A method for enhancing short-cut nitrification-denitrification processes

Abstract

This invention discloses a method for enhancing a short-cut nitrification-denitrification process. The process flow is as follows: influent → Feammox tank → short-cut nitrification tank → denitrification tank → NDFO tank → transition sedimentation tank → effluent. The transition sedimentation tank is used to hold NDFO sludge, thus facilitating the timed exchange of Feammox sludge and NDFO sludge. When the NDFO sludge and supernatant have completely entered the transition sedimentation tank, the Feammox sludge flows into tanks A / B. When the Feammox sludge has completely flowed into tanks A / B, the NDFO sludge flows from the transition sedimentation tank into tanks B / A. The sludge exchange frequency is adjusted according to changes in the influent / effluent water quality. This method, through the timed exchange of NDFO sludge and Feammox sludge, not only achieves the continuous execution of the Feammox and NDFO coupled denitrification process but also activates zero-valent iron, thereby establishing a stable and reliable iron source. The method of this invention can not only reduce the costs of carbon source addition, aeration volume and sludge disposal, but also reduce coupling risks while alleviating the pressure of mainstream denitrification and improving the quality of effluent.

Description

Technical Field

[0001] This invention belongs to the field of water treatment for nitrogen-containing wastewater, and relates to a method for enhancing short-cut nitrification-denitrification processes, especially a method for enhancing short-cut nitrification-denitrification processes based on the Feammox-NDFO coupling system using iron-carbon microelectrolysis balls as driving agents. Background Technology

[0002] With the rapid upgrading of agricultural and industrial activities, eutrophication of aquatic environments and related human diseases such as cancer and blue baby syndrome caused by direct or indirect pollution from ammonia nitrogen are becoming increasingly common. Therefore, in order to protect ecosystems and public health, it is necessary to remove ammonia nitrogen from wastewater. Currently, various denitrification technologies are in use. However, several factors limit the large-scale application of traditional physicochemical denitrification methods. Typical problems include the non-selective interception of reverse osmosis, the high cost of ion exchange and electrodialysis, the low efficiency of adsorption technology, and the immaturity of chemical denitrification technology. Biological denitrification processes can completely eliminate nitrogen and form harmless final products. They also offer low operating costs, high efficiency, and environmental friendliness. Overall, biological denitrification is considered one of the most promising denitrification methods. Among them, traditional nitrification-denitrification technology is mature and used to treat wastewater with high carbon-to-nitrogen ratios (C / N). However, when the BOD5 / TN ratio is below 2.47, additional carbon sources are usually required to support the denitrification process, increasing both operating costs and the risk of secondary water pollution. In other words, the lack of organic carbon sources is a bottleneck for traditional denitrification processes.

[0003] Short-cut nitrification-denitrification (PDN) is a denitrification process via the nitrite pathway. Compared to traditional nitrification and denitrification processes, PDN requires less oxygen to oxidize ammonia nitrogen to nitrite, and then uses less organic carbon source for nitrite denitrification. Theoretically, compared to nitrification-denitrification processes, PDN can reduce aeration by 25% in the aerobic stage, reduce electron donor requirements by 40% in the anoxic stage, reduce CO2 emissions by 20%, reduce sludge production in the nitrification process by 33-35%, and reduce sludge production in the denitrification process by 55%. Therefore, PDN has been reported as a low-cost nitrogen removal technology, especially for treating wastewater with high ammonia nitrogen and low C / N ratio. For PND, the successful and stable accumulation of nitrite is a key process for achieving PND, and the presence of nitrite-oxidizing bacteria means that further oxidation of nitrite is also necessary to drive PND. In other words, effectively inhibiting nitrite-oxidizing bacteria is crucial for the smooth operation of the PND process. Summary of the Invention

[0004] To address the problems of existing technologies, this paper proposes a method for enhancing short-cut nitrification-denitrification processes using a Feammox-NDFO coupling system based on iron-carbon microelectrolysis spheres as the driving agent. This method can effectively reduce the denitrification pressure of mainstream PND processes and improve effluent quality while reducing aeration and carbon source dosage. Furthermore, since the Feammox process (iron oxidation dissimilatory nitrite autotrophic biological denitrification technology) and the NDFO process (nitrate-dependent iron oxidation process) occur independently, the sludge concentration can be adjusted to respond to phased changes in influent quality.

[0005] The present invention achieves the above objectives through the following technical solutions:

[0006] A method for enhancing short-path nitration-denitrification processes using a Feammox-NDFO coupling system based on iron-carbon microelectrolysis spheres as a driving agent mainly includes the following steps:

[0007] Step S1. Add 500~1500 g of iron-carbon micro-electrolysis balls to both cell A and cell B;

[0008] Step S2. Discharge the wastewater into tank B for Feammox treatment to reduce the influent ammonia nitrogen concentration and the aeration amount required for short-cut nitrification;

[0009] Step S3. Discharge the wastewater treated with Feammox in step S2 into the short-cut nitrification tank for short-cut nitrification treatment, providing NO2 for the denitrification tank. – -N and some byproduct NO3 – –N;

[0010] Step S4. Discharge the wastewater that has undergone short-cut nitrification in step S3 into the denitrification tank for denitrification treatment;

[0011] Step S5. Discharge the wastewater after denitrification treatment in step S4 into tank A for NDFO treatment, further reducing the nitrogen concentration in the effluent while reducing the addition of carbon source in the early stage.

[0012] Step S6. If the effluent quality meets the standards, then directly perform mud-water separation in pool A.

[0013] Step S7. If the total nitrogen concentration in the effluent begins to increase, the NDFO sludge and the NDFO-treated wastewater from step S5 are discharged together into the transition sedimentation tank, and then allowed to settle and the supernatant is discharged. This step can prepare for the discharge of Feammox sludge into tank A and for the activation of zero-valent iron.

[0014] Step S8. After the NDFO sludge from step S7 and the NDFO-treated wastewater from step S5 are completely discharged into the transition sedimentation tank, the Feammox sludge from tank B is discharged into tank A for the regeneration of ferrous iron and the activation of zero-valent iron.

[0015] Step S9. After the Feammox sludge from step S8 has been completely discharged into tank A, the NDFO sludge from step S7 is discharged into tank B to consume the ferrous iron produced in the previous Feammox process and to continue to provide electron acceptors for the subsequent Feammox process.

[0016] Step S10. Discharge the wastewater into tank A for Feammox treatment to reduce the influent ammonia nitrogen concentration and the aeration amount required for short-cut nitrification;

[0017] Step S11. Discharge the wastewater treated by Feammox in step S9 into the short-cut nitrification tank for short-cut nitrification treatment, providing NO2 for the denitrification tank. – -N and some byproduct NO3 – –N;

[0018] Step S12. Discharge the wastewater that has undergone short-cut nitrification in step S10 into the denitrification tank for denitrification treatment;

[0019] Step S13. Discharge the wastewater after denitrification treatment in step S11 into tank B for NDFO treatment, further reducing the nitrogen concentration in the effluent while reducing the addition of carbon source in the early stage.

[0020] Step S14. If the effluent quality meets the standards, then directly perform mud-water separation in tank B.

[0021] Step S15. If the total nitrogen concentration in the effluent begins to increase, the NDFO sludge and the NDFO-treated wastewater from step S13 are discharged together into the transition sedimentation tank, and then allowed to settle before the supernatant is discharged. This step prepares for the discharge of Feammox sludge into tank B and for the activation of zero-valent iron.

[0022] Step S16. After the NDFO sludge from step S15 and the NDFO-treated wastewater from step S13 are completely discharged into the transition sedimentation tank, the Feammox sludge in tank A is discharged into tank B for the regeneration of ferrous iron and the activation of zero-valent iron.

[0023] Step S17. After the Feammox sludge from step S16 has been completely discharged into tank B, the NDFO sludge from step S15 is discharged into tank A to consume the ferrous iron produced in the previous Feammox process and to continue to provide electron acceptors for the subsequent Feammox process.

[0024] Step S18. Repeat the process of steps S2 to S17 to continuously enhance short-cut nitrification-denitrification.

[0025] More preferably, 500-1500 g, preferably 1000 g, of iron-carbon microelectrolysis spheres were added to both pool A and pool B. Before startup, the iron-carbon microelectrolysis spheres underwent a series of pretreatments to reduce the passivation layer on their surface. The iron-carbon microelectrolysis spheres in pool B underwent a 24-hour heat treatment (50°C) after pretreatment to form a fresh trivalent iron passivation layer, thereby initiating the Feammox process. The iron-carbon microelectrolysis spheres were loaded using carrier spheres, with each empty sphere containing 50 g of iron-carbon microelectrolysis spheres. The loaded iron-carbon microelectrolysis spheres were suspended / fixed to the SBR using nylon ropes / hot melt adhesive. The particle size of the iron-carbon microelectrolysis spheres was 2-5 mm.

[0026] More preferably, the ratio of Feammox sludge to NDFO sludge added is 1:1 to 9. The MLVSS (mixed liquor volatile suspended solids concentration) of the Feammox sludge is not less than 3500 mg / L.

[0027] More preferably, all reactors are SBR reactors, equipped with mechanical stirring and the internal reaction zone temperature is controlled at 30±1℃ by heating rods.

[0028] More preferably, water storage tanks are installed between tank A and the short-cut nitrification tank, between tank B and the short-cut nitrification tank, between the short-cut nitrification tank and the denitrification tank, between the denitrification tank and tank A, and between the denitrification tank and tank B, to store the wastewater treated by the previous process. The purpose of setting up water storage tanks is to facilitate the series connection of various processes in the early stage and rapid start-up.

[0029] More preferably, the exchange frequency of the Feammox sludge and NDFO sludge is determined according to the effluent quality.

[0030] This invention incorporates a Feammox process before short-cut nitrification to reduce influent ammonia nitrogen concentration and aeration required for short-cut nitrification. It also incorporates a ferrous autotrophic denitrification (NDFO) process after denitrification to further reduce effluent nitrogen concentration while minimizing initial carbon source addition. Furthermore, by periodically exchanging NDFO and Feammox sludge to activate zero-valent iron, the continuous addition of Fe(II) and Fe(III) is avoided while maintaining the normal operation of the Feammox-NDFO coupling system. Ultimately, this enhances the short-cut nitrification-denitrification process, thereby improving effluent quality.

[0031] The beneficial effects of this invention are as follows:

[0032] 1) This invention is applicable to industrial or domestic wastewater with high influent ammonia nitrogen concentration and low carbon-to-nitrogen ratio. The pre-treatment Feammox process can effectively reduce the aeration volume required for short-cut nitrification and other negative impacts caused by fluctuations in influent water quality. Considering the low carbon-to-nitrogen ratio influent conditions and the additional nitrate nitrogen generation during aeration, post-denitrification autotrophic NDFO technology can reduce the organic carbon source required for denitrification, thus helping to lower nitrogen removal costs.

[0033] 2) This invention employs zero-valent iron (Fe) as an indirect electron donor to drive the NDFO process. The generation of ferrous hydroxide allows NDFO bacteria to avoid the irreversible intracellular precipitation caused by ferrous salts in traditional NDFO processes. The trivalent iron generated during the NDFO process and the passivation layer formed on the surface of the zero-valent iron can act as electron acceptors for the Feammox process to oxidize ammonia nitrogen. This ingenious coupling method effectively solves the significant challenges faced by standalone Feammox and NDFO processes in the current environment. For example, standalone Feammox and NDFO processes require intermittent addition of trivalent or ferrous iron to continuously and effectively drive the Feammox and NDFO processes. Furthermore, concentrated iron salt addition not only requires substantial financial investment, but the hydroxide precipitates generated by hydrolysis are also extremely prone to causing irreversible oxidative damage and toxicity to microorganisms, as has been demonstrated in numerous experimental studies. It should also be noted that appropriate iron intervention can actually enhance the metabolic activity of conventional nitrifying and denitrifying bacteria.

[0034] 3) In the Feammox-NDFO coupling system involved in this invention, Feammox sludge and NDFO sludge are managed separately. This approach is advantageous for adjusting the activity of Feammox and NDFO by adjusting the concentration of Feammox sludge and NDFO sludge separately, and can effectively cope with the periodic fluctuations in influent water quality while avoiding the need to adjust the aeration rate and the amount of organic carbon source added as much as possible.

[0035] 4) The Feammox-NDFO coupling system carries minimal risk in enhancing short-cut nitrification-denitrification (SCD) nitrogen removal, as SCD remains the primary nitrogen removal process. The Feammox-NDFO coupling system acts as an auxiliary process, thus reducing economic investment while improving effluent quality. In summary, the Feammox-NDFO coupling system can serve as a bridge between current mainstream nitrogen removal processes and more advanced, large-scale application potential technologies in the future.

[0036] 5) The Feammox-NDFO coupling system can reduce the sludge disposal cost during the enhanced nitrogen removal process of short-cut nitrification-denitrification. This is because denitrification sludge itself possesses NDFO activity and can gradually accumulate in an anaerobic, iron-rich environment. Currently, most NDFO-enriched cultures are obtained through inoculation with traditional activated sludge. Furthermore, relevant studies have shown that using nitrite sludge as inoculation sludge is also beneficial for Feammox bacteria accumulation. Therefore, excess sludge generated during short-cut nitrification and denitrification can be partially introduced into the Feammox sludge and NDFO sludge systems, respectively. Attached Figure Description

[0037] The accompanying drawings are provided to further illustrate the invention and form part of the specification. They are used together with the embodiments of the invention to explain the invention, but do not constitute a limitation thereof. In the drawings:

[0038] Figure 1 This is a flowchart illustrating the present invention.

[0039] Figure 2 This is an exploded view of the overall process diagram of the present invention. Detailed Implementation

[0040] The embodiments of the present invention will be described below with reference to the accompanying drawings. It should be understood that the embodiments described herein are only for illustration and explanation of the present invention and are not intended to limit the process flow, structure, parameters, etc. of the present invention. The specific parameters given in the embodiments are merely examples to illustrate the present invention and are not parameters that must be used.

[0041] Example 1

[0042] Step S1. Discharge the wastewater into tank B for Feammox treatment to reduce the influent ammonia nitrogen concentration and the aeration amount required for short-cut nitrification;

[0043] Step S2. Discharge the wastewater treated with Feammox in step S1 into the short-cut nitrification tank for short-cut nitrification treatment, providing NO2 for the denitrification tank. – -N and some byproduct NO3 – –N;

[0044] Step S3. Discharge the wastewater that has undergone short-cut nitrification in step S2 into a denitrification tank for denitrification treatment to reduce nitrogen and COD concentrations;

[0045] Step S4. Discharge the wastewater after denitrification treatment in step S3 into tank A for NDFO treatment, further improving the effluent quality while reducing the initial addition of carbon sources.

[0046] Step S5. After ensuring that the effluent quality meets the standards, the mud-water separation is carried out directly in pool A.

[0047] To analyze the effects in depth, the experimental water used was artificially simulated low C / N ratio wastewater, with the synthetic wastewater primarily providing NH4. + -N and sodium acetate, macro- and micro-elements for microbial growth, are controlled by adjusting pH with the addition of sodium hydroxide and hydrochloric acid, and controlling the NH4+ in the influent. + -N is 240~250mg / L, COD is 540~550mg / L; the reactor is made of plexiglass and has an effective volume of 4.8L; the reactor is equipped with mechanical stirring; the reactor temperature is controlled at 30±1℃ by heating rods; the water intake is 2L each time; each operating cycle consists of 5 minutes of water intake, 1425 minutes of stirring reaction and 10 minutes of water output.

[0048] The synthetic wastewater first enters tank B via a peristaltic pump. Under the action of Feammox sludge, 21.6% of the ammonia nitrogen in the influent is consumed. Simultaneously, possibly due to the presence of a small amount of heterotrophic bacteria in the Feammox sludge, less than 5% of the COD is degraded. The wastewater then enters the short-cut nitrification tank of the short-cut nitrification-denitrification system. The function of the short-cut nitrification tank is to oxidize the remaining 78.4% of ammonia nitrogen into nitrite nitrogen as much as possible through AOB bacteria, and to reduce the formation of nitrate nitrogen. In actual operation, the nitrite nitrogen formation rate in the effluent from the short-cut nitrification tank was 75.7%, indicating that the vast majority of ammonia nitrogen was oxidized to nitrite nitrogen. It should be noted that, possibly due to the presence of a localized anaerobic environment in the short-cut nitrification tank, approximately 3% of the influent nitrogen was completely removed.

[0049] The effluent from the short-cut nitrification tank then enters the denitrification tank, where approximately 64.8% of the nitrogen is completely removed. The nitrite nitrogen concentration in the effluent is below the detection limit, the nitrate nitrogen concentration reaches 37 mg / L, and the COD concentration is close to 18 mg / L. After further treatment with NDFO sludge, the effluent COD concentration is below 5 mg / L, and the nitrate nitrogen concentration is almost zero. Considering that the NDFO sludge is obtained by acclimation to ordinary activated sludge, and that the NDFO process can improve efficiency in the presence of a small amount of organic matter, overall, after the above series of transformations and removals, the total nitrogen removal rate and COD removal rate of the target pollutants in the synthetic wastewater are close to 100%. This indicates that a Feammox-NDFO coupling system based on iron-carbon microelectrolysis balls as a driving agent has successfully enhanced the short-cut nitrification-denitrification process.

[0050] Example 2

[0051] This implementation method is based on Example 1, which runs continuously for 3 days. It explores the feasibility of enhancing the short-cut nitrification-denitrification process by replacing Feammox sludge with NDFO sludge.

[0052] This implementation method is based on Example 1, and the specific steps are connected to step S5 of Example 1.

[0053] Step S6. If the total nitrogen concentration in the effluent begins to increase, the NDFO sludge and the NDFO-treated wastewater from step S4 are discharged together into the transition sedimentation tank, and then allowed to settle and the supernatant is discharged. This step can prepare for the discharge of Feammox sludge into tank A and for the activation of zero-valent iron.

[0054] Step S7. After the NDFO sludge from step S6 and the NDFO-treated wastewater from step S4 are completely discharged into the transition sedimentation tank, the Feammox sludge from tank B is discharged into tank A for the regeneration of ferrous iron and the activation of zero-valent iron.

[0055] Step S8. After the Feammox sludge from step S7 is completely discharged into tank A, the NDFO sludge from step S6 is discharged into tank B. In addition to consuming the ferrous iron produced in the early Feammox process, it continues to provide electron acceptors for the subsequent Feammox process.

[0056] Step S9. Discharge the wastewater into tank A for Feammox treatment to reduce the influent ammonia nitrogen concentration and the aeration amount required for short-cut nitrification;

[0057] Step S10. Discharge the wastewater treated with Feammox in step S8 into the short-cut nitrification tank for short-cut nitrification treatment, providing NO2 for the denitrification tank. – -N and some byproduct NO3 – –N;

[0058] Step S11. Discharge the wastewater that has undergone short-cut nitrification in step S9 into the denitrification tank for denitrification treatment;

[0059] Step S12. Discharge the wastewater after denitrification treatment in step S10 into tank B for NDFO treatment, thereby reducing the nitrogen concentration in the effluent by reducing the addition of carbon source in the early stage.

[0060] Step S13. If the effluent quality meets the standards, then mud-water separation is carried out directly in pool B.

[0061] In this embodiment, the synthesis wastewater enters tank A via a peristaltic pump, where 25.8% of the ammonia nitrogen in the influent is consumed by the Feammox sludge. Simultaneously, possibly due to a small amount of residual NDFO sludge in tank A, 6.8% of the COD is degraded. Even so, as the synthesis wastewater passes through tank B, almost no nitrogen accumulates in the effluent. This fully demonstrates that the enhancement of the short-cut nitrification-denitrification process using a Feammox-NDFO coupling system based on iron-carbon microelectrolysis balls as a driving agent is sustainable.

[0062] The embodiments described above are merely examples of several implementations of the present invention, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the present invention. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these modifications and improvements all fall within the scope of protection of the present invention.

Claims

1. A method for enhancing a short-cut nitrification-denitrification process, characterized in that, The method includes the following steps: Step S1. Add iron-carbon micro-electrolysis balls to tank A and tank B, discharge the wastewater into tank B for Feammox treatment, reduce the influent ammonia nitrogen concentration and the aeration amount required for short-cut nitrification; Step S2. Continue to discharge wastewater into the short-cut nitrification tank for short-cut nitrification treatment, providing NO2 for the denitrification tank. – -N and some byproduct NO3 – –N; Step S3. Continue to discharge the wastewater into the denitrification tank for denitrification treatment; Step S4. Continue to discharge the wastewater into tank A for NDFO treatment, further reducing the nitrogen concentration in the effluent while reducing the addition of carbon sources in the early stage; Step S5. If the effluent quality meets the standards, then directly perform mud-water separation in pool A; If the total nitrogen concentration in the effluent begins to increase, the method further includes the following steps: Step S6. Discharge the NDFO sludge and the wastewater from step S4 into the transition sedimentation tank, then let it settle and discharge the supernatant to prepare for the discharge of Feammox sludge into tank A and for the activation of zero-valent iron. Step S7. Discharge the Feammox sludge in tank B into tank A for the regeneration of ferrous iron and the activation of zero-valent iron; Step S8. Discharge the sludge from step S6 into tank B to consume the ferrous iron produced in the previous Feammox process and to continue to provide electron acceptors for the subsequent Feammox process. Step S9. Discharge the wastewater into tank A for Feammox treatment to reduce the influent ammonia nitrogen concentration and the aeration amount required for short-cut nitrification; Step S10. Discharge the wastewater treated in step S8 into the short-cut nitrification tank for short-cut nitrification treatment, providing NO2 for the denitrification tank. – -N and some byproduct NO3 – –N; Step S11. Discharge the wastewater that has undergone short-cut nitrification in step S9 into the denitrification tank for denitrification treatment; Step S12. Discharge the wastewater treated in step S10 into pool B for NDFO treatment, thereby reducing the nitrogen concentration in the effluent by reducing the addition of carbon source in the early stage. Step S13. If the effluent quality meets the standards, then directly perform mud-water separation in tank B.

2. The method for enhancing a short-cut nitrification-denitrification process as described in claim 1, characterized in that, The ratio of Feammox sludge to NDFO sludge added is 1:1 to 9, wherein the MLVSS of Feammox sludge is not less than 3500 mg / L.

3. The method for enhancing a short-cut nitrification-denitrification process as described in claim 1, characterized in that, The reaction temperature for the enhancement method is 30±1℃.

4. The method for enhancing a short-cut nitrification-denitrification process as described in claim 1, characterized in that, Water storage tanks are installed between Tank A and the short-cut nitrification tank, between Tank B and the short-cut nitrification tank, between the short-cut nitrification tank and the denitrification tank, between the denitrification tank and Tank A, and between the denitrification tank and Tank B, to store the wastewater treated by the previous process.

5. The method for enhancing a short-cut nitrification-denitrification process as described in claim 1, characterized in that, Before startup, all iron-carbon microelectrolysis balls underwent pretreatment to reduce the passivation layer on their surface. In the B cell, the iron-carbon microelectrolysis balls underwent 24-hour heat treatment after pretreatment to form a fresh trivalent iron passivation layer and thus start the Feammox process.

6. The method for enhancing a short-cut nitrification-denitrification process as described in claim 1, characterized in that, The enhancement method described herein occurs within an SBR reactor.

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