Deodorization process of three commonly used sludge composting plants

There are three main types of odor gas treatment methods in sludge composting plants: physical methods (adsorption, absorption, concentration, etc.), chemical methods (chemical washing, thermal oxidation, catalytic oxidation, ozone oxidation, etc.) and biochemical methods (biofiltration, biological washing). , biological trickling, etc.). In the biological deodorization process, biofilters, biological washing and biological trickling filters are three widely used reactors. The three reactors are briefly described below.

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Biological filtration

Biological filtration is a treatment technique that utilizes a solid medium bed (filler) to absorb/adsorb odorous substances flowing through the gas and remove sludge odor through subsequent microbial activity. The components of the biological filter mainly include: a gas chamber, a support layer, a packing layer, a spray system, and the like. The sludge odor is sent into the air chamber through the fan and passes through the packing layer at a certain flow rate. The active biofilm is attached to the packing. The upper spray system of the filter ensures the filter material is wet and maintains the microbial activity. When the airflow flows through the packing, The malodorous compound undergoes a biochemical reaction with the microorganism attached to the filter material to convert the malodorous substance into an odorless substance. The carbon source and nutrients required for microbial reproduction are provided by the exhaust gas and filler material flowing through. The spray system not only ensures the wetness of the filler layer, but also provides nutrients such as N, P and K for microbial growth. The filler used in the biological filter requires a specific particle size, a suitable porosity, a large specific surface area, a strong acid-base buffering capacity, and a strong microbial adhesion ability, and the microorganism attached to the filler bears the task of material conversion. Therefore, microbial growth requires sufficient nutrients and energy sources, so the solid carrier must have a large amount of organic components, so that the microorganisms maintain a strong activity, so the filler of the biofilter is generally required to have "activity". The commonly used fillers for biological filters include soil, compost, peat, peat, wood chips, bark, perlite, etc. The biological filter in actual engineering often uses a variety of filler combinations.

The biofilter is the first bioreactor used to treat sludge odor control in wastewater treatment plants. The advantage is that it does not require the addition of chemicals during the operation and does not produce waste. It is an efficient "green" treatment technology. According to statistics, in 2005 alone, the number of biofilters used in Europe exceeded 15,000, of which biofilters used in sewage plants and composting plants were about 50%.

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2 biological washing

Biological washing is a biological treatment process in which exhaust gas flows through an absorbing liquid, and contaminated components are absorbed and purified by the washing liquid. The method is based on the solubility of the odorous substance in the gas, the odorous gas that is introduced is absorbed by the liquid, the odorless air is discharged from the upper part of the reactor, and the washing liquid dissolved in the odorous substance is transferred to the activation tank, and the liquid in the activation tank The absorbed odorous substance is degraded by microorganisms, and the washing liquid is recycled. The biological washing device is called a biological scrubber and is usually composed of a scrubber equipped with a packing and a bioreactor with activated sludge. In the scrubber, the gas and water are in countercurrent contact, so that the pollutants in the sludge exhaust gas are dissolved into the washing liquid, thereby achieving the purpose of purifying the exhaust gas. If the contaminant concentration is low and the water solubility is high, it is easily absorbed by water and brought into the bioreactor. In the bioreactor, contaminants are eventually removed by the oxidation of microorganisms in the activated sludge. This technique is suitable for water-soluble gases. The removal rate of H2S by the biological washing method is generally 90% to 99%.

The biological washing method has the advantages of easy control of pH, temperature, nutritional balance, and easy discharge of metabolites. However, this method also has its unavoidable disadvantages. The biological washing requires that the odor gas is dissolved and absorbed by the washing liquid in a short gas-liquid contact time, but many malodorous substances are hardly soluble in water, so the method also has certain limitations. Sex. In engineering practice, biological washing should be used in combination with biofilters. In the combined process, biological washing acts both as a humidifying gas and as a buffering agent. The washing section can remove most of the odorous substances and reduce the biofilter. load. In addition, when the temperature of the exhaust gas is high, if the high-temperature gas is directly introduced into the biological filter, the water in the filter bed will be dissipated too fast, the filter material will be easy to dry, and the biofilm attached to the filter material will be damaged. Adding a biological washing section in front of the pool helps to maintain good health of the biofilter.

3

Biological trickling

Bio-drip filtration is an odor gas treatment technique between biological filtration and biological washing. The structure of the biological trickling filter is similar to that of the biological filter. The exhaust gas enters from the lower part of the reactor and flows through the packing layer at a certain rate. The active microorganism attached to the wet packing layer metabolizes the malodorous compound into an odorless substance, thereby completing sludge deodorization. process. The difference between the biological trickling filter and the biological filter is that the spraying device is an essential component of the biological trickling filter, and the filter material used in the biological trickling filter is usually composed of a non-organic inert material, generally not required. replace. The difference between the biological drip filtration method and the biological washing method is that the absorption and biodegradation of pollutants in the sludge exhaust gas occur simultaneously in a reaction device, the filter is filled with the filler, the circulating water is continuously sprayed on the filler, and the surface of the filler is Biofilm formation by microbes. When the exhaust gas flows through the filter material, the pollutants are degraded by the microorganisms. A filtrate collection system is arranged at the lower part of the reactor, and the collected filtrate is recycled after being treated. Commonly used fillers for biological trickling filters include ceramsite, plastic spheres, activated carbon, and composite fillers.

Studies have shown that bio-trickling has good treatment effects on H2S, NH3, volatile organic acids and reducing sulfides produced in sewage treatment plants, etc., and is considered to be a low operating cost sludge odor instead of chemical washing. Gas control technology. However, the biological trickling method also has certain defects. The biological trickling filter treatment of odor is only effective for the wetted part of the filler, but the wetted part often only accounts for less than 50% of the total specific surface area of ​​the filler, although increasing the intensity of the spray can increase the wetting of the filler. Area, but the intensity of the destruction of the biofilm on the surface of the filler, but also increased the amount of subsequent sewage treatment