Landfill leachate biological denitrification method and system based on kitchen waste synergistic fermentation

Abstract

The invention discloses a landfill leachate biological denitrification method and system based on kitchen waste synergistic fermentation, kitchen wastewater and municipal sludge are mixed according to a specific ratio, a complex microbial inoculant is inoculated for two-stage anaerobic fermentation, and obtained fermentation liquor rich in propionic acid and butyric acid is injected into a landfill leachate treatment system as an external carbon source. According to the landfill leachate treatment system, sulfur-iron modified biochar is innovatively adopted to load denitrifying bacteria to construct a fixed bed reactor, and a pre-positioned short-cut nitrification process and an intelligent carbon source dynamic regulation and control system are combined, so that accurate supply of a carbon source and improvement of denitrification efficiency are realized. The method not only reduces the use cost of the traditional carbon source, but also synchronously realizes the cooperative treatment of the three wastes, the denitrification efficiency reaches 92% or above, and the total nitrogen removal load is increased by 40% compared with the traditional process.

Description

Technical Field

[0001] The present invention relates to the technical field of sewage treatment, and particularly relates to a method and system for efficient denitrification of landfill leachate based on waste resource utilization, which is particularly suitable for biological treatment of leachate with high ammonia nitrogen and low carbon-nitrogen ratio. Background Art

[0002] With the acceleration of the urbanization process, the leachate generated by domestic waste landfills and incineration plants has become a typical representative of highly polluted wastewater. Such wastewater usually has the characteristics of high ammonia nitrogen concentration, unbalanced carbon-nitrogen ratio, complex composition, etc. In particular, the problem of total nitrogen removal has long troubled the industry. Traditional treatment processes mostly adopt the "nitrification-denitrification" biological denitrification route, but the original water carbon source of the leachate is seriously insufficient, resulting in a lack of electron donors in the denitrification stage, forcing operators to add a large amount of commercial carbon sources such as methanol and sodium acetate. According to statistics, the cost of commercial carbon sources accounts for 35% - 50% of the total cost of leachate treatment, and excessive addition is likely to cause the effluent COD to exceed the standard, resulting in secondary pollution.

[0003] In the prior art, physical and chemical methods such as stripping method and breakpoint chlorination method can remove some ammonia nitrogen, but the stripping method has high energy consumption, and the steam consumption reaches 50 - 80 kg / m 3 ³. The breakpoint chlorination method will produce toxic by-products such as chloroform. Although the membrane separation technology can achieve deep denitrification, the frequent cleaning caused by membrane fouling has increased the operation and maintenance costs sharply, and the replacement cost of the reverse osmosis membrane reaches 300 - 500 yuan / m 2 ³. In terms of biological denitrification, the combined process of shortcut nitrification-anaerobic ammonium oxidation can reduce the carbon source demand, but it is sensitive to environmental conditions. For example, the water temperature needs to be maintained at 30 - 35 °C, and the pH needs to be strictly controlled at 7.5 - 8.0, and its stability is poor in actual engineering. In recent years, studies on using alternative carbon sources such as food waste fermentation broth (Bioresour. Technol. 2019, 294: 122218) and food waste hydrolyzate (Bioresour. Technol. 2021, 341: 125904) have gradually emerged, but there are technical bottlenecks such as low acid production efficiency and poor adaptability of carbon source components in the single waste fermentation.

[0004] In the field of waste co - treatment, the combined resource utilization of food waste wastewater and municipal sludge is still in the exploratory stage. Food waste wastewater is rich in easily degradable organic matter, but it is prone to excessive acidification during single - stage fermentation. Municipal sludge contains a large amount of microbial cell protein, but the dense cell wall structure leads to slow hydrolysis. Although the existing patent CN220976759U uses food waste and biogas slurry for mixed fermentation to extract fermentation broth as a carbon source in the denitrification system, it does not solve key problems such as carbon - nitrogen ratio regulation and optimization of fermentation product components. In addition, when the fermentation broth is directly used as a carbon source, the suspended solids and residual oil in it are likely to block the biological filter, reducing the denitrification efficiency. In terms of the denitrifying carbon source supply technology, most existing systems adopt an open - loop control strategy, adding carbon sources in a fixed ratio, which is difficult to adapt to the water quality fluctuations of leachate. The patent CN210193511U discloses a carbon source dosing device based on online nitrate monitoring, but it does not consider the biodegradability differences of the fermentation broth carbon source, resulting in deviations in the actual dosing amount. At the same time, traditional denitrification reactors use ceramsite and activated carbon as carriers, lacking electron transfer media, and the denitrification rate is often lower than 0.15 kgN / (m 3 ·d). Although some individual studies, such as the literature (Chem. Eng. J. 2025, 511:161958), have tried to add polyurethane biological carriers modified with nano - zero - valent iron and biochar to promote anaerobic ammonium oxidation and denitrification, no detailed description has been made on whether iron passivation will occur and the durability of the carrier. At the same time, when the system operates for 180 days, due to hydraulic scouring, the powder - state nano - zero - valent iron and biochar attached to the carrier surface are significantly reduced. The literature (Water. Res. 2023, 245:120569) proves that the system adding elemental sulfur to promote autotrophic denitrification will be hindered by sulfur element accumulation in mass transfer and sewage pipeline blockage, thus affecting the stable operation of the system.

[0005] In summary, the current denitrification treatment of landfill leachate faces three contradictions: firstly, the contradiction between the cost of commercial carbon sources and economy; secondly, the contradiction between the carbon production efficiency of single waste fermentation and the denitrification demand; thirdly, the contradiction between the electron transfer efficiency in the denitrification process and the system stability. There is an urgent need to develop an integrated technology for waste co - disposal, carbon source directional conversion, and denitrification efficiency enhancement to achieve a double breakthrough in environmental and economic benefits. Summary of the Invention

[0006] Aiming at the problems of high carbon source cost, insufficient denitrification efficiency, and low resource utilization rate of food waste and municipal sludge in the existing landfill leachate denitrification technology, the present invention proposes a biological denitrification method and system for landfill leachate based on the co - fermentation of food waste, realizing the goal of efficient, low - consumption, and stable denitrification through the integration of waste resource conversion, electron transfer enhancement, and intelligent control technologies.

[0007] The core of the present invention lies in constructing a three-in-one technical system of "synergistic conversion of waste - precise supply of carbon source - enhanced electron transfer", and the specific technical solutions are as follows:

[0008] 1. Co - treatment of food waste wastewater and sludge and two - stage fermentation process

[0009] In view of the technical defects such as low acid - production efficiency and unstable carbon - source components existing in the single - waste fermentation process, the present invention proposes a method for directional conversion of carbon source based on the co - fermentation of food waste wastewater and municipal sludge:

[0010] Mix food waste wastewater and municipal sludge at a volume ratio of 3:1 to 5:1. First, optimize and improve the biodegradability of the substrate through pretreatment. Use low - frequency ultrasonic waves (20 kHz, 0.5 W / mL) to break the zoogloeal matrix of municipal sludge and release intracellular organic matter, so that the proportion of soluble COD in the mixed substrate reaches more than 85%( Figure 1 ).

[0011] Adopt a two - stage composite microbial agent - enhanced fermentation process for the treated mixed material. In the first stage, add a composite microbial agent of Candida tropicalis CGMCC 2.3067, Bacillus subtilis ATCC 6051 and Clostridium butyricum CICC 10390 with a viable - cell number ratio of 3:2:1, and ferment at pH 5 - 6 and 35 - 38 °C for 48 - 72 h. Through the synergistic effect of the microbial community, decompose polysaccharides and proteins into acetic acid and propionic acid. In the second stage, adjust the pH to 7 - 7.5 and cool down to 25 - 28 °C to extend the fermentation for 24 - 36 h, promoting the directional conversion of acetic acid by Clostridium butyricum into butyric acid. Finally, the proportion of propionic acid and butyric acid in volatile fatty acids (VFAs) exceeds 75%, and the total yield reaches 0.45 - 0.52 g / g VS, which is more than 40% higher than that of the single - fermentation process.

[0012] Finally, achieve deep removal of suspended solids (SS < 50 mg / L) and macromolecular impurities through 0.1 - μm ceramic membrane filtration to ensure that the fermentation broth meets the carbon - source requirements of the denitrification system.

[0013] 2. Design of a sulfur - iron - modified biochar fixed - bed denitrification reactor

[0014] To break through the bottleneck of low electron - transfer efficiency of traditional denitrification carriers, the present invention develops a sulfur - iron - modified biochar and its application method:

[0015] Using walnut - shell biochar as the substrate, impregnate it with a mixed solution of 0.5 mol / L FeSO4 and 0.3 mol / L Na2S2O3 (volume ratio 2:1), and then calcine it at 600 °C for 1 h under nitrogen protection to form FeS x (x = 1 - 2) nanoparticle - loaded biochar composite material with a specific surface area ≥ 800 m 2 / g, FeS xThe loading amount is 3-5 wt%. This material combines the functions of a sulfur autotrophic denitrification electron donor (S 2- / S0) and a heterotrophic denitrification electron mediator (Fe 2+ / Fe 3+ redox cycle), and can increase the electron transfer rate by 2.3 times.

[0016] In a fixed-bed reactor ( Figure 2 ), sulfur-iron modified biochar (porosity 60-70%) is filled, and a mixed flora of Paracoccus denitrificans and Thiobacillus denitrificans (the viable bacteria ratio is 2:1) is inoculated to form a sulfur-iron-bacteria synergistic denitrification system. A porous water distributor (pore size distribution 0.5-2 mm) and a gas-liquid separation device are arranged in the reactor to ensure that under the condition of a hydraulic retention time (HRT) of 8-12 h, the total nitrogen removal load reaches 0.35-0.42 kg N / (m 3 ·d).

[0017] 3. Intelligent carbon source dynamic regulation system

[0018] To solve the problem of excessive or insufficient addition of traditional carbon sources, the present invention integrates the following intelligent control modules: a nitrate sensor with a detection limit of 0.1 mg / L and a COD spectrometer are used to obtain the influent C / N value in the denitrification section in real time; a control model with the C / N deviation, leachate flow rate, and temperature as input variables and the carbon source addition rate as the output variable is established to dynamically adjust the addition amount of the fermentation broth (control accuracy ±5%) to make the C / N in the denitrification section stable at 3.5-4.2; combined with the change trend of the oxidation-reduction potential (ORP) in the reactor, the stirring intensity is automatically adjusted between 30 and 50 rpm, and the aeration volume is controlled to keep the DO at 0.2-0.3 mg / L, saving 15% energy compared with the traditional PID control.

[0019] Through the above technical solutions, the denitrification system of the present invention has been significantly improved in the following aspects: First, for every 1 ton of leachate treated, 0.3 m 3 of food waste wastewater and 0.08 m 3 of sludge can be synergistically consumed, and the carbon source cost is reduced by 65-70%; second, when the influent TN is 1400 mg / L, the effluent TN < 70 mg / L, the total nitrogen removal rate ≥ 92%, and the denitrification rate reaches 0.38-0.45 kg N / (m 3 ·d); in addition, the anti-blocking period of the sulfur-iron modified biochar is extended to 6-8 months, and the system can continuously operate for 180 days without efficiency decay.

[0020] The implementation of the present invention can effectively solve the economic and technical contradictions in the denitrification treatment of landfill leachate, and provide an innovative solution for waste resource utilization and deep sewage denitrification. Brief description of the drawings

[0021] Figure 1 is the process flow chart of the present invention;

[0022] Figure 2 is the schematic diagram of the system structure. Specific Embodiments

[0023] The implementation process and technical effects of the present invention are described in detail below through examples and comparative examples. Examples 1 to 3 are the preferred solutions of the present invention, and Comparative Examples 1 to 2 are the controls of traditional processes. All experimental data are from pilot-scale verification (treatment volume 10m 3 / d).

[0024] Example 1: Treatment of landfill leachate

[0025] For the treatment of the leachate of a certain landfill in this example, the specific implementation process is as follows: For the raw water of landfill leachate with NH4+-N 1200 mg / L, TN 1400 mg / L, COD 4500 mg / L and C / N = 1.8, first mix the food waste wastewater with a COD of 35000 mg / L and municipal sludge at a volume ratio of 4:1, and pretreat it with ultrasonic waves at 20 kHz and 0.5 W / mL for 12 minutes to destroy the municipal sludge flocs, and then add a composite bactericide of Candida tropicalis, Bacillus subtilis and Clostridium butyricum, with a viable bacteria ratio of 3:2:1 and a total dosage of 0.6‰. Subsequently, two-stage anaerobic fermentation is carried out. In the first stage, fermentation is carried out at pH = 5.8, 37°C and 30 rpm for 60 h to make the VFAs concentration reach 8500 mg / L; in the second stage, the pH is adjusted to 7.2 and the temperature is lowered to 27°C, and fermentation is continued for 30 h, and the proportion of propionic acid and butyric acid is increased to 77%. Finally, a carbon source with SS below 40 mg / L and a VFAs production rate of 0.48 g / g VS is obtained through 0.1 μm ceramic membrane filtration. Subsequently, the carbon source is injected into the sulfur-iron modified biochar denitrification reactor. The filler of the sulfur-iron modified biochar denitrification reactor is biochar with a FeS x content of 4.2 wt% and a porosity of 65%. Inoculate a 2:1 flora of Paracoccus denitrificans and Thiobacillus, and dynamically adjust the carbon source dosage through a fuzzy control algorithm to maintain C / N = 3.8, and couple it with a short-cut nitrification reactor (DO 0.4 mg / L, pH = 8.0, HRT = 24 h, nitrite nitrogen accumulation rate > 90%), and operate under the conditions of HRT = 10 h and stirring intensity of 40 rpm. After treatment, the TN in the effluent is reduced to 68 mg / L, the total nitrogen removal rate is 95.1%, NH4 + -N 15 mg / L, COD 380 mg / L, the carbon source cost is 0.8 yuan / ton, which is 68% lower than the traditional process using methanol as the carbon source, and the biochar does not agglomerate after continuous operation for 6 months, and the TN removal rate fluctuates less than ±1.5%.

[0026] Example 2: Treatment of High Ammonia-Nitrogen Leachate from Waste Incineration Plant

[0027] In this example, the treatment of high ammonia-nitrogen leachate from a certain waste incineration plant is as follows: For the raw water of high ammonia-nitrogen leachate from the waste incineration plant with NH4 + -N 2000 mg / L, TN 2300 mg / L, COD 3800 mg / L and C / N = 1.2, first optimize the carbon source preparation process, increase the mixing ratio of food waste wastewater and municipal dewatered sludge to 5:1. After two-stage anaerobic fermentation, extend the fermentation time of the second stage to 36 h, increase the VFAs yield to 0.51 g / g VS and the proportion of butyric acid reaches 40%, and dynamically adjust the stirring intensity to 45 rpm through ORP online feedback, and adjust the dosage of the fermentation broth to 3.8%. Synchronously improve the denitrification system, use FeS x modified biochar with a sulfur-iron loading increased to 4.5 wt% and a pore size distribution optimized with 80% of the pore size in the range of 0.5 - 2 mm. Combined with a micro-aerobic environment with DO strictly controlled at 0.2 - 0.3 mg / L, extend the HRT to 12 h. After treatment, the effluent TN drops to 98 mg / L (removal rate 95.7%), NH4 + -N 22 mg / L, COD 420 mg / L, the denitrification rate reaches 0.44 kg N / (m 3 ·d), the operation cycle of the biochar is stable for 6 months without blockage, and at the same time, the system energy consumption is reduced by 18% through intelligent aeration control.

[0028] Example 3: Treatment of Low Carbon-Nitrogen Ratio Mixed Leachate

[0029] In this example, the treatment of a certain low carbon-nitrogen ratio mixed leachate is as follows: For the low carbon-nitrogen ratio mixed leachate with NH4 + -N 800 mg / L, TN 950 mg / L, COD 6200 mg / L and C / N = 2.5, first use an online spectrometer to monitor the C / N value in real time and dynamically adjust the dosage of the fermentation broth to 2.5% to ensure that the C / N in the denitrification section is 3.5; increase the proportion of Clostridium butyricum in the complex bacterial agent to 40% during the carbon source preparation stage, and optimize the VFAs components so that the proportion of butyric acid reaches 42%; synchronously strengthen the adaptation of the denitrifying bacteria group, increase the proportion of Paracoccus denitrificans in the denitrification reactor to 70%, and control the N2O emission rate below 0.5% by adding a gas-liquid separation device. After treatment, the effluent TN is 45 mg / L (removal rate 95.3%), NH4 + -N 8 mg / L, COD 520 mg / L, the carbon source cost is reduced to 0.6 yuan / ton and the comprehensive energy consumption is reduced by 22%. At the same time, for every 1 ton of leachate treated, 0.25 m 3 of food waste wastewater and 0.06 m 3, with the effects of efficient denitrification, low-carbon operation and waste resource utilization.

[0030] Comparative Example 1: Traditional methanol carbon source process

[0031] Treat the landfill leachate in the same way as in Example 1, use methanol as the carbon source, C / N is 4.0, and the denitrification reactor uses ordinary activated carbon with a specific surface area of 500 m 2 / g as the carrier, and control HRT = 16 h. The TN in the effluent after treatment only reaches 150 mg / L (removal rate 89.3%), and the COD exceeds the standard (>500 mg / L) due to methanol residue; the carbon source cost is as high as 2.8 yuan / ton, and the denitrification rate is as low as 0.18 kg N / (m 3 ·d); at the same time, the activated carbon needs to be backwashed 3 times a month due to serious pore blockage, resulting in a ±8% fluctuation in the TN removal rate and poor system operation stability.

[0032] Comparative Example 2: Single food waste fermentation carbon source

[0033] Treat the high-ammonia-nitrogen leachate from the waste incineration plant in the same way as in Example 2. Only food waste water is used for carbon source preparation, municipal sludge and composite bacterial agents are not added, and the VFAs production rate is as low as 0.21 g / g VS. The denitrification reactor uses ordinary ceramsite as the carrier, and controls HRT = 14 h. This process has the following defects: VFAs in the fermentation broth are mainly acetic acid (accounting for 65%), resulting in denitrification sludge bulking (SVI = 180 mL / g); SS>300 mg / L in the fermentation broth causes the reactor to be blocked 2 times a month, increasing the cleaning cost by 35%; the system denitrification performance is significantly limited, the TN removal rate is only 82.4%, and the denitrification rate is as low as 0.14 kg N / (m 3 ·d), and the comprehensive operation efficiency is low.

[0034] The effect comparisons of each example and comparative example are shown in Table 1.

[0035] Table 1 Comparative analysis of the effects of each example

[0036]

[0037] Note: The carbon source cost in Comparative Example 2 does not include the 35% cleaning cost increased due to reactor blockage.

[0038] Through the comparison between the examples and comparative examples of the present invention, significant technical advantages are demonstrated. By synergistically two-stage directional fermentation of food waste water and municipal sludge to prepare an efficient carbon source, combined with sulfur-iron modified biochar as the filler of the denitrification fixed bed and the intelligent control system, efficient denitrification and resource treatment of landfill leachate are realized. The TN removal rate is stably above 95% (only 82% - 89% for the traditional process), and the denitrification rate reaches 0.39 - 0.44 kg N / (m 3· d), which is 2.3 times higher than the methanol carbon source process; the carbon source cost is only 0.6 - 0.9 yuan / ton, saving 65% - 78% compared with the methanol process, and there is no risk of secondary pollution, with a COD compliance rate of 100%; the anti-clogging period of sulfur-iron modified biochar reaches 6 - 8 months, and the TN fluctuation is <±2%, far exceeding the 1-month lifespan and ±8% fluctuation of traditional carriers. The traditional methanol process in Comparative Example 1 has a high carbon source cost, serious COD over-standard, and low denitrification efficiency; the single food waste fermentation process in Comparative Example 2 has a low VFAs yield, suspended solid clogging, and weak nitrogen removal ability.

[0039] The present invention improves the VFAs yield to 0.48 - 0.51 g / gVS through the mixed fermentation of food waste wastewater and sludge, with the ratio of propionic acid / butyric acid > 75%, solving the problem of carbon source adaptability. The modified biochar synchronously provides electrons required for sulfur autotrophic and heterotrophic denitrification, and the denitrification rate is increased by 230%. Based on the fuzzy algorithm of C / N online feedback, precise carbon source dosing is achieved, and the comprehensive energy consumption is reduced by 15% - 22%. The examples of the present invention verify the wide applicability of the technical solution, while the comparative examples highlight the inherent defects of the traditional process in terms of cost, efficiency, and stability, further corroborating the innovation and practicality of the present invention. This technology provides an innovative "treating waste with waste" path for landfill leachate denitrification, with both environmental and economic benefits and broad application prospects.

Claims

1. A method for biological denitrification of landfill leachate based on co-fermentation of food waste, characterized in that It includes the following steps: (a) Mix municipal sludge after ultrasonic pretreatment with food waste wastewater at a volume ratio of 3:1 to 5:1 to form a mixed material; (b) Feed the material in step (a) into a two-stage continuous reactor after inoculating with a composite bacterium agent for two-stage acidogenic fermentation. The total amount of volatile fatty acids in the first stage reaches 10 - 15 g / L; in the second stage, adjust the reaction conditions to promote the proportion of propionic acid to increase to 35 - 40% and the proportion of butyric acid to increase to 25 - 30%; (c) Feed the leachate into a shortcut nitrification reactor, control the dissolved oxygen at 0.3 - 0.5 mg / L, pH at 7.8 - 8.2, and temperature at 25 - 35 °C to make the nitrite accumulation rate ≥ 85%; (d) Mix the shortcut nitrification effluent with the liquid carbon source obtained in step (b) at a C / N ratio of 3.5 - 4.2 and then feed it into a reactor. The fixed-bed reactor is filled with sulfur-iron modified biochar filler.

2. The method according to claim 1, wherein The composite bacterium agent described in step (b) includes: Candida tropicalis CGMCC 2.3067, Bacillus subtilis ATCC 6051, Clostridium butyricum CICC 10390, and the viable bacteria number ratio is 3:2:

1.

3. The method according to claim 1, wherein The two-stage fermentation described in step (b) includes: fermenting in the first stage at pH = 5 - 6, 35 - 38 °C for 48 - 72 h, and in the second stage, adjusting the pH to 7 - 7.5, temperature 25 - 28 °C and continuing to ferment for 24 - 36 h.

4. The method according to claim 1, wherein The sulfur-iron modified biochar described in step (d) is prepared by impregnating walnut shell biochar with a mixed solution of FeSO4 and Na2S2O3 and then calcining at high temperature, with a specific surface area ≥ 800 m 2 / g and an FeS x loading of 3-5 wt%.

5. The method according to claim 4, wherein The preparation method of sulfur-iron modified biochar includes: impregnating biochar in a mixed solution of 0.5 mol / L FeSO4 and 0.3 mol / L Na2S2O3 (volume ratio 2:1) for 2 h, and calcining at 600 °C for 1 h under nitrogen protection.

6. The method according to claim 1, wherein In the sulfur-iron modified biochar fixed-bed reactor described in step (d), a mixed bacterial community of Paracoccus denitrificans and Thiobacillus is inoculated, the bacterial community ratio is 2:1, and the filler porosity is controlled at 60 - 70%.

7. The method according to claim 1, wherein In step (d), the carbon source dosage is dynamically adjusted according to the C / N value of the leachate, and the C / N ratio in the denitrification section is controlled at 3.5 - 4.

2.

8. A system for biological nitrogen removal from landfill leachate based on co-fermentation of food waste, characterized in that, It includes: An ultrasonic pretreatment device (101), a mixing and blending tank (102), a two-stage anaerobic acidogenic reactor (201), a ceramic membrane filtration device (202), a fermentation liquid storage tank (203), a shortcut nitrification reactor (301), a sulfur-iron modified biochar fixed-bed denitrification reactor (302), and an intelligent carbon source dynamic regulation system (303).

9. The system according to claim 8, wherein The shortcut nitrification reactor is internally equipped with an online DO concentration regulation module to maintain the dissolved oxygen at 0.3 - 0.5 mg / L and pH = 7.8 - 8.

2.

10. The system according to claim 8, wherein The fermentation unit is equipped with an ultrasonic pretreatment device, and the treatment parameters are 20 kHz, 0.5 W / mL for 10 - 15 min.

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