Method and device for treating aged landfill leachate by ozone oxidation combined with short-cut denitrification-anaerobic ammonia oxidation

Abstract

The application discloses a method for treating aged landfill leachate by ozone oxidation and short-cut denitrification-anaerobic ammonia oxidation, and the aged landfill leachate is treated by an ozone oxidation unit and then treated by a short-cut denitrification-anaerobic ammonia oxidation (PDA) biological treatment unit, so that the treated leachate can be discharged up to the standard. The ozone oxidation unit continuously and efficiently cracks macromolecular refractory organic matters such as humic acid in the aged leachate by ozone, so that the biodegradability is significantly improved; and the proportion of nitrogen is simultaneously optimized, so that an ideal substrate of the PDA bacterial colony is formed. The PDA biological treatment unit is inoculated with mixed sludge of anaerobic ammonia oxidation sludge and denitrifying bacterial sludge in a UASB reactor, and after gradual domestication, the short-cut denitrification activity in the PDA biological treatment system is significantly higher than the nitrite reduction activity, so that the continuous supply of nitrite is ensured; and the anaerobic ammonia oxidation bacteria and the denitrifying bacteria are cooperatively metabolized, so that the problem of cracking of organic matters is solved. The process and device of the application provide a green and efficient innovative solution for high-ammonia-nitrogen and low-carbon-nitrogen-ratio refractory wastewater.

Description

Technical Field

[0001] This invention relates to the field of wastewater treatment technology, specifically to a method and apparatus for treating leachate from aged landfills using ozone oxidation in conjunction with short-cut denitrification and anaerobic ammonia oxidation. Background Technology

[0002] The composition and concentration of pollutants in landfill leachate change with the extension of landfill time. Landfill leachate produced after 8-10 years of landfilling is usually called aged landfill leachate, which is characterized by high ammonia nitrogen, low carbon-to-nitrogen ratio, and high content of recalcitrant organic matter. Its complex composition leads to low efficiency of traditional biological treatment processes: high ammonia nitrogen requires excessive aeration, while the low carbon-to-nitrogen ratio restricts the supply of carbon source for denitrification, resulting in insufficient total nitrogen removal rate; at the same time, large molecular organic matter such as humic acid inhibits microbial activity, further reducing the stability of biological treatment systems. Among the current mainstream processes, traditional nitrification-denitrification requires the addition of exogenous carbon sources and produces a large amount of sludge. Anaerobic ammonium oxidation (ANAO) has advantages such as no need for carbon sources, low aeration energy consumption, and low sludge production. However, stable partial nitrification is a prerequisite for achieving ANAO nitrogen removal. Existing short-cut nitrification-ANAO processes have difficulty exceeding 85% total nitrogen removal rate due to unstable nitrite accumulation and nitrate residue (>11%).

[0003] While ozone oxidation pretreatment of leachate from aged landfills can degrade some organic matter, its use alone cannot solve the denitrification bottleneck. Although the short-cut denitrification-anaerobic ammonia oxidation (PDA) process can achieve efficient denitrification by continuously supplying nitrite through short-cut denitrification, it faces the critical challenge of humic acid and other recalcitrant organic matter inhibiting the activity of anaerobic ammonia oxidizing bacteria. Existing technologies have not yet effectively addressed the common problems of organic matter inhibition and denitrification efficiency in a synergistic manner: in the simple combination of ozone pretreatment and PDA processes, ozone struggles to directionally break down humic acid to improve biodegradability and simultaneously optimize nitrogen speciation, while PDA microbial communities lack a gradual acclimatization mechanism to resist leachate toxicity, making it difficult to maintain the activity of functional microorganisms in the long term. Therefore, how to simultaneously achieve efficient conversion of recalcitrant organic matter, optimization of nitrogen speciation, and maintenance of functional microbial activity through process innovation has become the core challenge for the low-carbon and efficient treatment of leachate from aged landfills. Summary of the Invention

[0004] The purpose of this invention is to address two major problems existing in the simple combination of ozone pretreatment and PDA process in the treatment of leachate from aged landfills: ① Ozone does not completely degrade recalcitrant organic matter such as humic acid, resulting in limited improvement in the biodegradability of wastewater and no optimization of nitrogen forms; ② The PDA microbial community is inhibited by the toxicity of leachate, leading to a decrease in denitrification efficiency, and there is a lack of a gradual acclimation mechanism to ensure the long-term stability of the PDA system. The invention provides a method and apparatus for treating leachate from aged landfills by ozone oxidation in conjunction with short-range denitrification and anaerobic ammonia oxidation.

[0005] To achieve the above objectives, the technical solution provided by the present invention is as follows:

[0006] A method for treating leachate from aged landfills by ozone oxidation in conjunction with short-cut denitrification-anaerobic ammonium oxidation (PDA) involves treating the leachate from aged landfills by an ozone oxidation unit, followed by a short-cut denitrification-anaerobic ammonium oxidation (PDA) biological treatment unit, which enables the leachate to meet discharge standards.

[0007] When the ozone oxidation unit treats leachate from aged landfills, the mass ratio of ozone dosage to total nitrogen in the leachate is controlled to be (1-2):1, preferably 1.5:1.

[0008] In actual operation, the ozone generator produces ozone gas, the flow rate of ozone gas into the leachate of the aged landfill is set, and the time of ozone gas introduction into the leachate is controlled based on real-time monitoring of the mass transfer efficiency of ozone in the leachate, thereby controlling the amount of ozone added.

[0009] Among them, the NH4 in the influent of the short-cut denitrification-anaerobic ammonium oxidation (PDA) biological treatment unit is controlled. + -N:NO3 – -N=(0.9~1.1):1,COD:NO3 – -N = (2.4~2.8):1, to meet the ideal substrate requirements of PDA microbiota.

[0010] Preferably, the NH4 in the influent of the short-cut denitrification-anaerobic ammonium oxidation (PDA) biological treatment unit is controlled. + -N:NO3 – -N = 1:1, COD:NO3 – -N = 2.6:1.

[0011] The COD (chemical oxygen demand) content in the leachate from the aged landfill is not higher than 2500 mg·L⁻¹. –1 The BOD5 (five-day biochemical oxygen demand) content is 150–200 mg·L⁻¹. –1 The DOC (dissolved organic carbon) content is not higher than 300 mg·L⁻¹. –1 NH4 + -N (ammonia nitrogen) content not exceeding 800 mg·L –1 The TN (total nitrogen) content is not higher than 1000 mg·L⁻¹. –1 .

[0012] Preferably, the COD content in the leachate from the aged landfill is 1500–2000 mg·L⁻¹. –1 BOD5 content is 150-200 mg / L -1BOD5 / COD < 0.1, DOC content 200–300 mg / L -1 The TN content is 700–800 mg·L. –1 NH4 + -N content is 600-700 mg·L -1 .

[0013] More preferably, the COD content in the leachate from the aged landfill is 1886 mg·L⁻¹. –1 The BOD5 content is 157 mg·L⁻¹ -1 The BOD5 / COD ratio is 0.08, and the DOC content is 225 mg·L⁻¹. -1 The TN content is 745 mg·L. –1 NH4 + -N content is 629 mg·L -1 .

[0014] The organic matter in leachate from aged landfills is mainly composed of recalcitrant macromolecular organic compounds (i.e., humic substances). Due to long-term hydrolysis and fermentation, the nitrogen-containing organic matter in the leachate has an excessively high ammonia nitrogen concentration, resulting in a C / N imbalance and significant low-carbon, high-nitrogen characteristics. Furthermore, this type of wastewater has extremely poor biodegradability, with a low BOD5 / COD ratio (usually <0.1), which inhibits the microorganisms in the biological treatment process and causes the biological treatment system to operate unstablely. This makes leachate from aged landfills a challenging problem in landfill leachate treatment.

[0015] In this invention, in the ozone oxidation unit, by controlling the mass ratio of ozone participating in the ozone oxidation reaction to the total nitrogen (TN) in the leachate of aged landfill to be (1-2):1, efficient pyrolysis of humic acid, improved wastewater biodegradability, and controlled directional conversion of nitrogen forms are achieved. ① Improved wastewater biodegradability: When aged landfill leachate reacts with ozone, under strong oxidation, large molecular organic matter such as humic acid is oxidized and decomposed into small molecular hydrophilic substances, improving the biodegradability of the wastewater. Ozone pretreatment increases the SUVA (superoxide dismutase) of the aged landfill leachate. 254 (Comparison of UV absorbance, SUVA) 254 =UV 254 / DOC reflects the amount of natural humic macromolecular organic matter and aromatic compounds containing C=C and C=O double bonds present in water. SUVA 254 The higher the value, the higher the degree of aromatization of organic matter in the water and the greater the content of humic substances. (The value decreased to 2.5 L·(mg·m³)) –1 Below, UV 250 / UV 365(This ratio is negatively correlated with the molecular weight of dissolved organic matter in wastewater; an increase in the ratio reflects a decrease in the proportion of large molecular weight humic substances.) When it rises above 20, the BOD5 / COD ratio increases by more than 170%. ② Controlled directional conversion of nitrogen forms: After ozone oxidation, the nitrogen ratio in the leachate from aged landfills is optimized, and nitrogen-containing compounds in the wastewater are converted into NH4. + -N or NO3 – -N.

[0016] When leachate from old landfills is treated with ozone oxidation, the resulting wastewater contains COD and NO3. – When the COD:NO3 ratio is less than 2.4–2.8, an external carbon source (e.g., sodium acetate) can be added to the wastewater to meet the COD:NO3 ratio. – After meeting the requirement of -N=(2.4~2.8):1, the wastewater is then fed into the PDA biological treatment unit for further treatment. Because leachate from aged landfills has a low carbon-to-nitrogen ratio, this type of wastewater, after ozone oxidation treatment, will have a COD:NO3 ratio of [missing information]. – The ratio of -N is generally no greater than 2.8, therefore there is no need to consider COD:NO3 in the effluent after ozone oxidation treatment. – When the -N ratio is greater than 2.8, the NH4+ in the wastewater generated after ozone oxidation treatment of leachate from aged landfills... + -N and NO3 – When the -N ratio is not in the range of 0.9 to 1.1, NH4+ can be added to it. + -N (e.g., ammonium chloride) or NO3 – -N (e.g., sodium nitrate) makes it meet the influent requirements of the PDA biological treatment unit.

[0017] The short-cut denitrification-anaerobic ammonium oxidation biological treatment unit is a UASB reactor (upflow anaerobic sludge bed reactor) inoculated with mixed sludge composed of anaerobic ammonium oxidation sludge and denitrification sludge.

[0018] The MLVSS ratio of the anaerobic ammonia oxidation sludge to the denitrifying bacteria sludge is (2.5-3.5):1, preferably 3:1, and the sludge concentration of the mixed sludge is 10-15 g·L⁻¹. –1 Preferably 12 g·L –1 The anaerobic ammonia oxidation sludge and the denitrifying bacteria sludge were mixed at an MLVSS ratio of (2.5–3.5):1. The sludge concentration of the mixture was then adjusted to 10–15 g·L⁻¹ by adding physiological saline or phosphate buffer. –1 Preferably 12 g·L –1 .

[0019] The anaerobic ammonia oxidation sludge and denitrifying bacteria sludge mentioned are both commercially available ordinary anaerobic ammonia oxidation sludge and denitrifying bacteria sludge.

[0020] When the UASB reactor is running, the hydraulic retention time is 8-12 hours, preferably 10.4 hours, the operating temperature is 28-32°C, preferably 29-30°C, and the mixed liquor reflux ratio is 10-20%, preferably 14-15%.

[0021] The mixed sludge needs to undergo multi-stage gradient acclimatization after being inoculated into the UASB reactor.

[0022] The multi-stage gradient acclimatization method is as follows: In the first stage, simulated wastewater is used as the influent to the UASB reactor, during which the NH4 content in the influent is gradually increased. + After the -N concentration stabilizes, the second stage begins, using a mixed wastewater consisting of simulated and actual wastewater as the feed water to the UASB reactor. During this stage, the proportion of actual wastewater in the mixed wastewater is gradually increased. After the operation stabilizes, the third stage begins, using the actual wastewater as the feed water to the UASB reactor. Once the operation stabilizes, the acclimation is complete. Throughout the three stages of operation, the carbon and nitrogen content in the feed water to the UASB reactor is consistently maintained at NH4+. + -N:NO3 – -N=(0.9~1.1):1,COD:NO3 – -N=(2.4~2.8):1; The actual wastewater is the effluent from the leachate of the old landfill after ozone oxidation treatment; The simulated wastewater is the simulated wastewater of the actual wastewater.

[0023] Preferably, the multi-stage gradient acclimatization method is as follows: in the first stage, simulated wastewater is used as the influent to the UASB reactor, during which the NH4 content in the influent is gradually increased. + -N concentration to the actual NH4 in wastewater + With the same -N concentration, the microbial community in the activated sludge was trained to adapt to high ammonia nitrogen content. After stable operation, the second stage was carried out, using a mixed wastewater consisting of the simulated wastewater and the actual wastewater as the influent to the UASB reactor. During this stage, the volume ratio of the actual wastewater in the mixed wastewater was gradually increased from about 30% to about 70% to enhance the antitoxicity ability of the microbial community in the activated sludge. After stable operation, the third stage was carried out, using the actual wastewater as the influent to the UASB reactor. After stable operation, the acclimation was completed. During the operation of the above three stages, the carbon and nitrogen content in the influent of the UASB reactor was always maintained at NH4+. + -N:NO3 – -N=(0.9~1.1):1,COD:NO3 – -N=(2.4~2.8):1; The actual wastewater is the effluent from the leachate of the old landfill after ozone oxidation treatment; The simulated wastewater is the simulated wastewater of the actual wastewater.

[0024] The aforementioned operational stability refers to the effluent quality of the UASB reactor at each stage being consistently maintained at NH4. + -N≤25mg·L –1 TN≤40mg·L –1 COD≤100mg·L –1 And it should remain stable for at least 7 days.

[0025] The simulated wastewater contains NH4. + -N, NO3 – -N, magnesium ions, calcium ions, phosphate ions, trace elements, and common carbon sources (such as glucose, sodium acetate, methanol, ethanol, acetic acid, lactic acid, flour, citric acid, propionic acid, calcium carbonate, and sodium carbonate).

[0026] After acclimatization, the mixed sludge undergoes a short-cut denitrification-anaerobic ammonium oxidation biological treatment process. During this process, the denitrifying bacteria in the mixed sludge use COD as an electron donor to convert NO3 into nitrogen. – -N is selectively reduced to NO2. – -N, its short-range denitrification (reducing NO3) – -N is reduced to NO2 – -N) activity (2.68 kg N·(kg VSS·d) –1 The levels (around 100%) are significantly higher than those of its nitrite reduction (which reduces NO2). – -N reduction to N2) activity (0.076 kg N·(kg VSS·d)) –1 (Approximately), ensuring a continuous and stable formation of nitrite; anaerobic ammonia-oxidizing bacteria use NH4+. + -N is an electron donor, NO2 – -N is an electron acceptor, metabolized to produce N2 (anaerobic ammonia oxidation activity ≥ 0.5 kg N·(kgVSS·d)). –1 This allows for efficient nitrogen removal.

[0027] After treatment by the method of this invention, the leachate from the aged waste meets the requirements of the "Pollution Control Standard for Municipal Solid Waste Landfills" (GB 16889-2024): NH4 + -N≤25mg·L –1 TN≤40mg·L –1 COD≤100mg·L –1 .

[0028] The present invention also claims an apparatus for implementing the above-described method of ozone oxidation synergistic short-cut denitrification-anaerobic ammonium oxidation for treating leachate from aged landfills, comprising an ozone oxidation unit, an intermediate water tank, and a short-cut denitrification-anaerobic ammonium oxidation biological treatment unit connected in sequence.

[0029] The ozone oxidation unit includes an ozone generator and an ozone oxidation reaction vessel that are connected to each other.

[0030] Preferably, the ozone oxidation unit includes an ozone generator, a first ozone detector, an ozone oxidation reaction vessel, an ozone dryer, a second ozone detector, and an ozone absorber connected in sequence. The first and second ozone detectors are used to detect the ozone concentration in the ozone gas generated by the ozone generator before and after it is introduced into the leachate from the aged landfill, respectively.

[0031] The short-cut denitrification-anaerobic ammonium oxidation biological treatment unit includes a UASB reactor inoculated with a mixed sludge consisting of anaerobic ammonium oxidation sludge and denitrification sludge.

[0032] Preferably, the UASB reactor has an inlet on the bottom outer wall and an outlet on the top outer wall. A reflux outlet is located on the upper outer wall of the UASB reactor below the outlet. The reflux outlet is connected to the inlet via a pipe, and a circulation pump is installed on the pipe to reflux the liquid inside the UASB reactor.

[0033] Preferably, the intermediate water tank is provided with an inlet and an outlet. The inlet of the intermediate water tank is connected to the outlet of the ozone oxidation reactor, and the outlet of the intermediate water tank is connected to the inlet of the UASB reactor through a pipe. An inlet pump is installed on the pipe. The hydraulic residence time of the UASB reactor is controlled by controlling the speed of the inlet pump, and the mixed liquor reflux ratio of the UASB reactor is controlled by coordinating the speeds of the circulation pump and the inlet pump.

[0034] Preferably, the intermediate water tank is equipped with a water quality detection sensor and a dosing device.

[0035] After being treated with ozone oxidation, the leachate from aged landfills is introduced into an intermediate water tank. The NH4 content of the wastewater in the intermediate water tank is monitored by a water quality sensor. + -N, NO3 – -N and COD content: When the water quality of the wastewater in the intermediate tank does not meet the UASB influent water quality requirements, reagents are added through the dosing device to adjust it. After meeting the UASB influent water quality requirements, the wastewater in the intermediate tank is pumped into the UASB reactor through the influent pump for short-cut denitrification-anaerobic ammonia oxidation biological treatment.

[0036] Beneficial effects:

[0037] (1) This invention achieves efficient pyrolysis of humic acid by regulating the ozone oxidation process, thereby improving the biodegradability of wastewater, increasing the BOD5 / COD ratio by more than 170%, controlling the directional transformation of nitrogen forms, and directionally optimizing the substrates required by PDA bacteria in the UASB reactor influent, thus realizing efficient and stable nitrogen and carbon removal of the PDA biological system and improving the NH4 content of the effluent. + -N≤25mg·L –1 TN≤40mg·L –1 COD≤100mg·L –1 It meets the "Standard for Pollution Control of Municipal Solid Waste Landfills" (GB 16889-2024).

[0038] (2) This invention ensures a continuous and stable supply of nitrite by short-range denitrifying bacteria and stable metabolism of anaerobic ammonia oxidizing bacteria through the synergistic effect of gradually domesticating PDA bacteria, thus solving the problem of the toxic inhibition of microbial communities by organic matter. Attached Figure Description

[0039] The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments, and the advantages of the present invention in the above and / or other aspects will become clearer.

[0040] Figure 1 This is a schematic diagram of the device of the present invention.

[0041] Figure 2 Figure 2 shows the BOD5 / COD (a) and SUVA ratios in the wastewater from the continuous ozone oxidation treatment of leachate from aged landfills in Example 2. 254 (Figure b) and UV 250 / UV 365 The changes shown in Figure (c).

[0042] Figure 3 Figure a shows the concentrations of DOC and COD in the wastewater during continuous ozone oxidation treatment of leachate from aged landfills in Example 2, as well as the nitrogen conversion (Figure b).

[0043] Figure 4 The activity characteristics of functional microorganisms in the PDA biological system during the sludge acclimatization to stages 3 and 6 in Example 3 are shown.

[0044] Figure 5 Figure 3 shows the operational performance of the UASB reactor at each stage of sludge acclimation in Example 3; where Figure a shows the NH4+ in the influent and effluent. + -N and NO3 – -N, NO2 in the effluent – -N concentration and TN removal rate; Figure b shows the COD and DOC concentrations in the influent and effluent.

[0045] The reference numerals in the attached figures represent: 1. Ozone oxidation unit; 2. Intermediate water tank; 3. PDA biological treatment unit; 11. Ozone generator; 12. Ozone oxidation reaction vessel; 13. First ozone detector; 14. Ozone dryer; 15. Second ozone detector; 16. Tail gas absorption device; 31. UASB reactor; 32. Circulation pump; 33. Inlet pump. Detailed Implementation

[0046] The present invention will be further described below with reference to the following embodiments. It should be understood that the following embodiments are for illustrative purposes only and are not intended to limit the present invention.

[0047] Example 1

[0048] like Figure 1 The diagram shows an apparatus for treating leachate from aged landfills using ozone oxidation in conjunction with short-cut denitrification-anaerobic ammonia oxidation (PDA). The apparatus comprises an ozone oxidation unit 1, an intermediate water tank 2, and a PDA biological treatment unit 3, connected in sequence. The ozone oxidation unit 1 includes an ozone generator 11, a first ozone detector 13, an ozone oxidation reaction tank 12 (1L volume, made of 316L stainless steel), an ozone dryer 14, a second ozone detector 15, and a tail gas absorption device 16, all connected in sequence via pipelines. The PDA biological treatment unit includes a UASB reactor 31 (made of plexiglass, with an inner diameter of 80 mm, a height of 500 mm, and an effective volume of 1.3 L). The UASB reactor 31 has an inlet on its bottom outer wall and an outlet on its top outer wall. A reflux outlet is located on the upper outer wall of the UASB reactor 31, below the outlet. The reflux outlet is connected to the inlet via a pipe, and a circulation pump 32 is installed on the pipe to reflux the liquid inside the UASB reactor 31. An intermediate water tank 2 has an inlet and an outlet. The inlet of the intermediate water tank 2 is connected to the outlet of the ozone oxidation reactor 12, and the outlet of the intermediate water tank 2 is connected to the inlet of the UASB reactor 31 via a pipe. An inlet pump 33 is installed on the pipe. The hydraulic residence time of the UASB reactor 31 is controlled by controlling the speed of the inlet pump 33, and the mixed liquor reflux ratio of the UASB reactor 31 is controlled by coordinating the speeds of the circulation pump 32 and the inlet pump 33. The intermediate water tank is equipped with a water quality sensor and a dosing device.

[0049] After being treated by ozone oxidation unit 1, the leachate from aged landfills is introduced into intermediate water tank 2. The NH4 content of the wastewater in intermediate water tank 2 is monitored by a water quality sensor. + -N, NO3 –-N and COD content: When the water quality of the wastewater in the intermediate water tank does not meet the influent water quality requirements of UASB reactor 3, reagents are added through the dosing device to adjust it. After meeting the influent water quality requirements of UASB reactor 31, the wastewater in the intermediate water tank 2 is pumped into the UASB reactor through the influent pump 33 for short-cut denitrification-anaerobic ammonia oxidation biological treatment.

[0050] Example 2

[0051] The ozone oxidation synergistic short-range denitrification-anaerobic ammonia oxidation treatment device of Example 1 was used to treat 1 L of leachate from an aged (25-30 years old) municipal solid waste landfill in Shanghai. The physicochemical properties of the leachate are shown in Table 1.

[0052] The leachate from the aged landfill is coarsely filtered to remove suspended solids, and then passed into ozone oxidation reactor 12. The ozone generator produces an ozone concentration of 85–90 mg / L. –1 It was introduced into the leachate from the aged waste, with the ozone flow rate set at 200 L·min. –1 The ozone concentration before and after the leachate from the aged waste is monitored in real time using a first ozone detector and a second ozone detector. The ozone dosage (g) is calculated using the formula: Ozone dosage (g) = Q × ∫ 0t t ([O3)) in -[O3] out The calculation shows that when ozone gas is introduced into the leachate of the aged landfill for 6 hours, the requirement of an ozone dosage to total nitrogen in the leachate mass ratio of 1.5:1 is met. In the above formula, [O3] in The ozone concentration (90 mg·L⁻¹) before ozone gas is introduced into the leachate of aged landfill. –1 ), [O3] out To monitor the ozone concentration (mg·L) after ozone gas is introduced into the leachate of aged landfill in real time. –1 ), t is the ozone treatment time (h), Q is the ozone gas flow rate (200 L·min). –1 ).

[0053] During this period, the UV spectral parameters of the wastewater in ozone oxidation reactor 12 were monitored simultaneously, such as... Figure 2 As shown, SUV 254 From the initial 4.2 L·(mg·m –1 Reduced to 2.1 L·(mg·m³) –1 ( Figure 2 c) UV 250 / UV 365 The concentration increased from 4.5 to 21.8, indicating a rise in the proportion of small-molecule hydrophilic substances. Figure 2b); BOD5 / COD increased from 0.08 to 0.14, an increase of 170% ( Figure 2 a).

[0054] SUVA 254 =UV 254 / DOC, where UV 254 Ultraviolet absorbance of organic matter in wastewater at a wavelength of 254 nanometers (unit: m). -1 DOC stands for dissolved organic carbon content in wastewater (unit: mg / L). SUVA 254 This reflects the amount of natural humic macromolecular organic matter and aromatic compounds containing C=C and C=O double bonds present in the water. SUVA 254 The higher the value, the higher the degree of aromatization of organic matter in the water and the greater the content of humic substances. UV 250 / UV 365 The ratio is negatively correlated with the molecular weight of dissolved organic matter in wastewater; an increase in the ratio reflects a decrease in the proportion of macromolecular humic substances. Among these, UV... 250 and UV 365 These are the ultraviolet absorbance (in nm) of organic matter in wastewater at wavelengths of 250 nm and 365 nm, respectively. -1 ).

[0055] After 6 hours of ozone oxidation, the removal rates of COD and DOC (soluble organic carbon) in the leachate from aged landfills both reached over 60% (e.g., Figure 3 a) Simultaneously, nitrogen-containing compounds are converted into NH4 through ozone oxidation. + -N and NO3 – -N, ultimately NH4 in the water + -N:NO3 – -N=300mg·L –1 300mg·L –1 (The ratio is 1 ± 0.05) (e.g.) Figure 3 b) COD content is 530 mg·L⁻¹ –1 .

[0056] Table 1. Main Physicochemical Properties of Leachate from Aged Landfill

[0057]

[0058]

[0059] Example 3

[0060] PDA biological treatment system domestication:

[0061] Anaerobic ammonia oxidation sludge and denitrification sludge taken from a pilot wastewater treatment plant at a pig farm were mixed at a biomass (MLVSS) ratio of 3:1, and the sludge concentration was controlled at 12 g·L⁻¹. -1 The inoculated material was introduced into the UASB reactor described in Example 1 to form a PDA biological treatment system. The system was then started up and acclimatized. This process was divided into 6 stages, and the operating conditions of the UASB reactor in each stage are shown in Table 2.

[0062] In the first three stages, simulated wastewater from leachate from aged landfills was used as the influent to the UASB reactor to acclimate and cultivate a mixed sludge of anaerobic ammonia oxidation sludge and denitrification sludge. During this stage, the concentrations of ammonia nitrogen (derived from ammonium chloride) and nitrate (derived from sodium nitrate) in the influent were adjusted to ensure optimal NH4+ levels. + -N concentration from 100 mg·L –1 Gradually increase to 300 mg·L –1 NO3 – -N and NH4 + The ratio of -N concentration was maintained at 1 ± 0.05; sodium acetate was used as the carbon source to maintain the COD and NO3 concentrations in the influent. – The -N concentration ratio was 2.6 ± 0.2; the influent pH was controlled at 7.0 ± 0.2. The formulation of the simulated wastewater is shown in Table 3.

[0063] In stages 4 and 5, the UASB reactor influent was a mixture of simulated wastewater and the effluent from ozone oxidation treatment of actual aged landfill leachate in Example 2 (hereinafter referred to as Example 2 effluent). The NH4 content in the simulated wastewater was adjusted... + -N, NO3 – The concentrations of -N and COD cause NO3 in the influent to... – -N and NH4 + The ratio of -N concentration remained at 1 ± 0.05, and the ratio of COD to NO3... – The -N concentration ratio was maintained at 2.6 ± 0.2. The aim was to assess the impact of aged landfill leachate in the influent on the PDA reactor and to prepare for the final treatment of effluent from actual aged landfill leachate after ozone oxidation.

[0064] In stage 6, the effluent from Example 2 was supplemented with sodium acetate (the added carbon source sodium acetate reduced the COD and NO3 in the wastewater). – The long-term denitrification performance of the PDA process was investigated using water with a ratio of -N = 2.6:1 as the feed water to the UASB reactor.

[0065] Figure 4 The figure shows the functional microbial activity characteristics in the PDA biological treatment system of this invention. As can be seen from the figure, at the end of stages 3 and 6, short-cut denitrification (NO3)... – -N is reduced to NO2 –-N) Active SDAA > 2.6 kg N·(kg VSS·d) - 1; Anaerobic ammonia oxidation activity (SAA) > 0.5 kg N·(kg VSS·d) - 1; Nitrite reducing activity (SNRA) < 0.076 kg N·(kgVSS·d) –1 The SDAA / SNRA ratio > 35 indicates that the short-cut denitrifying bacteria and anaerobic ammonia oxidizing bacteria in the PDA process of this invention have high activity, and nitrite can accumulate stably, overcoming the instability of nitrite accumulation in existing technologies. Furthermore, the activity characteristics of the activated sludge at the end of stage 3 (simulated wastewater acclimatization stage) and the end of stage 6 (actual leachate treatment stage) are very similar, indicating that the addition of actual leachate did not affect the activity of functional microorganisms.

[0066] Figure 5 The figure shows the water quality of the UASB reactor influent and effluent during the above six stages of operation. As can be seen from the figure, at the end of the sixth stage (day 130, acclimatization ended, UASB reactor successfully started up), the UASB reactor was operating stably, and the TN (total nitrogen) in the original old landfill leachate was 745 mg·L⁻¹. –1 The total nitrogen (TN) in the effluent remained stable at around 33 mg·L⁻¹, with a TN removal rate of 95.6%. The COD in the original leachate from the old landfill was 1886 mg·L⁻¹. –1 The effluent COD remained stable at around 34 mg·L⁻¹, with a COD removal rate of 98.2%; effluent quality: NH₄⁺ + -N < 15 mg·L –1 TN < 37 mg·L –1 COD < 42 mg·L⁻¹, meeting the limit (NH₄) of GB 16889-2024. + -N≤25mg·L –1 TN≤40mg·L –1 COD≤100mg·L –1 It can meet emission standards.

[0067] Table 2 Operational Design for the Start-up and Acclimation Phase of the UASB Reactor

[0068]

[0069] Table 3 Simulated wastewater formulation

[0070]

[0071] The formulations for trace elements I and II are shown in Table 4 and Table 5, respectively.

[0072] Table 4 Trace Elements I (g·L) -1 )

[0073]

[0074]

[0075] Table 5 Trace Elements II (g·L) -1 )

[0076]

[0077] After the PDA biological treatment system was acclimatized, the effluent from Example 2 was treated using a UASB reactor to examine the long-term stability of the PDA biological treatment system. Figure 5 As shown, after the acclimatization period ended (day 130), the system continued to operate for another 20 days, and the effluent water quality remained stable throughout. The effluent water quality was: NH4 + -N < 15 mg·L –1 TN < 37 mg·L –1 COD < 42 mg·L⁻¹, meeting the limit (NH₄) of GB 16889-2024. + -N≤25mg·L –1 TN≤40mg·L –1 COD≤100mg·L –1 It can meet emission standards.

[0078] This invention provides a concept and method for treating leachate from aged landfills using ozone oxidation in conjunction with short-cut denitrification and anaerobic ammonia oxidation. Many methods and approaches exist for implementing this technical solution; the above description is merely a preferred embodiment of the invention. It should be noted that those skilled in the art can make various improvements and modifications without departing from the principles of this invention, and these improvements and modifications should also be considered within the scope of protection of this invention. All components not explicitly stated in this embodiment can be implemented using existing technologies.

Claims

1. A method for treating aged landfill leachate by ozone oxidation in combination with short-cut denitrification-anaerobic ammonia oxidation, characterized in that, The aged landfill leachate is treated by an ozone oxidation unit, and then treated by a short-cut denitrification-anammox biological treatment unit, so that the treated water can be discharged up to the standard. The COD content in the old landfill leachate is 1500-2000 mg / L -1 , the BOD5 content is 150-200 mg / L -1 , the BOD5 / COD is less than 0.1, the DOC content is 200-300 mg / L -1 , the TN content is 700-800 mg / L -1 , and the NH4 + -N content is 600-700 mg / L -1 . The mass ratio of the ozone oxidation unit processing aged landfill leachate to the total nitrogen in the aged landfill leachate is controlled to be (1-2):1; the mass ratio of the short-cut denitrification-anaerobic ammonia oxidation biological treatment unit to the total nitrogen in the influent is controlled to be (0.9-1.1):1, and the mass ratio of the short-cut denitrification-anaerobic ammonia oxidation biological treatment unit to the total nitrogen in the effluent is controlled to be (2.4-2.8):

1. + -N : NO3 - -N = (0.9 ~ 1.1) : 1, COD : NO3 - -N = (2.4 ~ 2.8) :

1.

2. The method of claim 1, wherein, The short-cut denitrification-anammox biological treatment unit is a UASB reactor inoculated with mixed sludge composed of anammox sludge and denitrification sludge.

3. The method of claim 2, wherein, The MLVSS ratio of the anaerobic ammonia oxidation sludge to the denitrification sludge in the mixed sludge is (2.5-3.5):1; and the sludge concentration of the mixed sludge is 10-15 g·L –1 .

4. The method of claim 2, wherein, When the UASB reactor is operated, the hydraulic retention time is 8-12 h, the working temperature is 28-32 DEG C, and the mixed liquid reflux ratio is 10-20%.

5. The method of claim 2, wherein, After the mixed sludge is inoculated into the UASB reactor, multi-stage gradient acclimation is needed.

6. The method of claim 5, wherein, The method of the multi-stage gradient acclimation is: in the first stage, simulated wastewater is used as the influent of the UASB reactor, during which the NH4 + -N concentration in the influent is gradually increased to the same as the ammonia nitrogen concentration in the actual wastewater; after stable operation, in the second stage, mixed wastewater composed of the simulated wastewater and the actual wastewater is used as the influent of the UASB reactor, during which the proportion of the actual wastewater in the mixed wastewater is gradually increased; after stable operation, the third stage is entered, in which the actual wastewater is used as the influent of the UASB reactor, and after stable operation, the acclimation is completed. During the above three stages, the carbon and nitrogen content in the influent of the UASB reactor is always kept as NH4 + -N: NO3 - -N = (0.9 ~ 1.1) : 1, COD : NO3 - -N = (2.4 ~ 2.8) : 1; the actual wastewater is effluent after the aged landfill leachate is treated by the ozone oxidation; and the simulated wastewater is simulated wastewater of the actual wastewater.

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