Anaerobic microbial treatment not only consumes less energy than aerobic microbial treatment, but can also produce biogas for secondary use as energy. Currently commonly used anaerobic treatment processes include: UASB, EGSB, CSTR, IC, ABR, UBF, etc. Other anaerobic treatment processes include: AF, AFBR, USSB, AAFEB, USR, FPR, two-phase anaerobic reactor, etc.
◆UASB – upflow anaerobic sludge bed reactor
Up-flow Anaerobic Sludge Bed/Blanket (UASB) is an anaerobic biological method for treating sewage, also called up-flow anaerobic sludge bed.
UASB consists of three parts: sludge reaction zone, gas-liquid-solid three-phase separator (including sedimentation zone) and gas chamber. A large amount of anaerobic sludge remains in the bottom reaction zone, and the sludge with good sedimentation and coagulation properties forms a sludge layer in the lower part. The sewage to be treated flows from the bottom of the anaerobic sludge bed and mixes and contacts with the sludge in the sludge layer. The microorganisms in the sludge decompose the organic matter in the sewage and convert it into biogas.
Due to the agitation of the biogas in the upper part of the sludge bed, a thin sludge concentration is formed, and the sludge and water rise together into the three-phase separator. When the biogas hits the reflecting plate at the bottom of the separator, it is deflected around the reflecting plate and passes through the water layer. After entering the air chamber, the biogas is concentrated in the air chamber and exported through a conduit. The solid-liquid mixture enters the sedimentation area of the three-phase separator after reflection. The sludge in the sewage flocculates, and the particles gradually increase in size and settle under the action of gravity.
The sludge that settles on the sloping wall slides back into the anaerobic reaction zone along the sloping wall, causing a large amount of sludge to accumulate in the reaction zone. The treated effluent separated from the sludge overflows from the upper part of the overflow weir in the settling zone, and then the sewage is discharged. mud bed.
◆EGSB–anaerobic granular sludge expanded bed reactor
Expanded Granular Sludge Blanket Reactor (EGSB) is a third-generation anaerobic reactor. Its structure is divided into an inlet water distribution system, a reaction zone, a three-phase separation zone and an outlet channel system.
The EGSB reactor is generally in the shape of a cylindrical tower and is equipped with a special effluent reflux system. It is characterized by a large height-to-diameter ratio, which can generally reach 3 to 5. The height of the reactor in the production device can reach 15 to 20 meters. The expanded bed of granular sludge improves the contact between organic matter and microorganisms in the wastewater, strengthens the mass transfer effect, increases the biochemical reaction speed of the reactor, thereby greatly improving the treatment efficiency of the reactor.
The sludge zone at the bottom and the three-phase separation zone of gas, liquid and solid in the middle and upper parts are combined into one. Through the backflow and structural design, the wastewater has a high upward flow rate in the reaction zone, and the granular sludge inside the reactor is in an expansion state. state anaerobic reactor.
◆CSTR – completely mixed anaerobic reactor
The continuous stirred tank reactor (CSTR), or continuous stirred reactor system, is an anaerobic treatment technology that keeps fermentation raw materials and microorganisms in a completely mixed state.
The fermentation of the feed liquid and the generation of biogas are completed in a closed tank. A stirring device is installed in the digester to completely mix the fermentation raw materials and microorganisms.
The feeding method adopts constant temperature continuous feeding or semi-continuous feeding operation. The newly entered raw materials are quickly mixed with all the fermentation broth strains in the fermenter due to the stirring effect, so that the concentration of the fermentation substrate is always kept relatively low to degrade organic pollutants in the wastewater and remove suspended solids from anaerobic wastewater organisms. processor.
◆IC – internal circulation anaerobic reactor
The IC tower is composed of two similar layers of UASB reactors connected in series. Each layer of anaerobic reactor is equipped with a gas, solid and liquid three-phase separator at the top. It consists of two reaction chambers, upper and lower. Wastewater flows from bottom to top in the reactor, pollutants are adsorbed and degraded by bacteria, and purified water flows out from the upper part of the reactor.
The IC tower uses the biogas generated by the first UASB reactor below as the internal driving force for upgrading. The density difference generated by the mixed liquid in the upflow pipe and the reflux pipe realizes the internal circulation of the lower mixed liquid, allowing the wastewater to receive enhanced pretreatment.
The second UASB above performs post-treatment (or fine treatment) on the wastewater to make the effluent meet the expected treatment requirements. The sludge zone at the bottom and the three-phase separation zone of gas, liquid and solid in the middle and upper parts are combined into one. Through the backflow and structural design, the wastewater has a high upward flow rate in the reaction zone, and the granular sludge inside the reactor is in an expansion state. state anaerobic reactor.
◆ABR—anaerobic baffle reactor
Anaerobic baffle reactor (ABR) is a new type of efficient anaerobic biological treatment device developed and developed based on the process performance of the second generation anaerobic reactor.
Its characteristic is that the reactor has a built-in vertical baffle, which divides the reactor into several series-connected reaction chambers. Each reaction chamber is a relatively independent upflow sludge bed system, in which the sludge is in granular form or flocculation. exists in form.
The water flow is guided by the baffle plate and flows up and down, passing through the sludge bed in the reaction chamber one by one. The substrate in the incoming water is fully contacted with the microorganisms and is degraded and removed. When the wastewater passes through the ABR, it flows from bottom to top and contacts the sludge multiple times during the flow process, which greatly improves the volume utilization of the reactor and eliminates the need for a three-phase separator.
◆Two-phase anaerobic reactor
The two-phase anaerobic digestion process allows the acidification and methanation stages to be carried out in two series-connected reactors, allowing acidogenic bacteria and methanogenic bacteria to grow under optimal environmental conditions. This is not only conducive to giving full play to their respective The activity is improved, and the treatment effect is improved, thereby achieving the purpose of increasing the volume load rate, reducing the reactor volume, and increasing operating stability.
From a biochemical point of view, the acidogenic phase mainly includes the stages of hydrolysis, acidogenesis, hydrogenation and acetogenesis, and the methanogenesis phase mainly carries out the methanogenesis stage. From a microbiological perspective, generally only acid-producing fermentation bacteria exist in the acid-producing phase, while not only methanogenic bacteria but also acid-producing fermenting bacteria exist in the methanogenic phase to varying degrees. Generally, the methanogenesis stage is the control stage of the entire anaerobic digestion. In order for the anaerobic digestion process to proceed completely, the growth conditions of the methanogenic phase bacteria must first be met, such as maintaining a certain temperature and increasing the reaction time. Especially for refractory or toxic wastewater, it requires a long period of acclimation to adapt.
The two-phase anaerobic digestion process separates the two stages of acidification and methanation in two series reactors, allowing the acidogenic bacteria and methanogenic bacteria to grow under optimal environmental conditions, which is not only conducive to giving full play to their respective activities , and improve the treatment effect, achieving the purpose of increasing the volume load rate, reducing the reaction volume, and increasing operating stability.
◆UBF – upflow anaerobic sludge bed – filter reactor
Upflow Blanket Filter (UBF) is a new type of composite anaerobic fluidized bed reactor developed on the basis of anaerobic filters and upflow anaerobic sludge beds. It has a high Biosolids retention time (SRT) and the ability to effectively degrade toxic substances are an effective and economical technology for treating high-concentration organic wastewater.
Its main structural features are that the lower part is an anaerobic sludge bed, which is the same as the sludge bed in the lower part of the UASB reactor, and the upper part is a packing filter layer similar to an anaerobic filter (AF). A large number of anaerobic microorganisms can be attached to the packing layer. Improve the biomass, processing capacity and impact resistance of the reactor.
◆AF–anaerobic biological filter
Anaerobic Biofilter (AF) is developed based on the traditional anaerobic activated sludge method. It consists of a bottom water inlet distribution system, a bottom water distribution system and the sludge between the filter material layer. It consists of five parts: layer, biological filler, pool surface water replenishment system, and biogas collection system.
The advantages of anaerobic biological filters are: high biosolids concentration, higher organic load can be obtained; short start-up time, and easier to start again after stopping operation; in the case of large changes in treated water volume and load, its operation is It can maintain greater stability; after practical application, no biogas treatment system is needed when treating low-concentration sewage.
In AF, water enters from the bottom of the reactor. After the water distribution system is evenly arranged at the bottom of the tank, the wastewater passes through the suspended sludge layer and biological filter layer in sequence. The organic matter contacts and fixes the microorganisms on the sludge and biofilm, and then be dissolved. The water is evenly discharged from the water supply system on the pool surface and enters the next-level processor.
Anaerobic biological filters can be divided into upflow anaerobic filters and downflow anaerobic filters according to the direction of water flow. The wastewater flowing upward through the reactor is an upflow anaerobic filter, and the opposite is a downflow anaerobic filter.
◆USSB – upflow segmented sludge bed
The reaction zone of the Upflow Staged Sludge Bed (USSB) is divided into several parts. The gas produced in each part is separately sealed with water and then escapes. The entire reactor is equivalent to a series of UASB reactions. device assembly.
◆USR – upflow anaerobic solid reactor
The upflow solid anaerobic reactor (USR) is a reactor with a simple structure and suitable for high suspended solid organic matter raw materials.
The raw materials enter the digester from the bottom and come into contact with the activated sludge in the digester, so that the raw materials are quickly digested. Undigested organic matter solid particles and biogas fermentation microorganisms are retained in the digester by natural sedimentation, and the supernatant overflows from the upper part of the digester. This can obtain a solid retention period and a microbial retention period that are much higher than the hydraulic retention period, thus improving the efficiency of the digester. Decomposition rate of solid organic matter and digester efficiency.
USR mainly treats waste liquid with high organic solids (organic solid matter >5%). The waste liquid enters from the bottom water distribution system. During its rise, it passes through the solid bed of high-concentration anaerobic microorganisms, causing the organic solids in the waste liquid to mix with the anaerobic microorganisms. Aerobic microorganisms fully contact and react, and organic solids are liquefied, fermented and anaerobically decomposed, thereby achieving the purpose of anaerobic digestion.
◆AAFEB-anaerobic attached membrane expanded bed
Anaerobic Attached microbial Film Expanded Bed (AAFEB) is an anaerobic digestion process. In this reactor, most microorganisms exist in the form of attachment to the carrier. The nutrients in the wastewater entering the biofilm through diffusion mode are produced under the combined action of anaerobic fermentation bacteria and hydrogen-producing acetogenic bacteria. hydrogen.
Carrier fluidization is an important feature of the AAFEB process. When the fluid flow rate in the reactor reaches a certain level, the head pressure drop exceeds the weight of the carrier, making the void ratio between the solid particles large enough to separate the carriers from each other, through the combination of the fluid buoyancy of the rising water flow and the friction generated when the hydrogen overflows. Under the action, the carrier is suspended, which makes the carrier fluidized.
◆FPR—plug flow reactor
Plug flow reactor, also called plug flow reactor (FPR for short), is a rectangular incomplete mixing reactor. High-concentration suspended solid fermentation raw materials enter from one end and are discharged from the other end. There is no need to install a flow booster and it is suitable for the treatment of high SS wastewater, especially for the anaerobic digestion of cow manure.
◆AFBR—anaerobic fluidized bed and expanded bed reactor
AFBR is an efficient biofilm treatment method that uses specially developed fillers with large specific surface areas as carriers. Anaerobic microorganisms adhere to the surface of the carrier in the form of biofilms, and a certain height of granular sludge bed can be formed in the reactor. , greatly improving the degradation efficiency of organic matter.
The wastewater is continuously pulsed by a pump and evenly enters the reaction area from the water distribution system, and fully contacts and reacts with the anaerobic biofilm on the carrier. At the same time, the reaction degree and contact time are increased, and the filler reaches a fluidized state, allowing the organic matter to be decomposed by anaerobic microorganisms to produce biogas. The three phases of solid, liquid and gas form a mixed liquid that is separated at the upper part to achieve the purpose of wastewater treatment.