A method for deep treatment of papermaking wastewater

Abstract

This invention relates to the technical field of papermaking wastewater treatment, specifically to a method for deep treatment of papermaking wastewater, comprising the following steps: After biochemical treatment of papermaking wastewater, the tailwater undergoes physicochemical coagulation or Fenton treatment followed by sedimentation; the supernatant obtained is mixed with a powdered activated carbon slurry; the slurry-water mixture is then uniformly mixed with freshly prepared powdered activated carbon slurry; the remaining slurry and water mixture is subjected to negative pressure filtration to separate the carbon and water; the solution is adsorbed using macroporous adsorption resin, and the effluent is discharged or reused; when the powdered activated carbon concentration reaches a certain value, the carbon is discharged, and the discharged waste carbon slurry is dehydrated, activated at high temperature, cooled, and mixed with new carbon to prepare a slurry for use in freshly prepared powdered activated carbon slurry; after the macroporous adsorption resin becomes saturated, it is regenerated using a regeneration liquid; the resulting regeneration waste liquid undergoes Fenton oxidation precipitation, and the supernatant is mixed with the waste carbon slurry. The combined process employed in this invention provides excellent effluent treatment results and offers advantages in investment and operating costs.

Description

Technical Field

[0001] This invention relates to the technical field of papermaking wastewater treatment, and specifically to a method for deep treatment of papermaking wastewater. Background Technology

[0002] The pulp and paper industry is one of the most important water users, and the wastewater generated during the production process is considered one of the main sources of environmental pollution.

[0003] Due to differences in their production processes, different enterprises employ different wastewater treatment processes. Most processes consist of primary pretreatment (sedimentation, flotation) followed by secondary biological treatment (anaerobic, aerobic + sedimentation). Some enterprises also implement tertiary chemical coagulation treatment at the downstream end to achieve compliant discharge. Generally, the COD of wastewater after biological treatment is [not specified]. Cr It can be reduced to 150-300 mg / L.

[0004] Advanced treatment is a purification process that further removes residual pollutants from the secondary treatment effluent. Currently, most paper mill wastewater undergoes secondary biological treatment, resulting in a COD level that is significantly reduced. Cr The COD levels, such as color, are difficult to meet the requirements of GB3544-2008 standards, making advanced treatment processes an inevitable trend to achieve compliant discharge. Currently, the main technologies for advanced treatment of wastewater from my country's paper industry include: coagulation, flotation, adsorption, advanced oxidation, membrane separation, and constructed wetlands. Conventional technologies can achieve COD levels of 30-40 mg / L; further reductions result in unsatisfactory treatment methods and effects.

[0005] Advanced oxidation technologies include Fenton oxidation, photocatalytic oxidation, electrochemical oxidation, and ozone oxidation, which offer advantages such as rapid reaction speed, high treatment efficiency, thorough destruction of toxic pollutants, no secondary pollution, wide applicability, and ease of operation. Currently, Fenton oxidation is the most widely used method in the industry. Further advanced treatment, including subsequent ozone catalytic oxidation combined with bioreactor (BAF), is also employed.

[0006] Membrane separation technology has advantages such as operation at room temperature, no phase change, high separation efficiency, simple equipment, easy operation, easy maintenance and control, small equipment footprint, and no secondary pollution. It can treat high-quality intermediate wastewater and achieve high-level reuse of wastewater. It is applicable to the treatment of almost all kinds of papermaking wastewater. However, high investment, short membrane life, and high power consumption are the shortcomings of membrane separation technology. The investment cost per ton of water is 1,000 to 2,000 yuan, and the operating cost per ton of water is 1.5 to 2.5 yuan. At the same time, the use of membrane separation technology will generate a certain amount of concentrated water. At present, the treatment of concentrated water is still in the process of continuous research and improvement. This is an important reason why this technology cannot be widely used in industrial production.

[0007] The selection of technical routes for the deep treatment of COD less than 20 mg / L is an important issue in the deep treatment and reuse of papermaking wastewater in my country. Summary of the Invention

[0008] The purpose of this invention is to provide a method for deep treatment of papermaking wastewater that is low in cost, highly efficient, and has good treatment effect.

[0009] The solution adopted by this invention to achieve its objective is: a method for deep treatment of papermaking wastewater, comprising the following steps:

[0010] Step 1: After the biochemical treatment of papermaking, the tailwater is precipitated by physicochemical coagulation or Fenton treatment. The supernatant obtained is mixed with the reflux carbon slurry of powdered activated carbon to make the powdered activated carbon in a suspended state and mixed evenly with water.

[0011] Step 2: Further mix the slurry mixture from Step 1 with the newly prepared powdered activated carbon slurry. A portion of the slurry is returned to Step 1 as a reflux slurry. The remaining mixture of slurry and water is filtered under negative pressure using an immersion ultrafiltration membrane module to separate the carbon and water.

[0012] Step 3: The solution separated in Step 2 is adsorbed using macroporous adsorption resin, and the effluent is discharged or reused;

[0013] Step 4: After the concentration of powdered activated carbon in Step 1 reaches a certain value, the carbon is discharged. The discharged waste carbon slurry is dehydrated by pressure filtration, dried and dehydrated to ≤10% moisture content, then activated at high temperature. After cooling, it is mixed with new carbon to form a carbon slurry for use in the newly prepared powdered activated carbon slurry in Step 2.

[0014] Step 5: After the macroporous adsorption resin is saturated, it is regenerated by desorption with regeneration liquid. The generated regeneration waste liquid is subjected to Fenton oxidation precipitation. The supernatant obtained is mixed with the waste carbon slurry generated in step 4, and the precipitated sludge is discharged into the sludge tank.

[0015] Preferably, in step 1, the supernatant and the reflux carbon slurry are mixed by plug flow and / or pulse aeration; the concentration of powdered activated carbon in the mixture is ≤30g / L.

[0016] Preferably, in step 2, the powdered activated carbon is prepared into a 5% carbon slurry, and added to the slurry-water mixture in multiple portions at a single addition amount of 5 to 500 mg / L, with the cumulative addition amount being 8 to 15 times the COD value.

[0017] Preferably, in step 2, when the effluent COD is greater than or equal to 25 mg / L, the activated carbon dosage is adjusted by an increase of 10%.

[0018] Preferably, in step 2, when the absorbance of the effluent at 254 nm ultraviolet light is greater than or equal to 0.083, the amount of activated carbon added is adjusted by an increase of 10%.

[0019] Using the absorbance of the effluent at 254nm ultraviolet light as a characteristic indicator to judge the effluent effect of the submerged ultrafiltration membrane, it is a characteristic absorption indicator in the COD index of papermaking effluent after the experiment. Compared with the traditional chemical oxidation method, it has the advantages of real-time monitoring and good responsiveness, and is a highly efficient and real-time technical means to monitor process operating parameters.

[0020] Preferably, in step 3, the macroporous adsorption resin uses anionic polystyrene as the framework and quaternary ammonium salt as the exchange group. The adsorption process involves water passing through the macroporous adsorption resin from top to bottom for adsorption treatment. The volume of the macroporous adsorption resin is 0.05% to 0.2% of the daily water treatment volume.

[0021] Under the condition of a filtration rate of 20 m / h, the macroporous adsorption resin has the characteristics of a long operating cycle of up to 4 days, low regeneration frequency, and a regeneration liquid ratio that can be as low as 0.1% of the treated water volume.

[0022] Preferably, in step 3, the COD of the effluent is less than 20 mg / L.

[0023] Preferably, in step 4, carbon removal is performed when the concentration of powdered activated carbon in step 1 is greater than 30 g / L, and the activation temperature is 850–950 °C.

[0024] The concentration of powdered activated carbon in step 1 is detected. When the concentration of powdered activated carbon is greater than 30 g / L, carbon discharge is implemented. The optimal carbon slurry control volume ratio is to balance different process condition parameters, so that the influencing factors such as the concentration of powdered activated carbon slurry, aeration gas ratio, stirring disturbance intensity, and gas-water ratio in the operation control conditions are balanced to achieve the best balance. This can effectively control the carbon slurry in the membrane fibers from accumulating into carbon cakes, reduce overall power consumption, reduce membrane fouling, and achieve long-cycle chemical cleaning.

[0025] Preferably, in step 5, the regenerated liquid is a sodium chloride solution with a mass percentage of 5% to 10% or a sodium hydroxide solution with a mass percentage of ≤2%, and the volume of the regenerated liquid is 2 to 4 times the volume of the macroporous adsorption resin. When a sodium hydroxide solution with a mass percentage of ≤2% is used as the regenerated liquid, it is added after 10 to 30 regeneration cycles.

[0026] Preferably, in step 5, the Fenton oxidation precipitation process involves adding ferrous sulfate solution and hydrogen peroxide, stirring and reacting under acidic conditions, followed by aeration, adding sodium hydroxide for neutralization, and then precipitating with flocculant. The Fenton reaction reagent addition ratio is 28% hydrogen peroxide: ferrous sulfate heptahydrate: COD value of 3-6: 8-10: 1. The supernatant and waste carbon slurry are mixed at a volume ratio of 1:3-5 and then filtered by pressure.

[0027] The macroporous adsorption resin is regenerated using sodium chloride and sodium hydroxide solutions. The regeneration wastewater first undergoes a Fenton reaction, utilizing hydroxyl radicals to oxidize and destroy the structure and decolorize humic acid, lignin, and other recalcitrant organic matter. Then, iron hydroxide flocculation precipitates suspended solids and colloids, significantly reducing COD and other indicators in the regeneration wastewater. Finally, waste carbon slurry is mixed for further adsorption to reduce COD, solving the problem of difficult concentrated wastewater treatment. This method combines the oxidation characteristics of Fenton and the adsorption characteristics of activated carbon.

[0028] In step 1, the effluent from the papermaking terminal coagulation process and the return carbon slurry are mixed in the mixing tank of the powdered activated carbon adsorption unit. The mixing method combines segmented flow propulsion and pulse aeration. Underwater propellers are installed in each segment for intermittent operation. Perforated aeration pipes are installed at the bottom of the tank, arranged in parallel. Pneumatic valves are installed on the aeration branch pipes for intermittent opening and adjusting the aeration time. Pneumatic valves are also installed on the aeration branch pipes of the mixing tank for intermittent opening and adjusting the aeration time from 15 to 60 minutes. A carbon discharge trough and perforated sludge discharge pipe are installed at the bottom of the mixing tank. When the concentration of powdered activated carbon in the mixing tank exceeds 30 g / L, carbon discharge is implemented. The deposited carbon slurry is pumped to the carbon slurry storage tank 12 hours after the addition of fresh activated carbon on the same day.

[0029] In step 2, the submerged ultrafiltration membrane separation unit is equipped with a submerged ultrafiltration membrane module, a bottom perforated aeration pipe, and a reflux pump. The powdered activated carbon is prepared into a 5% carbon slurry and added to the water tank in multiple batches at a single dosage of 5-500 mg / L. The cumulative dosage is 8-15 times the COD value. The reflux pump returns the carbon slurry with increased concentration in the reactor to the front end of the mixing tank. The pump inlet is located at the end of the tank inlet and is more than 1 m away from the membrane module and 0.2 m away from the bottom.

[0030] The absorbance of the effluent at 254nm ultraviolet light is used as a characteristic indicator to judge the effluent effect of the submerged ultrafiltration membrane. The judgment is based on the arithmetic mean of the effluent absorbance reading at 254nm ultraviolet light in a 1cm absorption cell multiplied by 300 over 1 hour. If it is less than the target COD value of the effluent, the addition of powdered activated carbon is not adjusted. If it is greater than the target value, the flow rate of the activated carbon addition pump is adjusted by 10%.

[0031] In step 3, the macroporous adsorption resin unit pumps the purified water separated in step 2 to the macroporous resin adsorption tank via a secondary lift pump. The tank is equipped with a control valve group on the outside and is filled with a water distributor and macroporous adsorption resin. The macroporous adsorption resin is anionic polystyrene with quaternary ammonium salt as the exchange group. The purified water passes through the filled macroporous adsorption resin from top to bottom. Organic pollutants are adsorbed into the internal pores of the resin by intermolecular forces and anion exchange, and the wastewater is finally purified.

[0032] In step 4, the carbon slurry is pumped to a high-pressure diaphragm filter press for dewatering. The high-pressure diaphragm filter press operates at a pressure of 1.0 MPa, gradually dewatering the carbon slurry from approximately 95% moisture content into carbon cake with a moisture content reduced to 50%. It is then conveyed by a screw conveyor to a paddle dryer for further drying and dewatering, forming carbon powder with a moisture content of approximately 10%. This powder is subsequently sent to a modular high-temperature furnace, where it is indirectly heated to 850–950°C in an oxygen-free environment for a period of time. After activation, it is cooled to room temperature by a cooling water jacket and then used to prepare carbon slurry for recycling.

[0033] In step 5, the regeneration process involves preparing a solution of sodium chloride and sodium hydroxide, with a sodium chloride concentration of 5 wt.%–10 wt.% and a sodium hydroxide concentration ≤2 wt.%. The volume of the regenerated liquid is 2–4 times the volume of the resin in a single tank. The sodium hydroxide solution is added after 10–30 regeneration cycles. The solution is pumped from bottom to top through the resin tank and discharged into a wastewater collection tank. The COD concentration is 1000–2000 mg / L, enriched by 200–500 times. It is then pumped to a Fenton tank, where ferrous sulfate solution and hydrogen peroxide are added. The mixture is stirred and reacted under acidic conditions, followed by aeration. Sodium hydroxide is added for neutralization, and the mixture flows into a sedimentation tank where flocculant is added for sedimentation. The supernatant is sent to a carbon slurry storage tank, mixed with carbon slurry at a 1:3 ratio, and then filtered. The sludge from the bottom of the sedimentation tank is pumped to a sludge storage tank.

[0034] This invention addresses the characteristics of papermaking wastewater by employing the following methods: (1) After biochemical treatment of papermaking wastewater, the supernatant is precipitated by physicochemical coagulation or Fenton treatment, and powdered activated carbon is added for mixing; (2) The powdered activated carbon is stirred in a water tank to suspend it and mix it with water; (3) A submerged ultrafiltration membrane is used for carbon-water separation; (4) The membrane effluent is sent to a macroporous resin adsorption tank to adsorb organic matter and further reduce chemical oxygen demand. The effluent is reused after meeting discharge and reuse standards; (5) After the macroporous adsorption resin is saturated, it is regenerated and desorbed using brine, then subjected to Fenton oxidation precipitation, followed by a second step of carbon-slurry mixing; (6) After the second step of powdered activated carbon is discharged, it is filtered by plate and frame filter press, dried, and regenerated at high temperature before reuse. The process of this invention produces high-quality effluent with stable performance and is economical. The COD of the effluent meets the Class III limit in the surface water environmental quality standards (specifically, COD ≤ 20 mg / L).

[0035] The present invention has the following advantages and beneficial effects:

[0036] 1. In the method of the present invention, steps 2 and 3 are mainly physical adsorption treatments. Powdered activated carbon and macroporous adsorption resin each play their respective adsorption advantages. Gradient adsorption is carried out on hydrophilic, neutral, and anionic humic acids and other pollutants in water that are difficult to biodegrade. The operation is simple, the process parameters can be adjusted quickly, the activated carbon has a large adsorption capacity, and it is highly targeted.

[0037] 2. In the method of the present invention, the macroporous adsorption resin adopts the form of adsorption followed by regeneration, which enriches the concentration of recalcitrant organic pollutants in the wastewater after papermaking physicochemical precipitation by about 400 times. The main mechanism is the specific surface area in the micropores plus anion adsorption. When the COD concentration of the incoming water is low, compared with powdered activated carbon, the adsorption capacity is larger, the COD value of the effluent is lower, the adsorption amount is stable, and the effluent fluctuation is small.

[0038] 3. In the method of the present invention, the powdered activated carbon has a good dehydration effect after use, the high temperature regeneration of powdered activated carbon is efficient and of good quality, and after recycling, the addition of new activated carbon is reduced.

[0039] 4. The combined process employed in this invention yields superior effluent quality, and under the same scale conditions, it offers advantages in investment and operating costs. Operating costs are low, as the reagents are conventional chemicals, eliminating the need for expensive reagents, and electricity consumption is low. Attached Figure Description

[0040] Figure 1 This is a schematic diagram of the papermaking wastewater deep treatment system according to Embodiment 1 of the present invention;

[0041] Figure 2 This is a schematic flowchart of a method for deep treatment of papermaking wastewater according to an embodiment of the present invention.

[0042] Figure 3 This is a graph showing the relationship between COD and UV254 in the effluent of Example 2 of the present invention;

[0043] Figure 4 This is a graph showing the relationship between influent COD and UV254 in Embodiment 2 of the present invention;

[0044] Explanation of icon numbers:

[0045] 1. Mixing tank; 2. Submersible jet mixer; 3. Aeration pipe; 4. Control valve; 5. Sludge discharge trough; 6. Sludge discharge pipe; 7. Membrane module; 8. Permeate pump; 9. Backwash pump; 10. Return pump; 11. Clear water tank; 12. Lift pump; 13. Macroporous resin adsorption tank; 14. Macroporous adsorption resin; 15. Intermediate water tank; 16. Regenerated liquid preparation tank; 17. Regenerated waste liquid collection tank; 18. Fenton tank; 19. Sedimentation tank; 20. Sludge thickening tank; 21. Powdered activated carbon slurry preparation equipment; 22. Waste activated carbon slurry storage tank; 23. Plate and frame filter press dewatering device; 24. Activated carbon drying device; 25. High-temperature regeneration device. Detailed Implementation

[0046] To better understand the present invention, the following embodiments are further illustrations of the present invention, but the content of the present invention is not limited to the following embodiments.

[0047] Example 1

[0048] like Figure 1 As shown, a papermaking wastewater deep treatment system includes: a powdered activated carbon adsorption unit, an immersion ultrafiltration membrane separation unit, a macroporous resin adsorption unit, and a powdered activated carbon recycling unit connected in sequence.

[0049] The powdered activated carbon adsorption unit includes a mixing tank 1 and a submersible jet mixer 2. The mixing tank 1 is a multi-compartment water tank connected in sequence. Each compartment is equipped with a submersible jet mixer 2. The bottom of each compartment is equipped with a perforated aeration pipe 3 for stirring and aeration. The first compartment is equipped with an inlet for adding papermaking wastewater. The bottom of the first compartment is equipped with an inclined sludge discharge trough 5, which is connected to a sludge discharge pipe 6. The last compartment is equipped with an outlet.

[0050] The submerged ultrafiltration membrane separation unit includes a separation tank, membrane modules 7, a return pump 10, a product water pump 8, a clear water tank 11, and a backwash pump 9. Both membrane modules 7 and the return pump 10 are installed in the separation tank, which contains multiple membrane modules 7 connected in parallel. The inlet of the separation tank is connected to the outlet of the last compartment, and the outlet of the return pump 10 is connected to the inlet of the first compartment. An aeration pipe 3 is installed in the separation tank for stirring and aeration. The outlet of the membrane module 7 is connected to the inlet of the clear water tank 11 via the product water pump 8. The outlet of the backwash pump 9, located in the clear water tank 11, is connected to the outlet of the membrane module 7. Water is drawn from the clear water tank 11 and pumped into the membrane module 7 through pipelines for backwashing.

[0051] The macroporous resin adsorption unit includes a macroporous resin adsorption tank 13, an intermediate water tank 15, a regenerated liquid preparation tank 16, a regenerated waste liquid collection tank 17, a Fenton tank 18, and a sedimentation tank 19. The inlet of the macroporous resin adsorption tank 13 is connected to a lift pump 12 installed in a clear water tank 11. The outlet of the macroporous resin adsorption tank 13 is connected to the inlet of the intermediate water tank 15. The liquid inlet of the macroporous resin adsorption tank 13 is connected to the outlet of the regenerated liquid preparation tank 16. The liquid outlet of the macroporous resin adsorption tank 13 is connected to the inlet of the regenerated waste liquid collection tank 17. The liquid outlet of the regenerated waste liquid collection tank 17 is connected to the inlet of the Fenton tank 18. The liquid outlet of the Fenton tank 18 is connected to the inlet of the sedimentation tank 19. The sludge in the sedimentation tank 19 is sent to the sludge thickening tank 20 through its sludge discharge end. The drainage end of the sedimentation tank 19 is connected to a powdered activated carbon recycling unit for the recycling and regeneration of powdered activated carbon. The effluent from the clear water tank 11 is lifted by the booster pump 12 and connected to the upper part of the macroporous resin adsorption tank 13 through the pipe. After contact with the macroporous adsorption resin 14, the pollutants are adsorbed and then flow by gravity into the intermediate water tank 15 through the pipeline. The regenerated liquid in the regenerated liquid preparation tank 16 is pumped to the macroporous resin tank that is saturated with adsorption for regeneration. The regenerated waste liquid flows by gravity into the regenerated waste liquid collection tank 17 and is then pumped to the Fenton tank 18 for chemical reaction. After the sludge is separated by the sedimentation tank 19, the sludge is sent to the sludge thickening tank 20 and the supernatant flows into the waste carbon slurry tank.

[0052] In this unit, the macroporous resin adsorption unit may include multiple macroporous resin adsorption tanks 13 arranged in series or in parallel to improve treatment efficiency. Each macroporous resin adsorption tank 13 is filled with a water distributor and macroporous adsorption resin 14. The outlet of the intermediate water tank 15 is connected to the inlet of the regenerated liquid preparation tank 16. In practical applications, a submersible pump and pipeline are installed in the intermediate water tank 15 and connected to the inlet of the regenerated liquid preparation tank 16. A filter layer is provided at the inlet of the regenerated liquid preparation tank 16 where it connects to the outlet of the intermediate water tank 15.

[0053] The powdered activated carbon recycling unit includes a waste carbon slurry storage tank 22, a plate and frame filter press dewatering device 23, an activated carbon drying device 24, a high-temperature regeneration device 25, and a powdered activated carbon slurry preparation device 21 connected in sequence. The inlet end of the waste carbon slurry storage tank 22 is connected to the outlet end of the sludge thickening tank 20, and the outlet end of the powdered activated carbon slurry preparation device 21 is connected to the inlet end of the first water tank. The sludge discharge pipe 6 is connected to the waste carbon slurry storage tank 22. After regeneration, the powdered activated carbon and newly purchased powdered activated carbon enter the powdered activated carbon slurry preparation equipment 21 and are mixed with clean water to form a carbon slurry aqueous solution. The solution is then pumped into the first water tank. The slurry discharge tank 5 is equipped with a perforated slurry discharge pipe 6, which pumps or allows gravity to transport the carbon slurry into the waste carbon slurry storage tank 22. The solution is then pressurized by a pump and enters the plate and frame filter press dewatering device 23 for filter dewatering. The carbon cake is then conveyed by a screw conveyor into the activated carbon drying device 24 to dry and remove moisture. Finally, it is transported to the high-temperature regeneration device 25 for pyrolysis activation. After cooling, the powdered activated carbon is recycled and enters the powdered activated carbon slurry preparation equipment 21.

[0054] For ease of control, control valves 4 for controlling the aeration volume and aeration time are installed on the aeration pipes 3 in the multi-compartment water tank and the separation water tank.

[0055] like Figure 2 As shown, a method for deep treatment of papermaking wastewater includes the following steps:

[0056] Step 1: After the papermaking biochemical treatment, the wastewater is treated by physical and chemical coagulation or Fenton treatment and the supernatant is settled. The supernatant is then mixed with carbon slurry delivered by the return pump 10 in the mixing tank 1. The powdered activated carbon is mixed with the slurry by the submersible thruster 2 and the bottom aeration pipe 3. The powdered activated carbon is then suspended and mixed with water.

[0057] Step 2: The mixed carbon slurry enters the water tank where the ultrafiltration membrane module 7 is located and is further mixed with the newly prepared activated carbon slurry of the powdered activated carbon slurry preparation equipment 21. Under the aeration and mixing state, the water pump 8 is used to draw water to form negative pressure filtration, thereby separating carbon and water, and the clear water enters the clear water tank 11.

[0058] Step 3: The membrane effluent is sent to the macroporous resin adsorption tank 13 to adsorb organic matter and further reduce the chemical oxygen demand. The effluent is reused after meeting the discharge and reuse standards.

[0059] Step 4: After the macroporous adsorption resin is saturated, it is regenerated by desorption with regeneration liquid. After the waste liquid undergoes Fenton oxidation precipitation, the clear water is sent to the waste carbon storage tank to be mixed with the carbon slurry to be pressed and filtered. The sludge in the sedimentation tank 19 is discharged into the sludge thickening tank 20.

[0060] Step 5: The carbon slurry in the mixing tank 1 and mud tank 5 is discharged into the waste carbon storage tank. The carbon slurry is dewatered by a plate and frame filter press, and then conveyed by a screw conveyor to a dryer for further drying and dewatering to a moisture content of 10%. It is then sent to a high-temperature regeneration furnace for regeneration and activation at 850°C. After being cooled to room temperature, it is mixed with new carbon and then mixed with water by a pulping equipment to form carbon slurry.

[0061] Further, in step 1, the papermaking terminal coagulation effluent and return carbon slurry are mixed in the mixing tank 1 of the powdered activated carbon adsorption unit. The mixing method adopts a combination of segmented flow propulsion and pulse aeration. Underwater propellers are installed in the segmented tanks for intermittent operation. Perforated aeration pipes 3 are installed at the bottom of the tank, and the aeration pipes 3 are arranged in parallel. Pneumatic valves are installed on the aeration branch pipes for intermittent opening and adjusting the aeration time. Control valves 4 are installed on the aeration branch pipes of mixing tank 1 for intermittent opening and adjusting the aeration time from 15 min to 60 min. The bottom of the front end of mixing tank 1 is equipped with a carbon discharge trough and a perforated sludge discharge pipe 6. When the concentration of powdered activated carbon in the water sample in mixing tank 1 is greater than 30 g / L, carbon discharge is implemented. After adding fresh activated carbon on the same day, the deposited carbon slurry is pumped to the carbon slurry storage tank 12 hours later.

[0062] In step 2, the submerged ultrafiltration membrane separation unit is equipped with a submerged ultrafiltration membrane module 7, a bottom perforated aeration pipe 3, and a reflux pump 10. The powdered activated carbon is prepared into a 5% carbon slurry and added to the water tank at a rate of 5-500 mg / L. The cumulative addition amount is 8-15 times the COD value. The reflux pump 10 refluxes the carbon slurry with increased concentration in the reactor into the front end of the mixing tank 1. The pump suction port is located at the end of the tank inlet and is more than 1m away from the membrane module 7 and 0.2m away from the bottom.

[0063] In step 3, the macroporous resin adsorption unit uses a secondary lift pump 12 to send clean water from the clear water tank 11 to the macroporous resin adsorption tank 13. A control valve 4 group is installed outside the tank. The tank is filled with a water distributor and macroporous adsorption resin 14. The macroporous adsorption resin is anionic polystyrene with quaternary ammonium salt as the exchange group. The clean water passes through the filled macroporous adsorption resin 14 from top to bottom. Organic pollutants are adsorbed into the internal pores of the resin by intermolecular forces and anion exchange, and the wastewater is finally purified.

[0064] In step 4, the regeneration process involves a solution prepared with sodium chloride and sodium hydroxide, where the sodium chloride concentration is 5-10% and the sodium hydroxide concentration is ≤2%. The volume of the regenerated liquid is 2-4 times the volume of the resin in a single tank. Sodium hydroxide is added after 10-30 regeneration cycles. The solution is pumped from bottom to top through the resin tank and discharged into a wastewater collection tank. The COD concentration is 1000-2000 mg / L, enriched by 200-500 times. It is then pumped to Fenton tank 18, where ferrous sulfate solution and hydrogen peroxide are added. The mixture is stirred and reacted under acidic conditions, followed by aeration. Sodium hydroxide is added for neutralization, and the mixture flows into sedimentation tank 19 where flocculant is added for sedimentation. The supernatant is sent to a carbon slurry storage tank, mixed with carbon slurry at a 1:3 ratio, and then filtered. The sludge from the bottom of sedimentation tank 19 is pumped to a sludge storage tank.

[0065] In step 5, the carbon slurry is pumped to a high-pressure diaphragm plate and frame for dewatering. The high-pressure diaphragm plate and frame operates at a pressure of 1.0 MPa. The carbon slurry is gradually dewatered from approximately 95% moisture content to form carbon cake with a moisture content reduced to 50%. It is then conveyed by a screw conveyor to a paddle dryer for further drying and dewatering, forming carbon powder with a moisture content of approximately 10%. This powder is subsequently sent to a modular high-temperature furnace, where it is indirectly heated to 850°C for a period of time in an oxygen-free environment. After activation, it is cooled to room temperature by a cooling water jacket and then used to prepare carbon slurry for recycling.

[0066] Example 2

[0067] At a pilot plant site for advanced wastewater treatment in paper mills, the influent flow rate is 16 m³ / s. 3 At a flow rate of 25 m³ / h, add 350 mg / L of powdered activated carbon according to the above process. The mixture is then contacted in mixing tank 1 for 2 hours, followed by contact in submerged membrane tank for 1 hour, activated carbon reflux for 1 hour, and then stopped for 1 hour. 3 / h, The combination of powdered activated carbon + submerged ultrafiltration membrane separation system (the main equipment and water tank in step 2 are referred to as CUF): This process organically combines powdered biological activated carbon adsorption technology with ultrafiltration membrane filtration separation. It integrates aeration, microbial biochemistry, activated carbon adsorption, and ultrafiltration into a single deep wastewater treatment process using powdered activated carbon coupled with submerged membrane technology. Similar to a membrane bioreactor (MBR), it utilizes powdered activated carbon adsorption combined with microbial oxidation of ammonia nitrogen, COD adsorption and degradation, and increased dissolved oxygen in the effluent. The system possesses both the adsorption characteristics of activated carbon and the biochemical characteristics of microorganisms under aerobic conditions. After submerged ultrafiltration membrane separation, the effluent is transparent with a dissolved oxygen content of over 5 mg / L. Approximately 100 mg / L of activated carbon is added to the membrane tank to adsorb recalcitrant organic matter in the water, and the attached microorganisms possess the characteristics of biochar, gradually accumulating to a high concentration of 30,000 mg / L of activated carbon slurry. This facilitates rapid adsorption equilibrium and enhances the system's stability in the face of water quality and quantity shocks. The macroporous adsorption resin 14 system consists of two resin tanks filled with 2 m³ of activated carbon. 3The system integrates volumetric resin, external main pipes for water distribution, resin-generated water discharge into a clean water tank, and electrical automatic control and regenerated brine preparation.

[0068] Running 4000m 3 The resin is then regenerated in a downstream tank. The regenerant is prepared using 10% sodium chloride and has a capacity of 8m³. 3 Volumetric countercurrent regeneration is performed. The waste liquid is then treated with Fenton dosing, with 28% hydrogen peroxide added at a mass selected based on 5 times the COD value, and ferrous sulfate heptahydrate added at a mass selected based on 8 times the COD value. Salt water is added to adjust the pH to acidity 4, and the mixture is stirred at a speed of 70 rpm for 40 minutes. Aeration is then carried out for 1 hour, followed by the addition of 5 mg / L polyacrylamide solution to promote the formation of large, easily settled flocs. The mixture is stirred for 10 minutes at a speed of 20 rpm, and the produced flocs are allowed to settle for 2 hours.

[0069] Sampling and analysis were performed on the influent and effluent, and the results are shown in Tables 1 and 2 below.

[0070] Table 1

[0071]

[0072]

[0073] Table 2 Results of Fenton + Activated Carbon Treatment of Regenerated Waste Liquid

[0074]

[0075] Figure 3 This is a graph showing the relationship between COD and UV254 in the effluent of this embodiment. As can be seen from the graph, the CUF effluent is the effluent after adsorption by powdered activated carbon and filtration by submerged ultrafiltration membrane. The COD concentration (mg / L) in the water sample is highly correlated with the UV254nm absorbance value of a 1cm cuvette. The COD concentration to UV254 absorbance ratio is approximately 205. The effluent effect can be monitored in real time using the UV254 absorbance index. Its change value can be linked with the addition of powdered activated carbon slurry to achieve precise control.

[0076] Figure 4 This is a graph showing the relationship between influent COD and UV254 in this embodiment. As can be seen from the graph, the influent is the supernatant after biological treatment of papermaking wastewater in the wastewater treatment plant, which is then settled in a coagulation and tertiary sedimentation tank. The COD concentration (mg / L) in the water sample was measured and compared with the UV254 absorbance value at 1cm cuvette. A graph comparing COD and UV254 in the tertiary sedimentation tank basically shows that COD and UV254 absorbance have the same trend. The COD in the tertiary sedimentation tank and UV254 absorbance have a linear ratio of about 100 times. The UV254 online instrument can be used as one of the control parameters of the CUF effluent automatic control parameter, and participates in the automatic control program to regulate the process operations such as activated carbon addition and carbon discharge.

[0077] Example 3

[0078] At a pilot plant site for advanced wastewater treatment in paper mills, the influent flow rate is 20 m³ / s. 3 / h, add 340mg / L of powdered activated carbon according to the above process, contact in mixing tank 1 for 1.5h, contact in submerged membrane tank for 0.8h, activate carbon reflux for 30min and stop for 30min, flow rate 25m³ / h. 3 / h, Powdered Activated Carbon Membrane Bioreactor (CUF): This process organically combines powdered activated carbon adsorption technology with ultrafiltration membrane filtration. It integrates aeration, microbial biochemistry, activated carbon adsorption, and ultrafiltration into a single, deep wastewater treatment process using powdered activated carbon coupled with a submerged membrane process. Similar to a membrane bioreactor (MBR), it utilizes powdered activated carbon adsorption combined with microbial oxidation of ammonia nitrogen, COD adsorption and degradation, and increased dissolved oxygen in the effluent. The system possesses both the adsorption characteristics of activated carbon and the biochemical characteristics of microorganisms under aerobic conditions. After submerged ultrafiltration membrane separation, the effluent is transparent with a dissolved oxygen content exceeding 5 mg / L. Approximately [amount missing] activated carbon is added to the membrane tank to adsorb recalcitrant organic matter in the water, and the attached microorganisms possess biochar characteristics, gradually accumulating to a high concentration of 30,000 mg / L of activated carbon slurry. This facilitates rapid adsorption equilibrium and enhances the system's stability against shocks in water quality and quantity. The macroporous adsorption resin 14 system consists of two resin tanks, filled with 2m³ of [missing information]. 3 The system integrates volumetric resin, external main pipes for water distribution, resin-generated water discharge into a clean water tank, and electrical automatic control and regenerated brine preparation.

[0079] Running 3800m 3 The resin is then regenerated in a downstream tank. The regenerant is prepared using 10% sodium chloride and has a capacity of 8m³. 3 Volumetric countercurrent regeneration is performed. The waste liquid is then treated with Fenton dosing, with 28% hydrogen peroxide added at a mass selected based on 6 times the COD value, and ferrous sulfate heptahydrate added at a mass selected based on 9 times the COD value. Salt water is added to adjust the pH to acidity 4, and the mixture is stirred at a speed of 70 rpm for 40 minutes. Aeration is carried out for 2 hours, and then 5 mg / L polyacrylamide solution is added to promote the formation of large, easily settled flocs. The mixture is stirred for 10 minutes at a speed of 20 rpm, and the produced flocs are allowed to settle for 1 hour.

[0080] Sampling and analysis were performed on the influent and effluent, and the results are shown in Tables 3 and 4 below.

[0081] Table 3. Effect of effluent COD on implementation

[0082]

[0083]

[0084] Table 4. Results of Fenton + Activated Carbon Treatment of Regenerated Waste Liquid

[0085]

[0086]

[0087] The above description is merely a preferred embodiment of the present invention, and should not be construed as limiting the scope of the invention. It should be noted that those skilled in the art can make various improvements and modifications without departing from the principles of the present invention, and these improvements and modifications are also considered to be within the scope of protection of the present invention.

Claims

1. A method for deep treatment of papermaking wastewater, characterized in that, Includes the following steps: Step 1: After the biochemical treatment of papermaking, the tailwater is precipitated by physicochemical coagulation or Fenton treatment. The supernatant obtained is mixed with the powdered activated carbon slurry in the mixing tank so that the powdered activated carbon is in a suspended state and is mixed evenly with water. Step 2: Further mix the slurry mixture from Step 1 with the newly prepared powdered activated carbon slurry. A portion of the slurry is returned to Step 1 as powdered activated carbon slurry, and the remaining slurry is filtered under negative pressure using an immersion ultrafiltration membrane module to separate the carbon and water. Step 3: The purified water separated in Step 2 is adsorbed using macroporous adsorption resin, and the effluent is discharged or reused. Step 4: After the concentration of powdered activated carbon in the mixing tank reaches a certain value in Step 1, the carbon is discharged. The discharged waste carbon slurry is dehydrated by pressure filtration and dried to a moisture content of ≤10%, then activated at high temperature. After cooling, it is mixed with new carbon to form a carbon slurry for the preparation of the newly prepared powdered activated carbon slurry in Step 2. Step 5: After the macroporous adsorption resin is saturated, it is regenerated by desorption with regeneration liquid. The generated regeneration waste liquid is subjected to Fenton oxidation precipitation. The supernatant obtained is mixed with the waste carbon slurry generated in step 4, and the precipitated sludge is discharged into the sludge tank. In step 2, powdered activated carbon is prepared into a 5% carbon slurry, and added to the slurry mixture in multiple portions at a single addition amount of 5~500mg / L, with the cumulative addition amount being 8~15 times the COD value. In step 2, when the COD of the effluent is greater than or equal to 25 mg / L, the amount of activated carbon added is adjusted by an increase of 10%. In step 3, the macroporous adsorption resin uses anionic polystyrene as the framework and quaternary ammonium salt as the exchange group. The adsorption process involves water flowing from top to bottom through the macroporous adsorption resin for adsorption treatment. The volume of the macroporous adsorption resin is 0.05% to 0.2% of the daily water treatment volume. In step 4, when the concentration of powdered activated carbon in the mixing tank in step 1 is greater than 30 g / L, carbon is discharged, and the activation temperature is 850~950℃.

2. The method for deep treatment of papermaking wastewater according to claim 1, characterized in that: In step 1, the supernatant and the powdered activated carbon reflux slurry are mixed by plug flow and / or pulse aeration.

3. The method for deep treatment of papermaking wastewater according to claim 1, characterized in that: In step 3, the COD of the effluent is less than 20 mg / L.

4. The method for deep treatment of papermaking wastewater according to claim 1, characterized in that: In step 5, the regenerated liquid is a sodium chloride solution with a mass percentage of 5%~10% or a sodium hydroxide solution with a mass percentage of ≤2%. The volume of the regenerated liquid is 2~4 times the volume of the macroporous adsorption resin. When a sodium hydroxide solution with a mass percentage of ≤2% is used as the regenerated liquid, it is added after 10~30 regeneration cycles.

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