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Most of wastewater discharged from food, biological and chemical industries belongs to high concentration of organic wastewater. It is difficult to achieve the purpose of treatment by the conventional physico-chemical and biochemical treatment. At the same time, there is a systematic problem of operation management, large investment and high operation cost. Anaerobic reaction treatment method, as an efficient organic wastewater treatment method, is widely used in sewage treatment. This article will explain UASB anaerobic reactor in detail, see below:
1) UASB anaerobic reactor works
The wastewater to be treated is first introduced into the bottom of the UASB anaerobic reactor. The water flows upwardly through the sludge bed, the sludge suspension layer to the three-phase separator and the settling zone at a certain flow rate. The water flow in the UASB anaerobic reactor is pushed Form, influent and sludge bed and sludge suspended layer of microorganisms fully mixed contact and anaerobic decomposition, and produce a large amount of biogas, biogas in the process of lifting the sludge particles, sludge bed significantly expanded, with the Increasing the amount of gas produced by the reactor, the agitation caused by the bubble rise becomes more and more severe, thereby reducing the resistance of entrained bubbles in the sludge and the gas escapes suddenly from the sludge bed, causing the sludge bed The surface was boiling and fluidized state. The flocculent sludge with poor sedimentation performance in the reactor forms a sludge suspension layer on the upper part of the reactor under the action of gas agitation. The granular sludge with good sedimentation performance is located at the lower part of the reactor to form a sludge bed with high concentration , With the rising flow of water, gas, water, mud three-phase mixture rose to the three-phase separator, the gas meets the reflective baffle folded to the plenum and effectively separated discharge; sludge and water into the upper Of the settling zone, under the action of gravity mud separated, the sludge back to the sludge layer, the supernatant was discharged into the follow-up treatment facilities.
2) UASB anaerobic reactor basic structure
The basic structure of UASB anaerobic reactor mainly consists of: â‘ sludge bed; â‘¡ sludge suspended layer; â‘¢ sedimentation area; â‘£ three-phase separator and other components. The functional characteristics of each component are described as follows:
â‘ sludge bed
The sludge bed is located at the bottom of the entire UASB anaerobic reactor and has a high sludge biomass in the sludge bed. The sludge MLSS is generally 40,000-80000 mg / L, even up to 150,000 mg / L. The sludge in the sludge bed consists of highly developed granular sludge accounting for more than 70-80% of the active biomass (or bacteria), and the particle size of the granular sludge in a normally operating UASB is generally in the range of 0.5-5 mm with excellent The settling velocity is generally 1.2-1.4 cm / s, with a typical SVI of 10-20 mg / L. The biological phase composition of granular sludge is more complex, mainly bacilli, cocci and granular bacteria.
The volume of the sludge bed generally accounts for about 30% of the total volume of the UASB anaerobic reactor, but it plays an extremely important role in the overall treatment efficiency of the UASB anaerobic reactor, and its amount of degradation of the organic matter in the reactor can generally be accounted for To 70-90% of the total degradation of the reactor. Sludge bed so effective degradation of organic matter, making a large number of biogas generated in the sludge bed, tiny biogas bubble after continuous accumulation, the merger and gradually form a larger bubble, and by its role in the rise and the entire The sludge bed is well mixed.
â‘¡ sludge suspended layer
The sludge suspension is located in the upper part of the sludge bed. It occupies about 70% of the volume of the entire UASB anaerobic reactor, the concentration of which is lower than the sludge bed, usuallymg / L, composed of highly flocculated sludge, generally non-granular sludge, Its sinking speed is obviously less than that of granular sludge. The volume index of sludge is generally between 30-40mg / L, and the sludge in this layer gets well mixed by the rising bubbles from the sludge bed. The concentration of flocculated sludge in sludge suspended layer shows a decreasing distribution from bottom to top. This layer of sludge is responsible for the entire UASB anaerobic reactor organic matter degradation of 10% -30%.
â‘¢ sedimentation area
The sedimentation zone is located at the top of the UASB anaerobic reactor, and its role is to make the solid particles (mainly the flocculant sludge in the suspended sludge layer) with the ascending water flow into the effluent zone precipitate in the sedimentation zone due to entrainment of the water flow, And slides down along the sloping wall at the bottom of the settling zone to return to the reaction zone (including the sludge particles and the sludge suspension layer) to ensure that the sludge in the reactor will not be lost and the sludge concentration in the sludge bed is ensured. Another effect of the sedimentation area is that the effective space height of the plenum of the reactor can be ensured by reasonably adjusting the water level in the sedimentation zone so as to prevent the plenum from being damaged.
â‘£ three-phase separator
The main function of the three-phase separator is to separate the gas (biogas generated during the reaction), solid (sludge in the reactor) and liquid level (the treated sewage) three phases to separate the biogas into the plenum, The treated water is introduced into the effluent zone and the solid particles are introduced into the reaction zone. It consists of gas collector and baffle and other components. The three-phase separator is one of the main characteristics of UASB anaerobic reactor, and its reasonable design is the key technology to ensure the normal operation of UASB.
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