A method for phosphate recovery and product separation in a digestion sludge system

Abstract

The application discloses a method for recovering phosphate in a digestion sludge system and separating products. The method uses the difference between the hydrophilicity and hydrophobicity of the vivianite particles and the digestion sludge in the digestion sludge system, uses a collector to improve the hydrophobicity of the vivianite, uses an inhibitor to improve the hydrophilicity of other impurity particles such as silicon dioxide, separates the vivianite particles and the impurities such as silicon dioxide in the digestion sludge through a froth flotation method, and can realize efficient separation and recovery of phosphorus resources.

Description

Technical Field

[0001] This invention belongs to the field of environmental engineering water treatment and resource utilization technology, specifically relating to a method for phosphate recovery and product separation in a sludge digestion system. Background Technology

[0002] Most of the phosphorus consumed by human activities ends up in wastewater treatment plants, with over 90% of it accumulating in sludge. Therefore, wastewater sludge is a secondary resource rich in phosphates. Currently, there are two main methods for phosphorus removal in wastewater treatment plants: enhanced biological phosphorus removal and chemical phosphorus removal. The main byproducts of phosphorus removal technologies include struvite crystals, lapis lazuli crystals, hydroxyapatite, and calcium phosphate.

[0003] The method of recovering nitrogen and phosphorus from struvite crystals has several problems in practical applications. First, it can only precipitate higher concentrations of nitrogen and phosphorus in anaerobic fermentation sludge. Second, calcium and aluminum phosphate compounds tend to precipitate preferentially, resulting in high recovery costs and low phosphorus recovery rates (below 50%). Furthermore, the operating conditions are complex and demanding, lacking significant advantages.

[0004] Studies have shown that during the anaerobic digestion of sludge, microorganisms in the sludge can convert Fe... 3+ Reduced to Fe 2+ This iron then reacts with phosphates in the sludge to form lapis lazuli (Fe3(PO4)2·8H2O). When the iron content is sufficiently high, lapis lazuli can account for 70-90% of the phosphorus content in the digested sludge. Because lapis lazuli has good stability (K... sp =10 -36 Due to its availability and economic feasibility, it has attracted increasing attention as a promising phosphorus recovery medium.

[0005] However, separating lapis lazuli from digested sludge presents several technical challenges. First, digested sludge is a complex mixture of various organic and inorganic substances; the presence of organic matter, minerals, and other impurities hinders the effective recovery of lapis lazuli. Second, the lapis lazuli formed in digested sludge has a small particle size (10-100 μm). These fine particles have a high specific surface area and readily interact with other particles or sludge flocs to form aggregates, generating strong viscous resistance and thus hindering the release of lapis lazuli. Furthermore, the conditions inherent in the digested sludge itself, such as pH, temperature, and redox potential, can affect the chemical formation process of lapis lazuli, leading to the formation of other compounds that are released into the solution.

[0006] Existing technologies propose methods such as magnetic separation, microbial dissimilatory iron reduction, and gravity separation to recover lapis lazuli from sludge. However, lapis lazuli is a typical paramagnetic mineral with very weak magnetism, making magnetic separation difficult. Microbial cultivation is a complex process that is difficult to implement on a large scale in actual wastewater treatment. Gravity separation requires high centrifugal speeds and large amounts of high-density heavy liquid, which places high demands on equipment, incurs significant costs, and is difficult to achieve on a large scale. Summary of the Invention

[0007] The purpose of this invention is to provide a method for phosphate recovery and product separation in a digested sludge system. By using foam flotation, lapis lazuli particles and impurities such as silica in the digested sludge can be separated, which can achieve efficient separation and recovery of phosphorus resources. Moreover, the separated lapis lazuli has high purity and high utilization value.

[0008] To achieve the above objectives, the present invention provides the following technical solution:

[0009] This invention provides a method for phosphate recovery and product separation in a digested sludge system, comprising the following steps: adding an inhibitor and a collector to digested sludge containing wollastonite particles, followed by flotation to obtain flotation sludge containing wollastonite particles.

[0010] The digested sludge has the following characteristics:

[0011] The pH range is between 6 and 9, preferably between 8 and 9;

[0012] The particle size of the solid particles is between 10 and 100 μm.

[0013] In practical applications, the higher the solids content and the lower the viscosity of the digested sludge, the better, as these factors contribute to improved flotation performance.

[0014] The inhibitor is sodium silicate; the amount of the inhibitor added is 1-10 ml / L, preferably 5 ml / L.

[0015] The collector is oleic acid; the amount of the collector added is 10-20 g / L, preferably 15 g / L.

[0016] The flotation method is foam flotation.

[0017] The flotation process conditions are: turbine speed of 2000-3000 rpm / min, and time not exceeding 2 min.

[0018] The method further includes the step of adding iron salts to sewage sludge, allowing precipitation and separation to obtain digested sludge containing lapis lazuli particles.

[0019] The iron salt is a divalent iron salt and / or a trivalent iron salt. In the digested sludge system, the molar ratio of Fe to P is (1.5-2):1, preferably 1.5:1.

[0020] In the method, iron salts are added during any one of the primary sedimentation, secondary sedimentation, and anaerobic treatments of the digested sludge system. Preferably, iron salts are added during the primary sedimentation, secondary sedimentation, and anaerobic treatments.

[0021] The beneficial effects achieved by this invention are as follows:

[0022] 1. This invention utilizes the hydrophilicity-hydrophobicity difference between lapis lazuli particles and digested sludge in a digested sludge system. A collector is used to improve the hydrophobicity of lapis lazuli, and an inhibitor is used to improve the hydrophilicity of other impurity particles such as silica. The lapis lazuli particles and impurities such as silica in the digested sludge are separated by froth flotation, which can achieve efficient separation and recovery of phosphorus resources.

[0023] 2. Compared with the method of using magnesium salts to form struvite crystals for recovery, the present invention adds cheaper iron salts to the sludge digestion system to form lapis lazuli particles from phosphates in the sewage sludge, and then separates them by adding reagents to obtain flotation sludge containing lapis lazuli particles, which can greatly reduce the recovery cost of phosphates in the sludge digestion system.

[0024] 3. The froth flotation process has advantages such as simple operation, low cost, strong adaptability, and minimal environmental impact. It only requires adjusting parameters such as the type and dosage of reagents and the aeration rate to achieve the separation and recovery of sappanite, greatly simplifying the phosphate recovery and separation process. At the same time, the properties of mineral particles such as sappanite can be changed by adjusting the dosage of collectors and inhibitors, thereby treating sludge with different properties. It has wide adaptability and can treat sludge from sewage treatment plants on a large scale, greatly reducing energy consumption costs and achieving high economic benefits.

[0025] 4. The blue iron stone separated by flotation in this invention has high purity and good application prospects. Attached Figure Description

[0026] Figure 1 This is a schematic diagram of the processing technology of the present invention.

[0027] Figure 2 This is an electron microscope image of the sapphire recovered in the processing technology of this invention. Detailed Implementation

[0028] The present invention will be further described below with reference to specific embodiments, but the present invention is not limited to the following embodiments.

[0029] Unless otherwise specified, the experimental methods used in the following examples are conventional methods.

[0030] Unless otherwise specified, all reagents, materials, instruments, etc. used in the following examples are commercially available.

[0031] In the quantitative experiments in the following examples, three replicate experiments were set up, and the average value of the results was taken.

[0032] The flotation agent used in the following examples is: XFD-Ⅲ type mechanically stirred flotation machine with detachable flotation cell.

[0033] Example 1

[0034] like Figure 1 As shown, the specific operation steps are as follows:

[0035] (1) Add iron salt ferric chloride to the primary sedimentation tank, secondary sedimentation tank and anaerobic digestion treatment unit of the digestion sludge system so that the molar ratio of Fe to P in the digestion sludge system is 1.5:1. The iron-containing sludge is stabilized and resource-based in the anaerobic digestion system, and then precipitated and separated to obtain digestion sludge containing blue iron particles.

[0036] The properties of the digested sludge containing wollastonite particles were as follows: pH 7.97±0.08, TSS 53260±270 mg / L, VSS 24630±180 mg / L, TCOD 34680±320 mg / L, SCOD 3792±24 mg / L, Fe 2+ The concentration was 225.84 mg / L and the viscosity was 114 mPa·s.

[0037] (2) Add 1L of digested sludge containing sapphire into the flotation machine. Stir at 1000rpm for 5min. Then add 1% hydrochloric acid or 1% sodium hydroxide solution to make the pH of the digested sludge reach 8-9 and continue stirring. Then add the collector oleic acid and the inhibitor sodium silicate. The concentration of oleic acid in the digested sludge system is 5ml / L and the concentration of the inhibitor sodium silicate is 15g / L. Stir at 1000rpm for 2min and start flotation to obtain flotation sludge containing sapphire and bottom sludge.

[0038] (3) The bottom sludge can be transported back to the anaerobic digestion unit of the sludge digestion system for continued anaerobic digestion treatment.

[0039] Analysis and calculation:

[0040] 1. Microstructural characteristics of sapphire

[0041] Figure 2 Electron micrographs of the recovered sapphire, by Figure 2It can be seen that lapis lazuli has a platy / massive structure. The elemental composition of the particle is Fe, P and O as shown by the EDS energy dispersive spectroscopy image, confirming that the particle is a lapis lazuli particle.

[0042] 2. Quality of flotation sludge and bottom sludge

[0043] The obtained flotation sludge and bottom sludge were dried at a constant temperature and weighed to obtain 29.0117g of flotation sludge containing lapis lazuli and 19.1935g of bottom sludge.

[0044] 3. Iron content analysis

[0045] Using the o-phenanthroline method, the iron content in the flotation sludge was measured to be 1042.4 mg / L, and the iron content in the bottom sludge was 607.7 mg / L.

[0046] The separation efficiency was determined by multiplying the iron content by the volume of hydrochloric acid used to dissolve the comfrey, then converting the iron content back to the comfrey content. The calculation showed that the comfrey content in the flotation sludge was 67.77%, and the comfrey content in the bottom sludge was 26.13%.

[0047] 4. Flotation recovery rate of lapis lazuli in digested sludge

[0048] The calculation formula is:

[0049] η = m1 / m1 + m2

[0050] in:

[0051] η is the recovery efficiency;

[0052] m1 represents the lapis lazuli content in the flotation sludge;

[0053] m2 represents the content of blue ironstone in the bottom sludge.

[0054] Calculations show that the flotation recovery rate of lapis lazuli in digested sludge is as high as 67.77%. This indicates that the flotation separation method provided by this invention can not only achieve efficient separation and recovery of phosphate in digested sludge systems, but also yield lapis lazuli with high purity and high utilization value.

[0055] 5. Phosphate recovery rate in the sludge digestion system

[0056] The calculation formula is:

[0057] γ = [n1 / (n1+n2+n3)]×η

[0058] in:

[0059] γ represents the phosphate recovery efficiency;

[0060] η is the recovery rate of sapphire flotation;

[0061] n1 represents the phosphate content in the wastewater;

[0062] n2 represents the phosphate content in the blue ironite of the flotation sludge;

[0063] n3 represents the phosphate content in the blue ironstone of the bottom sludge.

[0064] Calculations showed that the phosphate recovery rate in the sludge digestion system was 64.61%.

[0065] Although the present invention has been described in detail above with general descriptions and specific embodiments, modifications or improvements can be made to it, which will be obvious to those skilled in the art. Therefore, all such modifications or improvements made without departing from the spirit of the present invention are within the scope of protection claimed by the present invention.

Claims

1. A method for recovering phosphate and separating products in a digestion sludge system, comprising the following steps: adding an iron salt into sewage sludge, and precipitating and separating to obtain digestion sludge containing vivianite particles; adding an inhibitor and a collector into the digestion sludge containing vivianite particles, and floating to obtain flotation sludge containing vivianite particles; the digestion sludge has the following index characteristics: pH is in the range of 6-9; and particle size of solid particles is in the range of 10-100 μm; the inhibitor is sodium silicate; and the addition amount of the inhibitor is 1-10 ml / L; the collector is oleic acid; and the addition amount of the collector is 10-20 g / L; the flotation is froth flotation; the process conditions of the flotation are: turbine rotation speed is 2000-3000 rpm / min, and the time is not more than 2 min.

2. The method for phosphorus recovery and product separation in a digestion sludge system according to claim 1, characterized by: the iron salt is a divalent iron salt and / or a trivalent iron salt; in the digestion sludge system, the molar ratio of Fe element to P element is (1.5-2):

1.

3. The method for phosphorus recovery and product separation in a digestion sludge system according to claim 1 or 2, characterized by: the iron salt is added in any one of primary sedimentation, secondary sedimentation and anaerobic treatment of the digestion sludge system.

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