is prepared by a two-step redox impregnation method using manganese oxide / geopolymer microspheres, which does not require calcination and has a simple process. Both catalysts use geopolymer microspheres as carriers, and their macroporous structure is specially designed for fibrous wastewater, giving them strong anti-clogging ability.

[0036] 3. Both types of catalysts in this invention can simultaneously generate hydroxyl radicals (·OH) and singlet oxygen (¹O2) during the reaction, forming a free radical-non-free radical mixed degradation. Singlet oxygen has a positive effect on Cl-. - SO4 2- Inorganic salt anions are not sensitive, making it particularly suitable for the high-salt characteristics of fine chemical wastewater, thus solving the problem that traditional advanced oxidation processes are easily quenched in high-salt environments.

[0037] 4. The ozone oxidation unit of this invention adopts micro-nano bubble circulation dosing technology, and the ozone utilization rate reaches more than 95%, which is twice that of the traditional aeration method, significantly reducing ozone consumption and operating costs.

[0038] 5. This invention uses a heterogeneous catalyst, which avoids the large amount of iron salt added and iron sludge generated in the traditional Fenton process, reducing sludge production by more than 90%; the utilization rate of hydrogen peroxide and ozone is high, and the cost of reagents is reduced by 30-50%; the overall process is stable and easy to maintain, with significant economic and environmental benefits. Attached Figure Description

[0039] Figure 1 This is a process flow diagram of the treatment process for mixed wastewater from cassava fiber and fine chemicals in Example 1 of this application.

[0040] Figure 2 This is a SEM image of the Fenton-like catalyst prepared in Example 2 of this application.

[0041] Figure 3 This is a SEM image of the ozone catalyst prepared in Example 5 of this application. Detailed Implementation

[0042] The present invention will be further described in detail below with reference to the embodiments.

[0043] All materials used in the following examples are available for purchase on the market.

[0044] Example 1: This example provides a treatment process for mixed wastewater from cassava fiber and fine chemicals.

[0045] The influent wastewater from the mixture of cassava alcohol and fine chemical processing has the following characteristics: COD 4200 mg / L, BOD5 750 mg / L (B / C = 0.18), SS 1600 mg / L, NH3-N 130 mg / L, TP 12 mg / L, Cl... - 3500 mg / L, pH fluctuating between 4.5 and 9.8. The Fenton-like fixed-bed reactor is arranged from bottom to top as follows: a water distribution zone, a support layer, a catalyst bed, and a buffer zone. The support layer includes support beams, a covered grid, a pebble layer, and a quartz sand layer.

[0046] The process flow diagram for treating mixed wastewater from cassava fiber and fine chemicals is as follows: Figure 1 As shown. The specific steps are as follows: S1. Acid precipitation flotation treatment: Adjust the pH of the mixed wastewater to 3.5 and enter the acid precipitation flotation tank for flotation separation. The hydraulic retention time is 40 minutes.

[0047] S2. Fenton-like fixed-bed catalytic oxidation treatment: The sludge from the previous step enters the sludge thickener, then the sludge dewatering machine, and the effluent enters the pH adjustment tank to adjust the pH to 3.3. Then, it enters the Fenton-like fixed-bed reaction tank from the bottom with hydrogen peroxide and undergoes catalytic oxidation under the action of the zero-valent iron sulfide catalyst (prepared by the method of preparing zero-valent iron sulfide in Chinese patent publication number CN114950329A).

[0048] S3, Neutralization and Biological Treatment: The effluent from the previous step enters the neutralization and equalization tank to adjust the pH to neutral, and then enters the secondary A / O system for anoxic and aerobic biological treatment.

[0049] S4. Deep Oxidation Treatment: The effluent from the previous step enters the secondary sedimentation tank, the sludge enters the sludge thickener or is returned to the secondary A / O system, the supernatant enters the phosphorus removal tank, and then enters the ozone oxidation tank. The wastewater in the contact tank is pumped out by the circulation pump and mixed with ozone through the gas-liquid mixer to form micro-nano bubbles. Ozone is circulated and added, and deep oxidation is carried out under the action of manganese dioxide catalyst. Finally, the wastewater meets the discharge standards.

[0050] Example 2: This example provides a treatment process for mixed wastewater from cassava fiber and fine chemicals.

[0051] The influent wastewater from the mixture of cassava alcohol and fine chemical processing has the following characteristics: COD 4200 mg / L, BOD5 750 mg / L (B / C = 0.18), SS 1600 mg / L, NH3-N 130 mg / L, TP 12 mg / L, Cl... - 3500 mg / L, pH fluctuating between 4.5 and 9.8. The Fenton-like fixed-bed reactor is arranged from bottom to top as follows: a water distribution zone, a support layer, a catalyst bed, and a buffer zone. The support layer includes support beams, a covered grid, a pebble layer, and a quartz sand layer.

[0052] The specific steps are as follows: S1. Preparation of Fenton-like catalysts: S11. Preparation of geopolymer microsphere carrier: Metakaolin and water glass were mixed evenly at a mass ratio of 10:4 and stirred for 15 min to obtain a geopolymer slurry. The slurry was evenly dropped into hot silicone oil at 85℃ and dispersed by stirring at 300 rpm. After the droplets solidified in the silicone oil for 20 min, they were taken out, washed with deionized water to remove the surface silicone oil, and dried at 70℃ for 24 h to obtain porous geopolymer microspheres with an average particle size of 2.5 mm, a specific surface area of ​​65 m² / g, and a macropore diameter of 50-200 μm. S12, Iron-copper bimetallic loading: Prepare a mixed solution containing Fe(NO3)3·9H2O and Cu(NO3)2·3H2O with an iron-copper molar ratio of 1:1 and a total metal ion concentration of 0.8 mol / L. Immerse 10 g of geopolymer microspheres in 20 mL of the above mixed solution, sonicate for 30 min, let stand for 12 h, and then dry at 80 °C for 12 h. S13. Calcination and Activation: The dried microspheres are placed in a muffle furnace, heated to 450℃ at a rate of 5℃ / min, and calcined for 4 hours. After natural cooling, the desired product is obtained as follows: Figure 2 The catalyst shown is similar to Fenton's.

[0053] S2. Acid precipitation flotation treatment: Adjust the pH of the mixed wastewater to 3.5 and enter the acid precipitation flotation tank for flotation separation. The hydraulic retention time is 40 minutes.

[0054] S3. Fenton-like fixed-bed catalytic oxidation treatment: The sludge from the previous step enters the sludge thickener, then the sludge dewatering machine, and the effluent enters the pH adjustment tank to adjust the pH to 3.3. Then, it enters the Fenton-like fixed-bed reaction tank from the bottom with hydrogen peroxide and undergoes catalytic oxidation under the action of the above-mentioned Fenton-like catalyst.

[0055] S4. Neutralization and biological treatment: The effluent from the previous step enters the neutralization and equalization tank to adjust the pH to neutral, and then enters the secondary A / O system for anoxic and aerobic biological treatment.

[0056] S5. Deep Oxidation Treatment: The effluent from the previous step enters the secondary sedimentation tank, the sludge enters the sludge thickener or is returned to the secondary A / O system, the supernatant enters the phosphorus removal tank, and then enters the ozone oxidation tank. The wastewater in the contact tank is pumped out by the circulation pump and mixed with ozone through the gas-liquid mixer to form micro-nano bubbles. Ozone is circulated and added, and deep oxidation is carried out under the action of manganese dioxide catalyst. Finally, the wastewater meets the discharge standards.

[0057] Example 3: This example provides a treatment process for mixed wastewater from cassava fiber and fine chemicals.

[0058] The processing technology in this embodiment is the same as that in embodiment 2, except that the iron-copper molar ratio is 2:1.

[0059] Example 4: This example provides a treatment process for mixed wastewater from cassava fiber and fine chemicals.

[0060] The processing technology in this embodiment is the same as that in embodiment 2, except that the iron-copper molar ratio is 1.5:1.

[0061] Example 5: This example provides a treatment process for mixed wastewater from cassava fiber and fine chemicals.

[0062] The influent wastewater from the mixture of cassava alcohol and fine chemical processing has the following characteristics: COD 4200 mg / L, BOD5 750 mg / L (B / C = 0.18), SS 1600 mg / L, NH3-N 130 mg / L, TP 12 mg / L, Cl... - 3500 mg / L, pH fluctuating between 4.5 and 9.8. The Fenton-like fixed-bed reactor is arranged from bottom to top as follows: a water distribution zone, a support layer, a catalyst bed, and a buffer zone. The support layer includes support beams, a covered grid, a pebble layer, and a quartz sand layer.

[0063] The specific steps are as follows: S1. Preparation of ozone catalyst: S11. Preparation of geopolymer microsphere carrier: Metakaolin and water glass were mixed evenly at a mass ratio of 10:4 and stirred for 15 min to obtain a geopolymer slurry. The slurry was evenly dropped into hot silicone oil at 85℃ and dispersed by stirring at 300 rpm. After the droplets solidified in the silicone oil for 20 min, they were taken out and washed with deionized water to remove the surface silicone oil. They were then dried at 70℃ for 24 h to obtain porous geopolymer microspheres with an average particle size of 2.5 mm, a specific surface area of ​​65 m² / g, and a macropore size of 50-200 μm. S12, Manganese metal loading: 10g of porous geopolymer microspheres were immersed in 0.2mol / L potassium permanganate solution for 3h, and then dried at 80℃ for 2h. S13, Reduction and Transformation: The dried microspheres were immersed in a 1.0 mol / L citric acid solution for 2 hours. The microspheres were then removed, repeatedly washed with deionized water until neutral, and dried at 80℃ for 12 hours to obtain the desired product. Figure 3 The ozone catalyst shown.

[0064] S2. Acid precipitation flotation treatment: Adjust the pH of the mixed wastewater to 3.5 and enter the acid precipitation flotation tank for flotation separation. The hydraulic retention time is 40 minutes.

[0065] S3. Fenton-like fixed-bed catalytic oxidation treatment: The sludge from the previous step enters the sludge thickener, then the sludge dewatering machine, and the effluent enters the pH adjustment tank to adjust the pH to 3.3. Then, it enters the Fenton-like fixed-bed reaction tank from the bottom with hydrogen peroxide and undergoes catalytic oxidation under the action of zero-valent iron sulfide catalyst.

[0066] S4. Neutralization and biological treatment: The effluent from the previous step enters the neutralization and equalization tank to adjust the pH to neutral, and then enters the secondary A / O system for anoxic and aerobic biological treatment.

[0067] S5. Deep Oxidation Treatment: The effluent from the previous step enters the secondary sedimentation tank, the sludge enters the sludge thickener or is returned to the secondary A / O system, and the supernatant enters the phosphorus removal tank, followed by the ozone oxidation tank. The wastewater in the contact tank is pumped out by the circulation pump and mixed with ozone through the gas-liquid mixer to form micro-nano bubbles. Ozone is then circulated and added. Under the action of the ozone catalyst, deep oxidation is carried out, and finally the wastewater meets the discharge standards.

[0068] Example 6: This example provides a treatment process for mixed wastewater from cassava fiber and fine chemicals.

[0069] The influent wastewater from the mixture of cassava alcohol and fine chemical processing has the following characteristics: COD 4200 mg / L, BOD5 750 mg / L (B / C = 0.18), SS 1600 mg / L, NH3-N 130 mg / L, TP 12 mg / L, Cl... - 3500 mg / L, pH fluctuating between 4.5 and 9.8. The Fenton-like fixed-bed reactor is arranged from bottom to top as follows: a water distribution zone, a support layer, a catalyst bed, and a buffer zone. The support layer includes support beams, a covered grid, a pebble layer, and a quartz sand layer.

[0070] The specific steps are as follows: S1. Preparation of Fenton-like catalysts: S11. Preparation of geopolymer microsphere carrier: Metakaolin and water glass were mixed evenly at a mass ratio of 10:4 and stirred for 15 min to obtain a geopolymer slurry. The slurry was evenly dropped into hot silicone oil at 85℃ and dispersed by stirring at 300 rpm. After the droplets solidified in the silicone oil for 20 min, they were taken out, washed with deionized water to remove the surface silicone oil, and dried at 70℃ for 24 h to obtain porous geopolymer microspheres with an average particle size of 2.5 mm, a specific surface area of ​​65 m² / g, and a macropore diameter of 50-200 μm. S12, Iron-copper bimetallic loading: Prepare a mixed solution containing Fe(NO3)3·9H2O and Cu(NO3)2·3H2O, with an iron-copper molar ratio of 1.5:1 and a total metal ion concentration of 0.8 mol / L. Immerse 10 g of geopolymer microspheres in 20 mL of the above mixed solution, sonicate for 30 min, let stand for 12 h, and then dry at 80 °C for 12 h. S13. Calcination and activation: The dried microspheres are placed in a muffle furnace and heated to 450℃ at 5℃ / min for 4 hours. After natural cooling, a Fenton-like catalyst is obtained.

[0071] The preparation steps of S2 and ozone catalyst are as follows: S21. Preparation of geopolymer microsphere carrier: Metakaolin and water glass were mixed evenly at a mass ratio of 10:4 and stirred for 15 min to obtain a geopolymer slurry. The slurry was evenly dropped into hot silicone oil at 85℃ and dispersed by stirring at 300 rpm. After the droplets solidified in the silicone oil for 20 min, they were taken out and washed with deionized water to remove the surface silicone oil. They were then dried at 70℃ for 24 h to obtain porous geopolymer microspheres with an average particle size of 2.5 mm, a specific surface area of ​​65 m² / g, and a macropore diameter of 50-200 μm. S22, Manganese metal loading: 10g of porous geopolymer microspheres were immersed in 0.2mol / L potassium permanganate solution for 3h, and then dried at 80℃ for 2h. S23, Reduction and Transformation: The dried microspheres were immersed in a 1.0 mol / L citric acid solution for 2 hours. After soaking, the microspheres were removed, washed repeatedly with deionized water until neutral, and dried at 80℃ for 12 hours to obtain the ozone catalyst.

[0072] S3. Acid precipitation flotation treatment: Adjust the pH of the mixed wastewater to 3.5 and enter the acid precipitation flotation tank for flotation separation. The hydraulic retention time is 40 minutes.

[0073] S4. Fenton-like fixed-bed catalytic oxidation treatment: The sludge from the previous step enters the sludge thickener, then the sludge dewatering machine, and the effluent enters the pH adjustment tank to adjust the pH to 3.3. Then, it enters the Fenton-like fixed-bed reaction tank from the bottom with hydrogen peroxide and undergoes catalytic oxidation under the action of the above-mentioned Fenton-like catalyst.

[0074] S5. Neutralization and biological treatment: The effluent from the previous step enters the neutralization and equalization tank to adjust the pH to neutral, and then enters the secondary A / O system for anoxic and aerobic biological treatment.

[0075] S6. Deep Oxidation Treatment: The effluent from the previous step enters the secondary sedimentation tank, the sludge enters the sludge thickener or is returned to the secondary A / O system, and the supernatant enters the phosphorus removal tank, followed by the ozone oxidation tank. The wastewater in the contact tank is pumped out by the circulation pump and mixed with ozone through the gas-liquid mixer to form micro-nano bubbles. Ozone is then circulated and added. Under the action of the ozone catalyst, deep oxidation is carried out, and finally the wastewater meets the discharge standards.

[0076] Comparative Example 1: This comparative example is the same as Example 6, except that step S3 acid precipitation flotation treatment step is missing.

[0077] Comparative Example 2: This comparative example is the same as Example 6, except that in step S6, a conventional aeration disc is used instead of the micro-nano bubble circulation ozone addition method.

[0078] Comparative Example 3: This comparative example is the same as Example 6, except that in step S12, the iron-copper molar ratio is 3:1.

[0079] Comparative Example 4: This comparative example is the same as Example 6, except that in step S12, the iron-copper molar ratio is 1:3.

[0080] Comparative Example 5: This comparative example is the same as Example 6, except that no ozone catalyst is added to the ozone oxidation tank in step S6.

[0081] The wastewater treated in Examples 1-6 and Comparative Examples 1-5 were tested respectively, and the test results are shown in Table 1 and Table 2.

[0082] Table 1

[0083] Table 2

[0084] As shown in Tables 1 and 2, the treatment process of Example 6 performed best, with a final effluent COD of only 38 mg / L and a total removal rate of 99.1%. Other indicators were also better than those of other examples and comparative examples.

[0085] Compared with Example 1, Example 2 used the Fenton-like catalyst of the present invention, and all the indicators obtained were better than those of Example 1. Compared with Example 1, Example 5 used the ozone catalyst of the present invention, and all the indicators obtained were better than those of Example 1. This shows that both types of catalysts can improve the wastewater treatment efficiency at the same time during the reaction.

[0086] Compared with Examples 4 and 5, Example 6 shows that optimizing either the Fenton-like process or the ozone process alone is not as effective as optimizing both simultaneously as in Example 6, indicating that the dual-catalyst system of the present invention has a synergistic effect.

[0087] Examples 2-4 and Comparative Examples 3-4 demonstrate that the Fenton-like effect is optimal when the iron-copper molar ratio is 1.5:1. A ratio that is too high (3:1) or too low (1:3) leads to a decrease in all indicators, proving that the bimetallic synergistic effect requires a suitable ratio.

[0088] Compared to Example 6, Comparative Example 1, omitting acid precipitation flotation, resulted in fiber clogging of the catalyst bed. The COD in the Fenton-like effluent increased to 1450 mg / L, and the total removal rate decreased to 98.0%. Furthermore, after 72 hours of operation, the bed pressure drop increased from 0.4 kPa to 1.8 kPa, indicating severe fiber clogging. In contrast, Example 6 showed a pressure drop of only 0.4-0.5 kPa after 90 days of operation. This demonstrates that acid precipitation flotation not only removes suspended solids and COD but also protects the catalyst bed, ensuring long-term stable operation.

[0089] Comparative Example 2 showed that under conventional aeration, the ozone utilization rate was only 70%, and the effluent COD was 82 mg / L, which was higher than the 38 mg / L of micro-nano bubbles, indicating that micro-nano bubbles can significantly improve ozone mass transfer efficiency.

[0090] Compared with Comparative Example 5, Examples 5-6 show that the ozone catalyst of the present invention can reduce the COD of ozone effluent to 38-48 mg / L, while it only reduces to 135 mg / L without the catalyst. The ozone utilization rate is reduced from 96% to 92%, which proves that the ozone catalyst significantly improves the ozone oxidation efficiency.

[0091] The above are all preferred embodiments of the present invention and are not intended to limit the scope of protection of the present invention. Therefore, all equivalent changes made in accordance with the structure, shape and principle of the present invention should be covered within the scope of protection of the present invention.

Claims

1. A treatment process for mixed wastewater from cassava fiber and fine chemicals, characterized in that, The processing technology includes the following steps: (1) Acid precipitation flotation treatment: The pH of the mixed wastewater is adjusted to 3.0-4.0 and then enters the acid precipitation flotation tank for flotation separation; (2) Fenton-like fixed bed catalytic oxidation treatment: The effluent from step (1) enters the pH adjustment tank to adjust the pH to 3.0-3.5, and then enters the Fenton-like fixed bed reaction tank from the bottom with hydrogen peroxide, and carries out catalytic oxidation reaction under the action of Fenton-like catalyst; (3) Neutralization and biochemical treatment: The effluent from step (2) enters the neutralization and conditioning tank to adjust the pH to neutral, and then enters the secondary A / O system for anoxic and aerobic biological treatment; (4) Deep oxidation treatment: The effluent from step (3) is fed into a secondary sedimentation tank and a phosphorus removal tank, and then into an ozone oxidation tank. Ozone is added in a circulation manner through micro-nano bubbles, and deep oxidation is carried out under the action of ozone catalyst. Finally, the wastewater meets the discharge standards.

2. The treatment process for mixed wastewater from cassava fiber and fine chemicals according to claim 1, characterized in that, In step (2), the Fenton-like fixed bed reactor is provided with a water distribution zone, a support layer, a catalyst bed and a buffer zone from bottom to top; the support layer includes a support beam, a grid covering, a pebble layer and a quartz sand layer.

3. A treatment process for mixed wastewater from cassava fiber and fine chemicals according to claim 1 or 2, characterized in that, The Fenton-like catalyst is an iron-copper bimetallic oxide / geopolymer microsphere catalyst, wherein the catalyst uses porous geopolymer microspheres as a support, and iron oxide nanoparticles and copper oxide nanoparticles are loaded on the surface and in the pores of the support.

4. The treatment process for mixed wastewater from cassava fiber and fine chemicals according to claim 3, characterized in that, The iron oxide is Fe2O3 or Fe3O4, with a loading of 5-10 wt%; the copper oxide is CuO, with a loading of 3-8 wt%; the molar ratio of iron to copper is 2-1:

1.

5. The treatment process for mixed wastewater from cassava fiber and fine chemicals according to claim 3, characterized in that, The specific preparation steps of the Fenton-like catalyst are as follows: (1) Preparation of geopolymer microsphere carrier: Mix metakaolin and water glass at a mass ratio of 10:3-5 evenly and stir for 10-20 min to obtain geopolymer slurry. Drop the slurry evenly into hot silicone oil at 80-90℃ and stir to disperse at 200-400 rpm. After the droplets solidify in the silicone oil for 10-30 min, take them out, wash with deionized water to remove the surface silicone oil, and dry at 60-80℃ for 12-24 h to obtain porous geopolymer microspheres. (2) Iron-copper bimetallic loading: Prepare a mixed solution containing iron salt and copper salt, with a total metal ion concentration of 0.5-1.0 mol / L. Immerse geopolymer microspheres in the mixed solution, sonicate for 25-35 min, let stand for 10-15 h, and then dry at 75-85℃ for 10-15 h. (3) Calcination activation: The dried microspheres are placed in a muffle furnace and heated to 400-500℃ at 3-5℃ / min for 3-5h. After natural cooling, the Fenton-like catalyst is obtained.

6. The treatment process for mixed wastewater from cassava fiber and fine chemicals according to claim 1, characterized in that, The method of adding ozone in step (4) is as follows: wastewater in the contact tank is pumped out by a circulation pump, mixed with ozone by a gas-liquid mixer to form micro-nano bubbles, and then returned to the bottom of the tank.

7. The treatment process for mixed wastewater from cassava fiber and fine chemicals according to claim 1, characterized in that, The ozone catalyst is a manganese oxide / geopolymer microsphere catalyst, wherein the catalyst uses porous geopolymer microspheres as a support, and manganese oxide nanoparticles are loaded on the surface and in the pores of the support.

8. The treatment process for mixed wastewater from cassava fiber and fine chemicals according to claim 7, characterized in that, The manganese oxide is MnO2 and / or Mn2O3, and the loading is 5-10% of the total mass of the ozone catalyst.

9. The treatment process for mixed wastewater from cassava fiber and fine chemicals according to claim 7, characterized in that, The ozone catalyst is prepared in the following steps: (1) Preparation of geopolymer microsphere carrier: Mix metakaolin and water glass at a mass ratio of 10:3-5 evenly and stir for 10-20 min to obtain geopolymer slurry. Drop the slurry evenly into hot silicone oil at 80-90℃ and stir to disperse at 200-400 rpm. After the droplets solidify in the silicone oil for 10-30 min, take them out, wash with deionized water to remove the surface silicone oil, and dry at 60-80℃ for 12-24 h to obtain porous geopolymer microspheres. (2) Manganese metal loading: The porous geopolymer microspheres are immersed in a 0.1-0.3 mol / L potassium permanganate solution for 2-4 hours, and then dried at 75-85℃ for 1-3 hours. (3) Reduction and transformation: The dried microspheres are immersed in a reducing agent solution of 0.8-1.2 mol / L for 1-3 hours. After soaking, the microspheres are taken out, washed repeatedly with deionized water until neutral, and dried at 75-85℃ for 10-15 hours to obtain the ozone catalyst.

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