A method for treating biogas slurry by low-temperature catalytic air oxidation

Abstract

The present invention discloses a method for treating biogas slurry by low-temperature catalytic air oxidation, which includes: S1. Immerse the pretreated ceramic particles and ceramic membranes in a metal salt solution, and then dry and calcine them to obtain catalytic ceramic particles and catalytic ceramic membranes loaded with metal oxides; S2. Place the catalytic ceramic particles and the catalytic ceramic membranes in a reactor, introduce biogas slurry and air, and control an appropriate gas-water ratio and hydraulic retention time to carry out a catalytic oxidation reaction; S3. After the reaction is completed, discharge the gas, and the liquid is discharged after being filtered by the catalytic ceramic membrane to obtain purified biogas slurry.

Description

Technical Field

[0001] The present invention relates to the field of wastewater treatment, specifically to a method for purifying biogas slurry, especially a method for catalytic air oxidation of biogas slurry at low temperature. Background Art

[0002] Anaerobic digestion is the main method for the resource treatment of organic waste. Through the action of anaerobic microorganisms, organic matter is converted into biogas, which can be used for heat production and power generation. A large amount of biogas slurry remains after anaerobic digestion. Although it has the potential to be used as organic liquid fertilizer, for large-scale anaerobic digestion treatment facilities, the biogas slurry volume is large and cannot be consumed nearby, so it must be purified before discharge. The chemical oxygen demand (COD) and ammonia nitrogen concentration of biogas slurry are high, especially containing some refractory organic pollutants such as humic acid and lignocellulose. At present, biogas slurry is mainly treated by the combined method of physical and chemical methods and biochemical methods. First, coagulation precipitation or air flotation separation is carried out to remove particulate matter and part of COD, and then it enters the traditional anaerobic-anoxic-aerobic (AAO) or membrane bioreactor (MBR) for treatment. The biochemical effluent also needs to be finally purified through various membrane separation, activated carbon and advanced oxidation technologies to meet the effluent water quality standard. The above process is relatively complex, easily affected by the fluctuation of biogas slurry properties, with insufficient treatment efficiency, more chemical agent consumption and higher treatment cost.

[0003] Compared with the traditional treatment process, wet air oxidation (WAO) can utilize molecular oxygen (air or pure oxygen) to oxidize and degrade organic matter in wastewater under the action of a catalyst. However, this process requires relatively high temperature (200 - 260 °C) and operating pressure (1.5 - 6 MPa), with high equipment cost and operating cost, making it difficult to be applied on a large scale. Using a catalyst to form catalytic wet air oxidation (CWAO) can accelerate the reaction process and reduce the reaction conditions. However, at present, there is a lack of mature, stable and efficient catalysts, and there is also a lack of specific methods for combining catalysts with WAO. Summary of the Invention

[0004] In view of this, the present invention provides a method for catalytic air oxidation of biogas slurry at low temperature to overcome the problems existing in the above prior art.

[0005] A method for catalytic air oxidation of biogas slurry at low temperature includes the following steps: S1. Immerse the pretreated ceramic particles and ceramic membranes in a metal salt solution, and then dry and calcine them to obtain catalytic ceramic particles and catalytic ceramic membranes loaded with metal oxides;

[0006] S2. Place the catalytic ceramic particles and the catalytic ceramic membranes in a reactor, introduce biogas slurry and air, and control an appropriate gas-liquid ratio and hydraulic retention time to carry out catalytic oxidation reaction; S3. After the reaction is completed, discharge the gas, and the liquid is discharged after being filtered by the catalytic ceramic membranes to obtain purified biogas slurry.

[0007] Furthermore, the ceramic membrane and the ceramic particles are made of α-Al 2 O 3 as the internal filling material, and the oxides of Ti and / or Zr are used as the support material.

[0008] Furthermore, the particle size of the ceramic particles is 5 mm to 20 mm, with a hollow interior, and the surface of the shell is a porous structure with a pore diameter of 2 mm to 5 mm; the ceramic membrane has nano-scale pores with an average pore diameter of 50 nm to 200 nm and a total porosity of 30% to 60%.

[0009] Furthermore, the pretreatment steps of the ceramic particles and the ceramic membrane include: first, cleaning the ceramic particles and the ceramic membrane with a weak acid or weak base, soaking them in deionized water, then drying them at 80 - 120 °C for 2 - 4 h, and finally calcining them in an air atmosphere at 600 - 700 °C for 3 - 4 h, with a heating rate of 5 °C / min during calcination.

[0010] Furthermore, the metal ions in the metal salt solution are one or more of copper ions, iron ions, cobalt ions, nickel ions, and manganese ions, and the salt ions are Cl - .

[0011] Furthermore, the total concentration of the metal salt solution is 0.5 mol / L to 2 mol / L.

[0012] Furthermore, in step S1, the pretreated ceramic particles and ceramic membrane are first impregnated in the metal salt solution for 12 - 24 h, then dried at 80 - 120 °C for 2 - 4 h, and finally calcined in an air atmosphere at 600 - 700 °C for 3 - 4 h.

[0013] Furthermore, the catalytic ceramic particles loaded with metal oxides are the main reaction sites for the catalytic oxidation reaction; the catalytic ceramic membrane loaded with metal oxides serves as a filtration and water outlet device, and simultaneously further catalyzes the oxidation of the residual small-molecule organic substances after decomposition.

[0014] Furthermore, the catalytic oxidation reaction in step S2 is carried out under normal pressure and at a temperature below 100 °C.

[0015] Furthermore, in step S2, the gas-water ratio is controlled to be 3.5 - 7.0 L / g COD, and the hydraulic retention time is 1 - 5 h.

[0016] Compared with the existing wet air oxidation technology, in the present invention, special metal oxides are loaded on the surfaces of ceramic particles and ceramic membranes as catalysts, and then a packed-bed reactor is constructed. In the case where the catalytic ceramic particles are used as the main catalytic oxidation reaction, at the same time, the ceramic membrane is used to intercept ceramic particles and macromolecular organic matters (such as humic acid) from the effluent, increasing the catalytic oxidation degradation time of the latter, and finally mineralizing small-molecular organic pollutants (such as acetone and acetic acid). This low-temperature catalytic air oxidation method (LTCAO) proposed by the present invention can use air or oxygen as the oxidant to mineralize organic pollutants through surface reactions and free radical reactions, accelerating the reaction between oxygen and organic matter under low-temperature and normal-pressure conditions, without the need for other advanced oxidants such as ozone and persulfate, realizing the green and economical treatment of biogas slurry, and having many advantages such as fast reaction speed, wide application range, clean and safe process, and low treatment cost. Without a complex biochemical treatment process and without using special oxidation agents, only the oxygen in the air can be used to oxidize and degrade various organic pollutants in biogas slurry. The process is simple, the reaction is rapid, the conditions are mild, and the weather resistance is strong, and it can be used for the purification of biogas slurry and other high-concentration organic wastewater. Detailed implementation manners

[0017] The present invention will be further described below in conjunction with specific implementation manners.

[0018] The specific implementation manner of the present invention provides a method for treating biogas slurry by low-temperature catalytic air oxidation, including the following steps S1 to S3:

[0019] Step S1: Immerse the pretreated ceramic particles and ceramic membranes in a metal salt solution, and then dry and calcine them to obtain catalytic ceramic particles and catalytic ceramic membranes loaded with metal oxides.

[0020] In some embodiments, the ceramic membrane and ceramic particles use α-Al 2 O 3 as the internal filling material, and oxides of Ti and / or Zr as the support material; the particle size of the ceramic particles is 5 mm to 20 mm, the inside is hollow, the surface of the shell is a porous structure, and the pore diameter is 2 mm to 5 mm; the ceramic membrane has nanoscale pores, the average pore diameter is 50 nm to 200 nm, and the total porosity is 30% to 60%.

[0021] The metal ions in the metal salt solution are one or more of copper ions, iron ions, cobalt ions, nickel ions, and manganese ions. Correspondingly, the metal oxides are one or more of copper oxides, iron oxides, cobalt oxides, nickel oxides, and manganese oxides, and the salt ions are Cl - ; the total concentration of the metal salt solution is 0.5 mol / L to 2 mol / L.

[0022] Among them, the pretreatment process of the ceramic particles and the ceramic membrane includes: First, the ceramic particles and the ceramic membrane are cleaned with weak acid or weak base and soaked in deionized water, then dried at 80 - 120 °C for 2 - 4 h, and finally calcined in air atmosphere at 600 - 700 °C for 3 - 4 h, with a heating rate of 5 °C / min during calcination. The pretreated ceramic particles and ceramic membrane are first impregnated in the metal salt solution for 12 - 24 h, then dried at 80 - 120 °C for 2 - 4 h, and finally calcined in air atmosphere at 600 - 700 °C for 3 - 4 h to obtain catalytic ceramic particles and catalytic ceramic membranes with metal oxides loaded on the surface and / or in the pores.

[0023] Step S2: Place the catalytic ceramic particles and the catalytic ceramic membrane in a reactor, introduce biogas slurry and air, control the gas-liquid ratio (the ratio of air to biogas slurry) to be 3.5 - 7.0 L / g COD, and the hydraulic retention time to be 1 - 5 h, and carry out catalytic oxidation reaction.

[0024] The reaction process of step S2 is carried out under normal pressure and low temperature (below 100 °C), where the catalytic ceramic particles loaded with metal oxides are the main reaction sites for the catalytic oxidation reaction; the catalytic ceramic membrane loaded with metal oxides serves as a filtration and effluent device, and at the same time further catalyzes the oxidation of the residual small-molecule organic substances after decomposition.

[0025] Step S3: After the reaction is completed, the gas is discharged from the top of the reactor, and the liquid is discharged after being filtered by the catalytic ceramic membrane to obtain purified biogas slurry.

[0026] Example 1

[0027] Use titanium-zirconium oxide ceramic pellets and tubular ceramic membranes as carriers. The ceramic membrane uses α - Al 2 O 3 as the internal filling material and ZrO 2 as the support material. The ceramic particles and the ceramic membrane are soaked in deionized water for 2 h, dried in an oven at 120 °C for 2 h and calcined at 600 °C for 2 h after cleaning. The ceramic particles used are hollow porous zirconium-titanium oxide spheres with a diameter of 1 cm, and the ceramic membrane is a tubular ceramic membrane with a length of 25 cm, a diameter of 4 cm, a pore size of 200 nm, and 19 channels. The ceramic particles and the ceramic membrane after the above treatment are immersed in a 1 mol / L copper chloride solution, taken out after 24 h, dried in an oven at 120 °C for 2 h and calcined at 700 °C for 4 h (heating rate is 5 °C / min) to obtain Cu 3 O 4Catalytic ceramic particles and catalytic ceramic membranes of metal oxide nanoclusters such as etc. The catalytic ceramic particles and catalytic ceramic membranes are placed in a cylindrical reactor, where the catalytic ceramic particles fill the reactor, and the catalytic ceramic membrane is arranged at the center of the upper part of the cylindrical reactor. An inlet and an annular aeration head are provided at the bottom of the reactor. The treatment object is simulated biogas slurry, the main component of which is humic acid and the COD is 1000 mg / L. After the biogas slurry enters the reactor, it flows upward through the catalytic ceramic particles. At the same time, air enters the reactor in the form of microbubbles through the aeration head and also moves upward. The two react on the surface of the catalytic ceramic particles under the catalytic action of the catalyst (metal oxide), and the organic pollutants are oxidized and degraded. In the upper part of the reactor, unreacted oxygen, nitrogen, and generated carbon dioxide and other gases are discharged from the top discharge port. The treated biogas slurry is filtered through a tubular ceramic membrane to become the effluent. The reaction temperature in the reactor is set at 90 °C, under normal pressure conditions, the hydraulic retention time is 1 h, the gas-water ratio is 6.0 L / g COD, and the final COD removal rate reaches 90%.

[0028] The above content is a further detailed description of the present invention in combination with specific preferred embodiments. It cannot be determined that the specific implementation of the present invention is only limited to these descriptions. For those skilled in the technical field to which the present invention belongs, without departing from the concept of the present invention, several equivalent substitutions or obvious variations can be made, and as long as the performance or use is the same, they should all be regarded as belonging to the protection scope of the present invention.

Claims

1. A method for treating biogas slurry by low-temperature catalytic air oxidation, characterized in that, it includes the following steps: S1. Immerse the pre-treated ceramic particles and ceramic membrane in a metal salt solution, followed by drying and calcination to obtain catalytic ceramic particles and a catalytic ceramic membrane loaded with metal oxides; wherein, the ceramic membrane and the ceramic particles are made of α-Al 2 O 3 is the internal filling material, and oxides of Ti and / or Zr are the supporting materials; S2. Load metal oxides on the surfaces of ceramic particles and ceramic membranes as catalysts, construct a packed-bed reactor, place the catalytic ceramic particles and the catalytic ceramic membrane in the reactor, and introduce biogas slurry and air, and control an appropriate gas-water ratio and hydraulic retention time to carry out catalytic oxidation reaction; wherein: the catalytic ceramic particles loaded with metal oxides are the main reaction sites for the catalytic oxidation reaction; the catalytic ceramic membrane loaded with metal oxides serves as a filtering and effluent device, and simultaneously further catalytically oxidizes the residual small-molecule organic substances after decomposition; The catalytic oxidation reaction described in step S2 is carried out under normal pressure and at a temperature lower than 100 °C; S3. After the reaction is completed, the gas is discharged, and the liquid is discharged after being filtered by the catalytic ceramic membrane to obtain purified biogas slurry.

2. The method for treating biogas slurry by low-temperature catalytic air oxidation according to claim 1, characterized in that: The particle size of the ceramic particles is 5 mm to 20 mm, the inside is hollow, the surface of the shell is a porous structure, and the pore diameter is 2 mm to 5 mm; the ceramic membrane has nano-scale pores, the average pore diameter is 50 nm to 200 nm, and the total porosity is 30% to 60%.

3. The method for treating biogas slurry by low-temperature catalytic air oxidation according to claim 1, characterized in that, The pretreatment steps of the ceramic particles and the ceramic membrane include: First, the ceramic particles and the ceramic membrane are cleaned with weak acid or weak base and soaked with deionized water, then dried at 80-120 °C for 2 h-4 h, and finally calcined in an air atmosphere at 600-700 °C for 3 h-4 h, and the heating rate of the calcination is 5 °C / min.

4. The method for treating biogas slurry by low-temperature catalytic air oxidation according to claim 1, characterized in that: The metal ions in the metal salt solution are one or more of copper ions, iron ions, cobalt ions, nickel ions, and manganese ions, and the salt ions are Cl - .

5. The method for treating biogas slurry by low-temperature catalytic air oxidation according to claim 1 or 4, characterized in that: The total concentration of the metal salt solution is 0.5 mol / L to 2 mol / L.

6. The method for treating biogas slurry by low-temperature catalytic air oxidation according to claim 1, characterized in that: In step S1, the pretreated ceramic particles and ceramic membrane are first impregnated in the metal salt solution for 12 h-24 h, then dried at 80-120 °C for 2 h-4 h, and finally calcined in an air atmosphere at 600-700 °C for 3 h-4 h.

7. The method for treating biogas slurry by low-temperature catalytic air oxidation according to claim 1, characterized in that: In step S2, the gas-water ratio is controlled to be 3.5-7.0 L / g COD, and the hydraulic retention time is 1-5 h.