A method for in-situ suppression of hydrogen sulfide production

Abstract

This invention relates to a method for in-situ suppression of hydrogen sulfide generation using fermentation broth. The specific method includes: concentrating sludge from a municipal wastewater treatment plant to increase its solids content; treating anaerobic fermentation broth from an anaerobic sludge treatment tank to remove SCFAs and soluble phosphorus, then storing it for later use; mixing the concentrated sludge with the treated fermentation broth in a certain proportion; pretreating the sludge substrate by controlling pH and temperature; and finally, anaerobic treating the sludge, maintaining stable continuous flow operation of the reactor by controlling the sludge retention time. Results show that this treatment method can significantly suppress hydrogen sulfide generation during anaerobic sludge treatment. Through a simple, inexpensive, and effective operation, utilizing wastewater treatment plant byproducts, this method achieves waste-to-waste treatment, reducing the generation of toxic and harmful gases such as hydrogen sulfide during anaerobic sludge treatment, which is of great significance for sludge treatment and disposal.

Description

Technical Field

[0001] This invention belongs to the field of environmental protection and sludge treatment and resource utilization technology, specifically relating to a method for reducing hydrogen sulfide generation during anaerobic sludge treatment in wastewater treatment plants. Technical Background

[0002] To address the increasing volume of domestic wastewater, the number of urban wastewater treatment plants in my country has grown rapidly. Most of these plants utilize the activated sludge process. Therefore, while achieving wastewater discharge standards, this inevitably results in the generation of large amounts of primary and residual sludge. The dramatic increase in sludge quantity has caused serious environmental problems, making its treatment and disposal an urgent issue.

[0003] Sludge contains a large amount of usable organic matter such as proteins and sugars. Anaerobic treatment is a commonly used sludge treatment method. Anaerobic treatment can reduce sludge volume and the cost of final sludge disposal; it can inactivate pathogens and other microorganisms in the sludge, achieving harmlessness; and it can recover large amounts of high-value-added products such as short-chain fatty acids, hydrogen, and methane from the sludge, achieving the effect of turning waste into treasure, which plays a significant role in alleviating the current energy crisis.

[0004] During the anaerobic treatment of sludge, microorganisms produce hydrogen sulfide along with volatile fatty acids, hydrogen, and methane—all high-value-added products—as they degrade organic matter. Hydrogen sulfide is a colorless, highly toxic, and flammable gas with a rotten egg odor. It is highly corrosive, corroding pipes and other equipment, and its combustion produces sulfur dioxide, polluting the atmosphere. my country's environmental standards stipulate that when utilizing biogas energy, the hydrogen sulfide content in the biogas must not exceed 20 mg / m³. 3 The mass concentration of H2S in biogas is generally 1-12 g / m³. 3 The levels of hydrogen sulfide in biogas far exceed the limits set by my country's environmental protection standards. Hydrogen sulfide in biogas directly affects its quality, thus limiting its direct utilization, reducing the economic benefits of biogas production from anaerobic sludge treatment, and hindering the further promotion of anaerobic sludge treatment. Therefore, it is essential to find a simple, safe, inexpensive, and efficient method to suppress hydrogen sulfide production during anaerobic sludge treatment.

[0005] Existing technologies for suppressing hydrogen sulfide production during anaerobic sludge treatment mainly focus on adding various chemical agents, such as potassium permanganate, or using various pretreatment methods, such as alkaline pretreatment and thermal pretreatment, to inhibit the activity of sulfate-reducing bacteria, thereby reducing hydrogen sulfide production. For example, a report (Chemical Engineering Journal, 2022, 430, 133150) found that adding a certain amount of potassium permanganate to excess sludge significantly reduced the production of hydrogen sulfide gas during anaerobic sludge treatment. Patent CN201611213314.5 discloses a "method for promoting biogas production and reducing hydrogen sulfide content in anaerobic digestion of high-solids sludge by alkaline fermentation." By adjusting the pH in the system to an initial pH of 12 for the high-solids sludge, and then maintaining it under anaerobic conditions of 35-37℃, pH=10, and 130 rpm for 10 days of alkaline fermentation, the production of hydrogen sulfide was effectively reduced. However, the aforementioned methods have unavoidable drawbacks. The use of various chemical agents or pretreatment methods inevitably increases the operating costs of wastewater treatment plants and also increases indirect carbon emissions during the wastewater treatment process. With the intensification of the global resource and energy crisis and the proposal of my country's "dual carbon" target in the context of addressing global climate change, developing economical and efficient in-situ methods to suppress hydrogen sulfide generation in sludge treatment is particularly important and is currently a research focus in the field of sludge treatment.

[0006] Sludge fermentation broth is widely present in wastewater treatment plants. Its composition is complex, containing high concentrations of ammonia nitrogen, a large number of anaerobic microorganisms, and various released organic or inorganic substances such as proteins, polysaccharides, humic substances, lignocellulose, and metal ions. The presence of high concentrations of ammonia nitrogen and heavy metal ions may inhibit hydrogen sulfide-producing microorganisms (Bioresour Technol. 2017, 245, 598-605; Bioresource Technol. 2019, 276, 91-96). However, the large number and variety of anaerobic microorganisms (especially hydrolytic microorganisms) enriched in the fermentation broth increase the biomass of functional microorganisms in the fermentation system. Residual biodegradable organic matter (such as proteins) in the fermentation broth is continuously degraded as the anaerobic fermentation process progresses, providing additional substrate for subsequent hydrogen sulfide production. Therefore, the anaerobic microorganisms and biodegradable organic matter contained in the fermentation broth may promote hydrogen sulfide production during the anaerobic treatment of sludge. The complexity of the actual fermentation broth composition makes the technology of in-situ inhibition of hydrogen sulfide production from anaerobic sludge treatment based on fermentation broth highly uncertain. To date, no research teams, either domestically or internationally, have conducted relevant research on "in-situ inhibition of hydrogen sulfide production from anaerobic sludge treatment using fermentation broth".

[0007] In view of the above problems, this invention provides a method to suppress hydrogen sulfide production by using anaerobic fermentation liquid generated during the sewage sludge treatment process in sewage treatment plants. This method achieves a good suppression effect. By using sewage treatment byproducts to reduce hydrogen sulfide production in situ, the use of chemical agents and energy is reduced, greatly reducing the treatment cost. On the other hand, it treats waste with waste, providing a new approach to the treatment of sludge fermentation liquid, and has strong practicality. Summary of the Invention

[0008] The purpose of this invention is to provide a method for in-situ suppression of hydrogen sulfide generation during sludge treatment, namely, using fermentation broth, a byproduct of wastewater treatment plants, to suppress hydrogen sulfide generation during anaerobic sludge treatment.

[0009] To achieve the above objectives, the solution of the present invention is as follows:

[0010] A method for in-situ suppression of hydrogen sulfide production includes the following steps:

[0011] (1) Take the primary sludge and excess sludge from the urban sewage treatment plant and concentrate them to increase the solids content of the sludge.

[0012] (2) The fermentation broth comes from the anaerobic sludge treatment tank. It contains a large amount of short-chain fatty acids (SCFAs) and soluble phosphates. Before using the fermentation broth to treat sludge, it is necessary to recover SCFAs and phosphorus. The specific method is as follows: Adjust the pH of the fermentation broth to 7.8-11 using sodium hydroxide solution. Then, add calcium chloride solution at a calcium-to-phosphorus molar ratio of 1.5-2.1 and react for 10-30 minutes. Filter out the precipitate containing calcium phosphate crystals. Then, recover the SCFAs and other components in the fermentation broth by adsorbing and storing the intracellular polymeric polymer PHA of microorganisms. The reaction is carried out under aerobic conditions, with an aerobic reaction time of 0.5-2 hours, a sludge retention time of 3 days, and a temperature of 20±1℃.

[0013] (3) The fermentation broth after treatment with SCFAs and phosphorus recovery is stored in a storage tank for use.

[0014] (4) Take out the treated fermentation liquid from the storage tank and add it to the substrate to be treated (i.e., the concentrated sludge in (1)) in a certain proportion. Control the pH and temperature of the fermentation system and pretreat the substrate for a period of time.

[0015] (5) After pretreatment, nitrogen gas is introduced into the sludge substrate to maintain the anaerobic closed environment of the reactor. The pH of the reaction is not controlled, and the sludge is anaerobically treated.

[0016] (6) During the anaerobic treatment of sludge, a certain amount of anaerobic sludge mixture is taken out from the reactor every day and new sludge substrate after pretreatment is added to maintain the stable operation of the reactor. The concentration of hydrogen sulfide in the reactor is tested regularly. After the reactor has been running continuously for a period of time, the production of hydrogen sulfide reaches a stable level.

[0017] In step (1) above, the total suspended solids of the sludge are maintained in the range of 20-30 g / L as a substrate.

[0018] In step (4) above, the pretreatment pH of the system is controlled at 8.5, the temperature is controlled at room temperature (20℃), and the pretreatment time is 10 hours, which effectively reduces the consumption of energy and reagents in the treatment process.

[0019] The certain proportion mentioned in step (4) above refers to controlling the volume ratio of fermentation liquid to substrate to be 10-30%.

[0020] In step (6) above, the sludge retention time is set to 10 days, that is, the volume of the sludge anaerobic treatment mixture taken out each day and the volume of the new sludge substrate added is the total volume of sludge in the reactor / 10.

[0021] The conditions for anaerobic treatment of sludge in step (6) above are: temperature 20±1℃, shaking speed 100rpm / min.

[0022] The periodic measurement mentioned in step (6) above refers to detecting the concentration of hydrogen sulfide gas using a gas chromatograph every 24 hours.

[0023] The running period mentioned in step (6) above is 6 months.

[0024] The innovations and advantages of this study are as follows:

[0025] This invention utilizes fermentation broth, widely found in wastewater treatment plants, to in-situ inhibit the production of hydrogen sulfide during anaerobic sludge treatment. It significantly inhibits sulfate-reducing bacteria in anaerobic sludge treatment and reduces the activity of hydrogen sulfide-producing microbial enzymes such as hydrolases and amino acid lyases, thereby achieving hydrogen sulfide inhibition. Compared to existing technologies, this invention utilizes wastewater treatment byproducts to in-situ regulate sludge treatment, eliminating the need for large-scale addition of other chemical agents or energy, greatly reducing the operating costs of wastewater treatment plants. This is of great significance for the large-scale application of anaerobic sludge treatment. This invention inhibits the production of hydrogen sulfide, a toxic and harmful substance, during anaerobic sludge treatment, mitigating harm to the environment and human health, and promoting the safe and effective application of anaerobic sludge treatment technology. It is of great significance for sludge reduction and resource utilization. Attached Figure Description

[0026] Figure 1 This is a process flow diagram of the present invention. Detailed Implementation

[0027] The present invention will be further described below with reference to specific practical examples, but this does not limit the scope of protection of the present invention.

[0028] Implementation Case 1

[0029] (1) Preparation of substrate: The sludge produced by the urban sewage treatment plant was concentrated in an organic glass container with a working volume of 100L (i.e., natural sedimentation at room temperature, followed by removal of the supernatant) so that the total suspended solids of the sludge were 28.9g / L.

[0030] (2) Preparation and treatment of fermentation broth: First, 50L of fermentation broth taken from the anaerobic sludge treatment tank of an urban wastewater treatment plant was added to a 100L plexiglass container. Then, the original SCFAs and dissolved phosphorus in the fermentation broth were recovered to avoid affecting subsequent experiments. The specific method was as follows: the pH of the fermentation broth was adjusted to 7.8-11 using sodium hydroxide solution, and then calcium chloride solution was added at a calcium-to-phosphorus molar ratio of 1.5-2.1 for 10-30 minutes. The precipitate containing calcium phosphate crystals was filtered out. Then, the SCFAs and other components in the fermentation broth were recovered by adsorbing and storing the intracellular polymeric polymer PHA of microorganisms. The reaction was carried out under aerobic conditions, with an aerobic reaction time of 0.5-2 hours, a sludge retention time of 3 days, and a temperature of 20±1℃. The fermentation broth obtained after treatment was stored in a 100L storage tank.

[0031] (3) Pretreatment: Add 5L of sludge obtained in (1) to the reactor and add 1.5L of fermentation liquid obtained in (2) (the volume ratio of fermentation liquid to sludge is 30%). Control the treatment temperature at 20℃, control the pH at 8.5 and maintain it for 10 hours.

[0032] (4) Anaerobic treatment of sludge: After the pretreatment is completed, nitrogen gas is introduced into the reactor for 5 minutes to remove oxygen. The sealed reactor is placed in a shaker for anaerobic treatment. The shaker temperature is 20±1℃, the shaking speed is 100rpm / min, and the sludge retention time is 10 days. That is, 0.65L of anaerobic sludge mixture needs to be taken out from the running reactor every day, and 0.65L of the new sludge substrate after pretreatment in (3) is added. After the reactor runs continuously for 180 days, the concentration of hydrogen sulfide in the reactor reaches a stable value of 13ppm.

[0033] Implementation Case 2

[0034] (1) Preparation of substrate: The sludge produced by the urban sewage treatment plant was concentrated in an organic glass container with a working volume of 100L (i.e., natural sedimentation at room temperature, followed by removal of the supernatant) so that the total suspended solids of the sludge were 28.9g / L.

[0035] (2) Preparation and treatment of fermentation broth: First, 50L of fermentation broth taken from the anaerobic sludge treatment tank of an urban wastewater treatment plant was added to a 100L plexiglass container. Then, the original SCFAs and dissolved phosphorus in the fermentation broth were recovered to avoid affecting subsequent experiments. The specific method was as follows: the pH of the fermentation broth was adjusted to 7.8-11 using sodium hydroxide solution, and then calcium chloride solution was added at a calcium-to-phosphorus molar ratio of 1.5-2.1 for 10-30 minutes. The precipitate containing calcium phosphate crystals was filtered out. Then, the SCFAs and other components in the fermentation broth were recovered by adsorbing and storing the intracellular polymeric polymer PHA of microorganisms. The reaction was carried out under aerobic conditions, with an aerobic reaction time of 0.5-2 hours, a sludge retention time of 3 days, and a temperature of 20±1℃. The fermentation broth obtained after treatment was stored in a 100L storage tank.

[0036] (3) Pretreatment: Add 5L of sludge obtained in (1) to the reactor, and add 0.5L of fermentation liquid obtained in (2) (the volume ratio of fermentation liquid to sludge is 10%) and 1L of distilled water (to ensure that the total volume is still 6.5L). Control the treatment temperature at 20℃, control the pH at 8.5 and maintain it for 10 hours.

[0037] (4) Anaerobic treatment of sludge: After the pretreatment is completed, nitrogen is introduced into the reactor for 5 minutes to remove oxygen. The sealed reactor is then placed in a shaker for anaerobic treatment. The shaker temperature is 20±1℃, the shaking speed is 100rpm / min, and the sludge retention time is 10 days. That is, 0.65L of anaerobic sludge mixture needs to be taken out from the running reactor every day, and 0.65L of the new sludge substrate after pretreatment in (3) is added. After the reactor has been running continuously for 180 days, the concentration of hydrogen sulfide in the reactor has reached a stable level of 59ppm.

[0038] Comparative Example 1

[0039] (1) Preparation of substrate: The sludge produced by the urban sewage treatment plant was concentrated in an organic glass container with a working volume of 100L (i.e., natural sedimentation at room temperature, followed by removal of the supernatant) so that the total suspended solids of the sludge were 28.9g / L.

[0040] (2) Pretreatment: Add 5L of the sludge obtained in (1) to the reactor and add 1.5L of distilled water (to ensure that the total volume is still 6.5L). Control the treatment temperature at 20℃, control the pH at 8.5 and maintain it for 10 hours.

[0041] (3) Anaerobic treatment of sludge: After the pretreatment is completed, nitrogen is introduced into the reactor for 5 minutes to remove oxygen. The sealed reactor is placed in a shaker for anaerobic treatment. The shaker temperature is 20±1℃, the shaking speed is 100rpm / min, and the sludge retention time is 10 days. That is, 0.65L of anaerobic sludge mixture needs to be taken out from the running reactor every day, and 0.65L of the new sludge substrate after pretreatment in (2) is added. After the reactor runs continuously for 180 days, the concentration of hydrogen sulfide in the reactor reaches a stable value of 135ppm.

[0042] Comparative Example 2

[0043] (1) Preparation of substrate: The sludge produced by the urban sewage treatment plant was concentrated in an organic glass container with a working volume of 100L (i.e., natural sedimentation at room temperature, followed by removal of the supernatant) so that the total suspended solids of the sludge were 28.9g / L.

[0044] (2) Anaerobic treatment of blank group sludge: Without any pretreatment, 5L of sludge obtained in (1) was directly added to the reactor and 1.5L of distilled water was added (to ensure that the total volume is still 6.5L). Then, nitrogen was introduced and kept for 5 minutes to remove oxygen. The reactor was sealed and placed in a shaker for anaerobic treatment. The shaker treatment temperature was 20±1℃, the shaking speed was 100rpm / min, and the sludge retention time was 10 days. That is, 0.65L of sludge anaerobic treatment mixture needed to be taken out from the running reactor every day and 0.65L of sludge obtained in (1) was added. After the reactor ran continuously for 180 days, the concentration of hydrogen sulfide in the reactor reached a stable value of 197ppm.

[0045] The hydrogen sulfide concentrations for the implementation cases and comparative examples are shown in Table 1:

[0046] Table 1 Comparison of processing methods between the embodiments and the comparative examples

[0047]

[0048] As can be seen from the table, the hydrogen sulfide production of Examples 1 and 2 was significantly reduced compared to that of Comparative Examples 1 and 2. In particular, the hydrogen sulfide production of Example 1 under optimal conditions was the largest reduction compared to that of Comparative Example 2, which was only 6.6% of that of Comparative Example 2.

[0049] The above description of the embodiments is provided to enable those skilled in the art to understand and use the present invention. While the present invention has been disclosed above with reference to preferred embodiments, it is not intended to limit the invention. Without departing from the spirit and technical solutions of the present invention, those skilled in the art can make many possible modifications to the technical solutions of the present invention, or modify them into equivalent embodiments with equivalent changes. Therefore, any simple improvements and modifications made without departing from the scope of the present invention should be within the protection scope of the present invention.

Claims

1. A method for in-situ suppression of hydrogen sulfide generation, characterized in that, It mainly includes the following steps: Primary and excess sludge from urban wastewater treatment plants are concentrated to increase the solids content. Anaerobic fermentation broth from the anaerobic sludge treatment tank is treated to recover SCFAs and soluble phosphorus, and the treated fermentation broth is stored for later use. The concentrated sludge is mixed with the treated fermentation broth in a certain proportion, and the sludge substrate is pretreated by adjusting the pH and temperature. Finally, the sludge is anaerobic treated. The sludge retention time is controlled by taking a certain amount of anaerobic sludge mixture from the reactor each day and adding new pretreated sludge substrate to maintain stable reactor operation. The concentration of hydrogen sulfide in the reactor is monitored regularly. After the reactor has been running continuously for a period of time, the hydrogen sulfide production reaches a stable level.

2. The method for in-situ suppression of hydrogen sulfide generation according to claim 1, characterized in that: The total suspended solids in the concentrated sludge are maintained in the range of 20-30 g / L.

3. The method for in-situ suppression of hydrogen sulfide generation according to claim 1, characterized in that: To treat the fermentation broth, the pH value needs to be adjusted to 7.8-11. Then, calcium chloride solution is added at a calcium-to-phosphorus molar ratio of 1.5-2.1, and the reaction is carried out for 10-30 minutes. Finally, the precipitate containing calcium phosphate crystals is filtered out.

4. The method for in-situ suppression of hydrogen sulfide generation according to claim 1, characterized in that: The fermentation broth needs to be treated under aerobic conditions, with an aerobic reaction time of 0.5-2 hours, a sludge retention time of 3 days, and a temperature of 20±1℃.

5. The method for in-situ suppression of hydrogen sulfide generation according to claim 1, characterized in that: When using the treated fermentation broth to pretreat sludge, the volume ratio of the added fermentation broth to the sludge substrate is 10-30%.

6. The method for in-situ suppression of hydrogen sulfide generation according to claim 1, characterized in that: When using the treated fermentation broth to pretreat sludge, the pretreatment pH is controlled at 8.5, the temperature is controlled at 20℃, and the pretreatment time is 10 hours.

7. The method for in-situ suppression of hydrogen sulfide generation according to claim 1, characterized in that: After pretreatment, nitrogen gas was introduced into the sludge substrate for 5 minutes to maintain the anaerobic closed environment of the reactor. The pH of the reaction was not controlled, and the sludge was anaerobically treated.

8. The method for in-situ suppression of hydrogen sulfide generation according to claim 1, characterized in that: In the anaerobic treatment of sludge, the sludge retention time is set to 10 days, that is, the volume of anaerobic sludge mixture removed and new sludge substrate added each day is the total volume of sludge in the reactor / 10.

9. The method for in-situ suppression of hydrogen sulfide generation according to claim 1, characterized in that: During the anaerobic treatment of sludge, the reactor reached a steady state after running continuously for 6 months, and the production of hydrogen sulfide also stabilized.

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