Starch wastewater treatment resource recycling method and system

Abstract

The invention discloses a starch wastewater treatment resource recycling method which comprises the following steps: precipitating unhydrolyzed starch in strongly acidic starch wastewater to obtain precipitated effluent and precipitated slurry; performing membrane filtration on the precipitated effluent to generate membrane filtration produced water and membrane filtration concentrated water; adsorbing specific ions in the membrane filtration produced water by adopting a selective adsorbent to obtain adsorbed produced water and an adsorption saturated adsorbent; an acid removal agent is added into the adsorption saturated adsorbent for acid removal regeneration, a desorption solution and a regenerated adsorbent are obtained, and the regenerated adsorbent participates in adsorption of specific ions again; and concentrating the desorption liquid to obtain the compound fertilizer production raw material. Specific ions in the starch wastewater can be adsorbed, and the specific ions adsorbed in the adsorbent are subjected to acid removal, so that the adsorbent is recovered and can be used for adsorption again, the cyclic utilization of the adsorbent is realized, and meanwhile, a desorption solution generated by the acid removal of the adsorbent can form a production raw material of a compound fertilizer after being concentrated.

Description

A method and system for the resource recovery and reuse of starch wastewater Technical Field

[0001] This invention belongs to the field of wastewater treatment technology, specifically relating to a method and system for the resource recovery and reuse of starch wastewater. Background Technology

[0002] Currently, with the expansion of global lithium battery production capacity, the application of starch hydrolysis technology is also increasing. Every 10,000 tons of negative electrode material generates approximately 80,000 to 120,000 tons of hydrolysis waste liquid. The following is the process of producing battery nanomaterials from starch.

[0003]

[0004] As can be seen from the process flow, the presence of potassium, calcium, and magnesium ions has multi-dimensional effects on material properties, process stability, and equipment operation. Specifically, during the high-temperature carbonization stage (e.g., 1400℃), potassium ions react with the carbon matrix to form impurities such as potassium carbonate. These impurities clog the mesoporous structure of hard carbon (pore size 2-50nm), hindering the diffusion path of sodium ions, increasing the interlayer spacing (from 0.38nm to 0.42nm), and disrupting the stability of the honeycomb porous structure, ultimately leading to material pulverization. Similarly, during the high-temperature carbonization stage (1400℃), calcium and magnesium ions react with the carbon matrix to form impurities such as CaC2 and MgO, which embed themselves between carbon layers, reducing the graphitization degree from 20% to 12% and causing the sodium ion diffusion coefficient to decrease from 1×10⁻⁶. -10 cm² / s decreased to 5×10 -11 The flow rate is cm² / s. Therefore, a certain amount of wastewater needs to be discharged during the production process to balance the various impurity ions in the system. The turbidity of this discharged hydrolysis wastewater is 500~1000 NTU, mainly due to incomplete hydrolysis of starch; the pH of the hydrolysis liquid is 1-3 (due to excessive nitric acid, resulting in strong acidity), containing a large amount of organic matter (COD: 5000~10000 mg / L) and a large amount of inorganic ions such as nitrate (2500 mg / L), potassium ions (100-500 mg / L), calcium ions (≤100 mg / L), magnesium ions (≤200 mg / L), and total phosphorus (≤100 mg / L). Direct discharge of this water can cause eutrophication of water bodies and soil acidification due to disruption of soil pH balance.

[0005] Currently, the main treatment technology for starch hydrolysis wastewater is biochemical treatment, which removes organic matter, total nitrogen, and total phosphorus from starch hydrolysis. For example, patent CN105110553B discloses a treatment method for high-concentration starch wastewater, applicable to the degradation of organic pollutants after neutralization of nitric acid hydrolysis wastewater. Its process route involves pretreatment via a vertical flow sedimentation tank + equalization tank + neutralization tank, first completing SS sedimentation and pH adjustment; subsequent biochemical treatment via a hydrolysis acidification tank + EGSB anaerobic reactor + aerobic granular sludge reaction tank, followed by a contact oxidation tank + final sedimentation tank, which degrades organic matter such as glucose and oligosaccharides in the wastewater. The treated effluent exhibits stable compliance with COD and SS standards. Patent CN113526621B discloses a treatment method for nitrate-containing wastewater, applicable to high-concentration NO3 in nitric acid hydrolysis wastewater. - To address the removal requirements, an electrolytic reactor is used. The reactor is divided into an anode and cathode zone by an electrolytic separator. The cathode electrolyte is an acidic solution containing Fe ions and the wastewater to be treated. Through the synergistic effect of the electric field, Fe ions are continuously converted into ferrous ions, thereby efficiently decomposing nitrate. While the above treatment technologies utilize biological and electrolytic methods to degrade organic matter and nitrate nitrogen, the water is highly acidic. Therefore, biological treatment requires the addition of a large amount of alkali to adjust the pH to neutral to allow microorganisms to survive. Using biochemical methods to degrade organic matter and nitrate in the water to meet discharge requirements is costly and significantly affected by irregular drainage and unstable water volume. The method of using an electrolytic reactor to degrade nitrate requires first removing other metal ions in the wastewater through precipitation, then reducing iron salts to ferrous iron at the cathode. The ferrous iron decomposes nitrate into nitric oxide and ferric iron. Therefore, this method only degrades nitrate in the water, and removing other metal ions also requires the addition of a large amount of alkali to achieve alkalinity. This method cannot degrade organic matter; it can only reduce total nitrogen and does not meet discharge requirements. In the battery industry, the organic matter and nitrate in the hydrolysate, as well as the wastewater itself, are reusable resources, reducing the consumption of acid and water during the hydrolysis process.

[0006] Regarding the desalination problem of starch hydrolysate, some domestic patents for starch hydrolysate desalination processes have emerged. For example, patent CN109761434A discloses a combined process for desalination of starch hydrolysate, which uses a pretreatment process of precision filtration + ultrafiltration to remove suspended impurities and macromolecular substances. Then, electrodialysis is used for primary desalination, with a desalination rate of over 80%. Next, ion exchange is used for deep desalination, ultimately reducing the conductivity of the hydrolysate to below 5 μS / cm. This process is suitable for hydrolysates with a pH of 3-5. If this method is used, a large amount of alkali must first be added for pH adjustment. Electrodialysis removes all anions and cations simultaneously, and a large amount of nitric acid cannot be recovered. Moreover, electrodialysis produces concentrated water, and ion exchange needs to be regenerated, producing reclaimed water with a relatively complex composition.

[0007] Based on the above, there is an urgent need to develop a starch wastewater treatment and reuse process that removes only potassium, calcium, and magnesium ions from the hydrolysate, thereby achieving the resource recovery of starch, water, nitric acid, sodium, and other materials, and further utilizing the adsorbed potassium, calcium, and magnesium ions for fertilizer production. Summary of the Invention

[0008] In order to overcome the shortcomings of the prior art, the purpose of this invention is to solve the problems in the prior art and provide a method and system for the resource-based recycling of starch wastewater. This method can selectively remove potassium ions, calcium ions, magnesium ions and other ions from starch wastewater under strongly acidic conditions, meet the requirements for nitric acid hydrolysis and water reuse, realize the resource-based recovery of starch, water, nitric acid, sodium and other materials, and concentrate the adsorbed potassium, calcium, magnesium and other ions and make compound fertilizer with phosphogypsum, phosphate rock and other materials.

[0009] This invention is achieved through the following technical solution:

[0010] In a first aspect, the present invention provides a method for the resource recovery and reuse of starch wastewater, comprising the following steps:

[0011] Unhydrolyzed starch in strongly acidic starch wastewater is precipitated to obtain effluent and slurry.

[0012] The effluent is filtered through a membrane to produce membrane filtration permeate and membrane filtration concentrate.

[0013] The membrane filtration permeate is treated with a selective adsorbent to adsorb specific ions, resulting in adsorbed permeate and a selective adsorbent that is saturated with adsorption.

[0014] An acid desaturation agent is added to the selective adsorbent to perform acid desaturation and regeneration, resulting in a desorption solution and a regenerated selective adsorbent, which then participates in the adsorption of specific ions again.

[0015] The desorption solution is concentrated to obtain raw materials for compound fertilizer production.

[0016] To optimize the above technical solution, the specific measures also include:

[0017] Furthermore, the pH value of the starch wastewater is 1-3.

[0018] Furthermore, the settling time is 1-2 hours.

[0019] Furthermore, the film is made of polyvinylidene fluoride (PVDF), the film has a molecular weight cutoff of not less than 150,000 Da, and the flow channel diameter of the film is 5-12 mm.

[0020] Furthermore, the membrane-filtered permeate flows sequentially through multiple selective adsorbents to adsorb specific ions, specifically:

[0021] The membrane filtration permeate flows through adsorbent 1, where potassium ions are selectively adsorbed, resulting in permeate adsorbed by adsorbent 1.

[0022] The water produced by adsorbent 1 flows through adsorbent 2, where calcium and magnesium ions are selectively adsorbed, resulting in water produced by adsorbent 2.

[0023] Furthermore, the adsorbent 1 is a large-particle-size strong acid cation exchange resin, including 001x7MB, Amberlite IR-120 Plus, Lewatit S108, and D003; the adsorbent 2 is a conventional-particle-size strong acid cation exchange resin, including 001x7, Amberlite IR-120, and Dowex 50W.

[0024] Furthermore, an acid removal agent is added to the adsorbent that has become saturated for acid removal and regeneration, specifically as follows:

[0025] Add 1-3 BV of organic matter removal agent to the selective adsorbent that is saturated with adsorption, and soak for 15-90 min to elute the organic matter;

[0026] Add 3-5 BV of 5%-6% acid stripping agent to the eluted selective adsorbent at a flow rate of 1-2 BV / h to restore the selective adsorbent.

[0027] Furthermore, the acid removal agent is 5%-6% hydrochloric acid, and the organic matter removal agent is hot water or a hot alkaline solution with a mass concentration of 2-3%.

[0028] A second aspect of the present invention provides a starch wastewater treatment and resource recovery system, comprising,

[0029] The sedimentation unit is used for the precipitation and separation of unhydrolyzed starch to obtain precipitated effluent and precipitated slurry;

[0030] The filtration unit is used to filter the effluent through a membrane to produce membrane filtration permeate and membrane filtration concentrate; the membrane filtration concentrate is fed into the sedimentation tank.

[0031] The adsorption unit uses a selective adsorbent to adsorb specific ions into the membrane filtration permeate, obtaining adsorbed permeate and saturated selective adsorbent; the adsorbed permeate is output, and the saturated selective adsorbent is input into the acid desorption tank.

[0032] The acid desorption unit is used to add acid desorption agent to the saturated selective adsorbent for acid desorption regeneration, to obtain desorption solution and selective adsorbent;

[0033] The concentration unit is used to concentrate the desorption liquid to obtain raw materials for compound fertilizer production.

[0034] The sedimentation unit, filtration unit, adsorption unit, acid removal unit, and concentration unit are connected in sequence, and the concentrated water outlet of the filtration unit is connected to the inlet of the sedimentation unit.

[0035] The beneficial effects of this invention are:

[0036] 1. The sedimentation stage of this application can transport the separated starch slurry to the upstream processing technology to continue hydrolysis as a production raw material, thereby improving the utilization rate of process raw materials and achieving zero discharge of solid waste.

[0037] 2. The concentrated water from the membrane filtration of this application can be returned to the sedimentation tank for further treatment, thereby removing the precipitates and suspended solids in the starch wastewater again, and also achieving zero discharge treatment of the concentrated water from the membrane filtration.

[0038] 3. The membrane used in this application can withstand a certain acidic environment (pH 1-12), eliminating the need to neutralize the strong acidity of starch hydrolysate (such as nitric acid hydrolysate pH 1-2), allowing for direct filtration without damaging the membrane module. Furthermore, the membrane module can be backwashed after shutdown, quickly restoring membrane flux, extending membrane lifespan, and reducing membrane replacement frequency.

[0039] 4. The adsorbent used in this application is a strong acid cationic adsorbent with a strong acid sulfonic acid group (-SO3H) functional group. This type of adsorbent can undergo isocharge exchange with cations in the solution under strong acidic conditions (pH 1-2), which is highly compatible with the characteristics of the liquid to be treated in this application. The desalination process can be carried out directly under strong acidic conditions, realizing the separation of target ions. This not only simplifies the process, but also solves the technical problem of easy deactivation of adsorbents in acidic solutions.

[0040] 5. Through multiple combined design processes, the liquid adsorbed by the adsorbent can be desorbed, and the adsorbent can be restored for re-adsorption, thus realizing the recycling of the adsorbent. At the same time, the desorbed liquid generated by the adsorbent desorption can be evaporated and concentrated to form raw materials for the production of compound fertilizer.

[0041] 6. The process of this application achieves zero emissions while recycling resources. The entire treatment process does not require the addition of additional chemical reagents. At the same time, by utilizing the chemical properties of the adsorbent, the adsorbent can be recycled and reused, which greatly reduces the amount of adsorbent used. Attached Figure Description

[0042] Figure 1 is a process flow diagram of starch wastewater treatment and resource recycling in this invention. Detailed Implementation

[0043] To clarify the technical solution and working principle of the present invention, the present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments. It should be noted that, without conflict, the various embodiments or technical features described below can be arbitrarily combined to form new embodiments.

[0044] This invention provides a method for the resource recovery and reuse of starch wastewater, as shown in Figure 1, comprising the following steps:

[0045] Step S1: Unhydrolyzed starch in strongly acidic starch wastewater is precipitated in a sedimentation tank to obtain effluent and slurry.

[0046] Specifically: The starch wastewater to be treated in this scheme has a pH of 1-3, is in a strongly acidic environment, contains 1-15 g / L of incompletely hydrolyzed starch precipitate, has a turbidity of 2000-10000 NTU, a total dissolved solids (TDS) content of 1-5 g / L, and has a potassium ion content of ≤500 mg / L, a calcium ion content of ≤100 mg / L, and a magnesium ion content of ≤200 mg / L.

[0047] The sedimentation time in the sedimentation tank is 1-2 hours. The sedimented slurry obtained from sedimentation is then recycled back to the upstream processing stage, and the sedimented effluent is subjected to further processing.

[0048] Step S2: The precipitated water is subjected to membrane filtration to produce membrane filtration permeate and membrane filtration concentrate.

[0049] Specifically, the resulting membrane filtration concentrate is recycled back to the aforementioned sedimentation stage, where it is combined with the starch wastewater to be treated input from the sedimentation stage for further sedimentation treatment.

[0050] The selected membrane material is polyvinylidene fluoride (PVDF), which possesses high chemical and thermal stability, is resistant to strong acids, strong alkalis, and organic solvents, and is a high-strength, tear-resistant polymer material. Its membrane molecular weight cutoff is not less than 150,000 Da, and the membrane element has a wide flow channel, typically 5-12 mm, with a cross-flow design. The effluent flows at a velocity of 2.5-4 m / s within the channel, exhibiting turbulent flow, which effectively flushes the membrane surface and reduces the deposition of large organic molecules (such as proteins and dextrins in starch hydrolysate), colloids, and suspended particles. It can withstand suspended solids concentrations in the effluent not exceeding 10 g / L, eliminating the need for excessive pretreatment. Even if the starch hydrolysate is slightly turbid, it can operate stably, reducing pretreatment costs.

[0051] Meanwhile, this membrane element can withstand acidic environments of pH 1-12, eliminating the need to neutralize the strong acidity of starch hydrolysate (such as nitric acid hydrolysate pH 1-2), allowing for direct filtration without damaging the membrane module. After the membrane element stops operating, it can be directly backwashed, resulting in good cleaning performance, rapid restoration of membrane flux, extended membrane lifespan, and reduced membrane replacement frequency.

[0052] Step S3: The membrane filtration permeate is treated with a selective adsorbent to adsorb specific ions, resulting in adsorbed permeate and a saturated selective adsorbent.

[0053] Specifically, the starch wastewater in this application mainly contains potassium, calcium, and magnesium ions. Selective adsorbents include 001x7 strong acid styrene-based cation exchange resin, Amberlite IR-120 cation exchange resin, and Dowex 50W series strong acid cation exchange resin. These types of adsorbents can react with cations (such as potassium, calcium, and magnesium) in the solution under strongly acidic conditions (pH 1-2). + Ca 2+ Mg 2+ An isoelectric exchange occurs, and the principle of this exchange is: 2R - SO₃H + M 2+ →(R-SO3H)2M + 2H + (M) 2+ It is a divalent cation, such as Ca. 2+ Mg 2+ ), R-SO3H + K + → R-SO3K + H + The desalination process was carried out directly under strong acid conditions, achieving the separation of target ions. This not only simplified the process but also solved the technical problem of easy deactivation of adsorbents in acidic solutions. Furthermore, based on the type of adsorbent, the adsorbents were divided into Adsorbent 1 and Adsorbent 2. Adsorbent 1 includes large-particle-size strong acid cation exchange resins such as 001x7MB, Amberlite IR-120 Plus, Lewatit S108, and D003, while Adsorbent 2 includes conventional-particle-size strong acid cation exchange resins such as 001x7, Amberlite IR-120, and Dowex 50W.

[0054] S31: The membrane filtration permeate flows through adsorbent 1 to adsorb and remove potassium ions, resulting in permeate adsorbed by adsorbent 1.

[0055] S32: The water produced by adsorbent 1 is passed through adsorbent 2, where calcium and magnesium ions are selectively adsorbed to obtain water produced by adsorbent 2.

[0056] The adsorbed water can be recycled as process water. After adsorption by the adsorbent, the contents of potassium ions, calcium ions, and magnesium ions are all less than 20 mg / L, which meets the relevant requirements for process water.

[0057] Step S4: Add an acid desorbent to the saturated selective adsorbent for acid desorption and regeneration to obtain a desorption solution and a regenerated selective adsorbent, which then participates in the adsorption of specific ions again.

[0058] Specifically: In order to improve the efficiency of adsorbent use and achieve recycling, the adsorbent is subjected to acid desorption treatment.

[0059] S41: Add 1-3 BV of organic matter removal agent to the saturated selective adsorbent and soak for 15-90 min to elute the organic matter. The organic matter removal agent is hot water or a 2-3% (w / w) hot alkaline solution. 1-3 BV of organic matter removal agent refers to 1-3 times the volume of the adsorbent.

[0060] Hot water or hot alkaline solutions can elute the organic matter adsorbed on saturated selective adsorbents and allow the adsorbents to swell sufficiently to optimize mass transfer efficiency.

[0061] S42: Add 3-5 BV of 5%-6% acid stripping agent to the eluted selective adsorbent at a flow rate of 1-2 BV / h to restore the selective adsorbent. The acid stripping agent is 5%-6% hydrochloric acid or sulfuric acid. Where 1-2 BV / h indicates that the volume of acid stripping agent flowing through the adsorbent per hour is 1-2 times the volume of the adsorbent.

[0062] The deacidifying agent mainly adopts the principle of reversible ion exchange: (R-SO3H)2M + 2HCl → 2R-SO3H + MCl2, R-SO3K + HCl → R-SO3H + KCl. After acid desorption and regeneration, the adsorbent is transformed back into the hydrogen form and enters the next round of adsorption, realizing the reuse of the adsorbent.

[0063] Step S5: Concentrate the desorption solution to obtain the raw materials for compound fertilizer production.

[0064] Specifically: Concentration can be achieved by photothermal evaporation or membrane concentration, increasing the volume by 2.5-4 times. The evaporation temperature is 30-40℃, and the evaporation rate is 0.8-1 kg / (m³). 2 ·h), HCl volatilization ≤0.1% / h.

[0065] The final concentrate has a potassium ion content of ≥17500mg / L, a calcium ion content of ≤1000mg / L, a magnesium ion content of ≤3500mg / L, and an acid concentration of 7.5~10%. It can replace the acidic hydrolysis solution of potassium feldspar (potassium 15000mg / L, calcium 7500mg / L, magnesium 2500mg / L) as a raw material for compound fertilizer, reducing the waste residue and acid consumption generated during the acid leaching and hydrolysis process of potassium feldspar.

[0066] A starch wastewater treatment and resource recovery system includes,

[0067] The sedimentation unit is used to separate unhydrolyzed starch by precipitation, obtaining effluent and slurry.

[0068] The filtration unit is used to filter the effluent through a membrane to produce membrane filtration permeate and membrane filtration concentrate; the membrane filtration concentrate is fed into the sedimentation tank.

[0069] The adsorption unit uses a selective adsorbent to adsorb specific ions into the membrane filtration permeate, obtaining adsorbed permeate and saturated selective adsorbent; the adsorbed permeate is output, and the saturated selective adsorbent is input into the acid desorption tank.

[0070] The acid desorption unit is used to add acid desorption agent to the saturated selective adsorbent for acid desorption regeneration, to obtain desorption solution and selective adsorbent;

[0071] The concentration unit is used to concentrate the desorption liquid to obtain raw materials for compound fertilizer production.

[0072] The sedimentation unit, filtration unit, adsorption unit, acid removal unit, and concentration unit are connected in sequence, and the concentrated water outlet of the filtration unit is connected to the inlet of the sedimentation unit.

[0073] Example 1

[0074] The starch wastewater used in this embodiment was taken from a battery nanomaterial manufacturing enterprise in a certain province and city. The starch wastewater is corn starch hydrolysis wastewater, which is a white suspension with a pH value of 1.9. The suspended solids (SS) content is 11 g / L, the turbidity is 6240 NTU, the potassium ion content is 210 mg / L, the calcium ion content is 84 mg / L, the magnesium ion content is 121 mg / L, the total dissolved solids (TDS) content is 4.1 g / L, and there are also a small amount of incompletely hydrolyzed starch solids and other impurities.

[0075] The starch wastewater was treated according to the steps described above:

[0076] 1. The starch wastewater is settled in a sedimentation tank for 1 hour. The turbidity of the effluent from the sedimentation tank is 860 NTU and the suspended solids (SS) content is 5 g / L.

[0077] 2. The effluent from the sedimentation tank is subjected to membrane filtration. The membrane filter module has a molecular weight cutoff of 250,000 Da and a flow channel diameter of 8 mm. After membrane filtration, permeate and concentrate are obtained. The turbidity of the permeate is 1.395 NTU, the potassium ion content is 210 mg / L, the calcium ion content is 84 mg / L, and the magnesium ion content is 121 mg / L. The concentrate is returned to the sedimentation tank for further sedimentation.

[0078] 3. After the membrane filtration permeate is adsorbed by adsorbent 1, the permeate adsorbed by adsorbent 1 is obtained. The potassium ion content in the permeate adsorbed by adsorbent 1 is 2.1 mg / L, the calcium ion content is 22 mg / L, and the magnesium ion content is 83 mg / L.

[0079] 4. After adsorption of the water produced by adsorbent 1 with adsorbent 2, the water produced by adsorbent 2 is obtained. The potassium ion content in the water produced by adsorbent 2 is 0.91 mg / L, the calcium ion content is 4 mg / L, and the magnesium ion content is 9.6 mg / L.

[0080] 5. After adsorption saturation, adsorbent 1 and adsorbent 2 were desorbed and regenerated using 6% hydrochloric acid. The resulting desorption solution contained 7500 mg / L potassium ions, 400 mg / L calcium ions, 1400 mg / L magnesium ions, and 4% hydrochloric acid.

[0081] After the desorption liquid was concentrated 2.5 times by photothermal evaporation, the potassium ion content was 18750 mg / L, the calcium ion content was 1000 mg / L, the magnesium ion content was 3500 mg / L, and the hydrochloric acid concentration was 10%. This meets the recommended potassium concentration standard requirements for potassium element in the hydrolysate of potassium feldspar fertilizer enterprises (potassium ion concentration ≥15 g / L). Moreover, the total hardness of calcium and magnesium ions is much lower than that of potassium feldspar hydrolysate (calcium 7500 mg / L, magnesium 2500 mg / L). It can be used as a high-quality potassium source to replace the potassium source for potassium feldspar compound fertilizer enterprises.

[0082] Example 2

[0083] The starch wastewater used in this embodiment was taken from a battery nanomaterial manufacturing enterprise in a certain province and city. The specific composition of the starch wastewater is slightly different from that in Example 1. This starch wastewater is corn starch hydrolysis wastewater, which is a white suspension with a pH value of 2. The suspended solids (SS) content is 8 g / L, the turbidity is 4800 NTU, the potassium ion content is 180 mg / L, the calcium ion content is 12 mg / L, the magnesium ion content is 33 mg / L, the total dissolved solids (TDS) content is 3 g / L, and there are also a small amount of incompletely hydrolyzed starch solids and other impurities.

[0084] The starch wastewater was treated according to the steps described above:

[0085] 1. The starch wastewater is settled in a sedimentation tank for 1 hour. The turbidity of the effluent from the sedimentation tank is 450 NTU and the suspended solids (SS) content is 4 g / L.

[0086] 2. The effluent from the sedimentation tank is filtered using a membrane. The membrane module has a molecular weight cutoff of 250,000 Da and a channel diameter of 8 mm. After membrane filtration, membrane filtration permeate and membrane filtration concentrate are obtained. The turbidity of the membrane filtration permeate is 1.195 NTU, the potassium ion content is 180 mg / L, the calcium ion content is 12 mg / L, and the magnesium ion content is 33 mg / L. The membrane filtration concentrate is returned to the sedimentation tank for further sedimentation to remove suspended solids (SS) and other impurities before further treatment.

[0087] 3. The membrane filtration product water is adsorbed with adsorbent 1 to obtain adsorbent 1 adsorbent product water. The potassium ion content of adsorbent 1 adsorbent product water is 65 mg / L, the calcium ion content is 10 mg / L, and the magnesium ion content is 25 mg / L.

[0088] 4. The adsorbent 1 adsorbed water is then adsorbed with adsorbent 2 to obtain adsorbent 2 adsorbed water. The potassium ion content of the adsorbent 2 adsorbed water is 8 mg / L, the calcium ion content is 5 mg / L, and the magnesium ion content is 9 mg / L.

[0089] 5. The adsorbent after adsorption saturation was desorbed and regenerated using 6% hydrochloric acid. The resulting desorption solution contained 7000 mg / L potassium ions, 390 mg / L calcium ions, 1300 mg / L magnesium ions, and 4% hydrochloric acid.

[0090] 6. After the desorption liquid is concentrated 2.5 times by photothermal evaporation, the potassium ion content is 17500 mg / L, the calcium ion content is 975 mg / L, the magnesium ion content is 3250 mg / L, and the hydrochloric acid concentration is 10%. This meets the recommended potassium concentration standard requirements for potassium element in the hydrolysate of potassium feldspar fertilizer enterprises (potassium ion concentration ≥15 g / L). Moreover, the total hardness of calcium and magnesium ions is much lower than that of potassium feldspar hydrolysate (calcium 7500 mg / L, magnesium 2500 mg / L). It can be used as a high-quality potassium source to replace the potassium source for potassium feldspar compound fertilizer enterprises.

[0091] Comparative Example 1

[0092] The method for recycling starch wastewater provided in this comparative example differs from that in Example 1 in that step 3 uses a common aluminum-based adsorbent to adsorb and treat the membrane filtration permeate.

[0093] In this comparative example, the core adsorption sites of ordinary aluminum-based adsorbents are surface hydroxyl groups (-Al-OH). Under neutral or weakly acidic conditions, these hydroxyl groups undergo partial dissociation and become negatively charged (-Al-O). -), which binds positively charged cations (such as K+) through electrostatic attraction or coordination exchange. + Ca 2+ Because the pH of the water filtered by the adsorption treatment membrane is 1.9, protonation occurs at the surface adsorption sites (-Al-OH + H+). + →-Al-OH2 + Furthermore, the adsorbent undergoes acid dissolution, resulting in structural collapse and loss of active sites, which prevents cations from binding and causes the loss of selective adsorption function. Consequently, it has virtually no adsorption of potassium, calcium, and magnesium ions in the membrane filtration permeate.

[0094] Comparative Example 2

[0095] The method for recycling starch wastewater provided in this comparative example differs from that in Example 2 in that: after adsorption treatment with adsorbent 1 in step 2, adsorption treatment with adsorbent 2 is no longer performed.

[0096] In this comparative example, when only adsorbent 1 was used for adsorption treatment, the adsorbent 1 adsorbed water and the adsorbent 2 adsorbed water had potassium ion content of 19.7 mg / L, calcium ion content of 8.5 mg / L and magnesium ion content of 18.3 mg / L; the amount of water treated was reduced by 40% compared with Example 2.

[0097] Comparative Example 3

[0098] The method for recycling starch wastewater provided in this comparative example differs from that in Example 2 in that: the adsorbent 1 in step 3 and the adsorbent 2 in step 4 are the same as the adsorbent 1 and adsorbent 2 after acid de-regeneration in step 5 of Example 2.

[0099] In this comparative example, after adsorbent 1, which has undergone acid de-regeneration, was used to adsorb the membrane filtration permeate, the potassium ion content in the permeate was 62 mg / L, the calcium ion content was 10 mg / L, and the magnesium ion content was 25 mg / L. After the permeate from adsorbent 1 was further treated with adsorbent 2, which has undergone acid de-regeneration, the permeate from adsorbent 2 was obtained, with the potassium ion content being 7 mg / L, the calcium ion content being 5 mg / L, and the magnesium ion content being 8 mg / L. Under the same treatment capacity, the adsorption effects of the regenerated adsorbent 1 and adsorbent 2 on potassium ions, calcium ions, magnesium ions, etc., were basically the same as those in Example 1.

[0100] As can be seen from the above embodiments and comparative examples, the present invention, through a combined process of precipitation-membrane filtration-ion selective adsorption, can effectively separate and recover unhydrolyzed starch for reuse in upstream raw materials. The combined use of selective adsorbent 1 and adsorbent 2 can adsorb and recover potassium, calcium, and magnesium ions under pH conditions of 1-3, and the treated water volume increases by 40% compared to using either alone. After acid desorption regeneration of the saturated adsorbent, it enters the next adsorption cycle. The desorbed liquid, after photothermal evaporation or membrane concentration of 2.5-4 times, meets the recommended potassium concentration standard (potassium ion concentration ≥15g / L) for potassium feldspar fertilizer production hydrolysate, and can replace acidic potassium feldspar hydrolysate as a raw material for compound fertilizer production, solving the problem of regenerated wastewater treatment and truly achieving zero wastewater discharge.

[0101] The above are merely preferred embodiments of the present invention. The scope of protection of the present invention is not limited to the above embodiments. All technical solutions falling within the scope of the present invention's concept are within the scope of protection of the present invention. It should be noted that for those skilled in the art, any improvements and modifications made without departing from the principles of the present invention should be considered within the scope of protection of the present invention.

Claims

1. A method for treating and recycling starch wastewater, characterized in that, The process includes the following steps: precipitating unhydrolyzed starch in strongly acidic starch wastewater to obtain effluent and slurry; filtering the effluent through a membrane to produce membrane filtration permeate and concentrated permeate; using a selective adsorbent to adsorb specific ions into the membrane filtration permeate to obtain adsorbed permeate and saturated selective adsorbent; adding an acid descaling agent to the saturated selective adsorbent for acid desorption and regeneration to obtain desorbed liquid and regenerated selective adsorbent, wherein the regenerated selective adsorbent again adsorbs specific ions; and concentrating the desorbed liquid to obtain raw materials for compound fertilizer production.

2. The method for resource recovery and reuse of starch wastewater according to claim 1, characterized in that: The pH value of the starch wastewater is 1-3.

3. The method for resource recovery and reuse of starch wastewater according to claim 2, characterized in that: The settling time is 1-2 hours.

4. The method for resource recovery and reuse of starch wastewater according to claim 3, characterized in that: The film is made of polyvinylidene fluoride (PVDF), the film has a molecular weight cutoff of not less than 150,000 Da, and the flow channel diameter of the film is 5-12 mm.

5. The method for resource recovery and reuse of starch wastewater according to claim 4, characterized in that: The membrane filtration permeate flows sequentially through multiple selective adsorbents to adsorb specific ions. Specifically, the membrane filtration permeate flows through adsorbent 1, where potassium ions are selectively adsorbed to obtain adsorbent 1 adsorbed permeate; the adsorbent 1 adsorbed permeate flows through adsorbent 2, where calcium and magnesium ions are selectively adsorbed to obtain adsorbent 2 adsorbed permeate.

6. The method for resource recovery and reuse of starch wastewater according to claim 5, characterized in that: The adsorbent 1 is a large-particle-size strong acid cation exchange resin, including 001x7MB, Amberlite IR-120 Plus, Lewatit S108, and D003; the adsorbent 2 is a conventional-particle-size strong acid cation exchange resin, including 001x7, Amberlite IR-120, and Dowex 50W.

7. A method for the resource recovery and reuse of starch wastewater according to claim 6, characterized in that: Acid removal agent is added to the saturated selective adsorbent for acid removal and regeneration. Specifically, 1-3 BV of organic matter removal agent is added to the saturated selective adsorbent and soaked for 15-90 min to elute the organic matter. Then, 3-5 BV of 5%-6% acid removal agent is added to the eluted selective adsorbent at a flow rate of 1-2 BV / h to restore the selective adsorbent.

8. The method for resource recovery and reuse of starch wastewater according to claim 7, characterized in that: The acid removal agent is 5%-6% hydrochloric acid, and the organic matter removal agent is hot water or a hot alkaline solution with a mass concentration of 2-3%.

9. A starch wastewater treatment and resource recovery system, characterized in that: Includes a sedimentation unit for separating unhydrolyzed starch by sedimentation to obtain effluent and slurry. The filtration unit is used to filter the effluent through a membrane to produce membrane filtration permeate and membrane filtration concentrate; the membrane filtration concentrate is fed into the sedimentation tank. The adsorption unit uses a selective adsorbent to adsorb specific ions into the membrane filtration permeate, obtaining adsorbed permeate and saturated selective adsorbent. The adsorbed permeate is output, and the saturated selective adsorbent is input into the acid desorption tank. The acid desorption unit is used to add an acid desorption agent to the saturated selective adsorbent for acid desorption regeneration, obtaining desorbed liquid and selective adsorbent. The concentration unit is used to concentrate the desorbed liquid to obtain raw materials for compound fertilizer production. The sedimentation unit, filtration unit, adsorption unit, acid desorption unit, and concentration unit are connected in sequence, and the concentrated water outlet of the filtration unit is connected to the inlet of the sedimentation unit.

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