Common Processes and Operation of Coal Chemical Industry Wastewater Treatment

[Introduction] The coal chemical industry is a high-energy and high-polluting industry that requires a large amount of water resources and produces a large amount of industrial wastewater, which poses a great threat to the surrounding environment. Therefore, wastewater treatment is very important. It can not only achieve energy saving and emission reduction but also save its own production cost. This article briefly outlines the common processes and operating conditions of coal chemical industrial wastewater treatment.

1 Characteristics of Industrial Wastewater Produced in Coal Chemical Industry Process

The industrial wastewater discharged from coal chemical industry is mainly composed of high-concentration gas scrubbing water, which contains a large number of harmful and toxic substances such as phenol, oil, cyanide, and ammonia nitrogen. The COD content in waste water is mostly about 5000 mg/L, and the ammonia nitrogen content is about 200 to 500 mg/L. Among them, the organic pollutants mainly include polycyclic aromatic compounds, phenols, and heterocyclic compounds containing oxygen, nitrogen, and sulfur. Coal chemical wastewater is a typical production wastewater containing refractory organic compounds. Coal chemical industrial wastewater is hard to degrade organic compounds mainly pyridine, biphenyl, carbazole, terphenyl, etc.; easily degradable organic compounds are mainly benzene, phenolic compounds, such as pyrrole, furan, naphthalene, carbazole and so on.

2 Common processes of coal chemical wastewater treatment

Coal chemical wastewater treatment process is basically followed: first, materialized pretreatment; second, A/O biochemical treatment; and finally, materialized advanced treatment, such a process route. The following is a brief introduction to each step.

2.1 Pretreatment

Coal chemical industrial wastewater contains many oil components, and too much oil will affect the subsequent biochemical treatment effect. Therefore, the industrial wastewater treatment must remove the oils and fats. The best way to remove grease is to combine grease traps with air flotation. The purpose is to remove the oil from the waste water and recycle it. It also has the effect of equaling pre-aeration. The main forms of pretreatment of industrial wastewater are homogeneous adjustment, removal of large solids by primary sedimentation, and other forms.

2.2 Biochemical treatment

After the pretreated coal chemical industrial wastewater, we generally use the combination of anoxic biological method and aerobic biological method, ie, A/O process. Because coal chemical process wastewater contains heterocyclic and polycyclic compounds, it is used traditionally. The COD index in the wastewater after aerobic biological treatment is difficult to reach the standard. Therefore, in order to solve the above problems, some new aerobic biological treatment methods have been proposed, such as PACT method, anaerobic biological method, fluid bed biofilm method (CBR), aeration biological filter BAF method and the like. (1) PACT method PACT method is to add a certain amount of activated carbon powder to the activated sludge aeration tank and use the activated carbon to adsorb dissolved oxygen and organic substances to provide food for microbial growth to accelerate the oxidative decomposition of organic substances. . Activated carbon can be regenerated by means of wet air oxidation.

(2) Anaerobic biological method It is an upflow anaerobic sludge blanket (UASB) process applied to the treatment of coal chemical industrial wastewater. The reactor used in this method was successfully developed by G. Lettinga et al. of the Netherlands in 1977. A sludge layer was installed at the bottom of the reactor. The wastewater passed through the reactor from bottom to top and most of the organic matter could be converted into CO2 and CH4 by microorganisms. In the upper part of the reactor, there is a three-phase separator that can separate the gas, liquid and solid phases.

(3) The fluidized bed bio-film method CBR method is actually a kind of biological fluidized bed process based on special fillers. The process combines the activated sludge method with the bio-film method in the same processing unit and adds special carrier fillers to In activated sludge ponds, microorganisms can attach to the surface of suspended fillers to form microbial membranes. The biological concentration in the reaction pool is 2 to 4 times that of the suspended growth activated sludge treatment process, which can reach 8 to 12 g/L, and the degradation efficiency is doubled.

(4) Biological Aerated Filter Aerated Biological Aerated Filter (BAF) is a new type of high-load, submerged, and fixed biofilm reaction tank. This method consists of two methods: biofilm method and activated sludge method. The advantages are in one, and the two processes of physical filtration and biochemical reaction are also concentrated in the same reaction tank. The BAF method has been used to jointly treat coal chemical industrial wastewater and has achieved quite satisfactory results.

Advantages and disadvantages: PACT method is more environmentally friendly, but the adsorption rate is slower, and the adsorbent is difficult to recover. It is more suitable for the treatment of industrial wastewater containing more solids; the anaerobic biological method is carried out in the reactor, the pressure drop is relatively large, and the temperature is required. High, suitable for the treatment of industrial wastewater with many organic matters; the fluidized bed biofilm method is a combination of two methods with high processing speed, but the price is expensive and is suitable for the treatment of industrial wastewater treatment; aeration biological filter method, as a kind of The new method is expensive and the industrial wastewater treatment effect is good, but there is no large-scale application.

2.3 Advanced Processing

After the biochemical treatment of coal chemical industrial wastewater, the COD index and ammonia nitrogen concentration in the water are greatly reduced, but the refractory organics still make the wastewater color, COD and other indicators unable to meet the emission standards. Therefore, biochemically treated industrial wastewater still needs further processing. The advanced wastewater treatment methods mainly include immobilization biotechnology, coagulation sedimentation, adsorption and ultrafiltration, reverse osmosis membrane treatment.

(1) Immobilized biotechnology This is a newly developed technology that can selectively immobilize dominant strains and at the same time can specifically treat waste water containing refractory organics.

(2) Coagulation and sedimentation method This method is to use the coagulant such as aluminum salt, iron salt, polyaluminum, polyaluminum and polyacrylamide to enhance the precipitation effect in the production process. At the same time, the pH should be adjusted to make the waste water. The suspended solids can accelerate aggregation and sinking under the action of a coagulant to achieve solid-liquid separation. This can remove suspended organics in the wastewater, effectively reducing the turbidity of the wastewater.

(3) Adsorption method Since the solid surface has the ability to adsorb solutes and gums, when the industrial wastewater passes through an adsorbent with a large specific surface area, the contaminants therein may be adsorbed onto the solid particles. This method can obtain better results. At the same time, it may also have the problem of large amount of adsorbent and high cost, and it is prone to secondary pollution.

(4) Membrane treatment methods such as ultrafiltration and reverse osmosis Due to the increasing shortage of water resources and rising water prices, the recycling of industrial wastewater is imperative, and the application of membrane technology to wastewater treatment is becoming more and more common. Currently, the double membrane technology is an internationally hotspot technology for R&D and engineering applications. It is an effective engineering pretreatment method. It removes most of the turbidity and organic matter in wastewater by ultrafiltration, reduces the pollution of the reverse osmosis membrane, and can prolong the membrane. The longevity reduces operating costs. Reverse osmosis membrane can not only remove organic matter from industrial wastewater, reduce COD content, but also has a good desalination effect. Since the removal of COD, desalination and decolorization can be accomplished in one step, the quality of the effluent can be high, and it can be directly used as the production recycling water, and the zero emission of coal chemical industry wastewater treatment and the clean production of coal chemical industry can be realized.

Advantages and disadvantages: Immobilized biotechnology,

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