Method for simultaneously recovering ferrous vitriol and humic acid by pre-coagulation and phosphorus removal coupled with enzymatic pretreatment of sludge

Abstract

This invention provides a method for the simultaneous recovery of lapis lazuli and humic acid from pretreated municipal sludge. The method involves flocculation and sedimentation of the sludge-water mixture in the biological treatment tanks of a municipal wastewater treatment plant, followed by sludge-water separation. The effluent meets the Class A discharge standard, and the sludge is enriched with phosphorus and iron. The phosphorus- and iron-rich sludge undergoes anaerobic acidification using bioenzymes. The composite enzyme is lysozyme:protease:amylase:cellulase in a 1:1:1:1 ratio, with an enzyme addition of 2-3%, and treatment at 45°C for 11-13 hours. After sludge-water separation, the residue is rich in recalcitrant microbial organic matter, which can be used for land application or as an environmental remediation material. The pH of the supernatant is adjusted to the isoelectric point of protein 6.0 in stages to recover crude protein. The pH is further adjusted to 7.0-7.5, and lapis lazuli crystallizes to recover iron and phosphorus. Finally, the pH is adjusted to 10-10.5, and a mixture of lapis lazuli and struvite crystallizes to recover iron, manganese, phosphorus, and nitrogen. Crystallization can recover 97-98% of orthophosphate, 79-81% of total phosphorus, 25-27% of ammonia nitrogen, and 87-88% of total iron. This invention employs a coupled pretreatment method for the simultaneous recovery of lapis lazuli and humic acid from urban sludge. This method is environmentally friendly and green, enabling multifaceted resource utilization of urban sludge and has a significant market potential.

Description

Technical Field

[0001] This invention relates to the field of solid waste resource utilization technology, specifically to a method for recovering lapis lazuli and humic acid by using bio-enzymatic anaerobic hydrolysis and acidification pretreatment of urban sludge. Background Technology

[0002] In recent years, with the improvement of urbanization in my country and the higher requirements for environmental quality from social development, the amount of sewage treated has increased year by year, and the amount of sludge generated has also gradually increased. Sewage treatment plants use the activated sludge process to treat domestic sewage, and the daily residual sludge accounts for 1% to 2% of the sewage treated. The safe treatment and disposal of sludge has become one of the key and difficult issues in urban solid waste management.

[0003] Municipal sewage sludge is a byproduct of wastewater treatment, rich in organic matter and nutrients such as nitrogen and phosphorus, possessing potential for resource utilization. The organic matter in municipal sewage sludge mainly exists within microbial cells and surrounding extracellular polymers, exhibiting poor biodegradability. Humic acid is one of the main components of sludge organic matter, accounting for approximately 20% of its total organic matter. Humic acid is also an important raw material for fertilizers, chemicals, and water treatment agents. Therefore, recovering humic acid from sludge is one possible pathway for sludge resource utilization.

[0004] Vivianite, a novel product for phosphorus recovery from wastewater, is a highly stable phosphorus-iron crystal that typically forms in phosphorus- and iron-rich water environments with reducing conditions (ORP < -300mV) and a suitable pH (6–9). Wastewater often contains significant amounts of iron due to geological conditions or water treatment processes (such as the addition of iron coagulants). Iron is also readily available and inexpensive, particularly from industrial scrap iron filings, shavings, and even rust. Adding iron to wastewater or sludge can also improve sludge dewatering performance. Therefore, phosphorus recovery via vivianite crystallization is a simple, low-cost, and highly efficient method.

[0005] The hydrolysis of extracellular polymer macromolecules and the cell disruption process of microbial cells are rate-limiting steps in the resource recovery and utilization of sludge, and also key steps affecting the rate and amount of phosphorus release into the supernatant, thus influencing the recovery amount and purity of lapis lazuli from subsequent crystallization processes. Bioenzymes, produced by specific microorganisms, are low-cost, environmentally friendly, and have significant potential for application and promotion. Utilizing a bioenzymatic hydrolysis pretreatment process disrupts the sludge aggregate structure, dissolves microbial cell walls, and promotes the rapid hydrolysis of extracellular polymers in urban sludge microorganisms, releasing and hydrolyzing intracellular organic matter. This significantly improves the dissolution of solid organic matter in residual sludge and effectively degrades long-chain proteins into smaller molecules, carbohydrates, and lipids. Complex enzymes such as proteases, lipases, and amylases exhibit better hydrolysis effects than single enzymes. Enzymatic pretreatment can accelerate the rapid hydrolysis of polymers in urban sludge into bioavailable organic matter, playing a crucial role in wastewater and sludge treatment.

[0006] Pre-dosing of iron-containing coagulants can flocculate and enrich phosphorus in secondary effluent, while simultaneously introducing phosphorus and iron salts into the sludge, forming phosphorus-iron-rich sludge. Pre-treatment of this sludge using anaerobic enzymatic hydrolysis promotes rapid hydrolysis of organic particles and cell breakdown, significantly increasing the rate and amount of phosphorus release. After solid-liquid separation, high-purity lapis lazuli crystals can be directly recovered from the supernatant of the phosphorus-iron digestion. The residue is rich in recalcitrant microbial-derived organic matter, which can be used for land application or as an environmental remediation material. Summary of the Invention

[0007] This invention proposes a method for the simultaneous recovery of lapis lazuli and humic acid from pretreated municipal sludge. An iron coagulant is used to flocculate and precipitate phosphorus in the wastewater, forming phosphorus- and iron-rich residual sludge. The phosphorus- and iron-rich sludge is then anaerobically hydrolyzed by biological enzymes. After solid-liquid separation, the supernatant recovers phosphorus in the form of lapis lazuli, while the enzymatic hydrolysis residue is enriched with humic acid.

[0008] The technical solution of this invention is as follows: a method for simultaneously recovering lapis lazuli and humic acid from pretreated urban sludge. An iron coagulant flocculates and precipitates phosphorus in the wastewater, forming phosphorus- and iron-rich residual sludge. The phosphorus- and iron-rich sludge undergoes anaerobic hydrolysis pretreatment with biological enzymes, followed by solid-liquid separation. Lapis lazuli is recovered from the phosphorus- and iron-rich supernatant, while the humic acid-rich residue can be used for land application.

[0009] The wastewater source of the urban wastewater treatment plant is domestic sewage, and the effluent from the biological treatment tank is a mixture of sludge and water from the end of the secondary treatment biological tank.

[0010] The iron salt flocculant is either ferric chloride or ferric sulfate, with ferric chloride being the most effective.

[0011] The complex enzyme is prepared by mixing protease, amylase, cellulase and lysozyme in a mass ratio of 1:1:1:1.

[0012] Detailed technical solution (Figure 1 The procedure is as follows: a. Take the sludge-water mixture from the end of the biological tank and place it in a sealed container. Add flocculant at a concentration of 10–100 mg / L. The coagulation program is: 200 rpm for 2 minutes, then 60 rpm for 15 minutes. After flocculation, allow the sludge to settle by gravity for 30 minutes to separate the sludge and water.

[0013] b. The physicochemical properties of the separated water, such as chemical oxygen demand, total nitrogen, and total phosphorus, meet the Class A standard of the "Discharge Standard of Pollutants for Municipal Wastewater Treatment Plants" (GB 18918-2002).

[0014] c. The separated sludge is rich in phosphorus and iron. It is placed in a sealed container equipped with a stirrer and a water bath for heat preservation. A compound enzyme is added at a ratio of 2-3% (w / v), mixed well, and sealed.

[0015] d. Incubate in a sealed container at 45℃ in a water bath, with the stirrer running at 150 rpm, and perform anaerobic enzymatic hydrolysis for 11–13 hours. During this time, the pH of the anaerobic hydrolysate will be 4.0–4.5. Under acidic conditions, metal ions dissolve and enter the supernatant.

[0016] e. Allow to settle by gravity for 2–3 hours, separating the residue from the supernatant. The supernatant is enriched with phosphorus and iron (…). Figure 2 This material is used for phosphorus recovery from blue iron ore crystallization. The residue is rich in humic acid and other organic matter. Figure 8 It can be used for land use or as an environmental remediation material.

[0017] f. Add 0.1 mg / L Vitamin C to the phosphorus-rich iron supernatant to ensure an oxidation-reduction potential < -300. Adjust the pH to 6.0 using 0.5–1.0 mol / L NaOH, centrifuge at 8000 rpm for 10–15 min to remove and obtain crude protein. The separated crude protein can be used as feed or as a cement foaming agent, etc.

[0018] g. Continue to adjust the pH of the supernatant to 7.0-7.5 using 0.5-1.0 mol / L NaOH, allow the lapis lazuli crystals to settle by gravity, and separate the solid and liquid to obtain lapis lazuli crystals.

[0019] Mechanisms for the resource recovery of phosphorus and carbon:

[0020] This invention utilizes FeCl3 for flocculation and sedimentation to form phosphorus- and iron-rich waste sludge. It explores the release rates and amounts of phosphorus and iron during enzyme pretreatment, while simultaneously improving the efficiency and purity of lapis lazuli recovery, as well as other forms of phosphorus recovery, increasing the diversity and efficiency of phosphorus recovery, and recovering humic acid, etc. The coupling mechanism of pretreatment and lapis lazuli recovery is as follows:

[0021] 1. When iron salts dissolve in water, Fe... 3+Through dissolution and water absorption, strong hydrolysis occurs, forming polynuclear hydroxyl complexes. The zeta potential of colloids in the water decreases, causing colloids to coagulate and precipitate, removing phosphorus from the water and forming phosphorus- and iron-rich residual sludge.

[0022] 2. Under anaerobic conditions, lysozyme accelerates the lysis of the cell walls of sludge microorganisms, increasing the rate of intracellular substance dissolution. Amylase and protease rapidly hydrolyze large organic molecules into smaller organic molecules. Extracellular polymers and undegraded or recalcitrant large organic molecules, such as those from the cell walls, settle down by gravity.

[0023] 3. After anaerobic enzymatic hydrolysis, the mixed solution has a pH of 4.0–4.5, and most of the phosphorus and iron ions from orthophosphate are released back into the water. Upon settling, solid-liquid separation occurs; the supernatant is rich in phosphorus and iron and can be used for phosphorus recovery. The residue is rich in humic acid and other organic matter, which can be used for land application or as an environmental remediation material.

[0024] 4. Add vitamin C 0.1 mg / L to the supernatant or purge with nitrogen to maintain a reducing environment and prevent Fe from being released. 2+ Oxidized to Fe 3 + .

[0025] 5. To obtain high-purity lapis lazuli crystals, the crude protein precipitate in the phosphorus-rich supernatant was first obtained using the isoelectric point precipitation method. The pH of the phosphorus-rich iron supernatant was adjusted to 6.0, and the mixture was centrifuged at 8000 rpm for 10 min to recover the crude protein. During the sedimentation of the crude protein, residual large-molecule organic matter in the supernatant was swept and adsorbed, reducing the turbidity of the supernatant and further clarifying it.

[0026] 6. Azurite generally forms in aquatic environments rich in phosphorus and iron, under conditions of ORP < -300mV and a suitable pH (6-9). The pH of the supernatant is further adjusted to 7.0-7.5 to induce azurite crystallization. The azurite is then separated and purified using density differences.

[0027] By adopting the above technical solution, the beneficial effects of the present invention are:

[0028] This invention solves the problem of phosphorus removal from urban wastewater by using iron salt flocculants to flocculate the sludge-water mixture in biological treatment ponds. It simplifies or even eliminates tertiary physicochemical treatment, saving time and space in wastewater treatment. Simultaneously, it enriches the sludge with high concentrations of phosphorus and introduces iron necessary for the formation of lapis lazuli.

[0029] Anaerobic enzymatic hydrolysis promotes the rapid hydrolysis of organic particles and cell breakdown in municipal sludge. Hydrolysis takes 11–13 hours, with a pH of 4.0–4.5 in the hydrolysate. Most metal ions dissolve into the supernatant, leaving very little residual heavy metals in the residue. Anaerobic enzymatic hydrolysis also releases orthophosphate and ferrous ions, providing ample orthophosphate and ferrous ions for the formation of lapis lazuli, thus shortening the sludge treatment cycle.

[0030] The residue contains approximately 60-70% humic acid, which can promote plant growth and fix heavy metals. Humic acid is also an important raw material for fertilizers, chemicals, and water treatment. Therefore, recovering humic acid from sludge is one of the possible ways to utilize sludge resources.

[0031] By extracting crude protein using the isoelectric point of protein and reducing the turbidity of the supernatant, the supernatant can be further clarified. This not only helps to improve the crystallization purity of lapis lazuli, but also allows for the separation and purification of lapis lazuli by utilizing density differences, thus improving the overall process efficiency.

[0032] The pH was adjusted to 7.0–7.5, and phosphorus was recovered using lapis lazuli with a purity of 92.4–97.4%, which greatly improved the economic value and realized the resource utilization of the remaining sludge.

[0033] This method is simple and easy to implement. It involves flocculating and settling the sludge-water mixture in the biological treatment tank, enzymatically hydrolyzing and anaerobic treating the supernatant, and using the humic acid-rich residue for soil remediation and improvement. Crude protein is recovered from the supernatant, and iron and phosphorus are recovered in the form of blue iron ore. This method is beneficial for resource recovery and helps improve the quality of the fermentation liquid. It is also an effective measure to simultaneously reduce sludge volume and utilize resources.

[0034] The beneficial effects of this invention are:

[0035] (1) The sludge-water mixture in the biological treatment tank is pre-coagulated with FeCl3. The effluent COD is 40-50 mg / L, TN is 10-15 mg / L, and TP is 0.1-0.5 mg / L, which meets the Class A discharge standard of the "Discharge Standard of Pollutants for Municipal Wastewater Treatment Plants" (GB 18918-2002).

[0036] (2) Phosphorus was recovered by the crystallization method of lapis lazuli, with a phosphorus recovery rate of 98.1-99.6%, a ferrous iron recovery rate of 97.8-98.9%, and a lapis lazuli crystal purity of 96.1-97.4%.

[0037] (3) Humic acid extracted from the enzymatic hydrolysis residue is used to adsorb heavy metal Pb. 2+ Cr 2+ and Zn 2+ At adsorption equilibrium, the adsorption capacity was 6.98 mg·g. -1 4.97 mg·g -1 and 4.85 mg·g -1 . Attached Figure Description

[0038] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0039] Figure 1 This is a process flow diagram of the present invention.

[0040] Figure 2 The changes in phosphorus and iron levels in the supernatant during the anaerobic enzymatic hydrolysis of phosphorus- and iron-rich sludge by a compound enzyme.

[0041] Figure 3 The changes in phosphorus, iron, and other indicators in the supernatant during the anaerobic hydrolysis of raw sludge are shown.

[0042] Figure 4 The change in the molar ratio of iron and phosphate in the supernatant during pretreatment.

[0043] Figure 5 The changes in total nitrogen, ammonia nitrogen, and COD in the supernatant during sludge treatment are shown.

[0044] Figure 6 This is a scanning electron microscope image of vivianite.

[0045] Figure 7 X-ray photoelectron spectroscopy of vivianite.

[0046] Figure 8 The infrared spectrum of vivianite.

[0047] Figure 9 The infrared spectrum of humic acid.

[0048] Figure 10 For the adsorption of Pb by humic acid 2+ Isothermal adsorption line.

[0049] Figure 11 For the adsorption of Cr by humic acid 2+ The isothermal adsorption line.

[0050] Figure 12 Zn adsorption by humic acid 2+ The isothermal adsorption line.

[0051] Figure 13 Infrared spectra of humic acid before and after adsorption of heavy metals. Detailed Implementation

[0052] The technical solution of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0053] The process of pre-coagulation with FeCl3 to form phosphorus- and iron-rich sludge:

[0054] The sludge-water mixture at the terminal of the biological treatment tank in the municipal wastewater treatment plant was flocculated using FeCl3 and FeSO4, respectively, with an addition range of 10–100 mg / L. The coagulation program was: 200 rpm for 2 min, 60 rpm for 15 min, and settling for 30 min. Solid-liquid separation was performed, and the physicochemical properties of the water are shown in Table 1. The COD was 40–50 mg / L, TN 10–15 mg / L, and TP 0.1–0.5 mg / L, meeting the Class A discharge standard of the "Discharge Standard of Pollutants for Municipal Wastewater Treatment Plants" (GB 18918-2002). The total phosphorus in the flocculated sludge increased by 0.16–1.1 mg / L.

[0055] Table 1. Changes in the physicochemical properties of mud-water mixture before and after flocculation (Mean ± SD)

[0056]

[0057] Anaerobic hydrolysis of phosphorus- and iron-rich sludge and excess sludge using a compound enzyme was performed. The sludge was placed in a sealed device for anaerobic hydrolysis using a compound enzyme consisting of lysozyme, protease, amylase, and cellulase in a ratio of 1:1:1:1, at a dosage of 2-3%. The device was sealed, incubated at 45°C, and operated at 150 rpm for 11-13 hours for anaerobic enzymatic hydrolysis pretreatment. After standing for 2-3 hours, solid-liquid separation was performed to obtain a phosphorus- and iron-rich supernatant and residue. The control group consisted of excess sludge from a conventional secondary sedimentation tank (raw sludge), without flocculation or the addition of the compound enzyme. Anaerobic phosphorus release was performed under the same temperature and rotation speed conditions.

[0058] After 11–13 hours of enzymatic anaerobic treatment of phosphorus- and iron-rich waste sludge, the pH dropped to 4.0–4.5. The supernatant contained TN (total nitrogen) of 221.7–230.3 mg / L, TP (total phosphoric acid) of 203.0–205.7 mg / L, and orthophosphate of 181.0–186.3 mg / L, with orthophosphate accounting for approximately 90% of the total phosphorus content, indicating good phosphorus release. Total iron was 338.3–417.8 mg / L, with ferrous iron (Fe2+) at 246.7–242.2 mg / L, accounting for 60–70% of the total iron. Anaerobic digestion promoted the conversion of ferrous iron to ferrous iron. The molar ratio of ferrous iron to orthophosphate was approximately 2.3–2.4. Figure 2 ).

[0059] In the control group, after anaerobic pretreatment of the raw sludge and solid-liquid separation, the pH of the supernatant also decreased to 4.0–4.5. The TN (total phosphorus) in the supernatant was 79.8–114.9 mg / L, TP (total phosphorus) was 24.4–33.1 mg / L, and orthophosphate was 22.4–31.9 mg / L. Orthophosphate accounted for approximately 93% of the total phosphorus content, indicating good phosphorus release. However, after phosphorus release in the control treatment, the total phosphorus and orthophosphate contents were low, only 12–16% and 12–17% of the residual sludge from the combined pretreatment, respectively. Figure 3 As the pretreatment time increases, the molar ratio of iron to phosphate changes as follows: Figure 4 .

[0060] The combined flocculation and enzymatic hydrolysis pretreatment significantly increased the content of TP, orthophosphate, ammonia nitrogen, total nitrogen, and iron ions in the supernatant, providing sufficient phosphate and ferrous ions for subsequent lapis lazuli crystallization. Figure 5 ).

[0061] Resource recycling process and characterization:

[0062] Crude protein extraction: The high crude protein content and viscosity of the phosphorus-rich iron supernatant are unfavorable for the crystallization and deposition of lapis lazuli, and also reduce the purity of the lapis lazuli. Isoelectric point precipitation is used to obtain crude protein precipitate, while simultaneously reducing the turbidity and viscosity of the supernatant. Vitamin C 0.1 mg / L is added to the supernatant or nitrogen gas is introduced to maintain a reducing environment and prevent Fe... 2+ Oxidized to Fe 3+ Adjust the pH of the phosphorus-rich iron-rich supernatant to 6.0, centrifuge, and recover the crude protein. The protein can be used as feed or a foaming agent in foamed cement.

[0063] Phosphorus and iron are also lost during crude protein removal. The orthophosphate content in the supernatant decreased by 81.0–105.3 mg / L, with a loss rate of 43.5–56.5%; TP was 88.9 mg / L, with a loss rate of 56.6%; total iron was 156.6–181.7 mg / L, with a loss rate of 53.7–65.1%; and ferrous iron was 84.3 mg / L, with a loss rate of 65.1%. However, after crude protein removal, the molar ratio of ferrous iron to orthophosphate in the supernatant is approximately 1.6–1.8, which is beneficial for the formation of lapis lazuli. The effect of crude protein recovery on crystallization purity and phosphorus recovery rate is shown in Table 2.

[0064] Table 2. Effects of pH value and crude protein recovery on crystallization purity and phosphorus recovery rate.

[0065]

[0066] Bluestone Recovery and Characterization: Bluestone generally forms in phosphorus- and iron-rich aqueous environments under reducing conditions (ORP < -300mV) and with a suitable pH (6-9). Vitamin C 0.1 mg / L is added to the phosphorus- and iron-rich supernatant to maintain a reducing environment. NaOH is added uniformly while mixing until the pH reaches 7.0-7.5, causing bluestone crystallization and free sedimentation. After crystallization, the contents of orthophosphate, TP, total iron, and ferrous iron in the supernatant decrease significantly. The orthophosphate content is 0.83-1.78 mg / L, a decrease of 96.1-97.4%, and the ferrous iron content is 2.54-5.21 mg / L, a decrease of 97.8-98.9%. The ferrous iron content in the supernatant decreases by 78.1-80.2 mg / L, and the orthophosphate content decreases by 79.2-81.8 mg / L, with a molar ratio of 1.65-1.75. After crystallization, the phosphorus recovery rate was 98.1%–99.6%, and the purity of vivianite was 96.1%–97.4%. The changes in the physicochemical properties of the supernatant during crystallization are shown in Table 3, and the effect of pH value on crystallization purity and phosphorus recovery rate is shown in Table 2.

[0067] Table 3 Physicochemical properties of the supernatant during crystallization (mg / L)

[0068]

[0069] Blue lapis lazuli typically occurs as transparent blue crystals and belongs to the monoclinic crystal system. The morphological characteristics of the crystals are characterized using scanning electron microscopy. Figure 6 The crystal form is the recognized tabular crystal, consistent with the characteristics of standard lapis lazuli crystals. The XRD pattern of the lapis lazuli crystals shows obvious diffraction peaks at 11.16°, 13.18°, and 18.18°, consistent with the lapis lazuli standard card (PDF#01-080-9696). Figure 7 Azurite was the only crystalline form recovered from phosphorus, and the recovered azurite had a high purity, consistent with the calculated purity (97.44%). Infrared spectroscopy results showed that it was present in the 10¹⁰-11¹⁰ cm⁻¹ range. -1 950-980cm -1 P04 exists 3- Antisymmetric and symmetric stretching vibrations, in the range of 550-620 cm. -1 400-460cm -1 PO4 exists 3- Asymmetric and symmetric variable angle vibrations Figure 8 The results are consistent with the chemical formula of lapis lazuli, Fe3(PO4)2·8H2O, further verifying from the perspective of the functional groups contained therein that the phosphorus recovery product is high-purity lapis lazuli crystals.

[0070] Characterization and heavy metal adsorption kinetics of humic acid: Humic acid was extracted from the enzymatic hydrolysis residue and characterized using Fourier transform infrared spectroscopy. The test results are as follows: Figure 9 As shown, humic acid contains characteristic peaks of functional groups such as hydroxyl, amino, lipid carbon chain, aromatic ring, and carboxyl groups.

[0071] Humic acid on Pb 2+ Cr 2+ Zn 2+ It exhibits good adsorption performance. Adsorption kinetics experiments show that the pseudo-second-order kinetic model more accurately reflects the adsorption process (Table 4). The pseudo-second-order kinetic model includes all adsorption processes, such as intraparticle diffusion, surface adsorption, and external liquid film diffusion. The model assumes that the main mechanism of adsorption is the formation of chemical bonds (Table 5). Chemisorption is the main mechanism of the adsorption process.

[0072] Table 4. Humic acid adsorption of Pb 2+ Cr 2+ Zn 2+ Fitting parameters of the dynamic equation

[0073]

[0074] Table 5. HA adsorption of Pb 2+ Cr 2+ Zn 2+ Fitting parameters of the intraparticle diffusion equation

[0075]

[0076] Humic acid on Pb 2+ Cr 2+ Zn 2+ The adsorption isotherms are shown below. Figure 10 , 11 As shown in Figure 12. Experimental results show that the Freundlich model fits the effect of humic acid on Pb. 2+ Cr 2+ Zn 2+ The adsorption isotherm is superior to that of the Langmuir model. Humic acid adsorption of Pb... 2+ Cr 2+ Zn 2+ The isothermal adsorption fitting parameters are shown in Tables 6, 7, and 8, respectively. With increasing temperature, the adsorption capacity of humic acid for all three substances increased, indicating that the adsorption process is endothermic and readily achievable. Humic acid for Pb... 2+ Cr 2+ Zn 2+ The adsorption process can be divided into three stages: rapid adsorption, slow adsorption, and dynamic equilibrium. At adsorption equilibrium, the adsorption capacity is 6.98 mg·g⁻¹. -1 4.97 mg·g -1 4.85 mg·g -1 .

[0077] Table 6. Humic acid adsorption of Pb 2+ Isothermal adsorption fitting parameters

[0078]

[0079] Table 7 Humic acid adsorption of Cr 2+ Isothermal adsorption fitting parameters

[0080]

[0081] Table 8. Humic acid adsorption of Zn 2+ Isothermal adsorption fitting parameters

[0082]

[0083] The characterization and analysis of humic acid before and after adsorption of heavy metal ions were performed using infrared spectroscopy. Figure 13 After humic acid adsorbs heavy metal ions, the characteristic peaks corresponding to functional groups such as aromatic rings, carboxyl groups, alcohols, and phenols all change to varying degrees. Humic acid adsorbs Pb. 2+ Cr 2+ Zn 2+ The subsequent infrared spectra were quite similar, indicating that the adsorption mechanism of humic acid for the three ions was similar.

[0084] Pre-treatment of sludge by coagulation coupled with enzymatic hydrolysis reduces the retention time and amount of phosphorus in wastewater treatment, and allows for the simultaneous recovery of lapis lazuli and humic acid. The recovered humic acid is then used to adsorb heavy metals. Simultaneously, this invention shortens the wastewater treatment cycle, improves phosphorus recovery rate, and realizes the resource recovery and utilization of carbon, phosphorus, and other components from the sludge.

[0085] The above description is only a preferred embodiment of the present invention. It should be noted that those skilled in the art can make several changes and improvements without departing from the overall concept of the present invention. These changes should also be considered within the scope of protection of the present invention, and will not affect the effectiveness of the implementation of the present invention or the practicality of the patent.

Claims

1. A method for simultaneously recovering lapis lazuli and humic acid from pretreated municipal sludge, characterized in that, Includes the following steps: (1) Take the mud-water mixture at the end of the biological treatment tank, add iron salt flocculant for coagulation treatment, and obtain phosphorus-iron-rich sludge after solid-liquid separation. (2) Place the phosphorus-rich iron sludge in a sealed container, add the compound enzyme, and mix well; (3) Keep the sealed container warm in a water bath, stir with a stirrer, and perform anaerobic enzymatic hydrolysis until the pH of the anaerobic hydrolysate is 4.0–4.5; (4) Allow the mixture to stand and allow it to settle until the residue and supernatant are separated, resulting in phosphorus-rich iron supernatant and enzymatic hydrolysis residue. (5) Add a reducing agent to the phosphorus-rich iron supernatant to ensure that the redox potential is <-300mV, adjust the pH value to 6.0, and centrifuge to obtain crude protein; (6) Continue to adjust the pH of the supernatant to 7.0-7.5, and the blue iron crystals will settle by gravity. Solid-liquid separation will be performed to obtain blue iron crystals. (7) Humic acid is recovered from the enzymatic hydrolysis residue obtained in step (4).

2. The method according to claim 1, characterized in that, The humic acid recovered in step (7) is used to adsorb heavy metals.

3. The method according to claim 1, characterized in that, The complex enzyme described in step (2) is prepared by mixing protease, amylase, cellulase and lysozyme in a mass ratio of 1:1:1:

1.

4. The method according to claim 1, characterized in that, The iron salt flocculant mentioned in step (1) is FeCl3 or FeSO4.

5. The method according to claim 1, characterized in that, The reducing agent mentioned in step (5) is vitamin C.

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