FCDI wastewater treatment system based on calcium-based biochar and application of FCDI wastewater treatment system

Abstract

The invention discloses an FCDI wastewater treatment system based on calcium-based biochar and application of the FCDI wastewater treatment system. The system comprises an FCDI reactor, a positive circulating device, a negative circulating device and a wastewater drainage device, flowing electrode slurry in the positive electrode circulating device consists of calcium-based biochar and deionized water, and the mass volume ratio of the calcium-based biochar to the deionized water is 10-50%; the calcium-based biochar is obtained by calcining bone-based biochar and a calcium-containing material. According to the system, phosphorus and various heavy metal elements in anhydrous water can be synchronously removed under the synergistic effect of the continuous adsorption-desorption characteristic of a flowing electrode on the basis of the excellent specific surface area and conductivity of calcium-based biochar and a large number of phosphate radical adsorption sites. When the system is used for removing phosphorus and heavy metal elements in wastewater, the phosphorus concentration is reduced to 1.7 mg / L from 217.98 mg / L, the highest removal rate of phosphorus is 99.22%, the removal efficiency of various heavy metals is 95% or above, and the removal rate of heavy metals such as Sr and Cr is 99% or above.

Description

Technical Field

[0001] The present invention relates to a wastewater treatment system, specifically to an FCDI wastewater treatment system based on calcium-based biochar and its application, belonging to the technical field of sewage treatment. Background Art

[0002] Phosphorus is an important element on the earth and widely exists in nature. Due to the limited phosphorus resources and environmental problems caused by overuse, it is of great significance to recover phosphorus from sewage sludge. Sewage sludge contains a large amount of phosphorus. Through appropriate recovery technologies, not only can water pollution be reduced, but also the shortage of phosphorus resources in nature can be made up for. With the rapid development of industrialization and urbanization, a large amount of sewage containing heavy metals is discharged into the environment, posing a serious threat to the environment and human health. Therefore, recovering phosphorus from sewage sludge and simultaneously removing its heavy metals is of great significance for sewage treatment applications and the recycling of phosphorus resources.

[0003] In recent years, the progress of electrochemistry has made capacitive deionization (CDI) an attractive electroadsorption desalination technology, with advantages such as environmental protection, significantly reduced energy consumption, improved energy efficiency, and energy recovery. However, CDI has disadvantages such as limited ion removal ability, complex preparation of fixed electrodes, and intermittent desalination behavior. The FCDI technology is a new type of electro-driven desalination technology that combines a flow electrode with an ion exchange membrane. It shows good prospects in the fields of removing heavy metal ions, seawater desalination, and resource recovery. The performance of the FCDI system depends on the electrode material, mainly due to factors such as the specific surface area, pore size distribution, conductivity, and chemical stability of the electrode material. First, the specific surface area and pore size distribution of the electrode material have a significant impact on the performance of the FCDI system. The larger the specific surface area, the more adsorption sites can be provided on the electrode surface. In terms of pore size distribution, electrode materials with a larger mesoporous area can provide faster ion transport paths, thus improving the desalination rate. Second, the conductivity of the electrode material has an important impact on the performance of the FCDI system. Electrode materials with good conductivity can transport electrons faster, reduce internal resistance, and thus improve the desalination rate and efficiency of the system. Therefore, activated carbon and graphite-based materials are mostly used in the prior art. However, although these materials can improve their desalination performance, their adsorption ability for specific ions is still lacking, and it is difficult to achieve the simultaneous removal of heavy metal cations and phosphorus-containing anions in sewage wastewater.

[0004] Therefore, there is an urgent need in the prior art for an FCDI wastewater treatment system to achieve the simultaneous and deep removal of heavy metal cations and phosphorus-containing anions in wastewater. Summary of the Invention

[0005] Aiming at the problems existing in the prior art, the first object of the present invention is to provide an FCDI wastewater treatment system based on calcium-based biochar. This system uses calcium-based biochar as the flow electrode material. Among them, calcium-based biochar not only has excellent specific surface area and conductivity, but also has a large number of phosphate adsorption sites, has a high affinity for phosphorus, and can achieve the synchronous removal of phosphorus and various heavy metal elements in the wastewater under the synergistic effect with the continuous adsorption-desorption characteristics of the flow electrode.

[0006] The second object of the present invention is to provide an application of an FCDI wastewater treatment system based on calcium-based biochar for removing phosphorus and heavy metal elements from wastewater. Based on the excellent performance of the above-mentioned FCDI wastewater treatment system, when it is used for wastewater treatment, it can achieve the synchronous deep treatment of phosphorus elements and heavy metal elements in the wastewater. After testing, the phosphorus concentration in the phosphorus-releasing liquid wastewater is reduced from 217.98 mg / L to 1.7 mg / L after passing through the above-mentioned FCDI system, and the highest phosphorus removal rate is 99.22%. The removal efficiency of various heavy metals is above 95%, among which the removal rates of heavy metals such as Sr and Cr are above 99%.

[0007] In order to achieve the above technical objectives, the present invention provides an FCDI wastewater treatment system based on calcium-based biochar. This system includes an FCDI reactor, a positive electrode circulation device, a negative electrode circulation device, and a wastewater diversion device; the flow electrode slurry in the positive electrode circulation device is composed of calcium-based biochar and deionized water, and the mass-volume ratio of the two is 10-50%;

[0008] The calcium-based biochar is obtained by calcining bone-based biochar and calcium-containing materials.

[0009] The calcium-based biochar provided by the present invention combines bone-based biochar and calcium-containing materials. Among them, there are a large number of uniformly dispersed phosphorus element vacancies in the bone-based biochar, and the calcium-containing materials are decomposed into calcium oxide during high-temperature calcination and fixed on the bone-based biochar, further increasing the phosphorus adsorption sites; if only bone-based biochar is used, although a large number of phosphorus element vacancies will be generated after pickling, its adsorption performance is poor, which will cause partial phosphorus residue in the subsequent treatment of phosphorus-releasing liquid wastewater.

[0010] As a preferred solution, the flow electrode slurry in the negative electrode circulation device is composed of activated carbon and deionized water, and the mass-volume ratio of the two is 10-50%.

[0011] As a preferred solution, the preparation process of the bone-based biochar is as follows: in a protective atmosphere, the biological bone is carbonized and then cooled, and is successively pickled and dried to obtain it.

[0012] During the preparation process of bone-based biochar, a large amount of hydroxyapatite will be produced after high-temperature firing, and then acid washing is carried out. The purpose of acid washing is to wash away the phosphate ions in the hydroxyapatite, provide a large number of phosphate adsorption sites, greatly increase its specific surface area, and have a high affinity for phosphorus.

[0013] As a preferred solution, the particle size of the bone-based biochar is -60 mesh

[0014] As a preferred solution, the carbonization conditions are: carbonization temperature is 300-900°C; time is 1-3h.

[0015] As a preferred solution, the pickling solution in the pickling process is one of hydrochloric acid, sulfuric acid and nitric acid, with a concentration of 1 to 3M, and the pickling is performed until neutral.

[0016] As a preferred solution, the calcium-containing material is a biomass calcium material containing calcium oxide.

[0017] As a preferred solution, the mass ratio of the bone-based biochar to the calcium-containing material is 1:1-3.

[0018] As a preferred solution, the calcium-containing material is eggshell powder with a particle size of -100 mesh.

[0019] As a preferred solution, the mass ratio of the bone-based biochar to the eggshell powder is 1:3.

[0020] As a preferred solution, the calcination process is: in a protective atmosphere, the bone-based biochar and the calcium-containing material are fully mixed, the temperature is raised to 400-1000° C., and calcined for 1-5 hours.

[0021] The present invention also provides an application of an FCDI wastewater treatment system based on calcium-based biochar, which is used to remove phosphorus and heavy metal elements in wastewater.

[0022] The FCDI wastewater treatment system provided by the present invention can not only realize the removal of charged ions from the middle flow channel without the need for a desorption process, but also realize the continuous operation of the reactor by having a short inter-electrode distance, greatly shortening the ion transmission distance. Electrode regeneration can occur in the FCDI reactor by mixing the flowing cathode and anode, so that the ions in the feed solution are gradually transferred to the flowing electrode and then concentrated in the water phase of the flowing electrode, thereby realizing the synchronous removal and recovery of various ions in the wastewater.

[0023] As a preferred solution, the wastewater is sewage sludge subjected to electrochemical phosphorus release catalysis followed by acid leaching to obtain phosphorus release liquid wastewater.

[0024] As a preferred solution, the process of removing phosphorus and heavy metal elements from wastewater is as follows: After ultrasonic vibration and dispersion of the positive and negative flow electrode slurries until they are uniform, they are respectively added into the positive and negative circulation devices. The wastewater diversion device is connected to the wastewater to be treated, and the device is started to obtain the treated wastewater.

[0025] As a preferred solution, the flow rate ratio of the positive and negative flow electrode slurries to the wastewater is 4 - 8:10 - 15.

[0026] Compared with the prior art, the beneficial technical effects of the technical solution of the present invention are as follows:

[0027] 1) The FCDI wastewater treatment system provided by the present invention uses calcium-based biochar as the flow electrode material. Among them, calcium-based biochar not only has excellent specific surface area and conductivity, but also has a large number of phosphate adsorption sites and has a high affinity for phosphorus. Under the synergistic effect of the continuous adsorption-desorption characteristics of the flow electrode, it can synchronously remove phosphorus and various heavy metal elements in the wastewater.

[0028] 2) In the technical solution provided by the present invention, based on the excellent performance of the above FCDI wastewater treatment system, when it is used for wastewater treatment, it can realize the synchronous and in-depth treatment of phosphorus and heavy metal elements in the wastewater. After testing, the phosphorus concentration in the phosphorus-releasing liquid wastewater is reduced from 217.98 mg / L to 1.7 mg / L after being treated by the above FCDI system, and the highest phosphorus removal rate is 99.22%. The removal efficiency of various heavy metals is above 95%, and the removal rates of heavy metals such as Sr and Cr are above 99%. Description of the Drawings

[0029] Figure 1 Schematic diagram of the principle of phosphorus and heavy metal ion adsorption by the FCDI wastewater treatment system based on calcium-based biochar;

[0030] Figure 2 Schematic diagram of the FCDI wastewater treatment system based on calcium-based biochar;

[0031] Figure 3 Effect diagram of phosphorus removal by the FCDI wastewater treatment system based on calcium-based biochar;

[0032] Figure 4 Effect diagram of heavy metal removal by the FCDI wastewater treatment system based on calcium-based biochar;

[0033] Figure 5 Electron microscope image of calcium-based biochar. Detailed Embodiments

[0034] To facilitate the understanding of the present invention, the present invention will be described more comprehensively below with reference to specific embodiments. However, the present invention can be implemented in many different forms and is not limited to the embodiments described herein. On the contrary, these embodiments are provided to make the understanding of the disclosure of the present invention more thorough and comprehensive. Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the technical field to which the present invention belongs. The terms used in the description of the present invention herein are only for the purpose of describing specific embodiments and are not intended to limit the present invention.

[0035] Example 1

[0036] This example provides an FCDI wastewater treatment system based on calcium-based biochar, specifically as follows:

[0037] 1. Preparation of calcium-based biochar

[0038] The discarded fish bones and eggshells are washed, dried in an oven at 80 °C for 24 h, and then crushed. The fish bone powder is sieved through a 60-mesh sieve, and the eggshell powder is sieved through a 100-mesh sieve. The sieved fish bone powder is placed in a tubular furnace and pre-carbonized at 700 °C in a nitrogen atmosphere for 2 h with a heating rate of 5 °C / min. The obtained pre-carbonized fish bone powder is pickled with 1 M HCl, washed and filtered until neutral, and then dried in an oven at 80 °C for 24 h. The dried product is fully mixed with the eggshell powder at a mass ratio of 1:0 and 1:3, and then placed in a tubular furnace and calcined at 800 °C in a nitrogen atmosphere for 4 h with a heating rate of 5 °C / min to obtain calcium-based biochar.

[0039] 2. Construction of the FCDI wastewater treatment system

[0040] This system consists of an FCDI reactor, a positive electrode circulation device, a negative electrode circulation device, and a wastewater diversion device. Among them, the FCDI reactor is composed of two organic glass outer plates, two graphene current collector plates, anion and cation exchange membranes, four gaskets, and a DC power supply; the positive electrode circulation device is composed of a flowing electrode positive electrode slurry and a peristaltic pump, which is connected to the positive electrode of the FCDI reactor; the negative electrode is composed of a flowing electrode negative electrode slurry and a peristaltic pump, which is connected to the negative electrode of the FCDI reactor; the wastewater diversion device is a peristaltic pump;

[0041] The flowing electrode positive electrode slurry is a mixed slurry of 1 g of calcium-based biochar and 40 mL of deionized water; the flowing electrode negative electrode slurry is a mixed slurry of 1 g of activated carbon and 40 mL of deionized water.

[0042] To better illustrate the excellent technical effects of the technical solution provided by the present invention, the present invention uses it for wastewater treatment, and the process is as follows:

[0043] 1. The sludge and sewage are electrochemically catalyzed, and then 1.5 mL of concentrated sulfuric acid is added and left standing for 20 min to obtain the phosphorus-releasing liquid wastewater. Then, 100 mL of the phosphorus-releasing liquid wastewater is placed in a storage tank, and the peristaltic pump of the wastewater drainage device is connected.

[0044] 2. Start the FCDI wastewater treatment system to allow the phosphorus-releasing liquid wastewater and the positive and negative slurry of the flow electrode to enter the device. The flow rate of the positive and negative slurry of the flow electrode is 6 mL / min, and the flow rate of the phosphorus-releasing liquid wastewater is 19.5 mL / min.

[0045] 3. Turn on the DC power supply, connect two graphene current collectors, and keep the voltage at a constant 5V. Continuously input the voltage. Then, use a pH meter to measure the pH value in the wastewater storage tank every two hours, and use a 0.45 μm PES syringe filter to take the supernatant of the wastewater storage tank every two hours for filtration and sampling detection. The detection method for total phosphorus is the ammonium molybdate spectrophotometric method for the determination of total phosphorus in water quality (GB 11893-89). The detection instrument for heavy metals is an inductively coupled plasma optical emission spectrometer, and the detection basis is the general rules for inductively coupled plasma atomic emission spectrometry of chemical reagents (GB / T 23942-2009).

[0046] 4. Within 48 h of operation, it is detected that the conductivity and ion concentration of the wastewater remain stable and no longer change, indicating that the ions reach adsorption equilibrium and the electro-adsorption process is completed.

[0047] Through the above steps for treatment, the phosphorus and heavy metals in the wastewater reach adsorption equilibrium within eight hours. Among them, the removal efficiencies of phosphorus, non-heavy metals, and heavy metals are shown in Table 1.

[0048]

[0049] The present invention uses biological bone materials and biological materials of waste gas to prepare an intercalation and deintercalation-type biochar with high efficiency in adsorbing phosphate ions, promoting the resource utilization of waste and reducing the pollution of waste. Further, an FCDI wastewater treatment system is constructed with this biochar material as the positive slurry of the flow electrode, realizing the synchronous removal of phosphorus and heavy metals in the phosphorus-releasing liquid wastewater, greatly reducing the treatment time and cost of waste. Moreover, during the treatment process, heavy metal ions and phosphorus are respectively enriched in the positive, negative, and circulation systems, not only effectively reducing secondary pollution but also facilitating subsequent recycling.

Claims

1. A FCDI wastewater treatment system based on calcium-based biochar, characterized in that: It includes an FCDI reactor, a positive circulation device, a negative circulation device and a wastewater drainage device; the flowing electrode slurry in the positive circulation device is composed of calcium-based biochar and deionized water, and the mass volume ratio of the two is 10-50%; The calcium-based biochar is obtained by calcining bone-based biochar and calcium-containing materials.

2. The FCDI wastewater treatment system based on calcium-based biochar according to claim 1, characterized in that: The flowing electrode slurry in the negative electrode circulation device is composed of activated carbon and deionized water, and the mass volume ratio of the two is 10-50%.

3. The FCDI wastewater treatment system based on calcium-based biochar according to claim 1, characterized in that: The preparation process of the bone-based biochar is as follows: in a protective atmosphere, the biological bone is carbonized and then cooled, and then acid-washed and dried in sequence to obtain the bone-based biochar; the particle size of the bone-based biochar is -60 mesh.

4. The FCDI wastewater treatment system based on calcium-based biochar according to claim 3, characterized in that: The carbonization conditions are as follows: the carbonization temperature is 300-900°C; the time is 1-3 hours; the pickling solution in the pickling process is one of hydrochloric acid, sulfuric acid and nitric acid, with a concentration of 1-3M, and the pickling is performed until neutral.

5. The FCDI wastewater treatment system based on calcium-based biochar according to claim 1, characterized in that: The calcium-containing material is a biomass calcium material containing calcium oxide; the mass ratio of the bone-based biochar to the calcium-containing material is 1:1-3.

6. The FCDI wastewater treatment system based on calcium-based biochar according to claim 5, characterized in that: The calcium-containing material is eggshell powder with a particle size of -100 mesh; the mass ratio of the bone-based biochar to the eggshell powder is 1:

3.

7. The FCDI wastewater treatment system based on calcium-based biochar according to claim 1, characterized in that: The calcination process is as follows: in a protective atmosphere, the bone-based biochar and the calcium-containing material are fully mixed, the temperature is raised to 400-1000° C., and the calcination is performed for 1-5 hours.

8. The use of a calcium-based biochar-based FCDI wastewater treatment system according to claims 1 to 7, characterized in that: Used to remove phosphorus and heavy metal elements from wastewater.

9. The use of a calcium-based biochar-based FCDI wastewater treatment system according to claim 8, characterized in that: The wastewater is phosphorus-release liquid wastewater obtained by acid leaching of sewage sludge after electrochemical phosphorus release catalysis; the process of removing phosphorus and heavy metal elements from the wastewater is: the positive and negative electrode mobile electrode slurries are ultrasonically dispersed and then added to the positive and negative electrode circulation devices respectively, the wastewater drainage device is connected to the wastewater to be treated, and the device is started.

10. The use of a calcium-based biochar-based FCDI wastewater treatment system according to claim 8, characterized in that: The flow ratio of the positive and negative electrode flowing electrode slurries to the wastewater is 4-8:10-15.

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