Method for preparing biochar from waste iron-rich biological sludge to strengthen denitrification performance of iron-nitrogen coupling system

Abstract

The invention discloses a method for preparing biochar by using waste iron-rich biological sludge to strengthen the denitrification performance of an iron-nitrogen coupling system, and belongs to the field of biological sewage treatment. Through a high-temperature pyrolysis process, the waste biological sludge rich in iron element is converted into biochar with high specific surface area and rich surface redox functional groups. On one hand, the charcoal serves as an iron source to directly participate in a nitrogen metabolism process, and on the other hand, reversible redox active sites on the surface of the charcoal can mediate electron transfer between microorganisms and iron oxide, so that the denitrification rate is increased. Experimental results show that the biochar prepared at the pyrolysis temperature of 450 DEG C shows the optimal performance under the dosage of 1.0 g / L, and the denitrification efficiency and rate are remarkably improved. In a long-term test, the biochar is added into a Fe-N coupled denitrification system, the total nitrogen removal efficiency is improved to 93.52% + / -1.01%, and the long-term effectiveness of the biochar is proved. According to the invention, the waste sludge is recycled, so that the denitrification efficiency is effectively improved.

Description

Technical Field

[0001] The present invention relates to a method for preparing biochar from waste iron-rich biological sludge to enhance the nitrogen removal performance of an iron-nitrogen coupling system, belonging to the technical field of biological sewage treatment. Background Technique

[0002] As a key link in water pollution control, sewage treatment facilities face the dual challenges of high energy consumption and resource dependence while achieving pollutant emission reduction. Traditional biological nitrogen removal technologies generally have problems such as high energy consumption and strong dependence on chemical additives, resulting in a continuous increase in sludge production, which not only raises the subsequent treatment cost but also exacerbates the carbon emission burden. Therefore, developing new processes to simultaneously reduce energy consumption and resource requirements has become an important direction for the green and low-carbon transformation of sewage treatment.

[0003] In recent years, the biological nitrogen removal technology based on the iron redox cycle (anaerobic ammonium oxidation and nitrate-dependent ferrous oxidation synergistic process) has shown great potential. This technology drives nitrogen transformation through the conversion of iron valence states: anaerobic ammonium oxidation uses ferric iron as an electron acceptor to oxidize ammonia nitrogen to produce nitrogen gas or intermediate nitrogen oxides; nitrate-dependent ferrous oxidation uses ferrous iron as an electron donor to reduce nitrate to nitrogen gas. The coupling of the two can achieve the cyclic regeneration of iron elements, reduce the demand for iron-based material addition, and completely get rid of the dependence on organic carbon sources. Further integrating the iron cycle path with the anaerobic ammonium oxidation system to construct an iron-nitrogen coupling denitrification system can break through the 89% nitrogen removal efficiency bottleneck of short-cut nitrification-anaerobic ammonium oxidation. In this system, ferric iron as an alternative electron acceptor can alleviate the inhibition of the bacterial community caused by fluctuations in nitrite supply; the nitrate by-product of anaerobic ammonium oxidation can be secondarily removed using ferrous iron as an electron donor. In addition, the fully autotrophic metabolism mode can reduce sludge production, simultaneously reduce aeration energy consumption and organic carbon source consumption, providing a new idea for carbon emission reduction in sewage treatment plants.

[0004] Although the iron-nitrogen coupling denitrification system exhibits many advantages in sewage treatment, during long-term operation, the loss of dissolved iron and the decrease in iron bioavailability will weaken the electron transfer efficiency between microorganisms and the iron matrix, thereby affecting the stability and performance of the entire denitrification system. To maintain the denitrification rate, it is necessary to continuously add iron sources, but excessive addition of iron will trigger microbial ferroptosis and inactivate functional microbial communities. There are mainly two ways to improve the electron transfer efficiency between iron minerals and microorganisms: one is to improve the bioavailability of iron. For example, adding organic matter to prepare complexed iron, but this method may cause secondary pollution problems and heterotrophic bacteria to squeeze the ecological niche of autotrophic bacteria; the other is to add exogenous electron shuttles to shorten the electron transfer path between iron minerals and microorganisms. As a common soluble electron shuttle, AQDS can reversibly accept and provide electrons to increase the electron transfer rate. The oxygen-containing functional groups such as phenolic hydroxyl groups and quinone carbonyl groups are important reasons for AQDS to play a role. Compared with AQDS, biochar is insoluble in water and also contains abundant oxygen-containing functional groups, and will not cause secondary pollution due to drainage loss. Its excellent specific surface area and rich functional groups can adsorb or complex iron oxides, thereby improving the bioavailability of iron. The improvement of biological denitrification performance by biochar has been widely confirmed, including heterotrophic denitrification, dissimilatory nitrate reduction to ammonium, sulfur autotrophic denitrification, anaerobic ammonia oxidation, etc. In all aspects of sewage treatment, iron is widely used as a filler, coagulant, chemical phosphorus remover, and desulfurization agent. Due to its low solubility, iron often remains in biological sludge. This characteristic makes iron-rich biomass sludge a high-quality raw material for preparing biochar. Introducing the biochar prepared therefrom into the iron-nitrogen coupling denitrification system, iron can serve as an iron source and at the same time enhance the conductivity of the system and promote the metabolism of iron redox microorganisms. In addition, after the biomass is converted into biochar containing rich functional groups, it can improve the electron transfer efficiency between iron oxides and microorganisms. This method can also realize the recycling of waste resources and has both environmental and economic benefits. Summary of the Invention

[0005] The present invention provides a method for preparing biochar from waste iron-rich biological sludge to enhance the denitrification performance of the iron-nitrogen coupling system. This method prepares waste iron-rich biological sludge generated during the sewage treatment process into biochar to achieve resource utilization. On the one hand, the biochar provides an iron source for the denitrification system; on the other hand, the abundant redox functional groups on its surface can enhance the electron transfer efficiency between microorganisms and iron minerals, thereby improving the denitrification performance of the iron-nitrogen coupling system.

[0006] A method for preparing biochar from waste iron-rich biological sludge to enhance the nitrogen removal performance of the iron-nitrogen coupling system, which is characterized in that: using waste biological sludge rich in iron elements as raw materials to prepare biochar materials, and endowing it with a high specific surface area and abundant surface redox functional groups through a high-temperature pyrolysis process. On the one hand, this biochar directly participates in the nitrogen metabolism process as an iron source, and on the other hand, its surface reversible redox active sites can mediate the electron transfer between microorganisms and iron oxides, improve the nitrogen removal rate, and achieve the dual goals of sludge resource utilization and enhanced nitrogen removal performance. The specific steps are as follows:

[0007] (1) Construction of the iron-nitrogen coupling nitrogen removal system: Using anaerobic ammonium oxidation sludge as the inoculated sludge, placing it in a sequencing batch anaerobic reactor, and controlling the inoculated sludge concentration at 3000 - 4000 mg / L; adding the prepared simulated wastewater, whose components include 0.2 g / L NH4 + -N, 0.15 g / L NO2 - -N, 0.05 g / L MgSO4·7H2O, 0.05 g / L CaCl2·2H2O, 1.0 g / L NaHCO3, 0.027 g / L KH2PO4; in addition, 1.5 mL of trace element solution is added to each liter of simulated wastewater, and its composition includes 5 g / L EDTA, 0.25 g / L CuSO4·5H2O, 0.43 g / L ZnSO4·7H2O, 0.014 g / L H3BO4, 0.99 g / L MnCl2·4H2O, 0.22 g / L Na2MoO4·2H2O and 0.24 g / L CoCl2·6H2O; during the operation of the nitrogen removal system, the temperature is controlled at 30 ± 2 °C; a complete operation cycle includes: influent for 5 - 10 min, stirring for 23 h, sedimentation for 30 - 40 min, drainage for 5 - 10 min, and the drainage ratio is 50%; after the influent is completed in each cycle, Fe2O3 is added to the reactor to increase the Fe2O3 concentration in the reactor by 5 mg / L per cycle, and it is operated for 25 - 30 cycles under this condition; then the dosage of Fe2O3 is increased so that the Fe2O3 concentration in the reactor increases by 10 mg / L per cycle, and it is operated for 45 - 50 cycles; monitor the effluent NH4 + -N, NO2 - -N and NO3 - -N concentration until the removal efficiencies of NH4 + -N and TN are stable above 85%, and the iron-nitrogen coupling nitrogen removal system is successfully constructed;

[0008] (2) Preparation of iron-rich sludge-based biochar: The iron-rich biological sludge generated during the sewage treatment process with an iron content mass ratio greater than 10% was dehydrated, and then dried at a constant temperature of 100 °C for 24 h to remove the excess water in the sludge; after the dried sludge was pulverized, it was placed in a tubular furnace and rapidly pyrolyzed and carbonized under the protection of a nitrogen atmosphere. The heating rate during pyrolysis was 10 °C / min, and it was heated to 200, 450, and 700 °C respectively, and pyrolyzed and held at each temperature for 2 hours; after pyrolysis was completed, the sample was cooled to room temperature; after pyrolysis was completed, the sample was cooled to room temperature, ground, and passed through a 100-mesh sieve to ensure the uniformity of the biochar particles;

[0009] (3) Optimization of biochar pyrolysis temperature and dosage: Take the sludge of the iron-nitrogen coupling system, wash it three times with distilled water and transfer it to a 250 mL serum bottle, add the simulated wastewater prepared in step (1), and pass N2 for 10 min to remove the dissolved oxygen in the reaction system; then add the biochar prepared at pyrolysis temperatures of 200, 450, and 700 °C at 1 g / L to the serum bottle respectively. After sealing the serum bottle, react in a constant temperature shaker at 30 °C for 24 h. Samples were collected regularly during the reaction to analyze the nitrogen conversion characteristics and denitrification performance. The small-scale test was carried out for three cycles; after determining the optimal biochar pyrolysis temperature according to the total nitrogen removal efficiency and rate, the biochar prepared at this temperature was selected, and batch tests were further carried out to optimize the dosage of the biochar. The dosage gradients were 0, 0.5, 1.0, 2.5, and 5.0 g / L. The test was carried out in a constant temperature shaker at 30 °C for 3 cycles, and each cycle reacted for 24 h; the dosage with the maximum total nitrogen removal efficiency and rate was selected as the optimal dosage;

[0010] (4) Long-term denitrification performance of biochar-enhanced iron-nitrogen coupling system: After determining the optimal pyrolysis temperature and dosage, the biochar was added to the iron-nitrogen coupling denitrification system and operated for 30 - 50 cycles; the temperature was controlled at 30 ± 2 °C during the operation; a complete operation cycle included: influent for 5 - 10 min, stirring for 23 h, sedimentation for 30 - 40 min, drainage for 5 - 10 min, the drainage ratio was 50%, and the hydraulic retention time was 46 h; after operating for 30 - 50 cycles, the hydraulic retention time was shortened from 46 h to 32 h to further improve the denitrification load.

[0011] Innovation points of the present invention

[0012] (1) Converting the waste iron-rich biological sludge generated during the sewage treatment process into a biochar material with high added value, realizing the efficient conversion and reuse of waste resources;

[0013] (2) Utilizing the abundant redox functional groups on the biochar surface to improve the electron transfer efficiency between microorganisms and iron, thereby improving the denitrification performance of the iron-nitrogen coupling system;

[0014] (3) While realizing the resource utilization of sludge, improve the performance of the denitrification system, achieve the dual goals of sludge resource utilization and the improvement of sewage denitrification efficiency, and provide new ideas and methods for the sustainable development of the sewage treatment field.

[0015] Advantages of the present invention

[0016] (1) Improve denitrification efficiency: By introducing biochar, the electron transfer efficiency between microorganisms and iron is significantly improved, thereby optimizing the denitrification performance of the iron-nitrogen coupling system, and keeping the removal efficiencies of NH4 + -N and TN at a relatively high level, effectively enhancing the denitrification efficiency of sewage treatment;

[0017] (2) Realize sludge resource utilization: Convert the waste iron-rich biological sludge into biochar, realize the resource utilization of sludge, reduce the sludge treatment cost and environmental burden, and at the same time provide a sustainable iron source for the denitrification system, with significant environmental and economic benefits;

[0018] (3) Reduce operating costs: Use waste sludge to prepare biochar, reduce the dependence on external iron sources, reduce the iron source dosage and related treatment costs; at the same time, the preparation process of biochar is relatively simple, further reducing the operation and maintenance costs of the system. Brief description of the drawings

[0019] Figure 1 is a schematic structural diagram of the reaction device used in the embodiment of the present invention to construct an iron-nitrogen coupling denitrification system;

[0020] In the figure: 1--water inlet bucket; 2--peristaltic pump; 3--water inlet; 4--sequencing batch anaerobic reactor; 5--WTW on-line monitor; 6--stirring device; 7--drainage port; 8--drainage valve; 9--drainage bucket; 10--temperature control device;

[0021] Figure 2 is a schematic diagram of the denitrification performance of different batches when determining the pyrolysis temperature and dosage of biochar in the embodiment of the present invention;

[0022] Figure 3 is a schematic diagram of the long-term denitrification performance of the biochar-enhanced iron-nitrogen coupling system in the embodiment of the present invention. Detailed implementation manners

[0023] The specific implementation process is as follows:

[0024] (1) Construction of the iron-nitrogen coupling denitrification system: Use anaerobic ammonium oxidation sludge as the inoculated sludge and place it in the Figure 1 shown reaction device, and the concentration of the inoculated sludge is 3515±21 mg / L; Add the prepared simulated wastewater, and its components include 0.2 g / L NH4+ -N, 0.15 g / L NO2 - -N, 0.05 g / L MgSO4·7H2O, 0.05 g / L CaCl2·2H2O, 1.0 g / L NaHCO3, 0.027 g / L KH2PO4; In addition, 1.5 mL of trace element solution is added to each liter of simulated wastewater, and its composition includes 5 g / L EDTA, 0.25 g / L CuSO4·5H2O, 0.43 g / L ZnSO4·7H2O, 0.014 g / L H3BO4, 0.99 g / L MnCl2·4H2O, 0.22 g / L Na2MoO4·2H2O and 0.24 g / L CoCl2·6H2O; During the operation of the denitrification system, the temperature is controlled at 30 ± 2 °C; A complete operation cycle includes: influent for 10 min, stirring for 23 h, sedimentation for 40 min, drainage for 10 min, and the drainage ratio is 50%; After the influent is completed in each cycle, Fe2O3 is added to the reactor to increase the Fe2O3 concentration in the reactor by 5 mg / L per cycle, and it is operated for 25 cycles under this condition; Then, the dosage of Fe2O3 is increased to increase the Fe2O3 concentration in the reactor by 10 mg / L per cycle, and it is operated for 45 cycles; NH4 + -N and TN removal efficiencies are stably above 85%, and the iron-nitrogen coupled denitrification system is successfully constructed;

[0025] (2) Preparation of iron-rich sludge-based biochar: Biochar is prepared using inactivated iron-rich biological sludge eluted from a sponge iron biological filter with an iron mass ratio of 17% as the raw material; First, the sludge is dehydrated, and then dried at a constant temperature of 100 °C for 24 h to remove excess water in the sludge; After the dried sludge is pulverized, it is placed in a tubular furnace and rapidly pyrolyzed and carbonized under the protection of a nitrogen atmosphere. The heating rate during pyrolysis is 10 °C / min, and it is heated to 200 °C, 450 °C and 700 °C respectively, and pyrolyzed at each temperature for 2 hours; After pyrolysis is completed, the sample is cooled to room temperature, ground and sieved through a 100-mesh sieve to ensure the uniformity of biochar particles;

[0026] (3) Optimization of pyrolysis temperature and dosage of biochar: Take the sludge of the iron-nitrogen coupling system, wash it three times with distilled water and transfer it to a 250 mL serum bottle. Add the reaction matrix consistent with the mother reactor, and introduce N2 for 10 min to remove the dissolved oxygen in the reaction system. Then add the biochar prepared at pyrolysis temperatures of 200 °C, 450 °C, and 700 °C at 1 g / L to three serum bottles respectively. Seal the serum bottles and react them in a constant temperature shaker at 30 °C for 24 h. Compared with the control group (CK), the addition of biochar significantly improved the denitrification efficiency and rate (P < 0.001), which increased from 83.72 ± 0.70% and 6.11 mgN / h to 93.41 ± 0.76% and 6.82 mgN / h respectively. Among them, the biochar prepared at 450 °C showed the best performance( Figure 2 a); After determining that the optimal biochar pyrolysis temperature was 450 °C, the dosage was further optimized. The biochar at 0.5 g / L had little effect (P = 0.444), while the denitrification efficiency and rate were significantly improved at 1.0 - 5.0 g / L (P < 0.001); within the dosage range of 1.0 - 5.0 g / L, there was no significant difference in denitrification performance (P = 0.350)( Figure 2 b), indicating that the promoting effect of biochar had reached saturation; Based on the consideration of cost-effectiveness, the biochar prepared at a pyrolysis temperature of 450 °C and a dosage of 1.0 g / L was selected for subsequent long-term experiments;

[0027] (4) Long-term denitrification performance of the biochar-enhanced iron-nitrogen coupling system: Finally, the optimal pyrolysis temperature and dosage were determined to be 450 °C and 1 g / L respectively. Add the biochar to the iron-nitrogen coupling denitrification system and run for 47 cycles; During the operation, the temperature was controlled at 30 ± 2 °C; A complete operation cycle included: influent for 5 - 10 min, stirring for 23 h, sedimentation for 30 - 40 min, drainage for 5 - 10 min, the drainage ratio was 50%, and the hydraulic retention time was 46 h; Then the hydraulic retention time was shortened from 46 h to 32 h to further increase the denitrification load. After a short adaptation, the total nitrogen removal efficiency increased to 93.52 ± 1.01%, confirming the long-term effectiveness of biochar.

Claims

1. A method for preparing biochar from waste iron-rich biological sludge to enhance the nitrogen removal performance of an iron-nitrogen coupling system, characterized in that, The specific steps are as follows: (1) Construction of iron-nitrogen coupling denitrification system: Anaerobic ammonium oxidation sludge was used as inoculated sludge and placed in a sequencing batch anaerobic reactor, controlling the concentration of inoculated sludge at 3000 - 4000 mg / L; The prepared simulated wastewater was added, and its components included 0.2 g / L NH4 + -N, 0.15 g / L NO2 - -N, 0.05 g / L MgSO4·7H2O, 0.05 g / L CaCl2·2H2O, 1.0 g / L NaHCO3, 0.027 g / L KH2PO4; In addition, 1.5 mL of trace element solution was added to each liter of simulated wastewater, and its composition included 5 g / L EDTA, 0.25 g / L CuSO4·5H2O, 0.43 g / L ZnSO4·7H2O, 0.014 g / L H3BO4, 0.99 g / L MnCl2·4H2O, 0.22 g / L Na2MoO4·2H2O and 0.24 g / L CoCl2·6H2O; During the operation of the denitrification system, the temperature was controlled at 30 ± 2 °C; A complete operation cycle included: influent for 5 - 10 min, stirring for 23 h, sedimentation for 30 - 40 min, drainage for 5 - 10 min, and the drainage ratio was 50%; After the influent was completed in each cycle, Fe2O3 was added to the reactor to increase the concentration of Fe2O3 in the reactor by 5 mg / L per cycle, and it was operated for 25 - 30 cycles under this condition; Then the dosage of Fe2O3 was increased to increase the concentration of Fe2O3 in the reactor by 10 mg / L per cycle, and it was operated for 45 - 50 cycles; The concentrations of NH4 + -N, NO2 - -N and NO3 - -N were monitored daily until the removal efficiencies of NH4 + -N and TN were stable above 85%, and the iron-nitrogen coupling denitrification system was successfully constructed; (2) Preparation of iron-rich sludge-based biochar: The iron-rich biological sludge generated in the sewage treatment process with an iron content by mass percentage greater than 10% is dehydrated, and then dried at a constant temperature of 100 °C for 24 h to remove the excess water in the sludge; after the dried sludge is pulverized, it is placed in a tubular furnace and rapidly pyrolyzed and carbonized under the protection of a nitrogen atmosphere. The heating rate of the pyrolysis process is 10 °C / min, and it is heated to 200, 450, and 700 °C respectively, and pyrolyzed at each temperature for 2 h; after the pyrolysis is completed, the sample is cooled to room temperature; after the pyrolysis is completed, the sample is cooled to room temperature, ground, and sieved through a 100-mesh sieve to ensure the uniformity of the biochar particles; (3) Optimization of biochar pyrolysis temperature and dosage: Take the sludge of the iron-nitrogen coupling system, wash it three times with distilled water and transfer it to a 250 mL serum bottle, add the simulated wastewater prepared in step (1), and introduce N2 for 10 min to remove the dissolved oxygen in the reaction system; then add the biochar prepared at pyrolysis temperatures of 200, 450, and 700 °C at 1 g / L to the serum bottle respectively. After sealing the serum bottle, react it in a constant temperature shaker at 30 °C for 24 h. During the reaction, samples are collected regularly to analyze the nitrogen conversion characteristics and denitrification performance. The small-scale test is carried out for three cycles; after determining the optimal biochar pyrolysis temperature according to the maximum total nitrogen removal efficiency, the biochar prepared at this temperature is selected, and batch tests are further carried out to optimize the dosage of the biochar. The dosage gradient is 0, 0.5, 1.0, 2.5, 5.0 g / L; the test is carried out in a constant temperature shaker at 30 °C for 3 cycles, and each cycle reacts for 24 h; Select the dosage with the maximum total nitrogen removal efficiency as the optimal dosage; (4) Biochar-enhanced long-term denitrification performance of the iron-nitrogen coupling system: After determining the optimal pyrolysis temperature and dosage, add the biochar to the iron-nitrogen coupling denitrification system and run for 30 - 50 cycles; during the operation, the temperature is controlled at 30 ± 2 °C; a complete operation cycle includes: influent for 5 - 10 min, stirring for 23 h, sedimentation for 30 - 40 min, drainage for 5 - 10 min, the drainage ratio is 50%, and the hydraulic retention time is 46 h; after running for 30 - 50 cycles, the hydraulic retention time is shortened from 46 h to 32 h.

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