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Research Status of Concentration Technology for High Concentration Organic Wastewater
2019-2-2
Source:Publication
Clicks:  6803        作者:未知
  • Summary of High Concentration Organic Wastewater

    High concentration organic wastewater, such as alcohol wastewater, pharmaceutical industry wastewater and landfill leachate, refers to wastewater with COD concentration above 2000 mg/L. It is characterized by high suspended matter content, high color, peculiar odor, high concentration of organic matter, complex composition of water quality, difficult biodegradation and treatment. It is difficult to meet high concentration organic wastewater treatment methods. The technical and economic requirements of wastewater purification and treatment have gradually become one of the hot research topics of environmental protection technology. The sources of high concentration organic wastewater are mainly: wastewater produced in agricultural industry, which is highly degradable and contains harmless organic substances; pharmaceutical wastewater, chemical wastewater, etc., which contain certain harmful ions and ions. Chemical substances; fine chemical wastewater, which contains complex components and strong toxicity, has a great impact on the environment.

    Research Status of Concentration Technology for High Concentration Organic Wastewater

    The purpose of concentrated treatment of high concentration organic wastewater is to concentrate the high concentration organic wastewater first, and then to treat it by incineration method, so as to save the cost of treatment, so that the high concentration organic wastewater can be effectively treated. At present, the concentration methods of high concentration organic wastewater mainly include freeze concentration, evaporation concentration, combustion concentration and membrane concentration.

    Freeze concentration
    Freeze concentration is a new method to treat high concentration organic wastewater. It utilizes the principle of solid-liquid equilibrium of freeze separation. High concentration organic wastewater with COD concentration above 1000mg/L was treated by freeze concentration method.

    The removal rate of COD and TOC is more than 70% when the freezing time is 12-24 h and the freezing temperature is - 16-12 C. The combination of freeze concentration and membrane concentration was used to treat organic wastewater, and it was found that it could achieve good treatment effect and was more economical than using membrane concentration alone. Freeze concentration has no selectivity for wastewater, especially for the treatment of odorous and volatile organic wastewater. However, its application is limited, and the cost of equipment and operation is high, so the operation is not suitable for control.

    Evaporation concentration
    Evaporation concentration refers to the treatment of high concentration organic wastewater by evaporation and concentration through low-temperature vacuum or decompression. High concentration organic wastewater from a chemical plant was treated by vacuum evaporation and concentration. The removal rate of COD was over 90% when the concentration of COD was 45 *104~55 *104 mg/L. The reverse osmosis concentrate of landfill leachate treatment station was treated by low temperature vacuum evaporation method. The COD of waste liquid was 3000mg/L, and the evaporation rate of COD after treatment was 62.5%.

    The municipal landfill leachate treatment plant concentrates the landfill leachate by four-stage flash evaporation. The removal rate of CODcr and NH3-N can reach 99.5% and 98.5%, respectively. Evaporation concentration can recover valuable components from organic wastewater, but there will be scaling problems in the process of evaporation concentration.

    Combustion concentration
    Combustion method is to mix waste liquid and pulverized coal in combustion furnace, so that the organic matter in high concentration organic waste liquid can be concentrated. The organic matter content of alcohol waste mash is high and COD concentration is over 105 mg/L. The COD removal rate of alcohol waste mash can reach 99% by combustion method. After concentrated treatment of wastewater by combustion concentration, the heat of combustion and the condensate produced in the process of concentration can be used for production, but this method has a high investment cost, high power consumption, and the salt in wastewater will corrode the equipment during combustion.

    Membrane Separation and Concentration
    The principle of membrane concentration of high concentration organic wastewater is that when the wastewater passes through the membrane, the organic substances in the wastewater will selectively permeate through the membrane by exerting some driving force on both sides, so as to achieve the purpose of concentration of organic substances. According to the size of membrane pore, membrane separation technology can be divided into microfiltration (MF), ultrafiltration (UF), nanofiltration (NF), reverse osmosis (RO) and so on.

    Ultrafiltration Membrane Concentration
    Ultrafiltration is also called ultrafiltration. Mechanical screening on the membrane surface is the main mechanism of ultrafiltration separation. At the same time, the adsorption of membrane surface and pore and the blocking of membrane pore also play an intercepting role. Ultrafiltration intercepts molecular sizes ranging from 0.01 to 0.1 um. Under the action of external pressure, water and small molecular substances pass through the pore to form leachate, while colloids and bacteria in water are intercepted.

    Ultrafiltration technology was used to concentrate and separate PS-9415 microbial extracellular polysaccharide fermentation broth. The results showed that 5.8% of the concentrated broth could be obtained by ultrafiltration at 0.05 MPa, and the recovery rate of polysaccharide was 82.7%. The concentration of 0.5% of the broth was increased by 4.9 times at 0.1 MPa.

    Nanofiltration membrane concentration
    Nanofiltration is a pressure-driven membrane separation technology with operating pressure and separation effect between ultrafiltration and reverse osmosis. The separation principle is mainly similar to mechanical screening. At the same time, the charge of nanofiltration membrane itself also plays a role of interception. The size of intercepting molecules in nanofiltration ranges from 0.5 nm to 0.01 um. Compared with ultrafiltration and reverse osmosis, nanofiltration has a poor interception effect for organic compounds and monovalent ions with relative molecular mass less than 200, while it has a high interception rate for organic compounds and bivalent or multivalent ions with relative molecular mass between 200 and 500. Ultrafiltration-nanofiltration continuity experiment was used to separate and purify oxytetracycline. The results showed that the average yield of ultrafiltration was 95%, the crystallization yield was about 94.5%, the purity of the product was 96%, the CODcr value of the wastewater was 37% lower than the original average, the average crystallization yield was 96%, the purity was 98.4%, and the total amount of CODcr in the wastewater discharged was reduced after nanofiltration concentration of 2.5 times.

    Reverse osmosis concentration
    Reverse osmosis (RO), also known as reverse osmosis, is the reverse process of osmosis process, that is, solvent flows from concentrated solution to dilute solution through membrane. In the process of separation, solvent permeates in the direction of natural osmosis by increasing pressure greater than its own osmotic pressure. The pore size of RO membrane is small, and the size range of intercepted molecules is less than or equal to 0.5 nm, and permeates in the direction of natural osmosis.

    Reverse osmosis (RO) technology has become one of the fastest growing and most popular membrane separation technologies in recent years. High pollution resistance reverse osmosis technology was used to concentrate the marsh. The concentration of COD in the marsh liquid was above 10 000 mg/L. The removal rate of COD by reverse osmosis was over 95%, and the removal rate of NH3-N was over 90%. The water quality of the permeate could meet the reuse standard of slurry adjustment and so on.

    Membrane distillation concentration
    Membrane distillation technology refers to the use of hydrophobic microporous membranes (water solution can not pass through), because of the different pressure difference between the two sides, steam can be transferred from the hot side to the cold side through the membrane, while other non-volatile components are left in the hot side, so as to achieve the purpose of separation or purification. Membrane distillation (MD) was used to treat the high salinity organic wastewater with COD concentration of about 30 000 mg/L. The removal rate of COD was over 99.5%. Membrane treatment technology has the advantages of low energy consumption, strong adaptability and no phase change in concentration process, but it has selectivity for wastewater treatment.

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