生物膜法处理有机废气 英语.doc

Biofilm treatment of organic wasteLi Ruixue Cai Shenjian Shen ChengAbstract: Hazard organic waste has become the consensus, treatment of organic waste pollution is one of the key environmental work. This paper describes the sources of organic waste and hazards, describes the principles of biofilm treatment of organic waste, advantages and disadvantages, discussed its research status and development trends.Keyword: Biofilm; Organic waste;Treatment1:PrefaceBoiofilm organic gas mainly comes from the petroleum, the chemical industry in the production process emissions.It has the characteristic that the organic matter content of ups and downs, with combustible, have a certain toxicity and there will be some odor.Chlorofluorocarbon emissions will cause the destruction of the ozone layer.Petrochemical production process and storage equipment,printing and other related to petroleum and chemical industry,the use of organic solvents.,Petroleum products for a variety of transportation fuels all above these will cause organic gas.【1】The main components of organic waste are formaldehyde,acetone,acetic acid,ethyl -ester,additive and other organic gases containing carbon and oxygen and so on .Organic gas damage plant leaf tissue and destroy the ozone layer,For the harm to human body is reflected in many aspects.Benzene is highly toxic solvents,even small amounts can cause long-term damage to the human body,it can accumulate in the bone marrow and the nervous system,damage hematopoietic tissue and nervous system,cause neurological disorders, reduce the amount of white blood cells in the blood, platelet,worse is suffering from leukemia.PAH and organic compounds have strong carcinogenesis.Benzoic acid can make the protein in a cell deformation or solidification, the systemic poisoning.Nitriles can cause breathing difficulties, can cause suffocation seriously, loss of consciousness until death.Glycol ether solvent in the human body can be formed after the metabolism of toxic,cause permanent damage to the circulatory and nervous system of the body.Female reproductive system would also be affected, serious can lead to infertility.Organic phosphorus compounds can reduce blood cholinesterase activity, resulting in nervous system disorders.About organic sulfur compounds, low concentration of thiol can cause physical discomfort, but death at high concentration.Toluene diisocyanate with low vapor pressure, have a strong stimulating effect on the human cornea, causing eye irritation.Steam into the human body, will damage the function of human liver, kidney, long-term exposure to toluene diisocyanate steam high concentrations of carcinogenic.There are two main types to treat organic waste gas :one is recovery.The recovery method is physical method,we use the adsorbent and selectively permeable membrane to separate volatile organic compounds in a certain temperature and pressure including active carbon adsorption,condensation method,Pressure swing adsorption method and biofilm.Another is eliminate these organic waste we turn organic matter into carbon dioxide and water using of light, heat, catalyst and microbes, like light decomposition method, the thermal oxidation method, catalytic combustion method, biological oxidation, corona method, plasma decomposition and so on.【2】2 :Biofilm treatment of organic waste2.1 Mechanism of biofilm treatment of organic wasteMechanism of biofilm treatment of organic waste was first put forward by Ottengraf from Netherlands.The biofilm theory biochemical method of organic waste gas purification process into three steps: (1) First, the organic pollutants in the exhaust gas on contact with water and dissolved in water.That is, by diffusion into the film by the Film.(2) Dissolved in the liquid film of the concentration difference between the use of organic pollutants ingredients spread to the biofilm, and was one of the microorganisms to capture and absorb.(3) Microorganisms into organic contaminants in microbial metabolic processes as their energy and nutrients are broken down by biochemical reactions and eventually converted into harmless carbon dioxide and water.Later, Sun Pei Shi, who noted that some do not dissolve in water or water-soluble organic matter, difficult to use film diffusion method to explain.So they proposed adsorption - Biofilm Theory.And based on the treatment of low concentrations of toluene gas experiments to establish a dynamic model.【3】Highlights of the theory is:(1) Organic pollutants in the exhaust gas reaches the membrane by diffusion and adsorption to the moist biofilm surface .(2) Organic matter is captured and absorbed by microbes.(3)Microbial decomposes contaminants and finally turn into carbon dioxide and water.2.2 Advantages of biofilm treatment of organic waste(1) Biodiversity:Both aerobic and anaerobic bacteria (2) Biofilm low moisture content, a large biomass per unit volume make it has larger processing capacity.(3) Process is more stable, less consumption, high removal efficiency.2.3The development of organic waste gas treatmentAt present, processing technology of organic waste gas general development into two categories: decomposition elimination and concentration and recovery. Decomposition is used as the light, electricity, eliminating heat, plasma and microorganisms of the organic compounds into carbon dioxide and water. Concentration and recovery is by adsorption, absorption, condensation and membrane separation, the organic matter concentration recycling.Decomposition of eliminating treatment without recycling of organic waste gas value, its technology including direct combustion, catalytic combustion method, corona method, plasma method and biological method. Concentration and recovery for treatment of high concentration organic waste and recycling value, its technology absorption method, adsorption, condensation and membrane separation method.Organic waste gas treatment no recycling value, such as odor gas by catalytic combustion method, although the cleaning is thorough, but the cost is relatively high, but also the existence of two pollution; corona, plasma technology has a better application prospect, but there are still some distance from the practical aspects; biological method of saving energy, low operation cost, rarely formed two pollution, treatment of low concentration organic waste gas (3g/m-3) effect is better, in Europe and the United States, Japan and other nations have been put into industrial operation.The treatment of organic waste gas by using biological method although late, but the prospect, because of the low concentration organic industrial waste gas treatment and lack of economical and effective measures, biological method can play a role in 4 is very important.Biological methods mainly include biological filtration, biological washing method and biological trickling filter process of three types, including biological filtration and biological trickling through surface membrane biological filler in microbial treatment of organic waste gas, so these two kinds of methods are known collectively as the biological membrane method 5.2.4 The main process formThere are two forms to treat organic gas ：Biofiltration，Biotrickling filtration（1） Biofiltration. Process: organic waste-humidifier-biofilter-purge gas emissions.The main device is a humidifier and biofilter. Organic waste gets wet first in a humidifier ,and then into the biofilter，Filler layer in the filter is attached with the biofilm, Liquid substantially stays stationary or slow-speed flow .Moisture, pH, nutrient can be suppled if it is needed.Must ensure gas goes through filter continuously. The filler can be soil, plastic filter, ceramic filter, granular activated carbon, peat, compost, etc. Thickness is about 1m, the area is designed by the gas flow and the effect of treatment .（2） Biotrickling filtration. Vapor flow : organic waste-Biological filtration tower bottom -purge gas emissions.Liquid Flow: Circulating fluid-Biological filtration tower bottom-Circulating liquid tank- Biological filtration tower bottom (cycle) .In structure, biological filtration tower bottom is similar to biofilter but what different is biological trickling filter the circulating fluid spraying from the top down, the flow through the inside of the filler layer. Organic waste from the bottom to enter, after passing through the packing layer out through the top row. Because biological trickling filter pores larger than packing biofilter, so the smaller the resistance of the gas through the bed .Since the liquid flow is easy to control the reaction conditions (such as pH, nutrient concentrations, etc.) .Biological trickling filter treatment of high load of organic waste is stronger than the effect of biological filtration .3：Major design and craft parameters3.1 FilterBiofilm filler chosen should meet the following criteria :(1) Better surface properties of the filler, suitable for the growth of microorganisms;(2) The large surface area of filler;(3) There are certain structural strength and corrosion resistance;(4) Has a high porosity and low bulk density;(5) Easier to obtain and long life.There are two main filters :natural fillers and artificial fillers . Natural fillers include soil, compost, peat substance containing nutrients in general; Artificial filler like activated carbon, diatomaceous earth, coke, polystyrene and polyurethane foam beads need an additional adding ,because it does not contain nutritious matter. Some newly developed filler such as activated carbon fibers and adhered to the porous hydrophobic polypropylene film. Further, adding activated carbon, coke, etc. In the conventional filler, the filler can improve the performance and extend the life of use.Filler should be used to control the humidity, the humidity is too low, will make microbial inactivation, fillers shrinkage cracking, etc., so it is necessary to maintain the proper humidity.More appropriate humidity range of 40% -60%.3.2 Microbial adaptation and growth conditionsBiofilm in a wide variety of microorganisms, such as yeast, bacteria, fungi, protozoa, and a small amount of micro metazoan animals. Due to differences in the composition of contaminants, pH value, temperature, humidity and other conditions, the biofilm microorganisms have different types ,high humidity, pH value of 7 to 8 for the survival of microorganisms;low humidity, pH value of 3 to 5, the fungi multiply.According to this feature, the appropriate conditions to control the processing of organic waste can be of different composition to improve processing efficiency.Good water-soluble contaminants can degrade the water can be bacterial growth;for water-insoluble contaminants, fungal treatment effect than bacteria. Usually most of the bioreactor temperature at 25 35 ,35 aerobic microbial growth is the most suitable temperature.Meanwhile, the growth of microorganisms in the common existence of competition between species, dealing with the use of a specific component in the exhaust gas containing biofilm, bacteria cultured special advantages for better treatment effect.In addition, during the bioreactor treatment of pollutants in its internal conditions are changing,as the sulfide-containing process gas will accumulate sulfate, nitrate treatment is ammonia gas will accumulate, resulting in lower pH values, the need to add a basic substance to adjust the buffer, such as limestone dosing .3.3 NutrientsMicrobial treatment of organic waste is in addition to the use of pollutants as nutrients, but also need some inorganic compound ingredients, so you need to add a certain amount of inorganic.For example, sodium, magnesium, calcium, iron, potassium, phosphorus and other trace elements.Studies suggest that BOD: N: P = 100:5:1 is more appropriate.4 :Status and hte direction of biofilm treatment of organic wasteBiological treatment of waste gas is a new technology,because bioreactors involve gas, liquid / solid mass transfer and biodegradation processes are many and complex factors, relevant theoretical research and practical applications extensive enough, many issues need further discussion and study.4.1 Study on dynamics model reactionThe relationship between the growth rate kinetics study of the degradation rate and microbial contaminants and contaminant concentrations, biomass and other factors,these relationships but also directly determines the pollutant removal efficiency.Through the study of reaction mechanisms, and to identify the decision based on the intrinsic reaction rate and the effective rate of reaction control and regulation, improve the purification efficiency of pollutants.4.2 Study on filling characteristicsFor biological filter and biological trickling filter, certain characteristics of the filler is necessary.Filler surface area, porosity, etc. In addition biomass reactor, but also on the impact of the pressure drop across the packed bed and the bed is easy to fill the clogging problems.The more important point is that the filler has a greater impact on the liquid / solid mass transfer coefficient distribution.The life of the packing also affect the running costs of the processing apparatus,therefore, the study of the reactor to improve the fill characteristics of the operating state.4.3 Study on dynamic loadCurrently, the single component (or a combination of a few simple components) gas, load change is in order, smooth, and for abnormal load stream, multi-component gas is less studied.Therefore, the dynamic load research to solve a series of problems encountered in the practical application.4.4 Screening of high efficient dominant bacteriaOn the basis of the original strain, filter out toxic gases can efficiently degrade dominant species, thus shortening the reaction time, speed up the reaction process, improve processing efficiency.4.5 Research and development of equipmentOn the basis of more emphasis on the results of foreign research and development facilities, including process parameters automatic control system, water distribution, gas distribution systems, etc., to achieve the biological treatment kits, standardization, serialization lay a good foundation exhaust products.5 ：ConclusionFor the