Six common mainstream sewage treatment processes
time：2022-04-20
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The advantages and disadvantages of common urban domestic sewage treatment processes, and explore the improvement and application of the process, hoping to bring some inspiration to everyone.
01. AAO Process
A / A / O (anaerobic anoxic oxic) process is a combination of traditional activated sludge process, biological nitrification and denitrification process and biological phosphorus removal process. The main process is: anaerobic treatment first, followed by anoxic and aerobic treatment. The process can be used for secondary or tertiary sewage treatment and reclaimed water reuse. It is a common process for urban domestic sewage treatment.
Process advantages
The process can simultaneously remove nitrogen, phosphorus and organic matter in a short time. Sludge has high phosphorus content, high fertilizer efficiency and no sludge bulking. The overall operation of the equipment is stable and the energy consumption is low. It can maintain the removal efficiency of five-day biochemical oxygen demand (BOD5) and suspended solids (SS) at 90% ~ 95%.
Process disadvantage
The disadvantage of this process is that there is carbon source competition. When the carbon source of influent is low, phosphorus accumulating bacteria will preferentially use most carbon sources to inhibit the denitrification in anoxic section.
Denitrification is affected by nitrate oxygen in reflux solution. When the internal reflux is relatively low, the denitrification effect is not good; When the reflux ratio is too high, the dissolved oxygen and nitrate oxygen carried by the reflux sludge will consume the carbon source required for phosphorus removal, destroy the anoxic environment, affect the phosphorus removal effect, and can not achieve good nitrogen and phosphorus removal effect at the same time. Due to the long growth cycle of nitrifying bacteria and the short growth cycle of phosphorus accumulating bacteria, there is also a contradiction between sludge age.
Process improvement
The treatment performance of a / A / O process can be regulated through process optimization to make up for the defects of treatment efficiency and ensure the discharge of effluent up to standard. At present, a variety of improved a / A / O processes have been put into use.
For example, a pre anoxic section is added before the anaerobic section to distribute water in the ratio of 1:6 to the two stages to balance the required carbon source. At the same time, the sludge returns to the pre anoxic section and denitrifies with nitrate nitrogen as the receptor, so as to eliminate the inhibition of nitrate on anaerobic phosphorus release in the anaerobic section.
02. Ao process
A / O (anaerobic oxic) process is roughly divided into five parts: pretreatment unit, biological treatment unit, advanced treatment unit, auxiliary unit and sludge treatment unit. It is one of the widely used biological recovery processes in early China.
The process connects the anoxic section with the aerobic section. In the anoxic section, facultative anotrophic bacteria and anaerobic bacteria degrade pollutants and macromolecular organics into small molecular carbon compounds, conduct denitrification and denitrification at the same time, and the products enter the aerobic tank for further oxidative degradation to achieve the effect of phosphorus and nitrogen removal.
Process advantages
A / O process has the advantages of high treatment efficiency, large treatment water volume, low cost, small floor area and strong impact load resistance. At the same time, the sludge output of sewage treatment is low and there is no sludge reflux, which can effectively purify sewage.
Process disadvantage
The process has no sludge return system. Due to the lack of unique functional sludge, the degradation rate of refractory substances is low, and the phosphorus removal efficiency is not ideal. The nitrification and denitrification system is unstable, which makes the nitrogen removal effect difficult to control.
Process improvement
In view of the shortcomings of a / O, there have been a variety of improved multistage Ao processes. For example, by appropriately increasing the volume of the aeration tank to improve the process, so as to improve the intensity of the aeration tank and effectively reduce the organic load, the improved a / O process can achieve a removal rate of 85%.
Alternatively, by adding an anaerobic zone at the front end of the reaction unit, optimizing the phosphorus release environment and increasing the stage of a / O, the sewage enters the anoxic zones at all levels according to different proportions, which can form a multi-stage anoxic / aerobic alternating environment. After multistage action, the improved process improves the effect of dechlorination and phosphorus removal.
03. Oxidation ditch process
Oxidation ditch, also known as annular oxidation channel, takes a closed aeration channel with continuous ring structure as the reaction tank. The sewage sludge mixture carries out continuous circulating biochemical reaction in the reaction tank to remove biodegradable organic matter. The oxidation tank is equipped with a ventilation rotor or an electric brush providing ventilation and circulation to let the mixed liquid in the closed reaction tank pass through the ditch, so that the mixed liquid of sewage and activated sludge circulates in the closed channel along the fixed direction set in the process.
Process advantages
The oxidation ditch has the characteristics of push flow and complete mixing, which can effectively remove nitrogen and phosphorus, and its power density distribution is not conducive to oxygen transfer, liquid mixing and sludge flocculation. The process has the advantages of simple operation, impact resistance, high degree of purification and low energy consumption. It has become the main process of domestic sewage treatment in China.
Process disadvantage
Oxidation ditch belongs to an earlier process, which covers a large area and is prone to equipment failure. It has no treatment capacity for the water quality with small BOD5, and the sewage is easy to flow in a short time, and the water will be discharged without complete biodegradation. Now, the improved oxidation ditch process is mostly used.
Process improvement
There are many studies on the improvement of oxidation ditch process. For example, changing surface aeration to bottom aeration, so that microorganisms can fully oxidize sewage components, or adding internal return channels to prevent short flow of sewage, etc; In addition, the improved oxidation ditch process is to add an anaerobic tank in front of the oxidation ditch, where macromolecular organics are first decomposed into small molecular organics, and then enter the oxidation ditch for further treatment.
For example, the improved oxidation ditch based on Carrousel 2000 oxidation ditch is to add an anaerobic section (with biological selector function) in front of the oxidation ditch, and then the sewage runs alternately through anaerobic, anoxic and aerobic, so as to achieve the purpose of simultaneous removal of organic matter, nitrogen and phosphorus, improve the quality of effluent, inhibit the growth and reproduction of filamentous bacteria under the condition of alternating operation, and there is basically no problem of sludge bulking.
04. Sequencing batch activated sludge process
Sequencing batch reactor (SBR) is an activated sludge wastewater treatment technology operating in the mode of intermittent aeration. Sewage enters each reaction process in sequence and intermittently in the reaction tank, namely inflow, reaction, sedimentation, discharge and idle.
From the beginning of sewage inflow to the end of idle time is counted as a cycle. In one cycle, all processes are carried out in turn in a reactor equipped with aeration or stirring devices, without the need for sedimentation tanks, reflux Sludge pumps and other equipment that must be set in the continuous activated sludge process. The process is suitable for domestic sewage treatment plants in small and medium-sized cities.
Process advantages
SBR process can maintain biological selectivity by controlling relevant conditions, and has many advantages. First, the driving force of biochemical reaction is large and the purification effect is good; Second, the operation effect is stable and flexible; Third, impact load resistance; Fourth, sludge is easy to precipitate without sludge bulking; Fifth, it covers a small area; Sixth, high degree of automation.
Process disadvantage
The efficiency of nitrogen and phosphorus removal is low; Poor sludge stability; Intermittent periodic operation, high requirements for automatic control; High power consumption.
Process improvement
In order to improve the efficiency of nitrogen and phosphorus removal in SBR process, the anoxic section can be moved to the front of the aerobic section and reflux can be added to take the organic matter in the sewage as the carbon source, which not only solves the problem of insufficient organic carbon source in traditional SBR, but also improves the removal rate of total nitrogen (TN) and total phosphorus (TP) in sewage, and the improved SBR is more suitable for treating sewage with low C / n.
05. Intermittent cycle delayed aeration activated sludge treatment
According to the water flow direction, the reaction tank of intermittent cycle delayed aeration activated sludge treatment method is divided into pre reaction tank for regulating water flow and main reaction tank mainly for aeration and sedimentation.
The whole treatment process has maintained a continuous water inflow state, with the characteristics of continuous water inflow and intermittent drainage. The process has remarkable effect on the treatment of medium and low concentration organic wastewater, and is suitable for the treatment of various types of urban sewage.
Process advantages
The process has the function of phosphorus and nitrogen removal, and has the advantages of strong impact resistance, simple process, convenient management, flexible operation and low treatment cost.
Process disadvantage
The sludge loading rate and effective volume utilization rate of this process are low. During the sedimentation process, the reactor continues to feed water, making the sludge water separation vulnerable to the disturbance of the feed water.
Process improvement
The improvement of this process mainly lies in improving the removal efficiency of pollutants and reducing the impact of continuous influent on sludge water separation effect. For example, the reaction tank is divided into four main reaction tanks, a microporous aerator is installed at the bottom of the main reaction tank, a rotary decanter is installed on the tank, and a connected distribution tank and selection tank are set in front of the tank.
The improved process can maintain the uniformity of water distribution, flexibly control the inlet and outlet water, and continuously stir in the anoxic state, so that the biological nitrogen and phosphorus removal effect is better, with the characteristics of strong impact load resistance and easy maintenance.
06. Biological aeration filtration process
Biological aerated filter (BAF) is a new wastewater treatment technology, which is specially designed for various municipal and industrial wastewater treatment.
The process combines biochemical reaction and deep filtration for material separation, uses the microorganisms attached to the porous filter material to form a biofilm, and the sewage convected by high concentration microorganisms on the membrane is quickly purified. At the same time, biomass acts as a deep immersion biofilter to intercept most of the suspended solids and purify the sewage.
Process advantages
The process has the advantages of high purification efficiency, high volume load rate and sludge load rate, strong impact load resistance, low temperature resistance and less sludge bulking. At the same time, it also has the advantages of simple process, high degree of automation, small aeration, no secondary sedimentation tank and small floor area.
Process disadvantage
The main disadvantage of this process is that the phosphorus removal effect is not good, the biofilm needs regular backwashing, and the operation cost is relatively high.
Process improvement
For example, the process improvement is realized by series two-stage and three-stage aeration. The two stages are carbon oxidation / nitrification and denitrification biological aerated filter, C / n-baf adopts bottom aeration, n-baf carries out three-stage aeration in the middle of the filler, and BAF is Upflow Biological Aerated Filter. The nitrogen removal performance of the improved process is better than that of the ordinary biological aerated filter, and the organic matter is easier to degrade.
