Biological treatment technology in chemical wastewater treatment

Biological treatment technology in chemical wastewater treatment

Chemical wastewater contains a large amount of organic matter. If physical and chemical methods are used, it is not only difficult to effectively degrade organic matter, but also costly. Therefore, we need to "prescribe the right medicine" and adopt biological treatment technology to remove the vast majority of organic matter in it, achieving purification effect.

（1） What are the techniques of biological law?  

There are two common biological treatment technologies for chemical wastewater, which can be divided into aerobic biological treatment technology and anaerobic biological treatment technology based on their biological oxygen consumption.   

① Aerobic biological treatment technology can be divided into two categories based on the state of microorganisms (suspended or attached): activated sludge process and biofilm process. Currently, it is widely used in chemical wastewater treatment.

The activated sludge process mainly utilizes suspended microbial flocs in wastewater to digest and metabolize organic pollutants, achieving the purpose of treatment. By this method, aerobic microorganisms and their metabolism can be fully integrated, and the conversion of organic pollutants can be achieved through the treatment of organic and inorganic substances.    

With the development, the activated sludge process has undergone multiple improvements, and oxidation ditch process, sequencing batch reactor (SBR) and its derivative processes have also emerged. The SBR process can play a higher technical role through automation control, mainly by using batch reactors to achieve more reasonable control of sedimentation tanks, aeration tanks, and regulating tanks. It can also reduce the number of reflux sludge systems and secondary sedimentation tanks, achieving technological advantages such as lower cost, lower energy consumption, and smaller footprint.

The biofilm method includes biological contact oxidation method, aerated biofilter method, etc. These methods can reduce the generation and treatment cycle of residual sludge, without the need for secondary sedimentation tanks and sludge reflux links, and have the advantages of low infrastructure investment, small footprint, and strong shock load resistance.   

The biological contact oxidation method, also known as contact aeration method, purifies wastewater by treating it on a biofilm carrier. There is a large amount of suspended activated sludge in the biological contact membrane oxidation tank. When the wastewater comes into contact with the biofilm, the microorganisms on the biofilm will undergo metabolism to treat organic pollutants in the wastewater. Microbial oxidation methods can be used to decompose and remove them, and then purify them.  

② Anaerobic biological treatment technology refers to the process of using the biochemical reactions of various anaerobic bacteria under anaerobic conditions to degrade large organic pollutants in wastewater into small molecule alcohols and organic acids, and finally convert them into methane and carbon dioxide. There are many cases of chemical wastewater treatment using anaerobic biological treatment technology. Its application helps to reduce the COD value of chemical wastewater treatment effluent, improve the effectiveness of industrial wastewater treatment, and also enhance the biodegradability of wastewater, which is beneficial for subsequent aerobic biological treatment. Nowadays, anaerobic biological treatment technologies include Upflow Anaerobic Sludge Bed (UASB), Baffled Anaerobic Reactor (ABR), Internal Circulation Anaerobic Reactor (IC), Expanded Granular Sludge Bed (EGSB), etc.

The UASB reactor is a representative of the second-generation anaerobic reactor. We use an improved version of this reactor, which can reduce COD concentration in chemical wastewater by more than 80%, and has excellent characteristics such as high organic load, short HRT, high treatment efficiency, and stable operation.

（2） Case study on the application of biological methods in chemical wastewater treatment

We used a pure biochemical treatment process in the treatment of a certain chemical wastewater (NMP wastewater), which removes pollutants through biological methods. The process is "UASB+two-stage A/O", with effluent COD concentration below 200mg/L and ammonia nitrogen concentration below 15mg/L.  

In another chemical wastewater treatment project with higher COD concentration, we mainly use biological treatment method. After pretreatment, the wastewater enters the "hydrolysis acidification+UASB reactor+multi-stage contact oxidation method" in sequence, and the effluent COD concentration is below 300mg/L, meeting the discharge standard. The biological treatment of chemical wastewater has its own advantages, as it can remove pollutants and achieve purification, with two high concentration wastewater streams: COD concentration of 30000mg/L and COD concentration of 197000mg/L.

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