A pretreatment method and treatment process for cellulose ether-containing wastewater

Abstract

This invention relates to a pretreatment method for cellulose ether-containing wastewater, comprising the following steps: (1) heating the cellulose ether-containing wastewater to 90-100°C, adding catalyst A under stirring, and carrying out the reaction at normal pressure and temperature until white flocculent matter appears and there is no foam on the water surface, at which point the reaction ends; (2) adding oxidant B dropwise to the wastewater after the reaction, and continuing the reaction at 90-100°C under stirring and temperature and temperature until the foam disappears, at which point heating is stopped and the water is immediately cooled to 40-50°C; (3) the cooled wastewater contains a large amount of gluconic acid monomers, the pH of the wastewater is adjusted to neutral, and flocculent gluconic acid precipitates are formed in the water body, and solid-liquid separation is performed. At this time, the biodegradability B / C of the supernatant increases from 0.1 to over 0.5. This method can directionally convert recalcitrant cellulose ether macromolecules into gluconic acid monomers and reduce the subsequent COD load by about 50%.

Description

Technical Field

[0001] This invention relates to a wastewater treatment method, specifically a pretreatment method and treatment process for wastewater containing cellulose ethers, belonging to the field of environmental protection technology. Background Technology

[0002] Cellulose ethers, as high-molecular fine chemical materials made from modified natural cellulose, are widely used in essential industries such as building materials, pharmaceuticals, daily chemicals, food processing, and petrochemicals due to their core properties of thickening, water retention, binding, and sustained release. They are indispensable functional additives in modern industrial systems. Currently, the global cellulose ether industry has formed a stable tiered production and sales structure.

[0003] The domestic cellulose ether industry has achieved rapid development by relying on a complete industrial chain. Its product categories cover the full range of grades, including building materials, pharmaceuticals, and food. The two major categories of carboxymethyl cellulose (CMC) and methyl cellulose (HPMC / MC) account for more than 75% of the total output, while building materials grade products account for about 33%.

[0004] While meeting domestic demand, the export market covers multiple countries and regions such as India, Russia, and Turkey. The industry is gradually upgrading from exporting general-purpose products to exporting high-end functional and customized products in tandem, which aligns with the national policies encouraging green building materials and bio-based materials. Overall, it is steadily moving towards high performance and green development.

[0005] The production and application of cellulose ethers generate a large amount of wastewater containing cellulose ethers, which has the following characteristics: (1) The wastewater contains a large amount of modified cellulose ether pollutants. After etherification, the steric hindrance of the cellulose ether molecules is greatly increased. The molecular weight is large and the structure is stable. Ordinary hydrolytic enzymes cannot break its glycosidic bonds. It is easy to form sticky scum in the water treatment system, which in turn blocks the membrane module and pipeline, greatly increasing the operation and maintenance cost of the treatment system. (2) The COD concentration of the wastewater is extremely high, reaching 15,000-40,000 mg / L. At the same time, it contains a large amount of modified cellulose macromolecules and organic solvents, and the B / C ratio is maintained at around 0.1. Conventional biochemical systems cannot completely biodegrade it. Moreover, the intermediate products of anaerobic processes can easily lead to problems such as microbial inhibition and sludge disintegration, making it impossible to operate stably. (3) The salt content of the wastewater can be as high as 5-8% or even higher. High salinity will cause microorganisms to lose their activity, and the high concentration of salt solution will cause the viscosity of some non-ionic cellulose ethers to increase. Cellulose ethers will adhere to the evaporation crystallization tube and other facilities, affecting the heat transfer efficiency and increasing the cleaning difficulty. The energy consumption and maintenance cost of treatment are far greater than other wastewaters, and there are safety risks.

[0006] Currently, the wastewater is mainly treated using the following methods: (1) Salt-tolerant microbial biochemical treatment (anaerobic + aerobic) + advanced oxidation + membrane concentration (concentrated water to evaporation); (2) Advanced oxidation to remove COD + evaporation and crystallization (+ fractional distillation to recover salt) produces condensate + biochemical treatment (anaerobic + aerobic) + advanced oxidation.

[0007] However, both of the above methods have their own shortcomings.

[0008] Method (1): ① Due to the high salt content of the wastewater, conventional microorganisms become inactive, and the biochemical system loses its treatment capacity. Even when salt-tolerant microorganisms are used, the degradation efficiency of pollutants in a high-salt environment is very low, with poor shock resistance, poor stability, and a large footprint. ② The biochemical treatment is incomplete, requiring the use of more energy-intensive advanced oxidation processes to achieve some COD treatment effect. This consumes a large amount of reagents, is energy-intensive and highly polluting, and completely wastes the biomass resources in the wastewater. ③ After advanced oxidation, the requirements for RO reverse osmosis are barely met, and the treated water meets the standards, but there is a low water production rate, and the residual cellulose ethers and their derivatives easily clog the membrane, requiring frequent cleaning and replacement, resulting in high consumption per ton of water. The concentrated water produced by the membrane treatment still needs to be evaporated for further treatment.

[0009] Method (2): ① The salt in the wastewater after evaporation can be removed, thus relieving the inhibition of microbial activity by the salt; however, the molecular valence energy of cellulose ether is very strong, and a more energy-intensive advanced oxidation process is required before evaporation to have some effect on COD treatment. It consumes a large amount of reagents, resulting in high energy consumption and high pollution. ② Heavy cellulose ether can also be partially removed by evaporation. However, in addition to high molecular weight cellulose ether, the production wastewater also contains a large amount of unreacted low-substitution and low-polymerization small molecule cellulose ether. These substances have low boiling points and relatively stronger volatility, making them more likely to enter the condensate with the steam and then enter the subsequent biochemical treatment system, which is still difficult to degrade and remove. ③ Cellulose ether is a typical thickening polymer, which will significantly increase the overall viscosity of the wastewater, reduce the fluidity of the liquid in the evaporator, and easily adhere to the heat exchange tube wall, ultimately leading to a decrease in the evaporation heat transfer coefficient; in addition, the high viscosity liquid will inhibit the nucleation boiling effect inside the evaporator, causing the evaporation process to change from efficient bubble boiling to inefficient film boiling, directly reducing the evaporation treatment capacity per unit time.

[0010] Based on the problems existing in the above-mentioned treatment methods for cellulose ether-containing wastewater, there is an urgent need to propose a method that can convert cellulose ethers into easily biodegradable small molecules in the pretreatment stage. On the one hand, this method can improve the B / C ratio of the wastewater and enhance the treatment effect of the biological system; on the other hand, it can effectively improve the evaporation efficiency of the evaporator and reduce the cleaning frequency and cost; it can also significantly save on advanced oxidation agents, energy consumption, and membrane treatment costs without relying on advanced oxidation processes and membrane treatment processes; and most importantly, it can generate food additives or feed additives with high economic value. Summary of the Invention

[0011] This invention addresses the shortcomings of existing treatment methods for cellulose ether-containing wastewater by providing a pretreatment method and process specifically for such wastewater. Under heating conditions, this method uses a catalyst to directionally convert cellulose ethers in the wastewater into gluconic acid monomers. Crucially, the formed gluconic acid can be stabilized in the aqueous phase and effectively utilized, thus solving most of the problems existing in the treatment of cellulose ether-containing wastewater.

[0012] The present invention solves the above-mentioned technical problems by adopting the following technical solution: A pretreatment method for wastewater containing cellulose ethers includes the following steps: Wastewater containing cellulose ethers is heated to 90-100℃, the pH of the water is adjusted, and catalyst A is added under stirring. The reaction is carried out under normal pressure and heat until white flaky flocs appear and there is no foam on the water surface. The reaction ends when the catalyst A is one of persulfate, ferrate or perchlorate. Adjust the pH of the water body, then add oxidant B dropwise to the wastewater after the reaction in step (1), and continue to react at 90-100℃ under normal pressure with stirring until the foam disappears. Stop heating and immediately cool down to 40-50℃. At this time, the water body contains a large amount of soluble gluconate. The oxidant B is one of liquid bromine, hypobromic acid or bromine water. After cooling the wastewater in step (2), adjust the pH to 7-8. The water will form flocculent precipitates of gluconate. Then, perform solid-liquid separation. The B / C ratio of the obtained supernatant is ≥0.5, and it can be used for subsequent treatment.

[0013] Furthermore, the catalyst A is one of ferric persulfate, potassium ferrate, or sodium perchlorate.

[0014] Furthermore, the amount of catalyst A added in step (1) is 0.8-3 wt%.

[0015] Furthermore, the amount of oxidant B added in step (2) is 1-3 vol%.

[0016] Furthermore, the COD of the wastewater containing cellulose ethers in step (1) is ≤40000mg / L.

[0017] Furthermore, the stirring speed in steps (1) and (2) is 50-200 r / min.

[0018] The beneficial effects of the pretreatment method provided by this invention are: (1) Reduce costs and increase efficiency from the source: After treatment by this method, the recalcitrant cellulose ether macromolecules can be directionally converted into gluconic acid monomers, the B / C ratio of wastewater can be increased to more than 0.5, and the COD load of the subsequent water treatment system can be reduced by 40-45%; the thermal efficiency of the evaporator can be increased by about 30%, and the cleaning cycle can be extended to about 3 times the original; there is no need to rely on the advanced oxidation process and membrane treatment process at the back end, and conventional biochemical treatment can achieve stable compliance of wastewater.

[0019] (2) Empowering the development of the industry: It is estimated that this process can save RMB 25,000-30,000 per thousand tons of water compared with the traditional "advanced oxidation to remove COD + evaporation + condensate biochemical treatment + advanced oxidation / membrane treatment". In terms of the scale of the cellulose ether production industry, about 40-50 tons of water are generated for every ton of cellulose ether product produced. The total output in 2025 is 750,000 tons of product, and the total wastewater discharge is about 30-37.5 million tons. Therefore, it will save at least RMB 750-1.1 billion for the entire domestic industry every year. Due to the continuous increase in production capacity and wastewater volume (8% per year), the downstream pharmaceutical industry will also generate some wastewater containing cellulose ether. After the industry is widely implemented, the total annual cost savings will be about RMB 1.5-2 billion.

[0020] (3) Realize resource recycling: ① The cellulose ethers that were originally to be discarded are converted into gluconic acid monomers that are in short supply in the market. These monomers can be used to produce high-value-added products such as food acidulants and pharmaceutical calcium supplements, thus creating new profit points for enterprises; ② After the biodegradability of wastewater is improved, the biogas production in the anaerobic stage can be greatly increased, thereby increasing the biogas power generation.

[0021] (4) Reduce carbon emissions and help low-carbon transformation: This method can fix biocarbon in gluconic acid products and utilize the power generation of biogas produced by anaerobic digestion. Compared with the traditional cellulose ether wastewater treatment route, it can reduce carbon emissions by more than 65% and help enterprises achieve green and low-carbon transformation.

[0022] This invention also claims protection for a treatment process for cellulose ether-containing wastewater, comprising the following steps: Pretreatment: The wastewater containing cellulose ethers was pretreated according to the aforementioned pretreatment method to convert the cellulose ethers in the wastewater into ferric gluconate monomers. Evaporation and desalination: The supernatant obtained in step (1) is introduced into the evaporation system for distillation, where the salt remains in the solid phase, and the resulting condensate is subjected to subsequent processing; (3) Biochemical treatment: The condensate obtained in step (2) is introduced into the AO biochemical system for treatment, and the resulting water can be discharged in compliance with standards.

[0023] Furthermore, the biochemical treatment also includes a post-processing step.

[0024] Preferably, the post-processing step is one or more of precipitation, filtration, decolorization, and disinfection. Detailed Implementation

[0025] The principles and features of the present invention are described below with reference to examples. The examples are only used to explain the present invention and are not intended to limit the scope of the present invention. Example 1:

[0026] A pretreatment method for wastewater containing cellulose ethers includes the following steps: (1) Take 5L of production wastewater (COD=23000mg / L, pH=13-14, chloride ion about 22000 mg / L) from a cellulose ether production enterprise in Tai'an, Shandong Province, and place it in a 10L glass reactor. After heating to 95℃, adjust the pH to 2-3 with dilute sulfuric acid. Add 75g of catalyst A ferric persulfate at a stirring speed of 100r / min. After keeping the temperature for 25min, white flocculent granules appear and there is basically no viscous foam on the water surface. The reaction is then considered to be complete. (2) Adjust the pH to 4-5 with 10% NaOH solution, add 100g of oxidant B hypobromic acid to the reaction system, and carry out the reaction at 95℃ and 100r / min. Stop heating when there is basically no viscous foam on the water surface after about 35 minutes of reaction, and immediately add cooling water to reduce the temperature of the reaction system to 40-50℃. (3) Use 10% NaOH solution to adjust the pH of the system to about 8. Ferric gluconate flocs are formed in the water. Then, solid-liquid separation is performed. At this time, the B / C ratio of the supernatant is 0.57 and the COD is 11620. At this time, subsequent treatment can be carried out. Example 2:

[0027] A process for treating wastewater containing cellulose ethers includes the following steps: (1) Take 3.8L of the supernatant after pretreatment in Example 1, and distill it in batches using a laboratory evaporation apparatus. Collect all the condensate (COD=3550mg / L, chloride ion≦1000mg / L) for the next step of biochemical treatment; (2) Transfer 3L of condensate to the anaerobic experimental device and add 600mL of anaerobic granular sludge containing methanogens (10-30% inoculation ratio according to the actual engineering IC tower start-up ratio). Turn on mechanical stirring (200r / min), adjust pH to 7, mix (COD=3350mg / L, chloride ion≦1000mg / L) and carry out anaerobic reaction. After 24h of anaerobic reaction, the COD of the system drops to 680 mg / L. (3) Transfer the supernatant in the anaerobic device to the aerobic reaction device and add the cultured aerobic activated sludge (80% water content, sludge concentration controlled at 6-8 g / L) to it. Carry out the aerobic reaction under aeration and oxygenation conditions. After 24 hours of aerobic reaction, COD=200 mg / L, which can meet the COD discharge standard of all industrial park sewage treatment plants in China. Example 3:

[0028] A pretreatment method for wastewater containing cellulose ethers includes the following steps: (1) Take 5L of production wastewater (COD=12000mg / L, pH=9-10, chloride ion about 10000 mg / L) from a cellulose ether production enterprise in Tai'an, Shandong Province, and place it in a 10L glass reactor. After heating to boiling, add 40g of catalyst A potassium ferrate at a stirring speed of 50r / min. After keeping the temperature and reacting for 25min, white flocculent granules appear and there is basically no viscous foam on the water surface. The reaction is then judged to be over. (2) Adjust the pH to 5-6 with dilute sulfuric acid, add 50g of oxidant B liquid bromine to the reaction system, and carry out the reaction at 100℃ and 50r / min. Stop heating when there is basically no viscous foam on the water surface after about 30 minutes of reaction, and immediately lower the temperature of the reaction system to 40-50℃. (3) Use 10% NaOH solution to adjust the pH of the system to about 8. Potassium gluconate forms flocs in the water. Then, solid-liquid separation is performed. At this time, the B / C ratio of the supernatant is 0.52 and the COD is 6800 mg / L. Example 4:

[0029] A process for treating wastewater containing cellulose ethers includes the following steps: (1) The supernatant (3.5L) after the reaction in Example 3 was transferred to the laboratory evaporation device, heated to 100°C, evaporated and condensed, and the condensate (COD=2340mg / L, chloride ion≦1000mg / L) was collected for the next step of biochemical treatment; (2) Transfer 3L of condensate to the anaerobic experimental device and add 600mL of anaerobic granular sludge containing methanogens. Turn on the mechanical stirring (200r / min), adjust the pH to 7, and carry out anaerobic reaction after mixing (COD=2190mg / L). After 36h of anaerobic reaction, the COD of the wastewater system drops to 420 mg / L. (3) Transfer the supernatant of the anaerobic device to the aerobic reaction device and add the cultured aerobic activated sludge (80% water content) to it. Under the conditions of aeration, oxygenation and stirring, the aerobic reaction is carried out. After 24 hours of aerobic reaction, the COD is 156 mg / L, which meets the COD discharge standard of all sewage treatment plants in China. Example 5:

[0030] A pretreatment method for wastewater containing cellulose ethers includes the following steps: (1) Take 5L of production wastewater (COD=40000mg / L, pH=11-12, chloride ion about 40000 mg / L) from a cellulose ether production enterprise and place it in a 10L glass reactor. After heating to 90℃, adjust the pH to 4-5 with dilute sulfuric acid. Add 150g of catalyst A sodium perchlorate at a stirring speed of 150r / min. After keeping the temperature and reacting for 35min, white flocculent flocs appear and there is basically no viscous foam on the water surface. The reaction is then considered to be complete. (2) Add 150g of oxidant B bromine water to the reaction system and react at 90℃ and 150r / min. Stop heating when there is basically no viscous foam on the water surface after about 35 minutes of reaction, and immediately add cooling water to reduce the temperature of the reaction system to 40-50℃. (3) Use 10% NaOH solution to adjust the pH of the system to 7-8. Sodium gluconate will form flocs in the water. Then, solid-liquid separation will be carried out. At this time, the B / C ratio of the supernatant is 0.50 and the COD is 24330. It can then enter the biochemical system for treatment.

[0031] Comparative Example 1: The treatment of cellulose ether-containing wastewater, compared with Example 1, includes the following steps: (1) Take 5L of production wastewater (COD=23000mg / L, pH=13-14, chloride ion about 22000 mg / L) from a cellulose ether production enterprise in Tai'an, Shandong Province, place it in a 10L glass reactor, heat it to 95℃, add 75mL of tap water at a stirring speed of 100r / min, and keep it warm for 25min; (2) Add 100 mL of tap water to the reaction system and keep it at 95 °C and 100 r / min for 35 min. Then add cooling water to immediately lower the temperature of the reaction system to 40-50 °C. No precipitate is produced in the water. (3) Use 10% sulfuric acid solution to adjust the pH of the system to about 8. At this time, the water sample has B / C=0.11 and COD=21900mg / L.

[0032] Comparative Example 2: In contrast to Example 2, the wastewater containing cellulose ethers was not pretreated; it was directly subjected to biochemical treatment after distillation using an evaporator. The steps are as follows: (1) The production wastewater (COD=23000mg / L, pH=13-14, chloride ion about 22000 mg / L) of a cellulose ether production enterprise in Tai'an, Shandong Province was transferred to the evaporation device in the laboratory, evaporated and condensed, and the condensate (COD=5630mg / L, chloride ion=1330mg / L) was collected for further biochemical treatment. (2) Take 3L of the condensate water sample from the previous step and transfer it to the anaerobic experimental device. Add 600mL of anaerobic granular sludge containing methanogens to the device and turn on the mechanical stirring (200r / min). Adjust the pH to 7 and mix (COD=5460mg / L, chloride ion=1300mg / L) to carry out the anaerobic reaction. After 24 hours of anaerobic reaction, the COD of the system drops to 5050mg / L. After 3 days of anaerobic reaction, the COD of the anaerobic system drops to 4630mg / L. After 10 days, the COD drops to 4070mg / L. (3) Transfer the supernatant in the anaerobic device to the aerobic reaction device and add the cultured aerobic activated sludge (moisture content 80%, sludge concentration controlled at 6-8 g / L) to it. Carry out the aerobic reaction under aeration and oxygenation conditions. After 24 hours of aerobic reaction, COD=3720 mg / L, after 48 hours, COD=3330 mg / L, after 72 hours, COD=3050 mg / L, and after 96 hours, COD=2870 mg / L.

[0033] The experimental results above show that, after treatment by the pretreatment method of this invention, the B / C ratio of cellulose ether-containing wastewater can be increased to over 0.5, and COD can be reduced by 40-45%, significantly reducing the load on subsequent wastewater treatment systems. The treatment capacity of the front-end evaporator is increased by approximately 30%, and the cleaning cycle can be extended to three times the original length. Testing revealed that the membrane modules and advanced oxidation processes used in the deep treatment of wastewater can be eliminated; after pretreatment and distillation, conventional biochemical treatment can achieve stable compliance with wastewater standards. In the pretreatment method, the use of catalyst A and oxidant B plays a crucial role. Directly subjecting untreated cellulose ether-containing wastewater to subsequent distillation and biochemical treatments results in unsatisfactory degradation effects due to the non-biodegradability of cellulose ethers.

[0034] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A pretreatment method for cellulose ether production wastewater, characterized in that, Includes the following steps: (1) Heat the cellulose ether production wastewater to 90-100℃, adjust the pH of the water, add catalyst A under stirring, and carry out the reaction under normal pressure and heat until white flocculent granules appear and there is no foam on the water surface. The reaction ends when the catalyst A is one of persulfate, ferrate or perchlorate. (2) Adjust the pH of the water body, add oxidant B to the wastewater after the reaction in step (1), and continue to react at 90-100℃ under normal pressure with stirring until the foam disappears. Stop heating and immediately cool down to 40-50℃. The oxidant B is one of liquid bromine, hypobromic acid or bromine water. (3) Adjust the pH of the wastewater cooled in step (2) to 7-8. The water will form flocs and gluconate. Then, solid-liquid separation is performed. The B / C ratio of the supernatant is ≥0.5, and it can be used for subsequent treatment.

2. The pretreatment method according to claim 1, characterized in that, The catalyst A is one of ferric persulfate, potassium ferrate, or sodium perchlorate.

3. The pretreatment method according to claim 1 or 2, characterized in that, The amount of catalyst A added in step (1) is 0.8-3 wt%.

4. The pretreatment method according to claim 1 or 2, characterized in that, The amount of oxidant B added in step (2) is 1-3 vol%.

5. The pretreatment method according to claim 1 or 2, characterized in that, The COD of the cellulose ether production wastewater in step (1) is ≤40000mg / L.

6. The pretreatment method according to claim 3, characterized in that, The COD of the cellulose ether production wastewater in step (1) is ≤40000mg / L.

7. The pretreatment method according to any one of claims 1, 2, or 5, characterized in that, The stirring speed in steps (1) and (2) is 50-200 r / min.

8. A treatment process for wastewater from cellulose ether production, characterized in that, Includes the following steps: (1) Pretreatment: The cellulose ether production wastewater is pretreated using the pretreatment method described in any one of claims 1-7; (2) Evaporation and desalination: The supernatant obtained in step (1) is introduced into the evaporation system for distillation, where the salt remains in the solid phase, and the resulting condensate is subjected to subsequent processing; (3) Biochemical treatment: The condensate obtained in step (2) is introduced into the AO biochemical system for treatment, and the resulting water can be discharged in compliance with standards.

9. The processing technology according to claim 8, characterized in that, The biochemical treatment also includes a post-processing step.

10. The processing method according to claim 9, characterized in that, The post-processing steps include one or more of the following: precipitation, filtration, decolorization, and disinfection.