A Moving Bed Biofilm Reactor (MBBR) is a biological wastewater treatment technology. It uses living microorganisms to break down and remove pollutants, such as organic matter and nitrogen, from wastewater by having them consume the waste. This method combines features of other biological systems to create an efficient and compact process.
The MBBR Process Explained
The core of the MBBR process is the growth of a biofilm, a dense layer of microorganisms, on specially designed plastic carriers. These carriers are added to the wastewater reactor and are engineered with a large internal surface area to provide ample space for the biofilm to develop. This design allows a high concentration of biomass to be cultivated in a small volume.
The biocarriers are kept in constant motion throughout the treatment tank. In aerobic systems, an aeration grid pumps air from the bottom of the tank, which supplies oxygen to the microorganisms and ensures the carriers are mixed with the wastewater. For anoxic or anaerobic processes that do not require oxygen, mechanical mixers are used to keep the carriers circulating.
As wastewater flows through the reactor, it makes continuous contact with the biofilm-coated carriers. The microorganisms in the biofilm consume the organic pollutants and nutrients, cleaning the water. To ensure the biocarriers remain inside the reactor, retention sieves are installed at the tank’s outlet, allowing treated water to exit while blocking the media.
Essential Components of an MBBR System
An MBBR system is assembled from several components working in unison.
- Reactor Tank: This is the basin that contains the wastewater and all other components. It can be a newly constructed basin or an existing tank retrofitted for the purpose.
- Biocarriers: These are small, free-floating plastic media, often made of durable polyethylene, designed with a high protected surface area to support biofilm growth. Their density is engineered to be close to that of water, allowing them to mix freely throughout the reactor.
- Aeration or Mixing System: For aerobic treatment, a diffuser grid at the bottom of the tank provides the necessary oxygen for the microorganisms and keeps the carriers in motion. For anaerobic or anoxic processes, submersible mechanical mixers perform the agitation function.
- Retention Sieves: These screens are installed at the tank’s outlet. Their openings are large enough for treated water to pass through but small enough to keep the biocarriers inside the reactor.
Common Uses of MBBR Technology
MBBR technology is applied in both municipal and industrial wastewater treatment. For municipalities, it is used for secondary treatment to remove biochemical oxygen demand (BOD) and for nutrient removal, such as nitrification and denitrification. This makes it a practical choice for upgrading older plants to meet stricter effluent standards without requiring major new construction.
In the industrial sector, MBBR systems are effective at treating a wide range of effluents. The pulp and paper industry uses it for wastewater with high organic content. Food and beverage industries, including dairies, breweries, and slaughterhouses, also employ this technology to manage wastewater rich in organic materials and other byproducts.
MBBR systems are also used in chemical manufacturing, metal finishing, and pharmaceutical industries, which often produce wastewater with specific or complex organic compounds. Additionally, the technology is applied in aquaculture to treat water and maintain a healthy environment for the fish stock.
Unique Characteristics of MBBR Systems
MBBR systems have a compact physical footprint. By cultivating a high concentration of microorganisms on the vast surface area of the biocarriers, a smaller tank can achieve the same level of treatment as a larger conventional system. This space efficiency is a primary advantage for sites where land is limited or expensive.
The process is known for its stability and resilience. The biofilm attached to the carriers is less susceptible to shock loads or fluctuations in wastewater flow and composition. This protected, attached-growth design maintains a stable microbial community, ensuring consistent treatment performance even under variable operating conditions.
MBBR technology is easy to retrofit into existing infrastructure. It can often be installed within existing aeration tanks to upgrade a treatment plant’s capacity and efficiency. This adaptability allows for performance improvements without the cost and disruption of building new tanks.
The system’s operation is simplified by the absence of a sludge return loop. Unlike activated sludge processes, an MBBR retains its biomass on the carriers within the reactor. This design eliminates the complexities of managing sludge return rates and settling issues, leading to more straightforward operation and reduced maintenance.