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Conventional Sludge Treatment Methods And Those Techniques

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Sludge treatment is the process of stabilizing and reducing the sludge, which generally includes concentration, dehydration, stability (anaerobic digestion, aerobic digestion, composting) and drying, incineration and so on. Sludge sludge is mainly decomposed to reduce the amount of organic matter in the dry solids, the water is almost no change; sludge incineration is completely eliminate the organic matter, flammable. The sludge is mainly decomposed to reduce the amount of organic matter in the dry solid. Material and moisture, is the most thorough stabilization, reduction.

    1, sludge concentration

    The sludge concentration is mainly to remove the interstitial water between the sludge particles. Concentrated sludge water content of 95% -98%, the sludge can still maintain the fluid properties

    China's past a number of sewage treatment plants often use gravity concentration pool for sludge concentration, taking into account the sludge homogenization and regulation, gravity concentration of low power consumption, no drug consumption, low operating costs; but with the requirements of nitrogen and phosphorus removal, Gravity concentration of a long time, easy to release phosphorus, gravity pool supernatant reflux to the water, increase the sewage treatment of phosphorus load, therefore, the majority of new sewage treatment using mechanical enrichment. Some small sewage treatment plants use a more simple enrichment dehydration machine.

    2, sludge machinery dehydration

    Sludge mechanical dehydration is mainly to remove the capillary water between the sludge particles, mechanical dehydration after the sludge moisture content of 65% -80%, was mud cake.

    Mechanical dehydration equipment in the past mainly with belt filter press, plate and frame filter press and decanter centrifuge, is often used in the box filter, diaphragm and high pressure plate machine.

    Sludge dewatering can greatly reduce the accumulation of sludge and save the cost of the process. When the sludge is composted, the sludge dewatering can ensure the composting smoothly (during the composting process Sludge has a lower moisture content); if the sludge incineration, sludge dewatering rate can greatly reduce the heat consumption.

    However, the sludge composition is complex, the relative density is small, the particles are smaller, and often the colloidal state, determines its difficult to dehydrate the characteristics, so far so far. The further improvement of sludge dewatering is a hot topic in domestic and foreign research.

    Belt filter press low power consumption. Plastic plate and frame filter press filter water content is low, but the decanter centrifuge on the sludge flow fluctuations in the adaptability, good sealing performance, handling capacity, small footprint. China's past sewage treatment plants are mostly used centrifuge, belt filter and plate and frame filter press, small sewage treatment plant generally use concentrated dehydration machine. Is often used in the box filter press, diaphragm filter, and the latest sludge dewatering technology of high-pressure metal frame machine, sludge treatment costs are low, the aircraft from Foshan City, Kay to filter equipment Co., Ltd. R & D and production of patented products, technology Unique, ideal for sludge dewatering.

    3, sludge drying

    Sludge drying is mainly to remove the sludge between the adsorption of water and internal water, dry sludge was granular or powder.

    Natural dryness takes up more land. But also by the impact of climate conditions, spread the smell, in the sewage treatment of sludge treatment has been widely used.

    Mechanical drying is mainly the use of heat to further remove the moisture in the sludge, is the sludge and heat medium between the heat transfer process. Mechanical drying is divided into full dry (solidification rate greater than 90%) and semi-dry (including solid ratio of less than 90%).

    When the sludge water content is in the range of 40% -50%, the rheological characteristics of the sludge change significantly, and the sludge viscosity is strong, which leads to poor transport performance.

    In the process of drying, the sludge gradually lose water to form a granular form, with a large surface area at low water content.

    When the sludge is gradually formed into particles, the surface is drier than the inside, and the evaporation of the internal water becomes more and more difficult. With the decrease of the water content, the evaporation efficiency is gradually reduced.

    According to the heat transfer between the sludge and the heat medium, the sludge drying is divided into convection drying, conduction drying and heat radiation drying. In the sludge drying industry, convection and conduction are mainly used in two ways, or a combination of the two. In addition, the convection form of the drying machine due to heat and evaporation of water vapor, by-product gas - with the discharge dryer, the amount of exhaust gas, increase the follow-up processing burden.

    4, sludge stability

    Sludge stabilization refers to the removal of some of the organic matter in the sludge or the conversion of unstable organic matter from the sludge into a more stable substance. So that the organic matter content of sludge to reduce more than 40%, no longer distribute the smell, even after the mud after a long period of time stacked. Its main ingredient is no longer a significant change.

    Sludge stabilization methods include anaerobic digestion, aerobic digestion and composting.

    Anaerobic digestion is the process of degradation and stabilization of organic matter in the sludge under anaerobic conditions by anaerobic microorganisms. In order to reduce the investment in the project, the activated sludge is usually concentrated and then digested. Under the condition of hypoxia in the closed digestive tank, some of the cells are gradually transformed into anaerobic or facultative bacteria, degrade organic pollutants and the sludge is gradually digested Out. While releasing heat and methane gas. After anaerobic digestion, sludge can be part of the organic matter into methane, while the elimination of malodor and a variety of pathogens and parasites, so that the sludge to a safe and stable degree. In the sludge anaerobic digestion process, the temperature in the digestion (33-35 degrees) is the most commonly used.

    In Europe and North America, sewage treatment plants, sludge anaerobic digestion of the success stories more. In China, Hangzhou four Fort sewage treatment plant, Beijing Gaobeidian sewage treatment plant, the eastern suburbs of Tianjin sewage treatment plant using an anaerobic digestion. Shanghai Bailonggang sewage treatment plant sludge medium temperature anaerobic digestion project is also under construction.

    The basic principle of aerobic digestion is to pollute the sludge for a long time. The microorganisms in the sludge are in the endogenous breath and the oxidation stage. At this time, the cytoplasm is oxidized to CO2, and H2O and NO3 are stabilized. Aerobic digestion power consumption is higher, suitable for small sewage treatment plants.

    Most of the sludge composting is carried out under aerobic conditions. The effect of the thermophilic bacteria and thermophilic bacteria is used to decompose the organic matter in the sludge into CO2 and H20, and the effect of sterilization, stabilization and fertilizer increase is achieved. In order to make the compost has a good ventilation environment, usually using expansion agent mixed with the sludge to increase the porosity, adjust the sludge moisture content and carbon and nitrogen molar ratio. Composting time takes about 1 month. therefore. Sludge composting is suitable for small, local environment is not sensitive to the sewage treatment plant.

    5, sludge incineration

    Sludge incineration is the use of incinerator in the aerobic conditions of high temperature oxidation of sludge in the organic matter, so that the sludge is fully mineralized into a small amount of ashes disposal; to incineration technology as the core of the sludge treatment method is more thorough treatment, Widely used in industrialized countries.

    Sludge incineration can be divided into two main categories: - class is the dehydration of sludge directly to the incinerator burning. The other is to dry the dewatered sludge and then burn.

    Sludge incineration equipment mainly rotary incinerator, vertical incinerator, vertical multi-stage incinerator, fluidized bed incinerator, etc., in the past commonly used vertical multi-stage furnace, and now gradually evolved using fluidized bed incinerator

    The advantage of burning sludge is to occupy the site is small, fast processing, large amount, the reduction is obvious, but the heavy metal in the ash is not easy to leach. Sludge ash can be sent into the cement plant mixed with raw materials in the production of building materials. China has begun to realize the advantages of incineration, all around are actively exploring the application of local conditions of the case.