Method for relieving and eliminating sewage anaerobic fermentation stink

Abstract

The invention discloses a method for relieving and eliminating sewage anaerobic fermentation stink. The method comprises the following steps: mixing malodorous gas generated by anaerobic fermentation with nitrogen dioxide, and carrying out gas-phase oxidation reaction; the reacted gas is subjected to ultraviolet photolysis treatment, so that nitrogen dioxide is decomposed to generate ozone; and the generated ozone is utilized to continuously oxidize the malodorous substances. The method can also comprise a source sulfur fixation step: adding a sulfur fixation agent into the anaerobic fermentation system, and reducing the generation of hydrogen sulfide from the source. Nitrogen dioxide can be prepared from steel cylinder gas, industrial waste gas or on site, and the on-site preparation comprises an ammonia water / ammonium salt catalytic oxidation method and a nitric acid reduction method. Through multi-stage cooperation of'source sulfur fixation + NO2 gas-phase oxidation + UV ozone conversion + ozone continuous oxidation ', efficient removal of malodorous gas is achieved, an ozone generator does not need to be additionally arranged, nitrogen dioxide residues are thoroughly eliminated, secondary pollution is avoided, equipment is compact, and the operation cost is low.

Description

Technical Field

[0001] This invention belongs to the field of environmental protection technology, specifically relating to a method for reducing and eliminating the malodorous odor of anaerobic fermentation in wastewater. Background Technology

[0002] In wastewater treatment, landfilling, and aquaculture processes, anaerobic fermentation of wastewater produces large amounts of malodorous gases, primarily including hydrogen sulfide, thiols, sulfides, ammonia, and amines. In real-world environments, sulfate-reducing bacteria (SRB) in anaerobic environments reduce sulfate to sulfur dioxide (S). 2- With metal ions (such as Fe) 2+ The formation of black metal sulfide precipitates (such as FeS) causes the sludge to turn black, while the volatilization of organic sulfides such as hydrogen sulfide and thiols stimulates the sense of smell and produces a foul odor.

[0003] According to the Japan Environmental Management Center's measurement of the olfaction threshold of 223 chemical substances, 15 organosulfur compounds had an olfaction threshold of less than 1 μg / m³. 3 And below the 1.8 μg / m³ of hydrogen sulfide. 3 With the widespread use and emission of volatile organic compounds (VOCs), various new malodorous substances such as thioesters and thioketones are causing serious nuisance to residents. It has been reported that Cambridge University, using advanced instruments, has precisely measured the odor threshold of thioacetone to 0.3 ppt (parts per trillion), an extremely low level among known malodorous substances. Thioacetone has an extremely strong odor, causing intense sensory discomfort even at trace concentrations, making it a typical example of a strongly odorous substance. These malodorous substances have extremely low odor thresholds, not only seriously affecting the air quality of the surrounding environment but also posing a threat to human health. Long-term exposure may lead to health problems such as damage to the nervous system and respiratory diseases.

[0004] Currently, the main technologies for treating odorous gases include biological methods, physical adsorption methods, and chemical scrubbing methods. Biological methods, such as biofilters and biotrickling filters, suffer from unclear mechanisms, undefined methods, and poor effectiveness for highly volatile trace odorous substances using biochemical and physicochemical purification. Utilizing microbial metabolism to degrade odorous substances has the advantage of low operating costs, but it suffers from long strain acclimatization periods, sensitivity to temperature and pH, low treatment load, and large footprint. Furthermore, its effectiveness is unstable for high-concentration or highly fluctuating odorous gases. Physical adsorption methods, such as activated carbon adsorption, can effectively remove odorous substances, but after adsorption saturation, replacement or regeneration is required, generating secondary pollutants such as waste carbon, resulting in high operating costs. Chemical scrubbing involves spraying a chemical absorption liquid to react with the odorous gas, but it consumes large amounts of reagents, and the scrubbing waste liquid requires further treatment.

[0005] For the control of sulfides in anaerobic processes, existing technologies include methods that use iron salts to precipitate sulfides. For example, some patents disclose the installation of a desulfurization unit in a wastewater treatment system, which involves adding ferrous chloride or ferric chloride to react ferric ions with inorganic sulfur (S). 2- The process forms precipitates, thus separating sulfur from the water. However, this technology only targets the removal of sulfides from wastewater and does not address the synergistic treatment of gaseous odorous gases. In practical applications, experience has shown that while ferrous sulfate can remove sulfides, its sulfate ions promote the growth of sulfate-reducing bacteria, thereby inhibiting anaerobic reactions. Therefore, ferrous chloride is preferred as a sulfur-fixing agent.

[0006] In gas-phase oxidation, nitrogen dioxide (NO2), as a strong oxidant, exhibits extremely high reactivity with sulfur-containing odorous substances such as hydrogen sulfide and thiols, reacting rapidly even at trace concentrations to oxidize them into odorless products. This reaction can be carried out at room temperature and pressure without requiring complex equipment. Ultraviolet (UV) photolysis technology utilizes high-energy ultraviolet light beams to irradiate odorous gases, breaking down the molecular chain structures of odorous substances such as hydrogen sulfide, ammonia, and thiols, degrading them into low-molecular-weight compounds. While UV photolysis alone has limited efficiency in treating high concentrations of odorous gases, it is effective as an end-of-pipe treatment method.

[0007] In summary, existing odor control technologies generally suffer from problems such as difficulty in balancing treatment efficiency and operating costs, the potential for secondary pollution, and the inability of a single technology to achieve effective control throughout the entire process. Therefore, developing a highly efficient, economical, and environmentally friendly odor control method that can achieve full-process control from source to end is of significant practical importance. Summary of the Invention

[0008] Purpose of the invention

[0009] The purpose of this invention is to provide a method for reducing and eliminating the malodorous odor from anaerobic fermentation of wastewater. Through multi-stage synergistic treatment of "source sulfur fixation + gas phase oxidation + photolysis enhancement", the malodorous gases are efficiently removed while avoiding secondary pollution caused by residual oxidants.

[0010] Technical solution

[0011] A method for mitigating and eliminating the malodorous odor from anaerobic fermentation of wastewater includes the following steps:

[0012] (1) Source fixation of sulfur: Sulfur fixation agent is added to the anaerobic fermentation system to fix sulfur ions in the form of precipitation, thereby reducing the generation of hydrogen sulfide from the source;

[0013] (2) Gas phase oxidation: The malodorous gas produced by anaerobic fermentation is mixed with nitrogen dioxide and subjected to gas phase oxidation reaction, so that the reducing substances such as hydrogen sulfide, ammonia, and volatile organic compounds in the malodorous gas are partially oxidized and decomposed.

[0014] (3) Ultraviolet photolysis conversion: The gas after step (2) is subjected to ultraviolet photolysis treatment. Ultraviolet light irradiation decomposes the residual nitrogen dioxide to generate ozone.

[0015] (4) Ozone continued oxidation: The ozone generated in step (3) was used to continue oxidizing the malodorous substances and other reducing gases that were not completely oxidized in step (2).

[0016] In step (1), the sulfur-fixing agent is selected from at least one of iron salts, calcium salts, and magnesium salts, and the amount of sulfur-fixing agent added is 1.0-1.5 times the molar amount of sulfur ions. Preferably, the iron salt is ferrous chloride.

[0017] In step (2), the malodorous gases include at least one of hydrogen sulfide, ammonia, mercaptan, thioether, and volatile organic compounds. The amount of nitrogen dioxide added is 0.5-2.0 times the stoichiometric requirement of the malodorous substances. The gas-phase oxidation reaction is carried out at room temperature and pressure, and the reaction time is 1-30 seconds.

[0018] In step (3), the wavelength of the ultraviolet light is 200-400 nm and the irradiation time is 0.5-10 seconds.

[0019] In step (4), the ozone oxidation reaction and the ultraviolet photolysis in step (3) are carried out simultaneously in the same reactor, without the need to add an additional reactor.

[0020] The nitrogen dioxide is derived from cylinder gas, on-site preparation, or industrial waste gas. On-site preparation methods include ammonia / ammonium salt catalytic oxidation and nitric acid reduction.

[0021] The ammonia / ammonium salt catalytic oxidation method includes the following steps: (a) heating ammonia or ammonium salt as raw material to release ammonia gas; (b) reacting the ammonia gas with air in the presence of a Cr2O3 catalyst to generate nitric oxide; (c) mixing the nitric oxide with air to oxidize it into nitrogen dioxide; and (d) collecting the nitrogen dioxide for gas-phase oxidation reactions. The Cr2O3 catalyst is a self-made catalyst.

[0022] The nitric acid reduction method includes the following steps: using dilute nitric acid as a raw material, mixing it with a reducing agent to undergo a redox reaction to produce nitrogen dioxide, and collecting the nitrogen dioxide for a gas-phase oxidation reaction. The reducing agent is selected from at least one of starch, sucrose, copper shavings, and sodium sulfite.

[0023] Beneficial effects

[0024] Compared with the prior art, the present invention has the following beneficial effects:

[0025] First, there is a dual guarantee of source reduction and end-of-pipe treatment. Source sulfur fixation can reduce H2S production by 30%-70%, reducing the load on subsequent treatment; the end-of-pipe treatment uses a multi-stage oxidation process of "NO2 gas phase oxidation + UV conversion to O3 + O3 continued oxidation" to deeply treat residual odorous substances and ensure that emissions meet standards.

[0026] Secondly, no external ozone generator is required. Ozone is generated in situ from nitrogen dioxide via ultraviolet photolysis, eliminating the need for a separate ozone generator and reducing equipment investment and operating costs.

[0027] Third, it completely eliminates nitrogen dioxide residue. Nitrogen dioxide itself is acidic and toxic, and emission limits are strictly enforced. This invention converts it into ozone through ultraviolet photolysis. The ozone is consumed during the continued oxidation of odorous substances or naturally decomposes into oxygen, thus avoiding secondary pollution from nitrogen dioxide.

[0028] Fourth, the synergistic effect is significant. Nitrogen dioxide oxidizes reducing substances such as hydrogen sulfide faster than ozone, making it suitable for treating high concentrations of malodorous substances; ozone oxidation is more thorough, and its decomposition product is oxygen, which is environmentally friendly; the combination of the two achieves a relay oxidation effect of "rapid + thorough". Ultraviolet photolysis simultaneously achieves the two goals of "eliminating NO2 residue" and "generating O3", killing two birds with one stone.

[0029] Fifth, nitrogen dioxide has flexible sources. It can be produced from cylinder gas, industrial waste gas, or prepared on-site. On-site preparation includes ammonia / ammonium salt catalytic oxidation and nitric acid reduction. Raw materials are readily available and do not depend on external supply. The most economical and convenient preparation method can be selected according to actual conditions. It is particularly suitable for remote areas or mobile treatment plants without external supply.

[0030] Sixth, the equipment is compact and requires less investment. The core equipment consists only of a gas mixing section and an ultraviolet photolysis reactor, which requires little space, can be modularly designed, and facilitates the upgrading of existing facilities. Detailed Implementation

[0031] Example 1 (Sulfur fixation at the source + NO2 gas-phase oxidation + ultraviolet photolysis conversion)

[0032] An anaerobic digester at a wastewater treatment plant has a treatment capacity of 1000 m³. 3 The sulfide content in the feed sludge is approximately 50-100 mg / L per day. Ferrous chloride (FeCl2) is continuously added to the feed pipeline at a dosage of 1.2 times the molar amount of sulfur ions. After implementing source sulfur fixation, the H2S concentration in the digester biogas decreased from 800-1200 ppm to 300-500 ppm, a reduction of approximately 60%.

[0033] The odorous gases escaping from the top of the digester (main components: H2S 300-500 ppm, NH3 50-100 ppm, VOCs trace amounts) are collected and introduced into the treatment unit. The treatment unit includes a gas mixing section (nitrogen dioxide inlet) and an ultraviolet photolysis reaction section (254 nm UV lamps, total power 500 W). Nitrogen dioxide is supplied from purchased cylinders, with a dosage of 1.2 times the stoichiometric requirement (calculated based on H2S concentration). The odorous gases and nitrogen dioxide remain in the mixing section for approximately 10 seconds, undergoing a gas-phase oxidation reaction. After the reaction, the gas enters the ultraviolet photolysis reaction section, where it remains for approximately 8 seconds. Nitrogen dioxide decomposes to generate ozone, which further oxidizes any remaining H2S, NH3, etc.

[0034] After 30 days of continuous operation, the treatment results are as follows: H2S decreased from 300-500 ppm to <1 ppm, with a removal rate >99.5%; NH3 decreased from 50-100 ppm to <2 ppm, with a removal rate >97%; NO2 residual concentration was <0.5 ppm; and odor concentration (dilution method) decreased from 10000-30000 to <200, with a removal rate >98%. The treated gas meets the requirements of the "Odor Pollutant Emission Standard" (GB 14554).

[0035] Example 2 (Sulphur fixation without source, only gas phase oxidation + ultraviolet photolysis conversion)

[0036] For locations where source sulfur fixation is not feasible, only end-of-pipe treatment units are used. Treatment conditions are the same as in Example 1, but the source sulfur fixation step is omitted. The H2S concentration in the odorous gas is 800-1200 ppm, and NH3 is 80-150 ppm. The nitrogen dioxide dosage is adjusted to 1.5 times the stoichiometric requirement, and the UV lamp power is increased to 800 W. Treatment results: H2S decreased from 800-1200 ppm to <3 ppm, removal rate >99.5%; NH3 decreased from 80-150 ppm to <3 ppm, removal rate >96%; NO2 residual concentration <0.5 ppm. The treatment effect meets emission standards.

[0037] Example 3 (Intermittent Emission Scenario)

[0038] A livestock farm's manure collection pond emits foul-smelling gases intermittently (approximately 4 hours per day). A treatment capacity of 500 m³ is being installed. 3 A mobile treatment unit with a capacity of [number] h. Odorous gases are collected via pipelines and mixed with nitrogen dioxide in a static mixer (residence time approximately 5 seconds), then enter a UV photolysis reactor (254 nm UV lamp, total power 200 W, residence time approximately 3 seconds). The nitrogen dioxide dosing system is linked to the odorous gas emission, adding nitrogen dioxide and turning on the UV lamps only during emission periods. After 3 months of operation, the H2S removal rate remained stable above 95%, and the NH3 removal rate remained stable above 90%.

[0039] Example 4 (On-site preparation of nitrogen dioxide)

[0040] The nitrogen dioxide used in this invention can be obtained in-situ through the following two methods.

[0041] Method 1: Ammonia / Ammonium Salt Catalytic Oxidation Method

[0042] Nitrogen dioxide is prepared on-site using ammonia water as raw material. Industrial ammonia water (25% NH3·H2O) is heated to 70℃ to release ammonia gas. The ammonia gas is mixed with air at a volume ratio of 1:15 and passed into a fixed-bed reactor containing a self-made Cr2O3 catalyst. The reaction temperature is controlled at 600℃, where a catalytic oxidation reaction occurs to produce nitric oxide. The gas exiting the reactor enters an oxidation tower, where an appropriate amount of air is added, and the residence time is 3 minutes, during which nitric oxide is oxidized to nitrogen dioxide. The nitrogen dioxide concentration in the outlet gas is approximately 3000-4000 ppm. This gas is directly introduced into an odor gas treatment system, replacing the use of purchased cylinder-generated nitrogen dioxide. The preparation system and the treatment system operate in tandem, adjusting the ammonia water dosage according to changes in the H2S concentration in the odor gas. The cost of on-site nitrogen dioxide preparation is approximately 60% of that of purchasing cylinder-generated gas.

[0043] Method 2: Nitric Acid Reduction Method

[0044] Nitrogen dioxide is prepared using dilute nitric acid as a raw material. 30%-50% dilute nitric acid is placed in a reaction flask, and a reducing agent (such as starch, sucrose, copper filings, or sodium sulfite) is added, resulting in a redox reaction to produce nitrogen dioxide. The reaction is carried out in a fume hood or a closed system to prevent nitrogen dioxide leakage. Taking starch as an example, the reaction formula is as follows:

[0045] C6H 10 O5+ 12HNO3 → 6CO2 + 12NO2+ 11H2O

[0046] The reaction is carried out at room temperature, and the generated nitrogen dioxide gas is dried and directly introduced into the odor gas treatment system. The amount of reducing agent added is calculated according to the stoichiometric ratio based on the amount of nitric acid used. This method involves simple equipment, requires no heating, and is suitable for small-scale or intermittent operations. The cost of preparing nitrogen dioxide using the nitric acid reduction method is slightly higher than that using the ammonia method, but the equipment investment is lower, making it suitable for temporary or mobile treatment facilities.

Claims

1. A method for mitigating and eliminating the malodorous odor of anaerobic fermentation in wastewater, characterized in that, Includes the following steps: The malodorous gases produced by anaerobic fermentation are mixed with nitrogen dioxide to carry out a gas-phase oxidation reaction; The gas after the reaction is subjected to ultraviolet photolysis to decompose nitrogen dioxide into ozone. The generated ozone is used to further oxidize malodorous substances.

2. The method according to claim 1, characterized in that, It also includes the step of adding a sulfur-fixing agent to the anaerobic fermentation system, wherein the sulfur-fixing agent is selected from at least one of iron salts, calcium salts, and magnesium salts.

3. The method according to claim 2, characterized in that, The iron salt is ferrous chloride.

4. The method according to claim 1, characterized in that, The amount of nitrogen dioxide added is 0.5-2.0 times the stoichiometric requirement of the odorous substances, and the reaction time of the gas-phase oxidation reaction is 1-30 seconds.

5. The method according to claim 1, characterized in that, The wavelength of the ultraviolet photolysis is 200-400 nm, and the irradiation dwell time is 0.5-10 seconds.

6. The method according to claim 1, characterized in that, The ozone oxidation and ultraviolet photolysis are carried out simultaneously in the same reactor.

7. The method according to claim 1, characterized in that, The nitrogen dioxide is derived from gas cylinders, on-site preparation, or industrial waste gas.

8. The method according to claim 7, characterized in that, The on-site preparation includes ammonia / ammonium salt catalytic oxidation or nitric acid reduction. The ammonia / ammonium salt catalytic oxidation method includes: using ammonia or ammonium salt as raw material, heating to release ammonia gas; reacting the ammonia gas with air in the presence of a Cr2O3 catalyst to generate nitric oxide; mixing the nitric oxide with air and oxidizing it to nitrogen dioxide; and collecting the nitrogen dioxide. The nitric acid reduction method includes: using dilute nitric acid as raw material, mixing it with a reducing agent, and conducting a redox reaction to generate nitrogen dioxide, and collecting the nitrogen dioxide.

9. The method according to claim 8, characterized in that, The Cr2O3 catalyst is a self-made catalyst, and the reducing agent is selected from at least one of starch, sucrose, copper scrap, and sodium sulfite.

10. An odor gas treatment system for implementing the method according to any one of claims 1-9, characterized in that, include: The gas mixing unit is equipped with an odor gas inlet and a nitrogen dioxide inlet; The ultraviolet photolysis reactor is connected to the gas outlet of the gas mixing unit and is equipped with an ultraviolet lamp.