Method for realizing DNRA based on ferrate sludge wall breaking and carbon source utilization

Abstract

The invention discloses a method for realizing DNRA based on ferrate sludge wall breaking and carbon source utilization, and belongs to the technical field of sewage treatment and recycling. The method comprises the following steps: S1, in a strict anaerobic environment, adding ferrate into the excess sludge, and rapidly stirring to realize wall breaking of the sludge and release intracellular organic matters; s2, carrying out solid-liquid separation on the reacted mixture, collecting supernate, and diluting the supernate to a specific chemical oxygen demand (COD) concentration to obtain recovered carbon source liquid; and S3, adding the recovered carbon source liquid into the nitrate nitrogen-containing wastewater, regulating the carbon-nitrogen ratio and oxidation-reduction potential (ORP) of the system, and reducing the nitrate nitrogen into ammonia nitrogen by using functional microorganisms under anaerobic conditions to realize accumulation and recovery of the ammonia nitrogen. High-concentration carbon sources are released through efficient wall breaking of ferrate, and the problem that traditional nitrogen removal carbon sources are deficient is solved; the process of directionally inducing dissimilatory nitrate to be reduced into ammonium (DNRA) is regulated and controlled through environmental parameters, low-concentration nitrate nitrogen is converted into recoverable ammonia nitrogen, nitrogen loss is avoided, and the method has the advantages of efficient nitrogen removal and resource recovery and is environmentally friendly.

Description

Technical Field

[0001] This invention belongs to the field of wastewater treatment and resource recovery technology, and specifically relates to a method for using ferrate to break down the cell walls of residual sludge, recovering intracellular carbon sources, and achieving deep denitrification of low-concentration nitrogen-containing wastewater and recovery of ammonia nitrogen resources through the DNRA pathway. Background Technology

[0002] With increasingly stringent environmental regulations, urban wastewater treatment plants face higher nitrogen emission standards. Traditional biological nitrogen removal processes mainly rely on nitrification-denitrification. While this process effectively removes total nitrogen, denitrification requires a large amount of readily degradable carbon sources (such as methanol and acetic acid). Municipal wastewater typically has a low carbon-to-nitrogen ratio (C / N), necessitating the addition of expensive external carbon sources, significantly increasing operating costs. Furthermore, the final electron acceptor in denitrification is nitrate, and its final product is nitrogen gas (N2). This not only results in the permanent loss of nitrogen resources but, under certain conditions (such as short-cut denitrification), can also produce the potent greenhouse gas nitrous oxide (N2O). In addition, the large amount of excess sludge generated during wastewater treatment often accounts for 30%-50% of the total operating costs of the wastewater treatment plant. Currently, mainstream sludge treatment technologies (such as anaerobic digestion, incineration, and landfill) all suffer from high energy consumption, secondary pollution, or low resource utilization rates. On the other hand, in recent years, due to the development of isotope technology, people have gradually distinguished dissimilatory nitrate reduction to ammonium (DNRA) from denitrification. Under anaerobic conditions, DNRA transfers more electrons per mol of nitrate reduced than denitrification, and the final reduction product of DNRA is ammonia nitrogen (NH4). + -N), does not involve the emission of nitrous oxide (N2O), and ammonia nitrogen (NH4) + Ammonium ions (N-N) are more readily utilized by plants and other microorganisms. Compared to traditional denitrification, DNRA converts inorganic nitrogen into usable ammonia nitrogen, avoiding nitrogen volatilization loss and enabling subsequent nitrogen recovery (such as struvite sedimentation, stripping, etc.) or direct reuse as slow-release nitrogen fertilizer. Furthermore, the final product of the DNRA process is ammonium ions, which do not produce N2O, helping to reduce the carbon footprint of wastewater treatment. DNRA and denitrification are two competing microbial processes. Under hypoxic, high-COD conditions, DNRA bacteria can utilize complex organic matter as electron donors. Therefore, creating a suitable environment to induce nitrate flow to the DNRA pathway could help solve the nitrogen removal problem under low-carbon-source conditions. However, in existing technologies, the DNRA reaction rate is slow and extremely sensitive to environmental conditions (such as pH, ORP, and the type and concentration of carbon source). Furthermore, while traditional anaerobic sludge fermentation technology can produce volatile fatty acids (VFAs) as a carbon source, its fermentation cycle is long (typically 10-20 days), and the produced VFAs are easily utilized by methanogenic bacteria, resulting in low and unstable actual carbon source recovery rates. Therefore, how to develop a highly active carbon source that can quickly and efficiently release from residual sludge and use it for deep denitrification and resource recovery of low-concentration nitrogen-containing wastewater is a technical problem that urgently needs to be solved in the field of wastewater treatment. Summary of the Invention

[0003] 1. Technical problems to be solved This invention aims to overcome the shortcomings of existing technologies and provide a method for achieving DNRA (Dry Nyquist Removal and Recycling) based on ferrate sludge cell disruption and carbon source utilization. This method utilizes waste sludge from wastewater treatment plants as an internal carbon source. Through the efficient cell disruption effect of ferrate, high concentrations of soluble organic matter are rapidly released, and this organic matter is used to drive the DNRA process, achieving deep removal of nitrates and resource recovery of ammonia nitrogen from low-concentration nitrogen-containing wastewater. 2. Technical Solution To address the aforementioned problems, this invention provides a method for achieving DNRA based on ferrate sludge cell disruption and carbon source utilization, comprising the following steps: S1: Anaerobic cell wall disruption and carbon release: Take the residual sludge from the sewage treatment plant, and add ferrate to the sludge at a dosage of 20–150 mg Fe(VI) / g SS under an anaerobic environment with a dissolved oxygen concentration ≤0.5 mg / L. Control the sludge concentration to 25 g / L, and carry out rapid stirring reaction for 30–60 min to achieve sludge cell wall lysis and release intracellular organic matter; S2: Carbon source recovery and acclimatization: The sludge mixture after the reaction in step S1 is subjected to solid-liquid separation, and the supernatant rich in dissolved organic matter is collected; the supernatant is diluted to a chemical oxygen demand (COD) concentration of 180–220 mg / L to obtain the recovered carbon source liquid; S3: DNRA-directed conversion: The recovered carbon source solution obtained in step S2 is added to the wastewater to be treated, which contains nitrate nitrogen at a concentration of 15–25 mg / L, to adjust the carbon-to-nitrogen ratio (COD:NO3) of the mixed system. -The ratio of nitrate nitrogen to ammonia nitrogen is 8:1–12:1. Under anaerobic conditions with an oxidation-reduction potential (ORP) of -150 mV to -100 mV and a hydraulic retention time (HRT) of 4–8 h, functional microorganisms are used to reduce nitrate nitrogen to ammonia nitrogen, thereby achieving the accumulation and recovery of ammonia nitrogen. Furthermore, in step S1, the preferred conditions for the rapid stirring reaction are: stirring speed of 300–500 rpm and reaction time of 1–3 h. Further, in step S1, the ferrate is selected from potassium ferrate or sodium ferrate. Furthermore, in step S2, the sludge supernatant obtained after solid-liquid separation has a COD release of ≥1500 mg / L and a degradation rate of ≥60% for sludge extracellular polymeric substances (EPS). Furthermore, in step S3, by regulating ORP ≥ -150 mV, the activity of methanogens and the denitrification gas production side reaction are suppressed, ensuring that the DNRA metabolic pathway plays a dominant role in the nitrate reduction process. Furthermore, in step S3, after the DNRA reaction, the ammonia nitrogen accumulation concentration in the system is 8–15 mg / L, realizing the resource recovery of ammonia nitrogen from low-concentration nitrogen-containing wastewater. Furthermore, in step S1, the remaining sludge originates from the sludge return tank or the end of the aerobic tank of the wastewater treatment plant. 3 advantages Compared with the prior art, the present invention has the following significant advantages: (1) Ferrate has high cell wall breaking efficiency and rapid carbon source release: Ferrate is a strong oxidant with extremely strong oxidizing ability under alkaline or neutral conditions. This invention innovatively applies it to the anaerobic cell wall breaking of excess sludge. Ferrate can not only rapidly break down sludge flocs and microbial cell walls, releasing high-value organic matter such as polyhydroxyalkanoates (PHA) and glycogen stored intracellularly, but also assist in the breaking down of sludge flocs through the adsorption and bridging effect of its reduction product Fe(III) hydrolysis products. Compared with traditional hot water hydrolysis, acid-base treatment and other methods, the reaction time of this invention is short (only 30-60 minutes), no high temperature and high pressure equipment is required, and energy consumption is extremely low. At the same time, a suitable pH environment can be achieved without neutralization after the reaction, simplifying the process flow. (2) Solved the problem of carbon source scarcity and realized sludge resource utilization: The present invention transforms the surplus sludge that originally required high cost treatment into a high-concentration (COD>1500 mg / L) soluble organic carbon source. Through dilution and acclimatization, these carbon sources are precisely supplied to the DNRA process, which not only solves the problem of insufficient carbon source in traditional denitrification processes, but also achieves the dual goals of "treating waste with waste" and sludge reduction, and significantly reduces the operating cost of wastewater treatment plants. (3) Targeted DNRA Induction for Ammonia Nitrogen Recovery: This invention successfully inhibits the activity of methanogenic and denitrifying bacteria by precisely controlling the carbon-to-nitrogen ratio (8:1–12:1) and redox potential (ORP ≥ -150 mV) of the mixed liquor, forcing heterotrophic microorganisms to preferentially choose the DNRA metabolic pathway. This allows low concentrations (15-25 mg / L) of nitrate nitrogen to be efficiently converted into usable ammonia nitrogen (8-15 mg / L). Compared to traditional denitrification processes, this invention not only avoids permanent nitrogen loss but also lays the foundation for subsequent ammonia nitrogen recovery (such as as liquid fertilizer), demonstrating significant resource recycling value. (4) Environmentally friendly with few byproducts: The reduction product of ferrate is Fe(III), which forms ferric hydroxide colloid in water with good flocculation and sedimentation properties, and can synergistically remove suspended solids and phosphorus from water. At the same time, since the DNRA process does not produce N2O, this invention helps to reduce greenhouse gas emissions in the wastewater treatment process, which is in line with the green and low-carbon development concept. Attached Figure Description Appendix Figure 1 This is a graph showing the nitrate nitrogen test data of the reactor influent and effluent from reactors with low and high carbon-to-nitrogen ratios in this implementation case. Appendix Figure 2 This is a graph showing the ammonia nitrogen test data of the reactor influent and effluent from reactors with low and high carbon-to-nitrogen ratios in this implementation case. Appendix Figure 3 This is a graph showing the nitrite test data of the influent and effluent of reactors with low and high carbon-to-nitrogen ratios in the implementation case of this method; Appendix Figure 4 This is a graph showing the COD test data of the influent and effluent of reactors with low and high carbon-to-nitrogen ratios in the implementation case of this method; Appendix Figure 5 This is a graph showing the COD test data of supernatant from ferrate sludge with different dosages extracted in the implementation case of this method; Detailed Implementation The method is further illustrated below with specific implementation examples. It should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of the method. Furthermore, it should be understood that after reading the teachings of this method, those skilled in the art can make various modifications or alterations to the invention, and these equivalent forms also fall within the scope defined in this application. Example 1 This embodiment was conducted in a laboratory-scale continuous flow reactor to simulate the operating environment of a wastewater treatment plant. (a) Anaerobic cell disruption and carbon release stage Excess sludge from the sludge return tank of a municipal wastewater treatment plant was collected, and its mixed liquor suspended solids (MLSS) concentration was determined to be approximately 8000 mg / L. First, the sludge was centrifuged at 10000 rpm to dewater, the supernatant was discarded, and then deionized water was added to adjust the sludge concentration to 25 g / L. The sludge with the adjusted concentration was transferred to a sealed reaction bottle, and the dissolved oxygen (DO) concentration of the system was maintained at ≤0.5 mg / L by continuously introducing high-purity nitrogen (N2) to ensure a strict anaerobic environment. Weigh a certain amount of potassium ferrate (K2FeO4) powder and slowly add it to the sludge at a ratio of 100 mg Fe(VI) / g SS (dry sludge). Immediately turn on the mechanical stirrer, set the stirring speed to 400 rpm, and the reaction time to 60 min. After the reaction is complete, take a sample to determine the COD and EPS content of the sludge supernatant. (b) Carbon source recovery and domestication stage The sludge mixture after the reaction in step (a) was vacuum filtered through medium-speed filter paper, and the supernatant rich in dissolved organic matter was collected. The COD concentration of the supernatant was determined to be 1800 mg / L, and the EPS degradation rate was 70%. Take the supernatant and mix it with deionized water at a volume ratio of 1:9. Dilute the mixture to a COD concentration of approximately 200 mg / L and stir thoroughly to obtain the recovered carbon source solution. (c) DNRA-oriented conversion stage Artificially simulated wastewater containing nitrate nitrogen was prepared, with a nitrate nitrogen concentration of 20 mg / L, a phosphate concentration of 5 mg / L, and the remainder being a trace element solution. The recovered carbon source solution obtained in step (b) is added to the simulated wastewater to make the final carbon-to-nitrogen ratio of the mixture approximately 10:1. Simultaneously, a final carbon-to-nitrogen ratio (COD:NO3⁻-N) of approximately 5:1 is prepared in the mixture. This mixture is then pumped into the same reactor as a control group. In this invention, the carbon-to-nitrogen ratio refers to COD:NO3⁻-N, abbreviated as C / N. A carbon-to-nitrogen ratio of 10:1 is considered a high carbon-to-nitrogen ratio reactor, and a carbon-to-nitrogen ratio of 5:1 is considered a low carbon-to-nitrogen ratio reactor. The two mixtures were separately pumped into a continuous flow reactor with an effective volume of 2 L. The ORP was monitored using an online ORP meter, and a small amount of ascorbic acid (vitamin C) was added to maintain the ORP at approximately -130 mV. The reactor temperature was controlled at 30±1°C, and the hydraulic retention time (HRT) was 6 h. The concentrations of nitrate nitrogen, nitrite and ammonia nitrogen in the influent and effluent are monitored daily. Results and Discussion After 30 consecutive cycles (15 days) of stable operation, the results show that: 1. DNRA Efficiency: In step (c), by the attached Figure 1 It can be seen that the high C / N ratio system achieves an average removal rate of over 95% for nitrate nitrogen. More importantly, the attached... Figure 2 It can be seen that the ammonia nitrogen concentration in the effluent is stable at around 9.2 mg / L, which is 6.7 times higher than that in the influent. This indicates that under the high carbon-to-nitrogen ratio control conditions of this invention, the DNRA process has become the dominant pathway for nitrate reduction. Furthermore, from the attached... Figure 3 It can be seen that the nitrite content was very low in both reactors. (From the attached...) Figure 4 It can be seen that the high carbon-nitrogen ratio reactor has a carbon source utilization rate of 77.6%, which is 12.4% higher than that of the low carbon-nitrogen ratio reactor. 2. Suppression of side reactions: By controlling the ORP at -130 mV, the occurrence of methanogenesis was effectively suppressed, and no obvious N2O gas release was detected, proving that the process environment is conducive to the growth and metabolism of DNRA bacteria. Example 2 This embodiment examines the effect of different ferrate dosages on sludge cell disruption. Keeping all other conditions consistent with Example 1, only the amount of potassium ferrate added in step (a) was changed to 0 mg Fe(VI) / g SS (control group), 20 mg Fe(VI) / g SS, 40 mg Fe(VI) / g SS, 60 mg Fe(VI) / g SS, 80 mg Fe(VI) / g SS, 100 mg Fe(VI) / g SS, and 120 mg Fe(VI) / g SS. Experimental results, from the appendix Figure 5 The results showed that when the dosage was 0%, the COD release was only 54 mg / L, and the EPS degradation rate was less than 10%. When the dosage reached 100 mg Fe(VI) / g SS, the COD release reached its maximum of 1800 mg / L, and the EPS degradation rate exceeded 70%. Further increasing the dosage to 120 mg / g SS did not significantly increase the COD release, but the color of the system after the reaction darkened considerably, indicating a peroxidation side reaction. Therefore, considering both economic efficiency and treatment effectiveness, the optimal dosage of ferrate is recommended to be 100 mg Fe(VI) / g SS. Industrial Application Prospects The method proposed in this invention has broad application prospects, and is particularly suitable for the following scenarios: 1. Decentralized wastewater treatment plants: For rural or township wastewater treatment plants that lack external carbon sources and are small in scale, this invention can utilize the residual sludge generated within the plant as an internal carbon source to achieve low-cost deep denitrification. 2. Industrial wastewater treatment: Some industrial wastewater (such as rare earth smelting, chemical processing, etc.) contains high concentrations of ammonia nitrogen, but also suffers from insufficient carbon sources. This invention can be used as a pretreatment or bypass treatment technology to utilize sludge carbon sources for denitrification in specific processes. 3. Upgrading and retrofitting wastewater treatment plants: For existing wastewater treatment plants facing the pressure of simultaneously meeting the standards for total nitrogen and ammonia nitrogen, this invention can serve as an independent enhancement unit to achieve deep removal and recovery of nitrogen without changing the original main process, thus helping wastewater treatment plants transform from "meeting discharge standards" to "energy and resource recovery". Although the present invention has been described with reference to the above embodiments, it should be understood that the present invention may be further modified and varied without departing from the spirit of the present invention, and all such modifications and variations are within the protection scope of the present invention.

Claims

1. A method for achieving DNRA based on ferrate sludge cell disruption and carbon source utilization, characterized in that, Includes the following steps: S1: Anaerobic cell wall disruption and carbon release: Take the residual sludge from the sewage treatment plant, and add ferrate to the sludge at a dosage of 20–150 mg Fe(VI) / g SS under an anaerobic environment with a dissolved oxygen concentration ≤0.5 mg / L. Control the sludge concentration to 25 g / L, and carry out rapid stirring reaction for 30–60 min to achieve sludge cell wall lysis and release intracellular organic matter; S2: Carbon source recovery and acclimatization: The sludge mixture after the reaction in step S1 is subjected to solid-liquid separation, and the supernatant rich in dissolved organic matter is collected; the supernatant is diluted to a chemical oxygen demand (COD) concentration of 180–220 mg / L to obtain the recovered carbon source liquid; S3: DNRA-directed conversion: The recovered carbon source solution obtained in step S2 is added to the wastewater to be treated, which contains nitrate nitrogen at a concentration of 15–25 mg / L, to adjust the carbon-to-nitrogen ratio (COD:NO3) of the mixed system. - The ratio of nitrate nitrogen to ammonia nitrogen is 8:1–12:

1. Under anaerobic conditions with an oxidation-reduction potential (ORP) of -150 mV to -100 mV and a hydraulic retention time (HRT) of 4–8 h, functional microorganisms are used to reduce nitrate nitrogen to ammonia nitrogen, thereby achieving the accumulation and recovery of ammonia nitrogen.

2. The method according to claim 1, characterized in that: In step S1, the conditions for the rapid stirring reaction are: stirring speed 300–500 rpm, reaction time 1–3 h.

3. The method according to claim 1, characterized in that: In step S1, the ferrate is selected from potassium ferrate or sodium ferrate.

4. The method according to claim 1, characterized in that: In step S2, the sludge supernatant obtained after solid-liquid separation has a COD release of ≥1500 mg / L and a degradation rate of ≥60% for sludge extracellular polymeric substances (EPS).

5. The method according to claim 1, characterized in that: In step S3, by regulating ORP ≥ -150 mV, the activity of methanogens and the denitrification gas production side reaction are suppressed, ensuring that the DNRA metabolic pathway plays a dominant role in the nitrate reduction process.

6. The method according to claim 1, characterized in that: In step S3, after the DNRA reaction, the ammonia nitrogen accumulation concentration in the system is 8–15 mg / L, realizing the resource recovery of ammonia nitrogen from low-concentration nitrogen-containing wastewater.

7. The method according to claim 1, characterized in that: In step S1, the remaining sludge comes from the sludge return tank or the end of the aerobic tank of the sewage treatment plant.

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