CN106927571B - A method for enhancing denitrification of constructed wetlands by using modified biochar with strong carbon secretion - Google Patents

Abstract

The invention relates to a method for strengthening constructed wetland denitrification by utilizing strong carbon-secreting modified biochar, which is characterized in that the strong carbon-secreting modified biochar is used as a treating agent to strengthen the constructed wetland for denitrification, the strong carbon-secreting modified biochar is mixed with a matrix and filled into an artificial wetland bed body, or is directly used as a filler column and embedded into the artificial wetland bed body for denitrification, and the strong carbon-secreting modified biochar is obtained by taking wetland plants as raw materials, performing low-temperature dry distillation and then loading ferrous iron; the denitrification treatment temperature is 0-40 ℃, the pH is 6-8, and the total nitrogen content of the constructed wetland sewage is 5-60 mg/L. The invention utilizes strong carbon-secreting modified biochar to strengthen the denitrification of the constructed wetland, and obtains unexpected effect, when in application, Fe (II) can be used as an electron donor to transfer electrons to high-valence nitrogen (such as NO) through simple and convenient loading of Fe (II)₃ ^‑，NO₂ ^‑) The nitrogen in high valence state can be reduced into nitrogen while being oxidized, so that the chemical denitrification process is realized, and the high-efficiency denitrification is realized.

Description

A method for enhancing denitrification of constructed wetlands by using modified biochar with strong carbon secretion

technical field

The invention relates to a method for denitrification of artificial wetlands, in particular to a method for strengthening the chemistry of artificial wetlands and microbial denitrification and denitrification by using modified biochar with strong carbon secretion, and belongs to the technical field of environmental engineering sewage treatment

Background technique

As a unique composite ecological sewage treatment technology composed of plants, substrates, microorganisms, etc., constructed wetlands have outstanding application advantages in the advanced treatment of sewage treatment plants in developing regions. One of the emerging methods. However, due to the low carbon-to-nitrogen ratio and high nitrate nitrogen content in the up-to-standard tail water, the denitrification and denitrification effect of constructed wetlands is often inhibited. In addition, the area of wetland plant biomass produced in my country every year reaches more than 50 million hectares. Except for a part of wetland plants that are ingested by wetland animals and enter the biological chain, most plants directly wither and die. If a large number of wetland plants are not removed in time, they will become corrupt. After decomposing, it is released into the wetland water again, and in some places even incineration is adopted, which affects the quality of the atmospheric environment. The lack of high-value resource technology leads to huge waste of resources and potential secondary pollution risks.

With the increasingly stringent emission standards of total nitrogen in sewage, how to organically combine the efficient denitrification and denitrification of constructed wetlands with the utilization of plant resources is an urgent problem to be solved. There are studies that directly bury wetland plants into wetlands to provide carbon sources, but it is difficult to control the decay time of plants, and it is very easy to block the wetlands and increase the chromaticity of the effluent. A method and system for denitrification of low-carbon and high-nitrogen sewage by constructed wetlands. It uses plant hydrolyzate as a wetland organic carbon source to enhance the denitrification efficiency of sewage. maximum utilization.

Biochar is a kind of carbon-rich, tightly packed lamellar porous environmental functional material produced by carbonization of biomass in a low-oxygen environment. In recent years, biochar has shown great application potential in the reduction of greenhouse gas N ₂ O, soil improvement and remediation, and pollutant adsorption, and has received extensive attention. The preparation of biochar is simple and requires no activation, and the cost is only about 1/6 of that of activated carbon. The introduction of biochar into the constructed wetland system can provide a potential solution for the simultaneous utilization of plant resources and the improvement of wetland effects.

Chinese patent document CN 104761057A discloses a biochar modular composite vertical flow constructed wetland system, the concept of adding biochar to the vertical flow constructed wetland, but the patent does not specifically propose a biochar preparation method, biochar carbon source release Characteristics and mechanisms of microbial-biochar denitrification. Currently, biochar is mostly used as an adsorbent or soil conditioner, and the application of denitrification to enhance denitrification is rarely reported. Currently, biochar is mostly prepared at high temperature, and most organic matter is gasified, so its ability to provide carbon sources is extremely limited. Therefore, it is of great significance to develop a new type of high-carbon-secreting wetland substrate to achieve efficient utilization of wetland plant resources while promoting the denitrification and denitrification effect of wetlands.

SUMMARY OF THE INVENTION

Aiming at the deficiencies of the prior art, the present invention provides a method for strengthening the denitrification of constructed wetlands by using the modified biochar with strong carbon secretion, which has high treatment efficiency.

The present invention is achieved through the following technical solutions:

A method for strengthening the denitrification of constructed wetlands by using the modified biochar with strong carbon emission type, the modified biochar with strong carbon emission type is used as a treatment agent to strengthen the constructed wetland for denitrification and denitrification, and the modified biochar with strong carbon emission type is combined with a substrate. It is mixed and filled into the constructed wetland bed body, or directly embedded in the constructed wetland bed body as a packing column, and the strong carbon-secreting modified biochar is obtained by using wetland plants as raw materials, and after low-temperature dry distillation and then loading ferrous iron; The denitrification and denitrification treatment temperature is 0-40℃, the pH is 6-8, and the total nitrogen content of the constructed wetland sewage is 5-60mg/L.

Preferably in the present invention, the denitrification and denitrification treatment temperature is 10-30° C., the pH is 6-7, and the total nitrogen content of the constructed wetland sewage is 20-40 mg/L.

Preferably in the present invention, the volume ratio of the strong carbon-secreting modified biochar and the matrix is 1:20 to 1:2, and further preferably, the volume ratio of the strong carbon-secreting modified biochar and the matrix is 1:10 ~1:3, most preferably, the volume ratio of the mixture of the strong carbon-secreting modified biochar and the substrate is 1:3.

Preferably in the present invention, the matrix is one or a mixture of two or more of gravel, construction waste bricks or quartz sand.

Preferably in the present invention, the total coverage area of the strong carbon-secreting modified biochar mixed with the matrix accounts for 1/3 to 2/3 of the total area of the wetland, and the porosity of the strong carbon-secreting modified biochar mixed with the matrix is filled. is 20-50%; preferably, the porosity after the strong carbon-secreting modified biochar is mixed and filled with the matrix is 30-40%.

Preferably in the present invention, as a packing column directly, the biochar is filled into the packing column, and then the packing column is vertically embedded in the constructed wetland bed, and the ratio of the total volume of the biochar to the wetland volume is 1:20 to 1:4; the The packing column is a perforated column, the pore diameter is 0.5-1 cm, and the porosity is 40%-80%.

Further preferably, the covered area of the packing column accounts for 1/20 to 2/3 of the wetland surface area.

Preferably in the present invention, the described strong carbon secretion type modified biochar is prepared by the following method:

(1), take wetland plants as raw materials, wash the wetland plants, pulverize them into blocks with a diameter of 1-3 cm, and air-dry to constant weight;

(2), under the protection of inert gas, the wetland plants treated in step (1) are rapidly carbonized at low temperature by dry distillation to obtain biochar; the dry distillation temperature is 250～400 ℃, and the heating rate is 5 ～10℃/min, dry distillation time 30～60min;

(3), loading modification treatment: mix the biochar obtained in step (2) with 0.5-3 mol/L ferrous chloride solution, let stand for 12-16 hours to load ferrous, and the loaded biochar is used for Ionized water was washed to neutrality, and then dried in an anaerobic environment at 100-120 °C for 6-12 hours to obtain modified biochar with strong carbon secretion.

Preferably in the present invention, the raw materials in step (1) are the roots or stems of wetland plants.

Preferably in the present invention, the wetland plants in step (1) are one or a mixture of two or more of the commonly used plants in wetlands such as reed bamboo, water brocade, and willow.

Preferably in the present invention, the inert gas described in step (2) is nitrogen.

Preferably in the present invention, the dry distillation temperature in step (2) is 250-300° C., the heating rate is 5-8° C./min, and the dry distillation time is 40-60 min.

Most preferably, the dry distillation temperature in step (2) is 300° C., the heating rate is 5-8° C./min, and the dry distillation time is 60 minutes.

Preferably in the present invention, the concentration of the ferrous chloride solution in step (3) is 1-3 mol/L, and most preferably, the concentration of the ferrous chloride solution is 3 mol/L.

Preferably in the present invention, the load time of step (3) is 12h.

Preferably in the present invention, step (3) anaerobic drying temperature is 100-110°C and drying time is 8-12h, most preferably, step (3) anaerobic drying temperature is 105°C and drying time is 12h.

The present invention achieves an unexpected effect by using the strong carbon-secreting modified biochar to strengthen the denitrification of the constructed wetland.

The raw materials and equipment used in the present invention are all in the prior art.

Compared with the prior art, the present invention has the following advantages:

(1) The present invention achieves unexpected effects by using strong carbon-secreting modified biochar to strengthen the denitrification of constructed wetlands. During application, by simply loading Fe(II), Fe(II) can be used as an electron donor to transfer electrons It is transferred to high-valent nitrogen (such as NO ₃ ^- , NO ₂ ^- ), and the high-valent nitrogen can be reduced to nitrogen while being oxidized to realize the chemical denitrification and denitrification process. At the same time, microorganisms can also use ferrous and nitrate as electron donor and acceptor, respectively, to oxidize ferrous iron to ferric iron, and at the same time reduce nitrate, so as to convert NO ₃ ^- into N ₂ . In addition, when the NO ₃ ^- in the reaction system is consumed, the microorganisms can also reduce Fe(III) to Fe(II) by utilizing the organic matter released by the biochar, thereby realizing the iron-nitrogen redox cycle.

(2) The strong carbon-secreting modified biochar used in the present invention is prepared by dry distillation at low temperature, and its organic carbon dissolution capacity is much higher than that of biochar prepared at current high temperature (>400°C). Fig. 1 is the organic carbon dissolution curve of the reed bamboo biochar prepared by dry distillation method at different temperatures, it can be seen from the figure that the reed bamboo biochar prepared at low temperature 300 ℃ carries out the organic carbon dissolution determination according to the ratio of 1:20 with deionized water , its organic carbon concentration is as high as 135mg/L (2700mg/kg), which is nearly three times the COD effluent concentration (50mg/L) of the first-class A standard of the sewage treatment plant. Therefore, for the enhanced denitrification of low-carbon nitrogen ratio wastewater, the Some organic carbon will play an important role. With the increase of temperature, the amount of organic carbon dissolved in biochar is greatly reduced, so the effect of high temperature biochar on releasing carbon source and promoting denitrification is very limited.

(3) A large number of reports show that biochar can alleviate the release of greenhouse gas N ₂ O in the soil. In the present invention, the strong carbon-secreting modified biochar is applied to the deep denitrification treatment of constructed wetland sewage, which not only plays a role in carbon sequestration and emission reduction It can also alleviate the N ₂ O release from constructed wetlands by promoting the denitrification process.

The invention improves the efficiency of denitrification and denitrification in sewage with a low-carbon nitrogen ratio in a simple method, and at the same time provides a reference for solving the problem of plant resource utilization in situ. It is of great significance to improve the quality of total nitrogen and alleviate the global greenhouse effect.

Description of drawings

Fig. 1 is a graph of the organic carbon concentration of biochar dissolved at different temperatures;

Figure 2 is a schematic structural diagram of the strong carbon-secreting modified biochar used in the present invention.

FIG. 3 is a schematic structural diagram of a horizontal subsurface wetland in the method for strengthening denitrification of a constructed wetland according to the present invention.

In the figure: 1. Water inlet, 2. Packing column, 3. Strong carbon-secreting modified biochar matrix, 4. Wetland main matrix, 5. Water outlet, 6. Wetland plants, 7. Wetland bed.

Figure 4 is a bar graph showing the effect of different strong carbon-secreting modified biochar additions on total nitrogen removal.

Detailed ways

The present invention will be further described below through specific embodiments, but not limited thereto.

Example 1

A method for strengthening the denitrification of constructed wetlands by using the modified biochar with strong carbon secretion type, the modified biochar with strong carbon secretion type is used as a treatment agent to strengthen the constructed wetland for denitrification and denitrification, and the specific method is as follows:

The biochar is filled into the packing column, and then the packing column is vertically embedded in the bed of the constructed wetland, and the ratio of the total volume of the biochar to the wetland volume is 1:6; The rate is 40% to 80%. The packing column is round or square, and when the packing column is square, the width of the packing column is the same as that of the wetland, and a detachable sealing plug is arranged on the top of the packing column, which is used to seal the packing column or replace the biochar packing in the present invention. The coverage area of the packed column accounts for 1/20 to 2/3 of the wetland surface area. The horizontal subsurface wetland is composed of a pool body 7, wetland plants 6, a wetland main body matrix 4, a packing column 2, and a wetland strong carbon-secreting modified biochar 3, as shown in Figure 3. The wetland main matrix filler is one or any combination of gravel, construction waste bricks, and fly ash, and 15cm of coarse sand or quartz sand is laid on the top.

The specific working process of the above-mentioned vertical flow wetland is as follows:

It operates in the mode of continuous water inflow and push-out water. After the high-nitrate sewage enters the wetland bed 7 evenly through the water distribution pipeline, and the nitrate nitrogen in the influent is in contact with the biochar packing column of the present invention, on the one hand, the strong carbon-secreting biochar of the present invention The denitrifying microbial denitrification in sewage is directly promoted by releasing organic carbon sources; on the other hand, the modified biochar in the present invention transfers electrons to high-valent nitrogen (such as NO ₃ ⁻ , NO ₂ ^- ), while being oxidized, it can reduce high-valence nitrogen to nitrogen to realize chemical denitrification and denitrification process; at the same time, denitrifying microorganisms also use ferrous and nitrate as electron donors and acceptors, respectively. Ferrous iron is oxidized to ferric iron, while nitrate is reduced, converting NO ₃ ^- to N ₂ . The treated water is discharged from the wetland through an outlet.

The strong carbon-secreting modified biochar is prepared as follows:

(1) Take the Wetland plant reed bamboo root of the wetland plant, wash and chop it into a block with a diameter of 1-3 cm, air-dry, and air-dry to constant weight.

(2), under nitrogen protection, the wetland plants treated in step (1) are subjected to rapid carbonization at low temperature by dry distillation to obtain biochar; the dry distillation temperature is 300 ° C, and the heating rate is 8 ° C/min , dry distillation time 60min;

(3), loading modification treatment: mix the biochar obtained in step (2) with 3 mol/L ferrous chloride solution, let stand for 12h to load ferrous, and wash the loaded biochar with deionized water to Neutral, and then dried in an anaerobic environment at 105 °C for 12 h to obtain modified biochar with strong carbon secretion, as shown in Figure 2.

Example 2

A method for strengthening the denitrification of constructed wetlands by utilizing strong carbon-secreting modified biochar, the same as in Embodiment 1, the difference is:

The strong carbon-secreting modified biochar and the matrix were mixed and filled into the constructed wetland bed for enhanced denitrification. The volume ratio of the strong carbon-secreting modified biochar to the matrix was 1:3, and the coverage area of the mixed filler accounted for 30% of the total wetland area. 1/3 to 2/3. The other structures are the same as in Example 2, and the sewage flows out of the tank from the water outlet after being purified by deep denitrification and denitrification in the wetland.

Application experiment example

1. Carry out the application experiment of the method of using strong carbon-secreting modified biochar to strengthen the denitrification of the constructed wetland in Example 1 and Example 2, respectively. Nitrate sewage simulated wastewater, the total nitrogen content of the influent water was 25mg/L, the pH of the influent water was 7, the influent water load was 10L/h, and the denitrification treatment was carried out at an ambient temperature of 8 to 10 °C. Without biochar for comparison, under the condition of HRT (hydraulic retention time) for 5 days, the total nitrogen removal rate can reach 88%, and the total nitrogen content in the effluent is less than 8mg/L. The effect of nitrogen removal is shown in Figure 4. It can be seen from Figure 4 that the treatment effect of the modified biochar with strong carbon secretion is about 30%.

Claims (10)

1. A method for strengthening constructed wetland denitrification by using strong carbon-secreting modified biochar comprises the steps of using the strong carbon-secreting modified biochar as a treating agent to strengthen the constructed wetland for denitrification, mixing the strong carbon-secreting modified biochar with a matrix and filling the mixture into a constructed wetland bed body, or directly using the mixture as a filler column to be embedded into the constructed wetland bed body for denitrification, wherein the denitrification treatment temperature is 0-40 ℃, the pH value is 6-8, and the total nitrogen content of constructed wetland sewage is 5-60 mg/L;

the strong carbon-secreting modified charcoal is prepared by the following method:

(1) cleaning wetland plants serving as raw materials, crushing the wetland plants into blocks with the diameter of 1-3 cm, and air-drying the blocks to constant weight;

(2) carrying out rapid carbonization treatment on the wetland plants treated in the step (1) at a low temperature in a dry distillation mode under the protection of inert gas to obtain biochar; the dry distillation temperature is 250-400 ℃, the heating rate is 5-10 ℃/min, and the dry distillation time is 30-60 min;

(3) and load modification treatment: and (3) mixing the biochar prepared in the step (2) with 0.5-3 mol/L ferrous chloride solution, standing for 12-16 h for carrying ferrous, washing the carried biochar with deionized water to be neutral, and drying in an anaerobic environment at 100-120 ℃ for 6-12 h to obtain the strong carbon-secreting modified biochar.

2. The method for enhancing denitrification of the artificial wetland by using the strong carbon-secreting modified biochar as claimed in claim 1, wherein the denitrification treatment temperature is 10-30 ℃, the pH value is 6-7, and the total nitrogen content of the sewage of the artificial wetland is 20-40 mg/L.

3. The method for enhancing denitrification of the constructed wetland by using strong carbon-secreting modified biochar according to claim 1, wherein the volume ratio of the mixture of the strong carbon-secreting modified biochar and the matrix is 1: 10-1: 3.

4. The method for enhancing denitrification of the constructed wetland by using the strong carbon-secreting modified biochar as claimed in claim 1, wherein the matrix is one or a mixture of more than two of gravel, building waste bricks or quartz sand.

5. The method for enhancing denitrification of the artificial wetland by using the strong carbon-secreting modified biochar as claimed in claim 1, wherein the total coverage area of the strong carbon-secreting modified biochar mixed with the substrate accounts for 1/3-2/3 of the total area of the wetland, and the porosity of the strong carbon-secreting modified biochar mixed with the substrate is 20-50%.

6. The method for enhancing denitrification of the artificial wetland by using the strong carbon-secreting modified biochar as claimed in claim 1, wherein the biochar is directly used as a filler column, the biochar is filled into the filler column, then the filler column is vertically embedded into an artificial wetland bed body, and the ratio of the total volume of the biochar to the volume of the wetland is 1: 20-1: 4; the filler column is a perforated column, the aperture is 0.5-1 cm, and the aperture ratio is 40% -80%.

7. The method for enhancing denitrification of the artificial wetland by using the strong carbon-secreting modified biochar as claimed in claim 1, wherein the covering area of the filler columns accounts for 1/20-2/3 of the surface area of the wetland.

8. The method for enhancing the denitrification of the artificial wetland by using the strong carbon-secreting modified biochar as claimed in claim 1, wherein the root or stem of the wetland plant is selected as the raw material in the step (1).

9. The method for enhancing the denitrification of the artificial wetland by using the strong carbon-secreting modified biochar as claimed in claim 1, wherein the inert gas in the step (2) is nitrogen; the dry distillation temperature is 250-300 ℃, the heating rate is 5-8 ℃/min, and the dry distillation time is 40-60 min.

10. The method for enhancing denitrification of the constructed wetland by using the strong carbon-secreting modified biochar as claimed in claim 1, wherein the concentration of the ferrous chloride solution in the step (3) is 1-3 mol/L, the load time of the step (3) is 12 hours, the anaerobic drying temperature of the step (3) is 100-110 ℃, and the drying time is 8-12 hours.

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