Three common deodorization processes in sludge composting plants

Generally, there are three kinds of odor gas treatment methods in sludge composting plant: physical method (adsorption, absorption, concentration, etc.), chemical method (chemical washing, thermal oxidation, catalytic oxidation, ozone oxidation, etc.) and biochemical method (biological filtration, biological washing, biological trickling filtration, etc.) In biological deodorization process, biofilter, biological washing and biological trickling filter are three kinds of reactors which are widely used The following three types of reactors are briefly introduced 1 Biofiltration: biofiltration is a treatment technology that uses solid media bed (filler) to absorb / absorb odor substances in the gas and remove sludge odor through subsequent microbial activities The main components of biofilter are: air chamber, supporting layer, filler layer, spray system, etc The sludge odor is sent to the air chamber by the fan and passes through the packing layer at a certain flow rate There is an active biofilm attached to the packing The spray system on the upper part of the filter ensures that the filter material is wet and maintains the microbial activity When the air flow flows through the packing, the odor compound will have a biochemical reaction with the microorganism attached to the filter material and convert the odor substance into the odorless substance The carbon source and nutrients needed for microbial propagation are provided by the waste gas and filler materials flowing through The spray system can not only keep the packing layer wet, but also provide nutrients such as N, P, K for the growth of microorganisms The filler used in biofilter needs specific particle size, appropriate porosity, large specific surface area, strong acid-base buffer capacity and strong microbial adhesion At the same time, the microorganism attached to the filler undertakes the task of material conversion Therefore, the growth of microorganism needs sufficient nutrients and energy sources Therefore, the solid carrier must have a large number of organic components to maintain the microorganism Because of its strong activity, the filler of biofilter is generally required to be "active" The commonly used fillers of biofilter are soil, compost, peat, peat, wood chip, bark, perlite, etc in practical engineering, biofilter often uses a variety of filler combinations Biofilter is a kind of bioreactor which was used to control the odor of sludge in sewage treatment plant Its advantage is that it does not need to add chemicals in the process of operation, and does not produce waste It is a "green" treatment technology According to statistics, in 2005 alone, more than 15000 biofilters were used in Europe, of which about 50% were used for odor purification in sewage and composting plants 2.2 biological washing biological washing is a biological treatment process in which the waste gas flows through the absorption liquid and the pollution components are absorbed and purified by the washing liquid The method is based on the solubility of odorous substances in the gas, the odorous gases introduced are absorbed by the liquid, the odorless air is discharged from the upper part of the reactor, the washing liquid dissolved in the odorous substances is transferred to the activation tank, the odorous substances absorbed by the liquid in the activation tank are degraded by the microorganism, and the washing liquid is recycled The biological washing unit is called the biological washing tower, which is usually composed of a packed scrubber and a biological reactor with activated sludge In the scrubber, the gas water countercurrent contact makes the pollutants in the sludge waste gas dissolve into the washing liquid, so as to achieve the purpose of waste gas purification If the pollutant concentration is low and the water solubility is high, it is easily absorbed by water and carried into the bioreactor In the bioreactor, pollutants are finally removed through the oxidation of microorganisms in the activated sludge This technology is applicable to the gas with good water solubility The removal rate of H2S by biological washing method is generally 90% - 99% Biological washing method has the advantages of pH, temperature, nutrient balance easy to control, and metabolites easy to discharge However, this method also has its unavoidable shortcomings Biological washing requires odor gas to be dissolved and absorbed by the washing liquid in a short gas-liquid contact time, but many odor substances are difficult to dissolve in water, so this method also has certain limitations In engineering practice, the combination of biological washing and biological filter should be used In the combined process, biological washing not only plays the role of wetting gas, but also has the function of buffering The washing section can remove most odor substances and reduce the load of biological filter In addition, when the temperature of the waste gas is high, if the high temperature gas is directly introduced into the biofilter, the water in the filter bed will be lost too fast, the filter material is easy to dry, and the biofilm attached to the filter material will be damaged greatly Adding a biological washing section in front of the biofilter is conducive to maintaining the good operation of the biofilter 3 Bio trickling filtration is a odor treatment technology between bio filtration and bio washing The structure of biological trickling filter is similar to that of biological filter The waste gas enters from the bottom of the reactor and flows through the packing layer at a certain rate The active microorganism attached to the wet packing layer metabolizes the odor compounds into odorless substances, thus completing the process of sludge deodorization The difference between biological trickling filter and biological filter is that spray device is an essential part of biological trickling filter, and the filter material used in biological trickling filter is usually composed of inert materials of non organic matter, which generally does not need to be replaced The difference between bio trickling filtration and bio washing is that the absorption and biodegradation of pollutants in sludge waste gas occur in a reaction device at the same time The filter is filled with filler, and the circulating water is continuously sprayed on the filler, and the surface of the filler is covered by the biofilm formed by microorganisms When the waste gas flows through the filter material, the pollutants are degraded by microorganisms The lower part of the reactor is provided with a filtrate collection system, and the collected filtrate is recycled after treatment The commonly used fillers for bio trickling filter are ceramsite, plastic ball, activated carbon, composite fillers, etc Some studies have shown that bio trickling filtration has good treatment effect on H2S, NH3, VOC and reducing sulfide produced in sewage treatment plant and other occasions, and it is considered as a low-cost sludge odor control technology instead of chemical washing However, there are some defects in the biological trickling filter method The treatment of odor by biological trickling filter is only effective for the wetted part of the filler, but the wetted part usually accounts for less than 50% of the total specific surface area of the filler Although increasing the spray intensity can increase the wetted area of the filler, the excessive intensity will destroy the biofilm on the surface of the filler and increase the subsequent sewage treatment capacity