Odor treatment in sewage treatment plants

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Odor gas 2.1 Definition * * Standard GB14554-93 defines odor as: All gaseous substances that stimulate the olfactory organs, cause discomfort to people and damage the living environment. 2.2 Main sources Industrial production, municipal sewage, sludge treatment and garbage disposal facilities are the main sources of odorous gases. Odorous gases are mainly generated in the sewage pumping station, water inlet grille, air sedimentation tank, primary sedimentation tank, etc. in the sewage treatment process; in the sludge treatment process, sludge concentration, dehydration and drying, transfer, etc.; in the garbage treatment process, composting, landfill, incineration, transfer, etc., as well as in chemical pharmaceuticals, rubber plastics, paints and coatings, printing and dyeing leather, livestock breeding, and fermentation pharmaceuticals. 2.3 Treatment facilities and processes with different main components will produce various odorous gases. The main odor generated by the inlet lifting pump room of the sewage treatment plant is hydrogen sulfide. The odor generated during the anaerobic digestion of sludge in the primary sedimentation tank is mainly hydrogen sulfide and other sulfur-containing gases. Ammonia and other volatile substances will be generated during the sludge digestion and stabilization process. During the composting process, odors such as ammonia, amines, sulfides, fatty acids, aromatics and dimethyl sulfide will be produced. A very small amount of hydrogen sulfide may be produced during the oxidation and sludge air drying processes, but mainly mercaptan and dimethyl sulfide gases are produced. 2.4 There are many types of main harmful odorous substances and they come from a wide range of sources. They can cause varying degrees of poison to the human body's respiratory, digestive, cardiovascular, endocrine and nervous systems. Among them, aromatic compounds such as benzene, toluene, styrene, etc. can also cause distortion and cancer in the human body. 3 Current status of deodorization technology Sewage odor deodorization technology has decades of operating experience abroad. With the improvement of domestic economic level and the strengthening of environmental awareness, it is also beginning to emerge and show a vigorous trend in China. At present, the main sewage odor deodorization technologies at home and abroad include activated carbon adsorption method, thermal oxidation method, deodorizing solution deodorization method, oxygen ion group deodorization method, chemical washing method and biological filtration method. The activated carbon adsorption method mainly uses the physical adsorption of odor by activated carbon to deodorize. The advantage of this method is that it is simple in method and structure. The disadvantage is that it is only suitable for low-concentration odors and is suitable for the treatment of small-volume odors. It is usually not used as the first-stage main deodorization device, but as a subsequent fine treatment device. Thermal oxidation method mainly uses oxidation at high temperature to decompose odor into CO2 and H2O or partially oxidized compounds. The advantage of this method is that it is very effective against odors and volatile organic compounds. The disadvantages are high investment and high operating costs. It is suitable for high-flow, difficult-to-treat odors in large, heavily polluted facilities. Currently, no sewage treatment plants are known to use this method. The deodorizing solution deodorization method is mainly a method of masking and neutralizing the unpleasant odor of odorous gases by using gas odors with strong odors that are acceptable to people. The main advantages of this method are simplicity, low investment and quick results. The disadvantage is that it is difficult to completely change the composition of the odor gas, and it may still cause a small degree of damage to humans, animals, equipment and the environment. The oxygen ion group deodorization method mainly uses a high-voltage electrostatic device to generate oxygen ion groups in the fresh air supply air, and decomposes the odor into CO2, H2O and H2SO4 or partially oxidized compounds at normal temperature and pressure. The advantage of this method is that it is effective on odors and volatile organic compounds. The disadvantage is that there is still a lack of quantitative analysis data reports for practical applications. The investment is high and the operating costs are directly affected by factors such as the life of the "corona" lamp and the frequency of replacing the air pre-filter. It is suitable for odors in lightly polluted indoor spaces with ventilation and filtration systems. Special attention should be paid to the fact that the reaction product sulfuric acid may corrode indoor equipment and ventilation and air conditioning ducts. At present, no large-scale domestic sewage treatment plants using this method are known. The chemical washing method mainly uses chemical agents and the odor in the odor gas to react chemically to produce chemical products with no odor or low odor to eliminate odor. The advantage of this method is that it changes the composition of the odor and reduces the damage caused by the odor to people, animals, equipment and the environment. The disadvantage is that the investment is large and the operating cost is relatively high. In particular, the products after the chemical reaction have the possibility and tendency to cause new environmental pollution, and the chemical products after washing need to be strictly processed. The biological filtration deodorization method mainly uses the absorption and biodegradation process of odor by natural bacteria and microorganisms to naturally deodorize. The advantages of this method are moderate investment, quick results, low operating costs, and high efficiency. It is a truly green and environmentally friendly method. The disadvantage is that it is difficult to establish design standards and is not suitable for extremely high concentration odors. 4 Biological filtration and deodorization system Biological filtration and deodorization technology is now known internationally as a green solution to control odorous gas pollution. It has been recognized, accepted and adopted by more and more enterprises in China in recent years. Its treatment process is very popular for its environmental friendliness and economical construction and operation. 4.1 Composition of the system The biological filtration and deodorization system mainly consists of four parts: · Gas collection and delivery system·humidification and heat preservation system·biological filtration system·detection control system. The main function of the gas collection and transportation system is to collect the freely volatilizing gases of the structure and transport them to the subsequent treatment system. Specifically, it includes the structure capping sealing system, pipe collection system and fans. The humidification and insulation system is used to pretreat gases that do not meet the temperature and humidity treatment conditions to achieve a more ideal temperature and humidity to ensure that microorganisms can effectively remove odorous substances. The biological filtration system mainly uses the action of microorganisms growing on the surface area of ​​the carrier filler to deodorize under suitable conditions. When odorous substances pass through the filler, they are first adsorbed by the microbial film attached to the surface of the filler, and then oxidized and decomposed, thereby completing the deodorization process. The detection control system is mainly used to detect the operating status and technical parameters of the system. Through human-machine dialogue, it adjusts the process parameters and detects the operation of the equipment, so that the equipment is in optimal condition. During the sewage sludge treatment process in urban sewage treatment plants, a large amount of malodorous gases and odors will inevitably be produced. These odors are mainly caused by organic matter. * * caused by the gas produced. Odors generally include fish odor, ammonia odor, rotten meat odor, rotten egg odor (hydrogen sulfide H2S), rotten cabbage odor, manure odor and the special odor of some production wastewater. The odor is unpleasant to the senses and can even endanger human physiological health, such as difficulty breathing, nausea, chest tightness, vomiting, etc. With the development of human society and economy, the improvement of people's living standards and the increasing public environmental awareness, the odor problem generated during the operation of urban sewage treatment plants has attracted more and more attention from society. In order to prevent and eliminate the impact of the odor of urban sewage treatment plants on the surrounding environment and residents' lives, some developed countries * * Some relevant specific regulations have been formulated and gradually improved. At present, most of the urban sewage treatment plants built in our country are located in large and medium-sized cities and tourist attraction towns. Some of them are difficult to avoid residential areas, traffic arteries or villages. Therefore, the deodorization problem of sewage treatment plants is inevitably put on the agenda, and some have reached the point where it is urgent to be solved. In the future, my country's environmental department will propose odor control indicators for sewage treatment plants. 2 Deodorization technology and design There are many methods to treat odor in sewage treatment plants, such as direct incineration, catalyst oxidation, acid-base cleaning, ozone oxidation, chemical adsorption, activated carbon physical adsorption, biological deodorization, soil deodorization, etc., but the most economical and practical one is biological deodorization technology. When exhaust ventilation is used for deodorization, the ventilation volume of the treatment structure of the sewage treatment plant can refer to the values ​​in Table 2. This article will briefly discuss the soil method, biological method, and ion method. Table 1 Odor concentration control reference value serial number control item primary standard secondary standard 1 Ammonia 1.5 4.0 2 Hydrogen sulfide .06 .32 3 Methyl mercaptan .007 .02 4 Methyl sulfide .07 .55 5 Odor concentration (multiple) 20 60 6 Methane gas (highest concentration in the plant area) 5 5 7 Chlorine gas .4 .6 Table 2 Sewage treatment plant structure deodorization flux facility name ventilation volume remarks sand settling tank second-floor cover working space 3 to 5 times/hour non-working space 1 to 3 times/hour factory cover working space 5 to 10 times/hour cover service on the funnel 3 to 5 times/hour pump room 3 to 5 times/hour Or consider the internal combustion engine gas blower room 3 to 5 times/hour based on calorific value calculation, or calculate the electrical room based on calorific value to calculate the generator room 3 to 5 times/hour. Consider the internal combustion engine gas primary sedimentation tank second-floor cover working space 3 to 5 times/hour non-operating space 1 to 3 times/hour. Hourly factory cover working space 5 to 10 times/hour Aeration tank second floor cover working space 3 to 5 times/hour Non-working space 1.2×aeration air volume Factory type cover working space 3 to 5 times/hour chlorination machine room 5 to 7 times/hour sludge concentration tank second floor cover working space 3～ 5 times/hour + 1.5 × aeration air volume Non-working space 1 to 3 times/hour Factory cover working space 5 to 10 times/hour Sludge thickening machine room 3 to 10 times/hour Other methods are used for heat treatment General mechanical room 3 to 5 times/hour Pipe gallery 3 to 5 times/hour 2.1 Soil deodorization technology 2.1.1 Principles and characteristics of soil deodorization Soil deodorization mechanisms can be mainly divided into two categories: physical adsorption and biological decomposition. Odor gases - such as amines, hydrogen sulfide, lower fatty acids and other water-soluble odors - are absorbed and removed by water in the soil, while insoluble odors are physically adsorbed on the soil surface and then decomposed by microorganisms in the soil. Characteristics of soil deodorization method: ① Maintenance and management costs are low, and the effect is the same as activated carbon deodorization. ② It requires 2.5 to 3.3 m2 of land to treat 1m2 of odor ； ③ But it is not suitable for areas with heavy rain and heavy snow. ； Gases such as high temperature, high humidity, moisture, dust, and fine dust must be treated. 2.1.2 Soil and parameter design The soil index selected when deodorizing soil should be: Humus soil is better, and red soil such as loam needs to be mixed with chicken manure, garbage and sludge fertilizers for improvement before use. ； Mineral soil and clay are not suitable. The soil moisture content is 40-70%. Soil that is too dry requires the installation of water sprinklers. The soil surface for planting lawns is kept sloped as a protection against heavy rainfall. 　　Drawn from Japanese experience: 　　The speed of odor passing through the soil: 2mm～17mm/s ； 　　The design is generally selected as 5mm/s ； 　　Effective soil thickness is 50 cm ； 　　The contact time between odor and soil is 1 minute and 40 seconds ； 　　The speed of odor passing through activated carbon: 30cm～40cm/s ； 　　Effective thickness is 40cm ； 　　The contact time between odor and activated carbon is 1 second. 2.1.3 Project examples (1) Odor air volume of soil deodorization bed somewhere in Japan: 600m3/min contact time between odor and soil: 2.7m3/m2min soil area required: 1580m2 (2) Volume of soil deodorization bed dehydration machine room in a sludge dehydration machine room somewhere in my country: V＝450m3 Assume ventilation cycle: 3 times per hour (20min) Change the odor volume: 22.5m3/min (450m3/20min) deodorization load: Assume 2.7m3 (odor)/m2 (soil) min required soil area (calculated value): 8.3m2 (design value): 25m2 Structural design (from soil surface downward) Layer structure parameters 1 Soil vegetation continued: 2.3 High-energy ion deodorization technology 2.3.1 Technical introduction and working principle The high-energy ion purification system is a Swedish high-tech technology. It can effectively remove harmful substances such as bacteria, inhalable particulate matter, and sulfur compounds in the air. Make people's sense of smell feel the fresh air that simulates nature. Its core device is the BENTAX ion air purification system. Its working principle is that the ion generator placed indoors emits high-energy positive and negative ions. It can contact with organic volatile gas molecules (VOC) in the indoor air, open the chemical bonds of VOC molecules, and decompose into carbon dioxide and water. ； It also has decomposition effect on hydrogen sulfide and ammonia ； The ion generator emits ions that collide with dust particles and solid particles in the air, causing the particles to be charged and polymerized to form larger particles that settle by their own gravity to achieve the purpose of purification. ； The emitted ions can also interact with indoor static electricity, odors, etc., and at the same time effectively destroy the environment where bacteria live in the air, reduce the concentration of indoor bacteria, and completely eliminate them. The final effect is to make the indoor air as pure as a forest after rain. 　　High-energy ion purification systems are used in hospitals, office buildings, public halls, etc. in European countries to purify the air and achieve the effect of simulating the fresh air of natural forests. In recent years, it has been gradually developed and applied to deodorization in sewage treatment plants and sewage lifting pump rooms. There are many application examples in France, the United Kingdom, Scotland, Sweden and other countries. 2.3.2 Test results of a sewage treatment plant in Tianjin (1) Test site The deodorization pilot test site was selected in the sludge disposal laboratory of a sewage treatment plant in Tianjin. The odor source is the odor generated during the dewatered sludge disposal process. 　　(2) Test conditions: 　　①Total volume of sludge pilot laboratory: 30m3 (3×4×2.5m3) ； 　　Sludge fermentation bin diameter φ600mm, length 3m ； 　　The horizontal distance between the odor test point and the fermentation bin is 1m ； 　　The high-energy ion purification system host and ventilation system are placed indoors. 　　②260kg of dewatered sludge from the odor source is put into the rotary sludge fermentation bin ； 　　In order to enhance the odor intensity, the sludge is heated using solar energy. 　　③High energy ion purification system ion machine specifications and models: 2-E-S airflow: 0.42m3/s air handling capacity: 1500m3/h power: 22w ventilation system for ion emission system ； 　　④ Test item negative ion concentration ； Total amount of VOC (organic pollution) gases ； 　　H2S, O2, CO, CH4 concentration. 　　⑤ Test data analysis and evaluation: 9 hours of continuous operation, the odor source VOC concentration periodically changes from 25 to 100ppm, and indoors gradually decays from 15 to 16.7ppm to 0 to 1ppm ； The ion concentration at the indoor measuring point is always maintained at 160~170Ions/cm3 ； The H2S gas concentration also remains at 0. 　　The test result change curves are shown in Figures 1 and 2. 　　⑥ Test result evaluation The VOC meter, ion detector and toxic and harmful gas meter used in test A are all advanced portable instruments with high sensitivity and can ensure the reliability of the data. ； 　　Trial run B is the sludge odor after sludge fermentation bin and solar heating. The odor intensity is high. It is purified by the BENTAX ion air purification system. After only 1 hour, the VOC concentration is reduced to zero, the ion concentration is increased, the H2S gas is reduced from 4.0ppm to 0, and the smell of the personnel is significantly reduced. The load test was conducted under the conditions of dewatered sludge disposal odor source. The VOC concentration of the odor source ranged from 25 to 100 ppm, and the indoor measurement point gradually decayed from 15 to 16.7 ppm to 0 to 1 ppm. ； The ion concentration is always maintained at 160~170 Ions/cm3 ； The H2S gas concentration also remains at 0. 　　The technical conclusion is: By utilizing high-energy ions for deodorization, the deodorization effect is technically feasible under the above test conditions. 　　C Economic Analysis Under the conditions of this experiment, the high-energy ion purification system has a significant purification effect on the odor of dewatered sludge in the sewage plant. The operation cost analysis is as follows: 　　24-hour operation consumes only 0.53kwh ； 　　The power consumption per unit space is 0.018 kwh/m3.d ； 　　Calculated at 0.45 yuan per kilowatt hour of electricity, the cost of purifying 1 cubic meter of odor is approximately 0.0081 yuan/m3.d ； 　　The sludge dewatering workshop is calculated as 1000 m3 ； 　　Then the operating cost and direct electricity consumption are 8.1 yuan/d.