How Does MBBR Sewage Treatment Plant Work

Biofilm Formation on Carriers
The Moving Bed Biofilm Reactor (MBBR) sewage treatment plant uses small plastic carriers (media) that are usually made of high - density polyethylene. These carriers provide a large surface area for the growth of biofilms. Microorganisms such as bacteria, fungi, and protozoa attach to the surface of these carriers. The carriers are kept in constant motion within the reactor tank, either through mechanical agitation or the flow of the sewage itself. As the sewage enters the MBBR reactor, the microorganisms begin to colonize the carriers and form a biofilm.

Aerobic and Anaerobic Zones (if applicable)
In an aerobic MBBR system, an aeration system supplies oxygen to the reactor. The rising air bubbles not only provide the necessary oxygen for the aerobic microorganisms in the biofilm but also help to keep the carriers in motion. The microorganisms in the biofilm use the oxygen to metabolize the organic matter present in the sewage. Some MBBR systems may also have anaerobic or anoxic zones. In these zones, different types of microorganisms carry out processes such as denitrification (the conversion of nitrate to nitrogen gas) without the presence of free oxygen.

Contact between Sewage and Biofilm - covered Carriers
As the sewage flows through the MBBR reactor, it comes into contact with the biofilm - covered carriers. The organic pollutants in the sewage, such as carbohydrates, proteins, and lipids, are adsorbed onto the biofilm. The microorganisms in the biofilm then break down these pollutants through a series of biochemical reactions. For example, aerobic bacteria break down organic matter into carbon dioxide, water, and other simpler compounds. The movement of the carriers ensures that the biofilm is continuously exposed to fresh sewage, maximizing the treatment efficiency.

Sloughing and Renewal of Biofilm
Over time, the outer layer of the biofilm may become thick or inactive. The continuous movement of the carriers and the flow of sewage cause the outer layer of the biofilm to slough off. This sloughed - off material is then carried out of the reactor along with the treated sewage. At the same time, new biofilm growth occurs on the carriers as the microorganisms continue to multiply and attach to the surface. This process of sloughing and renewal helps to maintain an active and efficient biofilm for sewage treatment.

Settling and Separation of Treated Sewage
After passing through the MBBR reactor, the treated sewage usually enters a settling tank. Here, any remaining suspended solids, including the sloughed - off biofilm particles, are separated from the liquid. The settled solids may be recycled back to the MBBR reactor to maintain a sufficient biomass concentration, or they may be removed from the system for further treatment or disposal. The clarified, treated sewage can then be discharged into the environment or reused for non - potable purposes such as irrigation or industrial cooling, depending on its quality.

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