CN118026388A - Denitrifying biological filler based on iron-carbon micro-electrolysis and preparation method and application thereof - Google Patents

Abstract

The invention discloses a denitrification biological filler based on iron-carbon micro-electrolysis, a preparation method and application thereof, belonging to the technical field of sewage treatment; then adding sulfur powder, stirring at the melting point temperature of sulfur to enable sulfur and iron carbon particles to be tightly and uniformly combined, granulating and cooling after adding an adhesive to obtain spherical composite filler, wherein a microscopic level is a structure of sulfur molecules coated with elemental iron-activated carbon, and adding the filler and related autotrophic bacteria into nitrate nitrogen wastewater to be treated to form a coupling denitrification system. According to the invention, the iron-carbon micro-electrolysis reaction is introduced, so that the anaerobic ammonia oxidation and the sulfur autotrophic denitrification can be coupled in a faster and better integrated manner, the denitrification efficiency of the system is improved, and the system has stronger buffering capacity.

Description

A denitrification biological filler based on iron-carbon micro-electrolysis and its preparation method and application

Technical Field

The invention belongs to the technical field of sewage treatment, and in particular relates to a denitrification biological filler based on iron-carbon micro-electrolysis, and a preparation method and application thereof.

Background technique

In recent years, with the continuous acceleration of urbanization and industrialization, water environment problems have become increasingly prominent, and the eutrophication problem caused by excessive N and P in water bodies has become increasingly prominent, and new denitrification processes are urgently needed. The sulfur autotrophic denitrification process with sulfur source (such as elemental sulfur) as electron donor has the advantages of short process flow, no need for organic carbon source, low investment and operation costs, etc., and there are many research precedents at home and abroad; under the action of sulfur autotrophic denitrification functional bacteria, nitrate is preferentially reduced to nitrite as an electron acceptor and accumulated. This process is called sulfur autotrophic short-range denitrification. This part of the accumulated nitrite can participate in the anaerobic ammonia oxidation reaction as a substrate, and then the nitrite is reduced to nitrogen gas by sulfur. The reaction formula is as follows:

S ⁰ +3NO ₃ ^- +H ₂ O→SO ₄ ^2- +3NO ₂ ^- +2H ⁺ (1)

S ⁰ + 2NO ₂ ⁻ →SO ₄ ²⁻ + N ₂ (2).

The anaerobic ammonium oxidation (ANAMMOX) autotrophic denitrification reaction, which uses ammonia as an inorganic electron donor for nitrite denitrification, has been one of the hot topics in the field of biological denitrification in recent years because it can greatly save the power consumption of aerobic ammonium oxidation. The reaction formula is:

NH ₄ ⁺ +1.32NO ₂ ^- +0.066HCO ₃ ^- +0.13H ⁺ →1.02N ₂ +0.26NO ₃ ^- +0.066CH ₂ O _0.5 +2.03H ₂ O(3);

However, the Anammox process is limited in its application in actual engineering due to factors such as long reactor startup time, low cell yield, inhibition by high-concentration substrates, imbalance of influent NH ₄ ⁺ /NO ₂ ^- , and high sensitivity to the external environment. Iron-carbon micro-electrolysis technology is an electrochemical water purification technology that also has very broad application prospects in the denitrification level. It is often combined with other denitrification technologies to treat nitrogen in various wastewaters. It can not only maintain the pH stability of the system, but the iron ions produced can also promote cell growth and shorten the startup time of the reactor. The reaction formula is:

NO ₃ ^- +4Fe ⁰ +7H ⁺ →NH ₄ ⁺ +4Fe ²⁺ +3OH ^- (4)

2NO ₃ ^- +5Fe ⁰ +6H ₂ O→N ₂ +5Fe ²⁺ +12OH ^- (5)

At present, in the field of wastewater treatment, the coupling of the above technologies has been reported. For example, CN 115650426 A discloses an efficient denitrification process based on micro-electrolysis waste iron mud-based filling materials. The process uses micro-electrolysis waste iron mud as raw materials to make TF materials and TN materials, respectively providing the Feammox reaction zone and NDFO reaction zone with their respective iron sources, and the effluent of the Feammox reaction zone is the inlet of the NDFO reaction zone; by coupling the Feammox reaction with the NDFO reaction, after two biological denitrifications, efficient denitrification treatment of ammonia nitrogen-containing sewage is achieved, and the final effluent ammonia nitrogen, total nitrogen and COD can all reach the Class IV water standard limit in the surface water environmental quality standard (GB3838-2002); at the same time, the recycling and reuse of solid waste resources is also achieved, so that solid waste resources such as waste iron mud and agricultural and forestry waste generated by iron-carbon micro-electrolysis can be turned into treasures, avoiding secondary pollution to the environment. However, since it uses waste iron mud as a material, the removal rate of pollutants such as ammonia nitrogen is slow and the load is low. CN 115490322 B discloses a method for simultaneous denitrification and dephosphorization based on carbon-coated nano zero-valent iron materials. The coated nano zero-valent iron material and the mixed liquid volatile suspended solid MLVSS are added to the wastewater after nitrogen deoxygenation. Under anaerobic conditions, carbon and nano zero-valent iron are used as electron donors in the autotrophic denitrification system to synergistically remove nitrogen and phosphorus from the wastewater, breaking through the bottleneck of simultaneous phosphorus removal inhibiting the iron reaction activity and biological denitrification efficiency. However, the nano zero-valent iron material involved in this technology is not only active and easily oxidized, but also has a high cost, and is not ideal for practical application.

In summary, the filler made of elemental sulfur and iron-carbon particles as the main materials not only has a good removal effect on pollutants such as ammonia nitrogen, but also has a low cost and is ideal for practical application. In addition, in the system formed by this filler, the environmental conditions required for sulfur autotrophic denitrification, iron-carbon micro-electrolysis and Anammox are similar, and the substrate and product can complement each other well. If combined together, it can not only achieve the simultaneous removal of multiple nitrogen-containing compounds and improve the denitrification efficiency of the system, but also make it have a stronger buffering capacity. However, no research on the coupling of these three reactions has been reported so far.

Summary of the invention

The present invention provides a denitrification biological filler based on iron-carbon micro-electrolysis, a preparation method and application thereof, which solves the problems existing in the biological denitrification technology in the prior art, realizes the simultaneous removal of multiple nitrogen-containing compounds, improves the denitrification efficiency of the system, and also enables the system to have a stronger buffering capacity.

To achieve the above objectives, the present invention adopts the following technical solutions:

A denitrification biological filler based on iron-carbon micro-electrolysis, wherein the filler is a 3-5 mm spherical composite filler formed by sulfur powder coating elemental iron-activated carbon;

The mass ratio of elemental iron to activated carbon in the composite filler is 2-4:1; the mass ratio of sulfur powder to iron-carbon powder is 10-15:1.

The preparation method of the above-mentioned denitrification biological filler comprises the following steps:

Iron powder (Fe ⁰ ) and activated carbon powder (AC) are combined in a mass ratio of 2 to 4:1, and a proper amount of polylactic acid solution is added as an adhesive to combine them into tiny particles with a diameter of about 0.1 mm; then a proper amount of sulfur powder is added to make the mass ratio of sulfur to iron carbon (Fe ⁰ -AC) be 10 to 15:1, and at a melting point temperature of sulfur of 115°C±2°C, high-speed stirring is performed at 480r/min for 5-10min to make the sulfur and iron carbon small particles tightly and evenly combined, and after adding polylactic acid solution as an adhesive, granulation and cooling are performed to obtain a spherical composite filler with a diameter of 3 to 5 mm.

The above-mentioned denitrification biological filler is used for autotrophic biological denitrification. The biological filler and anaerobic sludge are added to the nitrate nitrogen wastewater to be treated to form a coupled denitrification system. The following reactions occur during the denitrification process: (1) Sulfur autotrophic denitrification: the elemental sulfur in the filler is consumed, and the nitrate nitrogen is converted into nitrogen gas, accompanied by the accumulation of a small amount of _NO2 ^-- N, and iron-carbon ( ^Fe0 -AC) particles are exposed; (2) the exposed ^Fe0 -AC undergoes a micro-electrolysis reaction in the wastewater, and strongly reducing hydrogen atoms are generated on the AC surface, which partially reduce the adjacent adsorbed nitrate to _NH4 ⁺ -N; (3) the anaerobic ammonia-oxidizing bacteria in the anaerobic sludge reduce the _NO2 ^-- N and _NH4 ⁺ -N produced in the above two steps to _N2 , and the small amount of nitrate nitrogen produced can be consumed by the first two reactions, so that the entire system can be organically combined.

The operating temperature of the above reaction is 25-35°C; the pH of the wastewater is controlled in the range of 6-9, and the hydraulic retention time (HRT) in the reactor is 2-8h.

Beneficial effects: The present invention provides a denitrification biological filler based on iron-carbon micro-electrolysis and a preparation method and application thereof, which has the following advantages over the prior art:

1. The iron-carbon in the biological filler of the present invention enables faster and better integrated coupling of anaerobic ammonia oxidation (Anammox) and sulfur autotrophic denitrification ( ^S0AD ), breaking through the bottleneck of microbial activity and biological denitrification efficiency when only ^S0AD is coupled with Anammox, and increasing the denitrification load of the original coupling system by about 20%, which not only improves the denitrification efficiency of the system, but also makes it have a stronger buffering capacity;

2. The addition of iron in the coupling system formed by the filler of the present invention is beneficial to the growth of the bacteria, improves the activity of the bacteria, and also improves the stability of the pH of the system;

3. The introduction of iron-carbon micro-electrolysis makes the coupling system of S ⁰ AD and Anammox unnecessary to add NH ₄ ⁺ -N and NO ₂ ^- -N, thus reducing the reaction cost and the SO ₄ ^2- production of the system, thus greatly avoiding the secondary pollution of the water body;

4. The method of the present invention has mild operating conditions and can be carried out under normal pressure without the need for specific conditions. It can be widely used in practice, and no toxic or harmful substances are generated, so it is safe and harmless to the environment.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG1 is a schematic diagram of the internal structure of a sulfur-iron-carbon composite filler in an embodiment of the present invention;

FIG2 is a schematic diagram of the changes in NO ₃ ^- -N concentrations in the influent and effluent of the bioreactors R1, R2, and R3 at various stages in an embodiment of the present invention;

FIG3 is a schematic diagram of the removal efficiency of NO ₃ ⁻ -N in each stage of the bioreactors R1, R2, and R3 in an embodiment of the present invention;

FIG. 4 is a schematic diagram of pH changes in bioreactors R1, R2, and R3 at various stages in an embodiment of the present invention.

Detailed ways

The present invention is described in detail below with reference to the accompanying drawings and specific embodiments:

In the following examples, the biofilter reactor formed in Example 1 is denoted as R1, the biofilter reactor formed in Comparative Example 1 is denoted as R2, and the biofilter reactor formed in Comparative Example 2 is denoted as R3, and continuous flow experiments are carried out to verify their denitrification effects.

Example 1

A sulfur-coated elemental iron-activated carbon (Fe ⁰ -AC) composite filler is prepared by the following method: elemental iron powder (Fe ⁰ ) and activated carbon powder (AC) are combined in a mass ratio of 3:1, and a proper amount of adhesive is added to combine them into tiny particles with a diameter of about 0.1 mm; then a proper amount of sulfur powder is added to make the mass ratio of sulfur to iron-carbon (Fe ⁰ -AC) be 15:1, and at the melting point temperature of sulfur, i.e. 115° C., high-speed stirring is performed for 5 minutes to partially melt the sulfur powder and adhere to the small iron-carbon particles, and after adding the adhesive, a disc machine is used for granulation to obtain a spherical composite filler with a diameter of 3-5 mm. The internal structure of the spherical composite filler is shown in FIG1 , and the sulfur powder coats the elemental iron-activated carbon to form a compact and uniform structure.

The newly prepared composite filler was used to treat wastewater and was filled into a biofilter reactor with a working volume of 0.5 L (4 cm in diameter and 40 cm in height).

Comparative Example 1

In this comparative example, a filler whose main component is elemental sulfur is prepared by the following method: adding an appropriate amount of sulfur powder, stirring at a high speed for 5 minutes at the melting point of sulfur, i.e., 115°C, so that the sulfur powder is partially melted and adheres to each other to form small particles, adding a binder and granulating using a disc machine to obtain a spherical composite filler with a diameter of 3 to 5 mm. The method is basically the same as that of Example 1, except that elemental iron-activated carbon ( ^Fe0 -AC) is not added in this comparative example.

The newly prepared composite filler was used to treat wastewater and was filled into a biofilter reactor with a working volume of 0.5 L (4 cm in diameter and 40 cm in height).

Comparative Example 2

In this comparative example, a filler whose main component is elemental iron-activated carbon (Fe ⁰ -AC) is prepared by the following method: elemental iron powder (Fe ⁰ ) and activated carbon powder (AC) are combined in a mass ratio of 3:1, and a proper amount of binder is added and granulated using a disc machine to obtain a spherical composite filler with a diameter of 3 to 5 mm. The method is basically the same as that in Example 1, except that elemental sulfur powder is not added in this comparative example.

The biofilter reactor formed by filling with the filler of Example 1 is recorded as R1, the biofilter reactor formed by filling with the filler of Comparative Example 1 is recorded as R2, and the biofilter reactor formed by mixing the fillers of Comparative Example 1 and Comparative Example 2 in a mass ratio of 15:1 is recorded as R3. The working volume is 0.5L (diameter is 4cm, height is 40cm). Under the same other conditions, a continuous flow experiment is carried out to verify its denitrification effect.

The reactor was inoculated with 5 g/L sulfur autotrophic bacteria sludge and 1 g/L anaerobic ammonia oxidizing bacteria sludge, respectively, and the operating temperature was 28°C; the pH of the simulated wastewater was controlled at 8, and the hydraulic retention time (HRT) in the reactor was 4 hours. After deoxygenation, the synthetic wastewater entered the reactor for denitrification.

The specific steps of the experiment are as follows:

(1) Before the denitrification filter is officially put into operation, the biofilter needs to be treated for biofilm formation. Denitrifying bacterial solution is inoculated into three biofilters and the bacterial solution for biofilm formation is replaced every 4 days. After 3 cycles, water quality indicators (culture medium utilization) are monitored daily. When the water quality indicators are stable for 3 consecutive cycles and the culture medium utilization is good, biofilm formation is considered successful.

(2) After the biofilter was formed, simulated wastewater was prepared with laboratory tap water, potassium nitrate (KNO ₃ ) was used as the only nitrogen source, and the nitrogen load was increased in a gradient of 20 mg/L. The specific water quality of the experimental inlet water at each stage is shown in Table 1. Water samples were taken from the outlet pool once a day and various water quality indicators were tested.

Table 1 Specific water quality of each stage of the experiment in the embodiment and the comparative example

Figure 2-4 shows the denitrification effect of reactors R1, R2 and R3 on simulated wastewater. It can be found that the denitrification performance of the water body of the R2 reactor without adding iron and carbon is poor, while the R1 and R3 after adding iron and carbon not only have better denitrification performance, but also have better pH stability of the system. Among them, the nitrate removal rate of the R1 reactor is about 15% higher than that of the R3 reactor, and its pH is also better than the R3 reactor in terms of shock resistance, basically maintaining above 7.0.

In the first stage (1-21d), when the HRT was 4h, R1 could achieve about 100%, that is, (20ppm) complete removal of nitrate nitrogen, and the pH in the reaction system was relatively stable. From the second to the fourth stage (22-84d), with the staged increase in the reactor load, the removal of nitrate nitrogen by the three groups of reactors also increased, but their removal efficiency of nitrate nitrogen continued to decline. Moreover, the pH of the system decreased very rapidly with the staged increase in nitrogen load. Overall, throughout the reaction stage, R1 had the best removal effect on nitrate nitrogen and the most stable system.

In summary, the sulfur-iron-carbon composite filler produced by the present invention not only has a simple production process, but also can promote autotrophic denitrification and improve the nitrate nitrogen treatment effect of the reactor.

The above are only preferred embodiments of the present invention, which will help those skilled in the art to further understand the present invention, but do not limit the present invention in any form. It should be pointed out that for those skilled in the art, without departing from the concept of the present invention, several modifications and improvements made are all protected by the present invention.

Claims (10)

1. A method for preparing a denitrification biological filler based on iron-carbon micro-electrolysis, characterized in that it includes the following steps: mixing iron powder and activated carbon powder, adding an adhesive to combine them into iron-carbon particles; then adding sulfur powder, stirring at a high speed at the melting point of sulfur at 115°C ± 2°C, so that the sulfur and the iron-carbon small particles are tightly and evenly combined, and after adding the adhesive, granulating and cooling to obtain a spherical composite filler. 2. The method for preparing a denitrification biological filler based on iron-carbon micro-electrolysis according to claim 1, characterized in that the mass ratio of the iron powder to the activated carbon is 2~4:1. 3. The method for preparing a denitrification biological filler based on iron-carbon micro-electrolysis according to claim 1 or 2, characterized in that the mass ratio of the sulfur powder to iron-carbon is 10-15:1. 4. The method for preparing a denitrification biological filler based on iron-carbon micro-electrolysis according to claim 1 or 2, characterized in that the iron-carbon particles are tiny particles with a diameter of 0.1 mm. 5. The method for preparing a denitrification biological filler based on iron-carbon micro-electrolysis according to claim 1, characterized in that the sulfur powder is added and stirred for 5-10 minutes. 6. The denitrification biological filler based on iron-carbon micro-electrolysis prepared by the method according to any one of claims 1 to 5, characterized in that the filler is a spherical composite filler with a diameter of 3-5 mm formed by sulfur powder coating elemental iron-activated carbon. 7. The denitrification biological filler based on iron-carbon micro-electrolysis according to claim 6 is characterized in that the filler has a structure of sulfur molecules coating elemental iron-activated carbon at the microscopic level. 8. The use of the denitrification biological filler based on iron-carbon micro-electrolysis according to any one of claims 6-7, characterized in that the biological filler is used for autotrophic biological denitrification, and the biological filler and anaerobic sludge are added to the nitrate nitrogen wastewater to be treated to form a coupled denitrification system. 9. The use of the denitrification biological filler based on iron-carbon micro-electrolysis according to claim 8 is characterized in that the coupled denitrification system undergoes the following reactions during the denitrification process: (1) Sulfur autotrophic denitrification: elemental sulfur in the filler is consumed, nitrate nitrogen is converted into nitrogen gas, accompanied by the accumulation of a small amount of _NO2 ^-- N, and iron-carbon ( ^Fe0 -AC) particles are exposed; (2) the exposed ^Fe0 -AC undergoes a micro-electrolysis reaction in the wastewater, and strongly reducing hydrogen atoms are generated on the AC surface, which partially reduce the adjacent adsorbed nitrate to _NH4 ⁺ -N; (3) the anaerobic ammonia-oxidizing bacteria in the anaerobic sludge reduce the _NO2 ^-- N and _NH4 ⁺ -N produced in the above two steps to _N2 , and the small amount of nitrate nitrogen produced is consumed by the first two reactions, so that the entire system can be organically combined. 10. The use of the denitrification biological filler based on iron-carbon micro-electrolysis according to claim 8 or 9, characterized in that the operating temperature of the system is 25-35°C; the pH of the wastewater is controlled in the range of 6-9, and the hydraulic retention time in the reactor is 2-8h.