UASB anaerobic tower

UASBAnaerobic tower, also known asusabAnaerobic reactor, with the dual characteristics of anaerobic filtration and anaerobic activated sludge process, is a technology that can convert pollutants in sewage into renewable clean energy - biogas. It has strong adaptability to sewage with different solid contents, and its structure, operation, maintenance and management are relatively simple. The cost is also relatively low, and the technology has matured. It is increasingly valued by the sewage treatment industry and widely welcomed and applied.

1UASBReactor Overview

UASBAnaerobic towerAs a utilization of the metabolic characteristics of anaerobic microorganisms, methane gas with energy value is produced by using reduced organic matter as a hydrogen acceptor without the need for external energy. Anaerobic biological treatment method is not only suitable for high concentration organic wastewater, but also for influentBODHigh concentration can reach tens of thousandsmg/lIt can also be applied to low concentration organic wastewater, such as urban sewage. The anaerobic biological treatment process has low energy consumption; Organic volume load is high, generally5－10kgCOD/m3.dHigh accessibility30-50kgCOD/m3.dLow amount of residual sludge; Anaerobic bacteria have low nutritional requirements, strong toxicity tolerance, and high molecular weight of biodegradable organic matter; Strong ability to withstand impact loads; The produced biogas is a clean energy source.

IIUASBWorking principle of anaerobic tower

UASBThe anaerobic tower consists of three parts: sludge reaction zone, gas-liquid solid three-phase separator (including sedimentation zone), and gas chamber. There is a large amount of anaerobic sludge stored in the bottom reaction zone, and 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 with the sludge in the sludge layer. The microorganisms in the sludge decompose the organic matter in the sewage and convert it into biogas.

Biogas is continuously released in the form of tiny bubbles, which merge and gradually form larger bubbles during their ascent. In the upper part of the sludge bed, due to the agitation of biogas, a sludge with a relatively thin concentration rises together with water and enters the three-phase separator. When biogas encounters the reflection plate at the lower part of the separator, it bends around the reflection plate and then enters the gas chamber through the water layer. It is concentrated in the gas chamber and discharged through a conduit. The solid-liquid mixture is reflected and enters the sedimentation zone of the three-phase separator. The sludge in the sewage undergoes flocculation, and the particles gradually increase and settle under the action of gravity.

The sludge settled on the inclined wall slides back into the anaerobic reaction zone, 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 sedimentation area overflow weir and is then discharged from the sludge bed.

Anaerobic treatment refers to the combined action of multiple (anaerobic or facultative) microorganisms under anaerobic conditions to decompose and produce organic matterCH4andCO2The process. Anaerobic is divided into three stages:

① Hydrolysis stage: Complex organic matter is first decomposed into simpler organic matter by extracellular enzymes of anaerobic bacteria, and then converted into fatty acids and alcohols such as acetic acid, propionic acid, and butyric acid through anaerobic fermentation and oxidation under the action of acid producing bacteria.

② Hydrogen and acetic acid production stage: Hydrogen and acetic acid producing bacteria can convert intermediate products (such as fatty acids and alcohols such as propionic acid and butyric acid) produced in the first stage, except for acetic acid, formic acid, and methanol, into acetic acid and hydrogenCO2Generated.

③ Methanogenic stage: Methanogenic bacteria convert the acetic acid, hydrogen, and other substances produced in the first and second stagesCO2Convert to methane.

Anaerobic does not require oxygen supply, and the sludge load is relatively high, which can treat substances that are difficult to biodegrade. However, it takes a long time, and the effluent generally requires subsequent treatment to meet emission standards.

IIIUASBBasic requirements for anaerobic tower

1Provide favorable physical, chemical, and mechanical conditions for sludge flocculation, enabling anaerobic sludge to obtain and maintain good sedimentation performance;

2A good sludge bed can often form a relatively stable biological phase, maintain a specific micro ecological environment, resist strong disturbance forces, and larger flocs have good sedimentation performance, thereby increasing the sludge concentration inside the equipment;

3By setting up a sedimentation zone in the sludge bed equipment, fine sludge particles are further flocculated and precipitated in the sludge layer of the sedimentation zone, and then returned to the sludge bed.

4UASBAdvantages and disadvantages of craftsmanship

UASBThe main advantages of anaerobic tower are:

1、UASBThe internal sludge concentration is high, with an average sludge concentration of20－40gVSS/1；

2High organic load and short hydraulic retention time. When using medium temperature fermentation, the volumetric load is generally10kgCOD/m3.dabout;

3Without mixing and stirring equipment, relying on the upward movement of biogas generated during the fermentation process, the sludge in the upper part of the sludge bed is in a suspended state, and the sludge layer in the lower part is also stirred to a certain extent;

4The sludge bed is not filled with carriers, which saves costs and avoids clogging problems caused by fillers;

5、UASBInternally equipped with a three-phase separator, usually without a sedimentation tank, the sludge separated from the sedimentation zone is returned to the sludge bed reaction zone, and usually no sludge reflux equipment is required.

The main drawbacks are:

1Suspended solids in the inflow need to be appropriately controlled and should not be too high;

2There is a short flow phenomenon in the sludge bed, which affects the treatment capacity;

3Sensitive to sudden changes in water quality and load, with slightly lower impact resistance.

In today's society where the promotion of circular economy and the implementation of resource recycling of industrial waste are emphasized, anaerobic biological treatment is clearly the preferred process for wastewater resource utilization. In recent years, the development of anaerobic sewage treatment technology has been very rapid, with various new processes and methods constantly emerging, including anaerobic contact method, upflow anaerobic sludge bed, baffle anaerobic method, anaerobic biofilter, anaerobic expanded bed and fluidized bed, as well as third-generation anaerobic processesEGSBandICAnaerobic reactors are developing rapidly.

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