The Anaerobic Sludge Bed Reactor (ASBR), also known as Upflow Anaerobic Sludge Bed (UASB), is an anaerobic biological method for wastewater treatment. Wastewater flows upwards through the UASB. At the bottom of the reactor, there is a high-concentration, high-activity sludge bed where most organic pollutants in the wastewater are anaerobically fermented and degraded into methane and carbon dioxide. Due to the disturbance of water flow and bubbles, there is a sludge suspension layer above the sludge bed. The upper part of the reactor is equipped with a three-phase separator to separate digestate gas, digestate liquid, and sludge particles. The digestate gas is discharged from the top of the reactor; the sludge particles automatically slide down and settle at the bottom of the sludge bed; and the digestate liquid exits from the clarified zone. The UASB has a high load capacity and is suitable for treating high-concentration organic wastewater. A well-operated UASB has a high removal rate of organic pollutants, does not require stirring, and can adapt to significant load shocks, temperature, and pH changes.

Operating Principle: The anaerobic reaction process in the UASB reactor is similar to other anaerobic biological treatment processes, including hydrolysis, acidification, acetic acid production, and methane generation. Substrates are converted into products such as biogas and inorganic water through the transformation process involving different microorganisms. The main anaerobic microorganisms involved in the anaerobic digestion reaction process are as follows: ①Hydrolysis-Fermentation (Acidification) Bacteria, which hydrolyze and ferment complex substrates into various organic acids, ethanol, sugars, hydrogen, and carbon dioxide; ②Acetic Acid Bacteria, which convert the hydrolysis-fermentation products into hydrogen, acetic acid, and carbon dioxide; ③Methanogenic Bacteria, which convert simple substrates such as acetic acid, methanol, carbon dioxide, and hydrogen into methane.

The UASB consists of three main parts: the sludge reaction zone, the gas-liquid-solid three-phase separator (including the sedimentation zone), and the gas chamber. A large amount of anaerobic sludge remains in the bottom reaction zone, with sludge having good sedimentation and flocculation properties forming a sludge layer at the bottom. The wastewater to be treated enters from the bottom of the anaerobic sludge bed, mixing and contacting with the sludge in the sludge layer. The microorganisms in the sludge decompose the organic matter in the wastewater, converting it into biogas. The biogas is released in the form of small bubbles, which merge as they rise, gradually forming larger bubbles. Due to the agitation by the biogas, a thin sludge layer and water rise together into the three-phase separator. When the biogas hits the reflector plate at the bottom of the separator, it deflects around the plate and then passes through the water layer into the gas chamber, where it concentrates. It is then channeled out through a pipe. The solid-liquid mixture reflects into the sedimentation zone of the three-phase separator, where the sludge in the wastewater絮凝, the particles gradually enlarge, and settle under gravity. The sludge that settles on the inclined wall slides back into the anaerobic reaction zone, accumulating a large amount of sludge there. The treated effluent, separated from the sludge, overflows from the top of the overflow weir and is then discharged from the sludge bed. The UASB's structural feature is the integration of biological reaction and sedimentation, making it a compact anaerobic reactor. The reactor is mainly composed of the following components.