Method and system for biological denitrification of landfill leachate based on synergistic fermentation of kitchen waste

Abstract

The application discloses a kind of waste leachate biological denitrification method and system based on kitchen waste synergic fermentation, by mixing kitchen waste water and municipal sludge according to specific proportion, inoculate composite inoculant and carry out two-stage anaerobic fermentation, and the fermentation liquor rich in propionic acid, butyric acid is injected into waste leachate treatment system as external carbon source.Waste leachate treatment system innovatively uses sulfur iron modified biochar to load denitrifying bacteria to construct fixed bed reactor, combined with pre-position short-path nitrification process and intelligent carbon source dynamic control system, realize carbon source precise supply and denitrification efficiency improvement.The application not only reduces the use cost of traditional carbon source, but also realizes the simultaneous treatment of three types of waste, and the denitrification efficiency is more than 92%, and the total nitrogen removal load is increased by 40% compared with traditional process.

Description

Technical Field

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

[0002] With the acceleration of urbanization, leachate from municipal solid waste landfills and incinerators has become a typical example of highly polluted wastewater. This type of wastewater typically features high ammonia nitrogen concentrations, an imbalanced carbon-to-nitrogen ratio, and complex composition, with total nitrogen removal being a particularly long-standing challenge for the industry. Traditional treatment processes often employ a biological denitrification route of nitrification-denitrification, but the raw carbon source in the leachate is severely insufficient, leading to a lack of electron donors during the denitrification stage. This forces operators to add large amounts of commercial carbon sources such as methanol and sodium acetate. Statistics show that the cost of commercial carbon sources accounts for 35% to 50% of the total cost of leachate treatment, and excessive addition can easily cause COD levels in the effluent to exceed standards, resulting in secondary pollution.

[0003] In existing technologies, physicochemical methods such as stripping and breakpoint chlorination can remove some ammonia nitrogen, but stripping is energy-intensive, with steam consumption reaching 50-80 kg / m³. 3 Breakpoint chlorination produces toxic byproducts such as chloroform. While membrane separation technology can achieve deep denitrification, frequent cleaning due to membrane fouling dramatically increases maintenance costs; the cost of replacing a reverse osmosis membrane reaches 300-500 yuan / m³. 2 In biological nitrogen removal, while the short-cut nitrification-anaerobic ammonium oxidation combined process can reduce carbon source demand, it is sensitive to environmental conditions, such as maintaining a water temperature of 30-35℃ and strictly controlling the pH at 7.5-8.0, resulting in poor stability in practical engineering. In recent years, research on alternative carbon sources, such as the use of food waste fermentation liquid in literature (Bioresour.Technol.2019,294:122218) and the use of food waste hydrolysate in literature (Bioresour.Technol.2021,341:125904), has gradually emerged. However, single-waste fermentation suffers from technical bottlenecks such as low acid production efficiency and poor carbon source component compatibility.

[0004] In the field of waste co-treatment, the joint resource utilization of kitchen wastewater and municipal sludge is still in the exploratory stage. Kitchen wastewater is rich in easily degradable organic matter, but it is prone to excessive acidification when fermented alone. Municipal sludge contains a large amount of microbial protein, but its dense cell wall structure leads to slow hydrolysis. Although the existing patent CN220976759U uses mixed fermentation of kitchen waste and biogas slurry to extract fermentation liquid as a carbon source in the denitrification system, it does not solve key problems such as carbon-nitrogen ratio control and fermentation product composition optimization. In addition, when the fermentation liquid is used directly as a carbon source, suspended solids and residual oils in it can easily clog the biological filter, reducing denitrification efficiency. In terms of denitrification carbon source supply technology, existing systems mostly adopt open-loop control strategies, adding carbon source in a fixed proportion, which is difficult to adapt to fluctuations in leachate water quality. Patent CN210193511U discloses a carbon source addition device based on online nitrate monitoring, but it does not consider the differences in the biodegradability of the carbon source in the fermentation liquid, which leads to deviations in the actual addition amount. Meanwhile, traditional denitrification reactors, which use ceramsite and activated carbon as carriers, lack electron transfer media, and their denitrification rates are often below 0.15 kgN / (m³). 3 •d). Although some studies, such as the literature (Chem.Eng.J.2025,511:161958), have attempted to add nano-zero-valent iron and biochar-modified polyurethane biocarriers to promote anaerobic ammonium oxidation and denitrification, they did not provide detailed explanations regarding the potential for iron passivation or the durability of the carrier. Furthermore, after 180 days of system operation, hydraulic scouring significantly reduced the amount of powdered nano-zero-valent iron and biochar adhering to the carrier surface. The literature (Water.Res.2023,245:120569) demonstrates that adding elemental sulfur to promote autotrophic denitrification can hinder mass transfer and clog wastewater pipes due to sulfur accumulation, thus affecting the stable operation of the system.

[0005] In summary, current landfill leachate denitrification treatment faces three major contradictions: first, the contradiction between the cost and economic viability of commercial carbon sources; second, the contradiction between the efficiency of carbon production from single waste fermentation and the demand for denitrification; and third, the contradiction between the electron transfer efficiency of the denitrification process and system stability. There is an urgent need to develop an integrated technology that combines waste co-processing, targeted carbon source conversion, and enhanced denitrification efficiency to achieve a breakthrough in both environmental and economic benefits. Summary of the Invention

[0006] This invention addresses the problems of high carbon source cost, insufficient denitrification efficiency, and low resource utilization rate of kitchen waste and municipal sludge in existing landfill leachate denitrification technologies. It proposes a biological denitrification method and system for landfill leachate based on the co-fermentation of kitchen waste. By integrating waste resource conversion, electron transfer enhancement, and intelligent control technologies, it achieves efficient, low-consumption, and stable denitrification.

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

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

[0009] This invention addresses the technical shortcomings of single-waste fermentation processes, such as low acid production efficiency and unstable carbon source composition, by proposing a method for targeted carbon source conversion based on the co-fermentation of kitchen wastewater and municipal sludge:

[0010] Kitchen wastewater and municipal sludge were mixed at a volume ratio of 3:1 to 5:1. First, pretreatment was performed to optimize the biodegradability of the substrate. Then, low-frequency ultrasound (20kHz, 0.5W / mL) was used to break up the municipal sludge flocs, releasing intracellular organic matter, resulting in a mixed substrate with a soluble COD content of over 85%. Figure 1 ).

[0011] A two-stage compound microbial inoculum-enhanced fermentation process was adopted for the treated mixture. In the first stage, a compound microbial inoculum of Candida tropicalis CGMCC 2.3067, Bacillus subtilis ATCC 6051, and Clostridium butyricum CICC 10390 with a live cell count ratio of 3:2:1 was added. Fermentation was carried out at pH 5-6 and 35-38℃ for 48-72 hours. Through the synergistic effect of the microbial community, polysaccharides and proteins were decomposed into acetic acid and propionic acid. In the second stage, the pH was adjusted to 7-7.5 and the temperature was lowered to 25-28℃ to extend the fermentation for 24-36 hours. This promoted the directional conversion of acetic acid to butyric acid by Clostridium butyricum. Ultimately, the proportion of propionic acid and butyric acid in volatile fatty acids (VFAs) exceeded 75%, and the total yield reached 0.45-0.52 g / g VS, which is more than 40% higher than that of the single fermentation process.

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

[0013] 2. Design of a fixed-bed denitrification reactor using ferrous-modified biochar

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

[0015] Walnut shell biochar was used as a substrate, impregnated with a mixture of 0.5 mol / L FeSO4 and 0.3 mol / L Na2S2O3 (volume ratio 2:1), and then calcined at 600℃ for 1 h under nitrogen protection to form FeS. x (x=1~2) Biochar composite material supported by nanoparticles, with a specific surface area ≥800m² 2 / g, FeS xThe loading is 3-5 wt%. This material also possesses sulfur autotrophic denitrification electron donors (S... 2- / S0) and the electron-mediating function of heterotrophic denitrification (Fe 2+ / Fe 3+ (Redox cycle) can increase electron transfer rate by 2.3 times.

[0016] In a fixed-bed reactor ( Figure 2 The reactor is filled with sulfur-iron modified biochar (porosity 60-70%) and inoculated with a mixed flora of Paracoccus denitrificans and Thiobacillus denitrificans (viable bacteria ratio 2:1) to form a sulfur-iron-bacteria synergistic denitrification system. A porous water distributor (pore size distribution 0.5-2 mm) and a gas-liquid separator are installed inside the reactor to ensure a total nitrogen removal load of 0.35-0.42 kg N / (m³) under a hydraulic retention time (HRT) of 8-12 h. 3 ·d).

[0017] 3. Intelligent carbon source dynamic control system

[0018] To address the issues of excessive or insufficient carbon source addition in traditional methods, this invention integrates the following intelligent control modules: It acquires the C / N ratio of the influent to the denitrification stage in real time using a nitrate sensor with a detection limit of 0.1 mg / L and a COD spectrometer; it establishes a control model with C / N deviation, leachate flow rate, and temperature as input variables, and carbon source addition rate as the output variable, dynamically adjusting the fermentation broth addition amount (control accuracy ±5%) to stabilize the C / N ratio in the denitrification stage at 3.5–4.2; and it automatically adjusts the stirring intensity between 30–50 rpm based on the changing trend of the oxidation-reduction potential (ORP) within the reactor, controlling the aeration rate to maintain DO at 0.2–0.3 mg / L, achieving 15% energy savings compared to traditional PID control.

[0019] Through the above technical solution, the denitrification system of the present invention achieves significant improvements in the following aspects: First, it can simultaneously absorb 0.3 m³ of kitchen wastewater for every 1 ton of leachate treated. 3 0.08m of sludge 3 Carbon source costs are reduced by 65-70%; secondly, when the influent TN is 1400 mg / L, the effluent TN is <70 mg / L, the total nitrogen removal rate is ≥92%, and the denitrification rate reaches 0.38-0.45 kg N / (m³). 3 ·d); In addition, the anti-clogging cycle of sulfur-iron modified biochar is extended to 6-8 months, and the system has no efficiency decay after 180 days of continuous operation.

[0020] The implementation of this invention can effectively resolve the economic and technical contradiction in landfill leachate denitrification treatment, and provide an innovative solution for waste resource utilization and deep wastewater denitrification. Attached Figure Description

[0021] Figure 1 This is a flowchart of the method of the present invention;

[0022] Figure 2 This is a schematic diagram of the system structure. Detailed Implementation

[0023] The following examples and comparative examples illustrate the implementation process and technical effects of the present invention in detail. Examples 1-3 represent preferred embodiments of the present invention, and comparative examples 1-2 represent conventional process controls. All experimental data are from pilot-scale verification (processing capacity 10m³). 3 / d).

[0024] Example 1: Landfill Leachate Treatment

[0025] The specific implementation process for treating leachate from a landfill in this embodiment is as follows: For the raw water of landfill leachate with NH4+-N 1200mg / L, TN 1400mg / L, COD 4500mg / L and C / N=1.8, kitchen wastewater with COD of 35000mg / L is first mixed with municipal sludge at a volume ratio of 4:1. After pretreatment with ultrasonic waves at 20kHz and 0.5W / mL for 12 minutes to break down the flocs of municipal sludge, a compound bacterial agent of Candida albicans, Bacillus subtilis, and Clostridium butyricum is added with a live bacteria ratio of 3:2:1 and a total addition amount of 0.6‰. A two-stage anaerobic fermentation was then carried out. The first stage was conducted at pH 5.8, 37℃, and 30 rpm for 60 hours, achieving a VFA concentration of 8500 mg / L. The second stage involved adjusting the pH to 7.2, lowering the temperature to 27℃, and continuing fermentation for another 30 hours, increasing the propionic acid to butyric acid ratio to 77%. Finally, the product was filtered through a 0.1 μm ceramic membrane to obtain a carbon source with SS below 40 mg / L and a VFA yield of 0.48 g / g VS. This carbon source was then injected into a sulfur-iron modified biochar denitrification reactor, with FeS as the packing material. x Biochar with a content of 4.2 wt% and a porosity of 65% was inoculated with a 2:1 ratio of denitrifying *Paracoccus* and *Thiobacillus*. The carbon source dosage was dynamically adjusted using a fuzzy control algorithm to maintain a C / N ratio of 3.8. This was coupled with a short-cut nitrification reactor (DO 0.4 mg / L, pH 8.0, HRT 24 h, nitrite accumulation >90%), operating at an HRT of 10 h and a stirring intensity of 40 rpm. After treatment, the effluent TN decreased to 68 mg / L, and the total nitrogen removal rate was 95.1%, with NH4+... + -N 15mg / L, COD 380mg / L, carbon source cost 0.8 yuan / ton, which is 68% lower than the traditional process using methanol as carbon source, and the biochar does not clump after 6 months of continuous operation, and the TN removal rate fluctuates less than ±1.5%.

[0026] Example 2: Treatment of high ammonia nitrogen leachate from waste incineration plants

[0027] This embodiment describes the treatment of high ammonia nitrogen leachate from a waste incineration plant. The specific implementation process is as follows: Regarding NH4... + The raw leachate from a waste incineration plant with high ammonia nitrogen content (N 2000 mg / L, TN 2300 mg / L, COD 3800 mg / L, C / N = 1.2) was treated by first optimizing the carbon source preparation process, increasing the mixing ratio of kitchen wastewater and municipal dewatered sludge to 5:1. After two-stage anaerobic fermentation, the second-stage fermentation time was extended to 36 hours, increasing the VFA yield to 0.51 g / g VS and the butyric acid content to 40%. The stirring intensity was dynamically adjusted to 45 rpm using online ORP feedback, and the fermentation broth dosage was adjusted to 3.8%. The denitrification system was simultaneously improved, using FeS... x Sulfur-iron modified biochar with a loading rate increased to 4.5 wt% and pore size optimized (80% pore size: 0.5–2 mm) was used, combined with a micro-aerobic environment where dissolved oxygen (DO) was strictly controlled at 0.2–0.3 mg / L, and the treatment time (HRT) was extended to 12 hours. After treatment, the effluent TN decreased to 98 mg / L (removal rate 95.7%), and NH4+ decreased... + -N 22mg / L, COD 420mg / L, denitrification rate reaches 0.44kg N / (m 3 •d) The biochar operation cycle remained stable for up to 6 months without clogging, while intelligent aeration control reduced system energy consumption by 18%.

[0028] Example 3: Treatment of low C / N ratio mixed leachate

[0029] This embodiment describes the treatment of a low carbon-to-nitrogen ratio mixed leachate, and the specific implementation process is as follows: Regarding NH4... + A low C / N ratio mixed leachate with N 800 mg / L, TN 950 mg / L, COD 6200 mg / L, and C / N = 2.5 was first treated by monitoring the C / N value in real time using an online spectrometer and dynamically adjusting the fermentation broth dosage to 2.5% to ensure a C / N ratio of 3.5 in the denitrification stage. During the carbon source preparation stage, the proportion of Clostridium butyricum in the compound bacterial agent was increased to 40%, and the VFA composition was optimized to achieve a butyric acid content of 42%. Simultaneously, the denitrifying bacterial community was enhanced, increasing the proportion of denitrifying Paracoccus in the denitrification reactor to 70%, and the N2O emission rate was controlled below 0.5% by adding a gas-liquid separation device. The treated effluent had a TN of 45 mg / L (removal rate 95.3%) and NH4+ of... + -N 8mg / L, COD 520mg / L, carbon source cost reduced to 0.6 yuan / ton and overall energy consumption reduced by 22%, while achieving the simultaneous treatment of 0.25m³ of kitchen wastewater per ton of leachate treated. 3 and 0.06m of municipal sludge 3It combines efficient nitrogen removal, low-carbon operation, and waste resource utilization.

[0030] Comparative Example 1: Traditional Methanol Carbon Source Process

[0031] For treating landfill leachate similar to that in Example 1, methanol was used as the carbon source, with a C / N ratio of 4.0, and the denitrification reactor had a specific surface area of ​​500 m². 2 Using ordinary activated carbon as a carrier, with a treatment time (HRT) of 16h, the effluent TN reached only 150mg / L (removal rate 89.3%), and COD exceeded the standard (>500mg / L) due to methanol residue; the carbon source cost was as high as 2.8 yuan / ton, and the denitrification rate was as low as 0.18kg N / (m³). 3 ·d); Meanwhile, the activated carbon needs to be backwashed 3 times a month due to severe pore blockage, resulting in a TN removal rate fluctuation of ±8% and poor system operation stability.

[0032] Comparative Example 2: Carbon Source for Fermentation of Single Kitchen Wastewater

[0033] The high-ammonia nitrogen leachate from the waste incineration plant, treated in the same manner as in Example 2, used only kitchen wastewater as the carbon source, without adding municipal sludge or compound microbial agents, resulting in a VFA yield as low as 0.21 g / g VS. The denitrification reactor used ordinary ceramsite as a carrier, with a controlled HRT of 14 h. This process has the following drawbacks: acetic acid is the main VFA in the fermentation broth (65%), leading to denitrification sludge bulking (SVI = 180 mL / g); SS > 300 mg / L in the fermentation broth causes the reactor to clog twice a month, increasing cleaning costs by 35%; the system's denitrification performance is significantly limited, with a TN removal rate of only 82.4% and a denitrification rate as low as 0.14 kg N / (m³). 3 ·d), low overall operational efficiency.

[0034] Table 1 shows a comparison of the effects of each embodiment and the comparative example.

[0035] Table 1 Comparison and analysis of the effects of each embodiment

[0036]

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

[0038] This invention demonstrates significant technical advantages through a comparison of examples and comparative examples. It achieves efficient denitrification and resource recovery of landfill leachate through a two-stage directional fermentation process involving kitchen wastewater and municipal sludge to prepare a high-efficiency carbon source. This is combined with sulfur-iron modified biochar as the packing material for the denitrification fixed bed and an intelligent control system. The total nitrogen (TN) removal rate is consistently above 95% (compared to only 82%–89% in traditional processes), and the denitrification rate reaches 0.39–0.44 kgN / (m³). 3•d) This process improves upon the methanol carbon source process by 2.3 times; the carbon source cost is only 0.6-0.9 yuan / ton, saving 65%-78% compared to the methanol process, and there is no risk of secondary pollution. The COD compliance rate is 100%; the sulfur-iron modified biochar has an anti-clogging cycle of 6-8 months, and the TN fluctuation is <±2%, far exceeding the 1-month lifespan and ±8% fluctuation of traditional carriers. In contrast, the traditional methanol process in Comparative Example 1 has high carbon source costs, serious COD exceedances, and low denitrification efficiency; the single kitchen waste fermentation process in Comparative Example 2 has low VFA yield, suspended solids clogging, and weak denitrification capacity.

[0039] This invention increases the yield of VFAs to 0.48–0.51 g / gVS through co-fermentation of kitchen wastewater and sludge, with a propionic acid / butyric acid ratio >75%, thus solving the problem of carbon source compatibility. Modified biochar simultaneously provides the electrons required for sulfur autotrophic and heterotrophic denitrification, increasing the denitrification rate by 230%. Based on a fuzzy algorithm with online C / N feedback, precise carbon source addition is achieved, reducing overall energy consumption by 15%–22%. The embodiments of this invention verify the broad applicability of the technical solution, while comparative examples highlight the inherent defects of traditional processes in terms of cost, efficiency, and stability, further demonstrating the innovation and practicality of this invention. This technology provides an innovative "waste-to-waste" approach for denitrification of landfill leachate, possessing both environmental and economic benefits, and has broad application prospects.

Claims

1. A method for biological denitrification of landfill leachate based on co-fermentation of food waste, characterized in that... Includes the following steps: (a) Municipal sludge is pretreated by ultrasound and then mixed with kitchen wastewater at a volume ratio of 3:1 to 5:1 to form a mixture. (b) The material from step (a) is passed through an inoculated compound microbial agent and then into a two-stage continuous reactor for two-stage acid-producing fermentation; wherein the compound microbial agent comprises: Candida tropicalis CGMCC 2.3067, Bacillus subtilis ATCC6051, and Clostridium butyricum CICC 10390, with a viable cell ratio of 3:2:1; the two-stage acid-producing fermentation includes: the first stage fermentation at pH=5~6 and 35~38℃ for 48~72 h, and the second stage adjusting the pH to 7~7.5 and the temperature to 25~28℃ for 24~36 h; the total volatile fatty acid content in the first stage reaches 10~15 g / L; the second stage adjusts the reaction conditions to increase the proportion of propionic acid to 35~40% and the proportion of butyric acid to 25~30%; (c) Pass the leachate into a short-cut nitrification reactor, controlling the dissolved oxygen at 0.3~0.5 mg / L, pH at 7.8~8.2, and temperature at 25~35℃, so that the nitrite accumulation rate is ≥85%; (d) The short-cut nitrification effluent and the liquid carbon source obtained in step (b) are mixed at a C / N ratio of 3.5~4.2 and then fed into a reactor. The fixed-bed reactor is filled with ferrous sulfate modified biochar. The ferrous sulfate modified biochar is obtained by impregnating walnut shell biochar with a mixed solution of FeSO4 and Na2S2O3 and then calcining it at high temperature. It has a specific surface area ≥800 m² / g and a FeSO4 content of 100 g / g. x Loading capacity: 3~5 wt%.

2. The method according to claim 1, characterized in that, 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 at a volume ratio of 2:1 for 2 h, and calcining at 600℃ for 1 h under nitrogen protection.

3. The method according to claim 1, characterized in that, In step (d), the fixed-bed reactor of sulfur-iron modified biochar is inoculated with a mixed bacterial community of denitrifying paracoccus and thiobacillus, with a bacterial community ratio of 2:1, and the porosity of the packing is controlled at 60-70%.

4. The method according to claim 1, characterized in that, In step (d), the amount of carbon source added is dynamically adjusted according to the C / N value of the leachate, and the C / N ratio in the denitrification section is controlled to be 3.5~4.2.

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