Introduction to biological purification of VOCs
Biological method to control VOCs pollution is an air pollution control technology developed in recent years. This technology has been applied on a large scale in Germany and the Netherlands, and the removal rate of organic matter is mostly above 90%. Compared with conventional treatment methods, biological methods have the advantages of simple equipment, low operating costs, and less formation of secondary pollution, especially when dealing with low-concentration, good biodegradable gaseous pollutants .
The main components of VOCs are: hydrocarbons, halogenated hydrocarbons, oxygen hydrocarbons and nitrogen hydrocarbons, which include: benzene series, organic chlorides, Freon series, organic ketones, amines, alcohols, ethers, esters, acids and petroleum hydrocarbon compounds Wait. And teratogenic and carcinogenic polycyclic aromatic hydrocarbons are one of the important killers of human health.
Standard Practice for Determination of Volatile Organic Compounds in Coatings and Related Coatings ASTMD3960-2005 defines volatile organic compounds (VOC) as any organic compound that can participate in atmospheric photochemical reactions. US Federal Environmental Protection Agency (EPA) definition: Volatile organic compounds are any carbon compounds that participate in atmospheric photochemical reactions except CO, CO 2 , H 2 CO 3 , metal carbides, metal carbonates and ammonium carbonate. The World Health Organization (WHO, 1989) defines total volatile organic compounds (TVOC) as the general term for volatile organic compounds with a melting point below room temperature and a boiling point between 50 and 260 ¡ã C.
The essence of the VOCs biological purification process is that the microorganisms attached to the filter medium use the organic components in the exhaust gas as a carbon source and energy under the appropriate environmental conditions to maintain their life activities and decompose organic substances into CO 2 and H 2 O. the process of. VOCs in the gas phase body first undergo a mass transfer process from the gas phase to the solid or liquid phase, and then are decomposed by the microorganisms in the solid or liquid phase.
Common biological methods for treating VOCs include biological washing method, biological filtration method and biological trickling method.
The biological washing method is to use a microbial absorption liquid composed of microorganisms, nutrients and water to treat waste gas. Suitable for absorbing soluble gaseous pollutants.
The gas-liquid contact method in the biological washing method, in addition to the liquid-phase spray. Gas phase bubbling can also be used. Generally, if the gas phase resistance is large, the spray method can be used; on the other hand, when the liquid phase resistance is large, the bubbling method is used. Since the circulating washing liquid of the biological washing method needs to be regenerated by the activated sludge method. Therefore, under normal circumstances, the circulating washing solution is mainly water. Therefore, this method is only applicable to VOCs with good water solubility, such as ethanol and ether, and it is not applicable to poorly soluble VOCs. 
VOCs gas enters from the bottom of the tower and is purified by contact with the biofilm during the flow process. The purified gas is discharged from the top of the tower. The circulating spray liquid enters the filter bed from above the filler layer, flows through the surface of the biofilm, and precipitates at the bottom of the filter tower. The supernatant is added for recycling by adding N, P, and pH adjuster, and the precipitate is discharged from the system.
The biological filtration purification system consists of a humidification tower and a biological filtration tower. Volatile organic gases enter the filter tower after being humidified, and are contacted with the biological filter material inoculated with the membrane to be degraded. CO 2 , H 2 O and microbial matrix are finally generated , and the purified gas is discharged from the top. Spray the nutrient solution regularly on the top of the tower to provide nutrients, moisture and maintain a constant pH value for the microorganisms on the filter.
The biological washing tower is mainly composed of activated sludge tank and washing tower. The washing tower includes two parts, absorption and biodegradation. The circulating liquid acclimatized with organic matter is sprayed down by the liquid distribution device on the top of the washing tower, and is in countercurrent contact with the main body of the gas phase along the tower. Decomposed and degraded.
The biggest difference between the biological drip filter tower and the biological filter tower is that the circulating liquid is sprayed from the top of the packing. In addition to the mass transfer process in the equipment, there is a strong biodegradation effect. The VOCs gas enters from the bottom of the tower, and is contacted with the biological filter material inoculated with the membrane during the flow to be purified. The purified gas is discharged from the top of the tower. The drip filter tower integrates the absorption of exhaust gas and the regeneration of the liquid phase. A filler with microorganisms attached is added to the tower to provide conditions for the growth of microorganisms and the degradation of organic matter.
The working principle of biological filtration tower purification of VOCs is: VOCs gas enters the filtration tower from the top of the tower, and is contacted with the biological filter material inoculated with the membrane during the flow to be purified. The purified gas is discharged from the bottom of the tower.
Advantages: high removal rate, simple equipment, low operating costs, less secondary pollution, especially economical when dealing with low concentration and good biodegradable gaseous pollutants.
Disadvantages: large pressure loss, poor impact load capacity, high requirements for growth environment, sensitive to temperature and humidity changes, large volume, not suitable for high halogen compounds.
Bioprocessed organic compounds include:
Hydrocarbons: benzene, toluene, xylene, ethane, naphtha, cyclohexane, etc .;
Halogens: trichloroethylene, tetrachloroethylene, trichloroethane, dichloromethane, trichlorobenzene, trichloromethane, carbon tetrachloride, etc .;
Ketones: acetone, cyclohexanone, etc .;
Esters: ethyl acetate, butyl tartrate, methylcyclohexane, etc .;
Ethers: ethyl acetate, dioxane, furfural, methyl cellosolve, etc .;
Alcohols: methanol, ethanol, isopropanol, butanol, etc .;
Monomolecular objects for overlap: vinyl chloride, acrylic acid, acrylate, styrene, vinyl acetate, etc.
Industries that the technology is suitable for include: organic waste gas from automotive, shipbuilding, motorcycles, bicycles, household appliances, pianos, paint spraying, coating workshops or production lines at container manufacturing plants; printed iron cans, chemical plastics, printing inks, cables, Organic waste gas from enameled lines and other production lines; organic waste gas from shoe viscose, tanning and kneading; odor from sewage treatment plant, garbage treatment plant and slaughter plant; organic waste gas from chemical production and storage ; Organic waste gases from film production and pharmaceutical processes.