AO Process of Integrated Sewage Treatment Equipment，Zhongqiao Enlightenment

Today, the AO process I am going to introduce to you is the actual treatment process used in our project. It is mainly used to treat food production wastewater with a daily treatment capacity of 200 cubic meters.

The AO (Anoxic-Oxic) process is a mature and efficient biological sewage treatment technology widely applied in integrated sewage treatment equipment. It integrates the anoxic denitrification and aerobic degradation processes into a single integrated device, which is characterized by compact structure, stable operation, high treatment efficiency and strong adaptability. This process is mainly used to treat domestic sewage, small-scale industrial sewage and other low-to-medium concentration sewage, effectively removing organic pollutants, nitrogen, phosphorus and other harmful substances in sewage, so as to meet the relevant national discharge standards and realize the recycling and harmless treatment of sewage. The following is a detailed introduction to the AO process flow of the integrated sewage treatment equipment, including the function of each unit, process principle and operation characteristics.

The overall process flow of the AO process of the integrated sewage treatment equipment is as follows: Regulating Tank → Air Flotation Machine → (Hydrolysis Acidification Tank 1 → Hydrolysis Acidification Tank 2 → Primary Sedimentation Tank) → (Anoxic Tank → Aerobic Tank 1 → Aerobic Tank 2) → (Aerobic Tank 3 → Aerobic Tank 4) → Secondary Sedimentation Tank → Clean Water Tank → Effluent Discharge. It should be emphasized that the parts enclosed in parentheses in the process flow are the core components of the integrated equipment, which are integrated and installed in a single equipment body, reducing the floor space and facilitating transportation, installation and operation management.

The first link of the process is the Regulating Tank, which is an important pre-treatment unit of the integrated sewage treatment equipment. The sewage produced in daily life or industrial production often has unstable water quality and water quantity, with large fluctuations in pH value, temperature, pollutant concentration and other indicators. The main function of the Regulating Tank is to collect the incoming sewage, adjust the water quantity and balance the water quality, so as to ensure that the subsequent treatment units can operate under stable working conditions. In the Regulating Tank, the sewage is fully mixed by the stirring device, which reduces the impact of sudden changes in water quality and quantity on the follow-up process, avoids the overload operation of the treatment equipment, and lays a solid foundation for the efficient operation of the whole AO process. In addition to this, the Regulating Tank can also precipitate some large granular impurities in the sewage, reducing the burden of the subsequent treatment links.

After the sewage is adjusted in the Regulating Tank, it enters the Air Flotation Machine, which is the key pre-treatment equipment in the integrated device. The Air Flotation Machine uses the principle of dissolved air flotation to generate a large number of fine air bubbles through the dissolved air system. These air bubbles adhere to the suspended solids, oil substances and other light pollutants in the sewage, making the pollutants float to the water surface and form scum. Then, the scum is scraped off by the scum scraping device to achieve the purpose of separating pollutants from water. The air flotation treatment can effectively remove the suspended solids (SS) and oil pollutants in the sewage, and also reduce the chemical oxygen demand (COD) and biological oxygen demand (BOD) in the sewage to a certain extent. This link is particularly important for the treatment of sewage containing oil and more suspended solids, which can prevent the subsequent biological treatment units from being blocked or the treatment efficiency from being reduced due to excessive pollutants.

After the pre-treatment of the Air Flotation Machine, the sewage enters the integrated core unit composed of Hydrolysis Acidification Tank 1, Hydrolysis Acidification Tank 2 and Primary Sedimentation Tank. This unit is mainly used to improve the biodegradability of the sewage and remove part of the organic pollutants, creating favorable conditions for the subsequent anoxic and aerobic treatment. The hydrolysis acidification process is an anaerobic biological reaction process under mild conditions, which does not require strict anaerobic environment and high energy consumption. In Hydrolysis Acidification Tank 1 and Hydrolysis Acidification Tank 2, a large number of hydrolytic acidifying bacteria are attached to the filler. These bacteria decompose the macromolecular organic substances (such as starch, cellulose, protein, etc.) in the sewage into small molecular organic substances (such as acetic acid, propionic acid, butyric acid, etc.) that are easy to be degraded by aerobic microorganisms. At the same time, the hydrolysis acidification process can also reduce the pH value of the sewage, adjust the acid-base balance of the water quality, and improve the adaptability of the subsequent aerobic microorganisms to the water quality. In addition to this, the hydrolysis acidification process can also remove part of the COD and BOD in the sewage, reducing the treatment load of the subsequent aerobic tank.

After the treatment of the two-stage Hydrolysis Acidification Tanks, the sewage flows into the Primary Sedimentation Tank. The main function of the Primary Sedimentation Tank is to precipitate the flocculent substances and residual suspended solids produced in the hydrolysis acidification process. Under the action of gravity, the solid particles in the sewage settle at the bottom of the tank to form sludge, which is discharged regularly through the sludge discharge device. The supernatant after sedimentation enters the subsequent anoxic tank for further treatment. The setting of the Primary Sedimentation Tank can effectively remove the solid pollutants in the sewage, avoid the accumulation of sludge in the subsequent anoxic and aerobic tanks, and ensure the smooth operation of the biological treatment process. The sludge discharged from the Primary Sedimentation Tank can be treated uniformly after being collected, so as to avoid secondary pollution.

The sewage treated by the Primary Sedimentation Tank enters the anoxic zone of the AO process, that is, the Anoxic Tank, which is the core unit for denitrification in the integrated equipment. The Anoxic Tank is in an anoxic environment (dissolved oxygen content is less than 0.5mg/L), and a large number of denitrifying bacteria are cultivated in the tank. The denitrifying bacteria use the organic substances in the sewage as carbon sources and the nitrate nitrogen (NO3-N) and nitrite nitrogen (NO2-N) produced in the subsequent aerobic tank (which are returned to the Anoxic Tank through the internal reflux system) as electron acceptors to carry out denitrification reaction. In this process, the nitrate nitrogen and nitrite nitrogen are reduced to nitrogen gas (N2), which is discharged into the atmosphere, thus realizing the removal of total nitrogen (TN) in the sewage. The Anoxic Tank is equipped with a stirring device to ensure that the sewage, return sludge and reflux liquid are fully mixed, providing a good reaction environment for the denitrifying bacteria. The carbon source required for the denitrification reaction is mainly from the small molecular organic substances produced in the hydrolysis acidification process, which not only improves the denitrification effect, but also reduces the need for additional carbon sources, saving the operation cost.

After the denitrification treatment in the Anoxic Tank, the sewage flows into the aerobic zone, which is composed of four-stage aerobic tanks (Aerobic Tank 1, Aerobic Tank 2, Aerobic Tank 3 and Aerobic Tank 4). The aerobic zone is the core unit for degrading organic pollutants and nitrification in the AO process, and it is also the key part of the integrated equipment. The four-stage aerobic tanks are set in series, and each aerobic tank is equipped with an aeration device, which continuously supplies air to the tank to maintain a high dissolved oxygen content (usually 2-4mg/L) in the tank, creating a good aerobic environment for the growth and reproduction of aerobic microorganisms.

In the four-stage aerobic tanks, a large number of aerobic microorganisms (including heterotrophic bacteria, nitrifying bacteria, etc.) are attached to the biological filler. The heterotrophic bacteria use the organic substances in the sewage as nutrients to carry out aerobic respiration, decomposing the organic pollutants into carbon dioxide (CO2) and water (H2O), thus realizing the removal of COD and BOD in the sewage. The COD removal rate of the aerobic zone can reach more than 85%, and the BOD removal rate can reach more than 90%, which can effectively degrade the organic pollutants in the sewage to the standard. At the same time, the nitrifying bacteria in the aerobic tanks carry out nitrification reaction, oxidizing the ammonia nitrogen (NH3-N) in the sewage into nitrate nitrogen (NO3-N) and nitrite nitrogen (NO2-N). These nitrates and nitrites are returned to the Anoxic Tank through the internal reflux system to participate in the denitrification reaction, forming a complete nitrogen removal cycle.

The four-stage series design of the aerobic tanks adopts a layered treatment mode, which can realize the gradient degradation of organic pollutants and the step-by-step completion of nitrification reaction. The concentration of organic pollutants in the sewage gradually decreases as it flows through the four aerobic tanks, and the nitrification reaction is more sufficient. This design not only improves the treatment efficiency, but also enhances the stability of the process. Even if the water quality and quantity of the incoming sewage fluctuate, the four-stage aerobic tanks can still ensure the stable treatment effect. In addition to this, the aeration device in each aerobic tank adopts a uniform aeration design, which ensures that the dissolved oxygen in the tank is evenly distributed, avoids the occurrence of dead zones, and makes the aerobic microorganisms fully contact with the sewage and pollutants, improving the degradation efficiency.

After the treatment of the four-stage aerobic tanks, the sewage enters the Secondary Sedimentation Tank, which is the solid-liquid separation unit of the integrated equipment. The main function of the Secondary Sedimentation Tank is to separate the activated sludge (which contains a large number of aerobic microorganisms) in the sewage from the treated water. Under the action of gravity, the activated sludge settles at the bottom of the tank to form excess sludge, which is discharged regularly through the sludge discharge device. A part of the settled activated sludge is returned to the Anoxic Tank and Aerobic Tank through the return sludge system to maintain the concentration of microorganisms in the tanks and ensure the normal operation of the biological treatment process. The supernatant after solid-liquid separation is the treated clean water, which flows into the Clean Water Tank.

The Clean Water Tank is the final storage and stabilization unit of the integrated sewage treatment equipment. The treated clean water is stored in the Clean Water Tank, and the water quality is further stabilized through physical precipitation and aeration. The Clean Water Tank is equipped with a water quality detection device, which can monitor the water quality indicators (such as COD, BOD, SS, NH3-N, TN, etc.) of the treated water in real time. Only when the water quality meets the discharge standard can it be discharged through the effluent pipe. In addition to this, the clean water in the Clean Water Tank can also be reused for greening irrigation, road cleaning, toilet flushing and other purposes, realizing the recycling of water resources and saving water resources.

The integrated sewage treatment equipment adopting the AO process integrates all the above treatment units into a single equipment body, which has many advantages. First of all, the equipment has a compact layout, small floor space, which is suitable for occasions with limited space, such as residential communities, small factories, rural areas and other places. Secondly, the equipment is easy to install and debug, and can be put into operation quickly after transportation to the site, reducing the construction cycle and construction cost. Thirdly, the process operation is stable, the treatment effect is reliable, and it has strong adaptability to the fluctuation of inlet water quality and quantity. Fourthly, the equipment has low energy consumption and operation cost, and the daily operation only needs to consume a small amount of electricity and chemicals, which is suitable for long-term operation. Finally, the sludge production of the equipment is small, and the sludge can be treated harmlessly through simple dehydration, reducing the environmental pollution caused by sludge.

In conclusion, the AO process of the integrated sewage treatment equipment is a efficient, stable and economical sewage treatment technology. Through the reasonable combination of pre-treatment, hydrolysis acidification, anoxic denitrification, aerobic degradation and solid-liquid separation, it can effectively remove various pollutants in the sewage, realize the standard discharge and recycling of sewage. This process not only solves the problem of sewage pollution, but also saves water resources, which has important practical significance for protecting the ecological environment and promoting sustainable development. It is widely used in various fields of sewage treatment and has broad application prospects.