The wastewater discharged by coal chemical enterprises is mainly high-concentration gas washing wastewater, which contains a large amount of toxic and harmful substances such as phenol, cyanide, oil, and ammonia nitrogen. It is a typical industrial wastewater containing refractory organic compounds. If it is not treated in time, It will cause great pollution to water resources and environment. At present, domestic and foreign countries generally use flocculant polyacrylamide for coal chemical wastewater.
The easily degradable organic substances in coal chemical industry wastewater are mainly phenolic compounds and benzene compounds; pyrrole, naphthalene, furan, and azole compounds are degradable organic substances; the difficult-to-degrade organic substances are aridine, carbazole, biphenyl, triplet Benzene and so on.
At present, the domestic technology for treating coal chemical wastewater mainly adopts the biochemical method. The biochemical method has a good removal effect on phenols and benzene substances in the wastewater, but it has some effects on quinolines, indoles, pyridines, carbazoles, etc. The poor treatment effect of refractory organics makes it difficult for the CODcr of coal chemical industry to reach the first-class standard.
At the same time, after the biochemical treatment of coal chemical wastewater, it has the characteristics of high color and turbidity (because of the organic substances containing various chromophores and auxiliary chromophores, such as 3-methyl-1,3,6heptatriene, 5 -Norbornene-2-carboxylic acid, 2-chloro-2-norbornene, 2-hydroxy-benzofuran, phenol, 1-methanesulfonyl-4-methylbenzene, 3-methylbenzothiophene, Naphthalene-1,8-diamine, etc.).
Therefore, to treat such coal gasification wastewater to achieve reuse or discharge standards, mainly to further reduce CODcr, ammonia nitrogen, color and turbidity and other indicators.
Coal chemical wastewater treatment method:
The process route of coal chemical wastewater treatment basically complies with "physical and chemical pretreatment + A/O biochemical treatment + advanced physical and chemical treatment". The following is a brief introduction.
1. Physical and chemical pretreatment
Common methods of pretreatment: oil separation, air floatation, etc.
Because too much oil will affect the effect of subsequent biochemical treatment, the role of air floatation coal chemical wastewater pretreatment is to remove the oil and recycle it. In addition, it also plays the role of pre-aeration.
2. Biochemical treatment
For pre-treated coal chemical wastewater, anoxic and aerobic biological methods (A/O process) are generally used at home and abroad, but due to the polycyclic and heterocyclic compounds in coal chemical wastewater, aerobic biological methods are used The COD index in water is difficult to reach the standard stably.
In order to solve the above problems, some new treatment methods have emerged in recent years, such as PACT method, carrier fluid bed biofilm method (CBR), anaerobic biological method, anaerobic-aerobic biological method, etc.:
1). Improved aerobic biological method
(1) PACT method
The PACT method is to add activated carbon powder to the activated sludge aeration tank, and utilize the adsorption of activated carbon powder on organic matter and dissolved oxygen to provide food for the growth of microorganisms, thereby accelerating the oxidative decomposition ability of organic matter. Activated carbon uses wet air oxidation method regeneration.
(2) Carrier fluid bed biofilm method (CBR)
CBR is actually a kind of biological fluidized bed technology based on special structure filler. This technology combines the biofilm method and the activated sludge method in the same biological treatment unit, by adding a special carrier filler in the activated sludge tank The microorganisms are attached to the surface of the suspended filler to form a microbial film with a certain thickness. The attached microorganisms can reach a high biomass, so the biological concentration in the reaction tank is 2-4 times that of the suspended growth activated sludge process, up to 8 -12g/L, the degradation efficiency is also doubled.
The uniquely designed filler floats with the water flow in the reaction tank under the disturbance of blast aeration, which drives the attached and growing biological flora to fully contact with the pollutants and oxygen in the water body. The pollutants enter the biofilm through adsorption and diffusion. Degraded by microorganisms, the overall system has high degradation efficiency.
Because the microorganisms are attached to the growth mode (unlike the suspended growth of activated sludge), the microorganisms on the surface of the fluid bed carrier have a very long sludge age (20-40 days), which is very conducive to slow-growing autotrophic microorganisms such as nitrifying bacteria There are a lot of nitrifying bacteria on the surface of the filler, so the system has a strong ability to remove ammonia and nitrogen.
At the same time, the attachment growth mode is conducive to the natural selection of other special flora, and these special flora can effectively degrade the characteristic pollutants in coal gasification wastewater, especially some difficult-to-degrade pollutants, so as to obtain lower effluent COD concentration.
CBR technology can be applied to the treatment of high-concentration coal chemical wastewater, and can also be applied to the subsequent advanced treatment and reuse unit.
2). Anaerobic biological method
A technology called Upflow Anaerobic Sludge Bed (UASB) is used to treat coal chemical wastewater. The reactor used in this method was developed by G. Lettinga of the Netherlands in 1977. The wastewater passed from bottom to top In the reactor with a sludge layer at the bottom, most of the organic matter is converted into CH4 and CO2 by microorganisms in the upper part of the reactor. A three-phase separator is provided to complete the separation of gas, liquid and solid three phases. Oxygen expanded bed technology is also used to treat coal chemical wastewater. This technology can effectively remove phenolic and heterocyclic compounds in wastewater.
3). Anaerobic-aerobic combined biological method
The use of aerobic or anaerobic technology alone to treat coal chemical wastewater cannot achieve satisfactory results. The combined biological treatment of anaerobic and aerobic treatment has gradually attracted the attention of researchers.
After the anaerobic acidification treatment of coal chemical wastewater, the biodegradation performance of organic matter in the wastewater is significantly improved, so that the subsequent aerobic biological treatment CODcr removal rate reaches more than 90%, among which the removal of the more difficult to degrade organic substances naphthalene, quinoline and pyridine The rates are 67%, 55% and 70%, respectively, and the removal rate of these organic substances in general aerobic treatment is less than 20%.
The use of anaerobic fixed membrane-aerobic biological method to treat coal chemical wastewater has also achieved relatively satisfactory results.
3. In-depth processing
After the biochemical treatment of coal chemical wastewater, the concentration of CODcr and ammonia nitrogen in the effluent has greatly decreased, but due to the presence of refractory organic matter, the COD and chromaticity of the effluent have not yet reached the discharge standard. Therefore, the The effluent still needs further treatment. The advanced treatment methods mainly include coagulation and sedimentation, immobilized biological technology, adsorption catalytic oxidation method and reverse osmosis and other membrane treatment technologies.
1), coagulation and precipitation
The sedimentation method utilizes the settling properties of suspended matter in water and sinks under the action of gravity to achieve the process of solid-liquid separation. Its purpose is to remove suspended organic matter to reduce the organic load of subsequent biological treatment.
In production, coagulants such as aluminum salts, iron salts, polyaluminum, polyiron, and polyacrylamide are usually added to strengthen the precipitation effect. The influencing factors of this method are the pH of the wastewater, the type and amount of coagulant, etc.
2). Immobilized biotechnology
Immobilized biotechnology is a new technology developed in recent years. It can selectively fix dominant bacteria and treat wastewater containing refractory organic poisons in a targeted manner.
The domesticated dominant strains degrade quinoline, isoquinoline and pyridine two to five times higher than ordinary sludge, and the degradation efficiency of dominant strains is higher. After 8 hours of treatment, quinoline and isoquinoline can be treated 2. Degradation of pyridine is more than 90%.
3) Advanced oxidation technology
As the organic matter in coal chemical wastewater is complex and diverse, phenols, polycyclic aromatic hydrocarbons, nitrogen-containing organic matter and other refractory organic matter account for the majority. The existence of these refractory organic matter seriously affects the subsequent biochemical treatment effect.
Advanced oxidation technology produces a large amount of HO in the wastewater. Free radicals HO. Free radicals can degrade organic pollutants in wastewater into carbon dioxide and water without selectivity. Advanced oxidation technology can be divided into homogeneous catalytic oxidation method and photocatalysis Oxidation method, heterogeneous wet catalytic oxidation method and other catalytic oxidation methods.
Catalytic oxidation method can be applied in the front stage of coal chemical wastewater treatment process to remove part of COD and enhance the biodegradability of wastewater, but there are problems of large consumption and uneconomical operation, so this technology can be obtained in the subsequent advanced treatment unit Better economy and degradation effect.
4), adsorption method
Because the solid surface has the ability to adsorb solutes and colloids in water, when wastewater passes through solid particles with a large specific surface area, the pollutants in the water are adsorbed to the solid particles (adsorbent), thereby removing pollutants, this method can achieve Good results, but there are problems such as large amount of adsorbent, high cost and secondary pollution, which are generally suitable for small-scale sewage treatment applications.
Type selection of polyacrylamide for coal chemical wastewater:
The composition and content of pollutants in coal chemical industry wastewater are very different, and the treatment process is also different, so the type of polyacrylamide used is also different, should pass a small laboratory test, and then test on the machine to determine the input of polyacrylamide PAM And PH value, in order to achieve less water consumption, low cost, good effect of water purification.