Method for removing heavy metals in sludge
By combining asymmetric alternating electric field with bioleaching technology, the problems of long treatment cycles and high energy consumption of heavy metals in sludge are solved, achieving efficient and low-energy removal of heavy metals, especially in organically bound and residual sludge.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2026-01-16
- Publication Date
- 2026-03-20
AI Technical Summary
Existing technologies for treating heavy metals in sludge suffer from problems such as long treatment cycles, poor removal efficiency, and high energy consumption. In particular, they are difficult to effectively remove heavy metals that are tightly bound to organic matter and stable minerals.
By employing the synergistic effect of an asymmetric alternating electric field and bioleaching technology, solid-liquid separation is achieved by adding bioleaching bacterial solution and nutrient solution to dewatered sludge, adjusting the pH, and then applying an asymmetric alternating electric field for bio-electrochemical coupling treatment.
It significantly improves the removal efficiency of heavy metals, especially the removal rate of organically bound and residual forms, shortens the treatment cycle, reduces energy consumption, and is simple to operate and easy to apply industrially.
Smart Images
Figure CN121698548A_ABST
Abstract
Description
Technical Field
[0001] This invention relates to the fields of environmental protection technology and solid waste treatment, specifically to a method for removing heavy metals from sludge, and particularly to a method for removing heavy metals from sludge using bioleaching and asymmetric alternating current electric field chemical coupling technology. Background Technology
[0002] Municipal and industrial sludge are inevitable byproducts of wastewater treatment processes. They are produced in large quantities and contain high concentrations of heavy metals such as Cu, Zn, Pb, Cd, and Cr. Improper treatment poses a serious threat to the environment and human health. Currently, land application is one of the best disposal methods for sludge, but the heavy metal content is a key bottleneck restricting its safe utilization.
[0003] Bioleaching technology utilizes the metabolic activity of chemoautotrophic bacteria such as Thiobacillus thiooxidans and Thiobacillus ferrooxidans to produce sulfuric acid and Fe. 3+ This method uses acid dissolution and oxidation to leach heavy metals from the solid phase, offering advantages such as low cost and environmental friendliness. However, this technology suffers from drawbacks, including a long treatment cycle (typically 10-15 days) and poor removal efficiency for heavy metals tightly bound to organic matter and stable minerals in sludge, such as oxidizable and residual forms.
[0004] Electrokinetic remediation technologies, especially direct current (DC) technologies, can drive the directional movement of heavy metal ions through mechanisms such as electromigration and electroosmosis. However, DC can easily lead to excessive acidification of the anode and severe alkalization of the cathode, causing problems such as electrode polarization and agglomeration of soil / sludge particles. This can cause some heavy metals to reprecipitate in the cathode area, reducing the overall removal efficiency and resulting in high energy consumption.
[0005] Therefore, developing a new method that can overcome the above-mentioned technical defects and achieve efficient, rapid, and low-energy removal of heavy metals is of great significance for promoting the safe resource utilization of heavy metal sludge. Summary of the Invention
[0006] The purpose of this invention is to address the shortcomings of existing technologies by providing a method for removing heavy metals from sludge. This method significantly improves the removal efficiency of heavy metals and shortens the treatment cycle through the synergistic effect of an asymmetric alternating electric field and bioleaching.
[0007] The technical solution of the present invention is as follows: A method for removing heavy metals from sludge includes the following steps: Add bioleaching bacteria solution and nutrient salt solution to dewatered sludge, adjust pH to form mixed sludge; An asymmetric alternating electric field is applied to the mixed sludge for bio-electrochemical coupling treatment. The treated sludge is then subjected to solid-liquid separation to obtain purified sludge and leachate containing heavy metals, respectively.
[0008] In a preferred embodiment of the present invention, the bioleaching solution is a bacterial solution of *Thiobacillus ferrooxidans* and / or *Thiobacillus thiooxidans*, with an inoculum amount of 5% to 20% of the mixed mud volume and a bacterial solution concentration of 1×10⁻⁶. 8 Cells / mL ~ 1×10 9 per mL.
[0009] More preferably, the pH is adjusted to 2.0–4.5. Under these pH conditions, the growth of *Thiobacillus ferrooxidans* and / or *Thiobacillus thiooxidans* is optimal.
[0010] In a preferred embodiment of the present invention, the nutrient solution contains 0.1 g / L~0.5 g / L (NH4)2SO4, 0.01 g / L~0.05 g / L K2HPO4, 0.1 g / L~0.5 g / L MgSO4·7H2O, 0.01 g / L~0.05 g / L KCl, and 5 g / L~20 g / L FeSO4·7H2O; or The nutrient solution contains 5 g / L to 15 g / L of sulfur.
[0011] In a preferred embodiment of the present invention, the waveform of the asymmetric alternating electric field is a sine wave, a square wave, or a sawtooth wave.
[0012] More preferably, the waveform of the asymmetric alternating electric field is a square wave.
[0013] In a preferred embodiment of the present invention, the frequency of the asymmetric alternating electric field is 0.1 Hz to 5 Hz. More preferably, the frequency of the asymmetric alternating electric field is 0.5 Hz to 2 Hz.
[0014] In a preferred embodiment of the present invention, the voltage gradient of the asymmetric alternating electric field is 1V / cm to 4V / cm.
[0015] More preferably, the voltage gradient of the asymmetric alternating electric field is 1.5V / cm to 2.5V / cm.
[0016] In a preferred embodiment of the present invention, the bio-electrochemical coupling treatment time is 1 to 7 days.
[0017] In a preferred embodiment of the present invention, the electrode used in the bio-electrochemical coupling treatment is a graphite electrode or a titanium-coated ruthenium electrode.
[0018] In a preferred embodiment of the present invention, the mass ratio of the mixture of dewatered sludge, bioleaching solution, and nutrient solution in the mixed slurry is 1:5~10.
[0019] The present invention also provides a purified sludge obtained by the above method. The purified sludge can be directly used for land application, brick making, or landfill.
[0020] The present invention also provides a leachate containing heavy metals obtained by the above method. The leachate containing heavy metals can be transported to a heavy metal recovery unit to recover valuable metals.
[0021] Compared with the prior art, the beneficial effects of the present invention are as follows: 1. Synergistic Effect: The periodic commutation of the asymmetric alternating current field effectively suppresses extreme pH changes in the electrode region, avoiding electrode polarization and sludge aggregation, and creating a more stable metabolic environment for microorganisms. At the same time, the electroosmotic oscillation and ion reciprocating migration generated by the alternating current can effectively destroy the sludge floc structure, especially the binding of extracellular polymers and heavy metals, exposing the encapsulated heavy metals and greatly enhancing the attack efficiency of biological acids.
[0022] 2. High treatment efficiency and short cycle: Compared with single bioleaching, the present invention improves the removal rate of heavy metals, especially stable organic bound and residual forms, by 15% to 30%, and shortens the treatment cycle by 30% to 50%.
[0023] 3. Low energy consumption and environmentally friendly: The operating energy consumption of the asymmetric alternating current electric field is lower than that of traditional direct current, and it does not require the addition of a large amount of chemical agents, resulting in a low risk of secondary pollution. It is a green and efficient deep sludge detoxification technology.
[0024] 4. Simple operation and easy to promote: This method can be directly modified on the basis of existing bioleaching reactors. Only an asymmetric AC electric field source and electrodes need to be added. The modification cost is low and it is easy to realize industrial application. Attached Figure Description
[0025] Figure 1 This is a process flow diagram provided by the present invention. Detailed Implementation
[0026] The present invention will be further illustrated by the following examples, but the scope of protection of the present invention is not limited thereto.
[0027] Municipal and industrial sludge are inevitable byproducts of wastewater treatment processes. They are produced in large quantities and contain high concentrations of heavy metals such as Cu, Zn, Pb, Cd, and Cr. Improper treatment poses a serious threat to the environment and human health. Bioleaching technology utilizes the metabolic activity of chemoautotrophic bacteria, such as *Thiobacillus thiooxidans* and *Thiobacillus ferrooxidans*, to produce sulfuric acid and Fe. 3+This method, which dissolves heavy metals from the solid phase through acid dissolution and oxidation, has the advantages of low cost and environmental friendliness. However, this technology has drawbacks, such as long treatment cycles (typically 10-15 days) and poor removal efficiency for heavy metals tightly bound to organic matter and stable minerals in sludge, including oxidizable and residual forms. Electrokinetic remediation technology, especially direct current (DC) technology, can drive the directional movement of heavy metal ions through mechanisms such as electromigration and electroosmosis. However, DC power can easily lead to excessive acidification of the anode and severe alkalization of the cathode, causing problems such as electrode polarization and soil / sludge particle agglomeration. This can cause some heavy metals to redeposit in the cathode area, reducing overall removal efficiency and resulting in higher energy consumption.
[0028] Based on this, the present invention provides a method for removing heavy metals from sludge, comprising the following steps: Add bioleaching bacteria solution and nutrient salt solution to dewatered sludge, adjust pH to 2.0~4.5, and form mixed sludge; Asymmetric alternating electric field was applied to the mixed sludge for bio-electrochemical coupling treatment. The treated sludge was then subjected to solid-liquid separation to obtain purified sludge and leachate containing heavy metals.
[0029] This invention utilizes the polarization suppression and oscillatory mass transfer effect of an asymmetric alternating electric field to significantly enhance the removal efficiency of heavy metals, especially organically bound and residual heavy metals, in sludge through bioleaching. It has outstanding advantages such as short treatment cycle, low energy consumption, no electrode polarization, and high heavy metal removal rate.
[0030] For detailed steps, please refer to... Figure 1 As shown, dewatered sludge is added to the electrochemical reactor, and bioleaching bacterial solution and nutrient salt solution are added to it using a pump. After adjusting the pH, an asymmetric alternating electric field is applied to the electrochemical reactor using an AC power supply and a signal amplifier to carry out bio-electrochemical coupling treatment. All procedures are controlled and implemented on the PC.
[0031] Example 1 A sample of dewatered sludge from an electroplating plant containing Cu, Zn, and Ni was taken. The main heavy metal contents were: Cu 1500 mg / kg, Zn 800 mg / kg, and Ni 500 mg / kg.
[0032] (1) Weigh 1 kg of the sludge and place it in a 5 L plastic reactor. Add 4 L of *Thiobacillus ferrooxidans* bacterial solution. The bacterial solution concentration is approximately 1 × 10⁻⁶. 8 Cells / mL were prepared, and nutrients were added to achieve the following final concentrations: (NH4)2SO4 0.3 g / L, K2HPO4 0.03 g / L, MgSO4·7H2O 0.3 g / L, KCl 0.03 g / L, FeSO4·7H2O 10 g / L. The initial pH was adjusted to 3.0 with dilute H2SO4.
[0033] (2) Insert a pair of graphite electrodes into the reactor with a spacing of 10 cm and connect them to an asymmetric AC square wave power supply. Set the frequency to 1 Hz, the voltage to 20 V, apply a voltage gradient of 2 V / cm, turn on the power supply for coupling treatment, and the treatment time is 1 day.
[0034] (3) After treatment, centrifugation was performed. The removal rates of Cu, Zn and Ni in the purified sludge were measured to be 92%, 95% and 88%, respectively.
[0035] Using the group that received no electric field and underwent a single bioleaching treatment for 7 days as a control, the removal rates of Cu, Zn, and Ni were 75%, 80%, and 70%, respectively.
[0036] Example 2 The dewatered sludge from a municipal wastewater treatment plant was found to contain the following main heavy metals: Pb 200 mg / kg and Cd 5 mg / kg.
[0037] (1) Weigh 1 kg of the sludge and place it in a 10 L reactor. Add 9 L of Thiobacillus thiooxidans bacterial solution. The bacterial solution concentration is approximately 1 × 10⁻⁶. 8 cells / mL, and add S 0 The energy substrate was 10 g / L, and the nutrient concentration was the same as in Example 1. The initial pH was adjusted to 4.0.
[0038] (2) Insert a graphite electrode, apply an asymmetric AC sine wave with a frequency of 0.5 Hz and a voltage gradient of 1.5 V / cm, and treat for 2 days.
[0039] (3) Solid-liquid separation after treatment. The removal rates of Pb and Cd in the purified sludge were measured to be 85% and 90%, respectively, which meet the standard of "Sludge for Forest Land Disposal in Urban Wastewater Treatment Plants". However, the removal rates of Pb and Cd by single biological leachate treatment for 10 days were only 65% and 75%, respectively.
[0040] Example 3 Take the dewatered sludge from Example 1 and process it according to the following steps: (1) Weigh 1 kg of the sludge and place it in a 5 L plastic reactor. Add 4 L of *Thiobacillus ferrooxidans* bacterial solution. The bacterial solution concentration is approximately 1 × 10⁻⁶. 8 Cells / mL were prepared, and nutrients were added to achieve the following final concentrations: (NH4)2SO4 0.3 g / L, K2HPO4 0.03 g / L, MgSO4·7H2O 0.3 g / L, KCl 0.03 g / L, FeSO4·7H2O 10 g / L. The initial pH was adjusted to 3.0 with dilute H2SO4.
[0041] (2) Insert a pair of graphite electrodes into the reactor with a spacing of 10 cm and connect them to an asymmetric AC square wave power supply. Set the frequency to 0.8 Hz, the voltage to 20 V, and the voltage gradient to 4 V / cm. Turn on the power supply for coupling treatment for 7 days.
[0042] (3) After treatment, centrifugation was performed. The removal rates of Cu, Zn and Ni in the purified sludge were measured to be 96%, 97% and 92%, respectively.
[0043] Example 4 Take the dewatered sludge from Example 1 and process it according to the following steps: (1) Take 1 kg of the sludge and place it in a 5 L plastic reactor. Add 4 L of *Thiobacillus ferrooxidans* bacterial solution. The bacterial solution concentration is approximately 1 × 10⁻⁶. 9 Cells / mL were prepared, and nutrients were added to achieve the following final concentrations: (NH4)2SO4 0.3 g / L, K2HPO4 0.03 g / L, MgSO4·7H2O 0.3 g / L, KCl 0.03 g / L, FeSO4·7H2O 10 g / L. The initial pH was adjusted to 3.0 with dilute H2SO4.
[0044] (2) Insert a pair of graphite electrodes into the reactor with a spacing of 10 cm and connect them to an asymmetric AC square wave power supply. Set the frequency to 5 Hz, the voltage to 20 V, and the voltage gradient to 2 V / cm. Turn on the power supply for coupling treatment, and the treatment time is 1 day.
[0045] (3) After treatment, centrifugation was performed. The removal rates of Cu, Zn and Ni in the purified sludge were measured to be 94%, 93% and 85%, respectively.
[0046] Example 5 Take the dewatered sludge from Example 1 and process it according to the following steps: (1) Weigh 1 kg of the sludge and place it in a 5 L plastic reactor. Add 4 L of *Thiobacillus ferrooxidans* bacterial solution. The bacterial solution concentration is approximately 1 × 10⁻⁶. 8 Cells / mL were prepared, and nutrients were added to achieve the following final concentrations: (NH4)2SO4 0.1 g / L, K2HPO4 0.01 g / L, MgSO4·7H2O 0.1 g / L, KCl 0.01 g / L, FeSO4·7H2O 5 g / L. The initial pH was adjusted to 3.0 with dilute H2SO4.
[0047] (2) Insert a pair of graphite electrodes into the reactor with a spacing of 10 cm and connect them to an asymmetric AC square wave power supply. Set the frequency to 1 Hz, the voltage to 20 V, and the voltage gradient to 2 V / cm. Turn on the power supply for coupling treatment, and the treatment time is 1 day.
[0048] (3) After treatment, centrifugation was performed. The removal rates of Cu, Zn and Ni in the purified sludge were measured to be 90%, 92% and 89%, respectively.
[0049] Example 6 Take the dewatered sludge from Example 1 and process it according to the following steps: (1) Weigh 1 kg of the sludge and place it in a 5 L plastic reactor. Add 4 L of *Thiobacillus ferrooxidans* bacterial solution. The bacterial solution concentration is approximately 1 × 10⁻⁶. 8 Cells / mL, and added nutrients to achieve the following final concentrations: (NH4)2SO4 0.5 g / L, K2HPO4 0.05 g / L, MgSO4·7H2O 0.5 g / L, KCl 0.05 g / L, FeSO4·7H2O 20 g / L. Adjust the initial pH to 2.0 with dilute H2SO4.
[0050] (2) Insert a pair of graphite electrodes into the reactor with a spacing of 10 cm and connect them to an asymmetric AC square wave power supply. Set the frequency to 1 Hz, the voltage to 20 V, and the voltage gradient to 2 V / cm. Turn on the power supply for coupling treatment, and the treatment time is 1 day.
[0051] (3) After treatment, centrifugation was performed. The removal rates of Cu, Zn and Ni in the purified sludge were measured to be 92%, 91% and 90%, respectively.
[0052] Example 7 Take the dewatered sludge from Example 2 and process it according to the following steps: (1) Weigh 1 kg of the sludge and place it in a 10 L reactor. Add 9 L of Thiobacillus thiooxidans bacterial solution. The bacterial solution concentration is approximately 1 × 10⁻⁶. 8 cells / mL, and add S 0 The energy substrate was 15 g / L, and the nutrient concentration was the same as in Example 1. The initial pH was adjusted to 4.0.
[0053] (2) Insert a graphite electrode, apply an asymmetric AC sine wave with a frequency of 0.5 Hz and a voltage gradient of 1.5 V / cm, and treat for 2 days.
[0054] (3) Solid-liquid separation after treatment. The removal rates of Pb and Cd in the purified sludge were measured to be 89% and 92%, respectively, which meet the standard of "Sludge for Forest Land Disposal in Urban Wastewater Treatment Plants". However, the removal rates of Pb and Cd by single biological leachate treatment for 10 days were only 63% and 77%, respectively.
[0055] Example 8 Take the dewatered sludge from Example 2 and process it according to the following steps: (1) Weigh 1 kg of the sludge and place it in a 10 L reactor. Add 9 L of Thiobacillus thiooxidans bacterial solution. The bacterial solution concentration is approximately 1 × 10⁻⁶. 8 cells / mL, and add S 0 A nutrient concentration of 5 g / L was used as the energy substrate, the same as in Example 1. The initial pH was adjusted to 4.0.
[0056] (2) Insert a graphite electrode, apply an asymmetric AC sine wave with a frequency of 0.5 Hz and a voltage gradient of 1.5 V / cm, and treat for 2 days.
[0057] (3) Solid-liquid separation after treatment. The removal rates of Pb and Cd in the purified sludge were measured to be 87% and 93%, respectively, which meet the standard of "Sludge for Forest Land Disposal in Urban Wastewater Treatment Plants". However, the removal rates of Pb and Cd by single biological leachate treatment for 10 days were only 66% and 73%, respectively.
[0058] The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in the present invention should be included within the scope of protection of the present invention.
Claims
1. A method for removing heavy metals from sludge, characterized in that, Includes the following steps: Add bioleaching bacteria solution and nutrient salt solution to dewatered sludge, adjust pH to form mixed sludge; An asymmetric alternating electric field is applied to the mixed sludge for bio-electrochemical coupling treatment. The treated sludge is then subjected to solid-liquid separation to obtain purified sludge and leachate containing heavy metals, respectively.
2. The method for removing heavy metals from sludge according to claim 1, characterized in that, The bioleaching solution is a bacterial solution of *Thiobacillus ferrooxidans* and / or *Thiobacillus thiooxidans*, with an inoculum amount of 5% to 20% of the mixed mud volume and a bacterial solution concentration of 1×10⁻⁶. 8 Cells / mL ~ 1×10 9 Cells / mL, adjust pH to 2.0~4.
5.
3. The method for removing heavy metals from sludge according to claim 1, characterized in that, The nutrient solution contains: 0.1 g / L~0.5 g / L (NH4)2SO4, 0.01 g / L~0.05 g / L K2HPO4, 0.1 g / L~0.5 g / L MgSO4·7H2O, 0.01 g / L~0.05 g / L KCl, and 5 g / L~20 g / L FeSO4·7H2O; or The nutrient solution contains 5 g / L to 15 g / L of sulfur.
4. The method for removing heavy metals from sludge according to claim 1, characterized in that, The waveform of the asymmetric alternating electric field is a sine wave, a square wave, or a sawtooth wave.
5. The method for removing heavy metals from sludge according to claim 1, characterized in that, The frequency of the asymmetric alternating electric field is 0.1 Hz to 5 Hz.
6. The method for removing heavy metals from sludge according to claim 1, characterized in that, The voltage gradient of the asymmetric alternating electric field is 1V / cm to 4V / cm.
7. The method for removing heavy metals from sludge according to claim 1, characterized in that, The bio-electrochemical coupling treatment lasts for 1 to 7 days.
8. The method for removing heavy metals from sludge according to claim 1, characterized in that, During the bio-electrochemical coupling treatment, the electrode is a graphite electrode or a titanium-coated ruthenium electrode.
9. A purified sludge obtained by the method for removing heavy metals from sludge according to any one of claims 1 to 8, characterized in that, The purified sludge is used for land application, brick making, or landfill.
10. A leachate containing heavy metals obtained by the method for removing heavy metals from sludge according to any one of claims 1 to 8, characterized in that, The leachate containing heavy metals is used to recover valuable metals.