What is a Moving Bed Biofilm Reactor (MBBR)?

A Moving Bed Biofilm Reactor (MBBR) is a highly efficient biological wastewater treatment process that utilizes thousands of small plastic biofilm carriers suspended in a reactor tank. These carriers provide a large surface area for microorganisms to grow as a biofilm, which then degrades pollutants in the wastewater. This technology combines the benefits of both activated sludge and fixed-film systems.

How does the MBBR process work?

The MBBR process works by creating an optimal environment for microbial growth. In a reactor tank, thousands of small, free-floating plastic carriers are kept in suspension through aeration or mechanical mixing. These carriers act as a protected habitat for beneficial bacteria to form a biofilm, which then consumes and breaks down organic pollutants from the wastewater.

What are the main advantages of MBBR technology?

MBBR technology offers numerous advantages, including a compact footprint, high treatment efficiency for BOD, COD, and nutrients, and reduced sludge production. It is also highly flexible and can be used to upgrade existing plants without requiring extensive modifications. Its sim

How is MBBR different from conventional activated sludge?

Unlike conventional activated sludge systems, MBBR does not require sludge recirculation from a secondary clarifier. Instead, the biomass grows on plastic carriers that are suspended in the tank, eliminating the risk of sludge bulking. This allows the system to be more compact, efficient, and resilient to hydraulic and organic shock loads

What types of wastewater can be treated with MBBR technology?

MBBR technology is highly versatile and can be used to treat a broad range of wastewater types. It has been successfully applied to both municipal sewage and various industrial wastewaters, including those from the pulp and paper, food and beverage, dairy, and pharmaceutical industries. It is also effective for treating aquaculture waste.

What are biofilm and biological carriers?

Biofilm is a community of microorganisms that grows on a surface. In an MBBR system, the biological carriers are the specially designed plastic media made from materials like HDPE or PP that provide this surface. They have a large surface area for the biofilm to colonize and grow, which is essential for the pollutant degradation process.

Is MBBR technology suitable for existing wastewater treatment plants?

Yes, MBBR technology is excellent for upgrading existing facilities. It can be easily integrated into overloaded activated sludge systems or trickling filters to increase treatment capacity and efficiency without requiring a completely new plant design. Its flexibility makes it a cost-effective solution for facility improvements.

What factors affect the performance of an MBBR system?

The performance of an MBBR system is influenced by several factors. The carrier filling fraction, which is the percentage of the tank volume filled with media, is crucial for optimal mixing. Other key factors include the Dissolved Oxygen (DO) concentration, the specific surface area of the carriers, and the water temperature and pH

How much space does an MBBR system require?

MBBR systems are known for their compact footprint. They are significantly smaller than conventional activated sludge systems for the same treatment capacity, making them ideal for urban areas or facilities with limited space. The high concentration of biomass on the carriers allows for efficient treatment in a smaller reactor volume.

Are MBBR systems difficult to operate or maintain?

No, MBBR systems are known for being relatively simple to operate and maintain. They do not require the complex sludge recirculation and settling control needed for conventional activated sludge. The system operates continuously and is not influenced by clogging, reducing the need for frequent maintenance work.

Can MBBR technology be used for nitrification and denitrification?

Yes, MBBR technology is very effective for both nitrification and denitrification. The system's ability to retain slow-growing microorganisms, such as nitrifiers, on the biofilm carriers ensures that these processes are achieved successfully, leading to effective nutrient removal

What is the typical carrier filling fraction in an MBBR reactor?

The typical carrier filling fraction, which is the percentage of the reactor volume occupied by the carriers, normally varies from 60% to 70%. This range is crucial because it allows for the free suspension and movement of the carriers, which is necessary for efficient mixing and system performance.

What are some commercial brands of MBBR carriers?

Some popular commercial brands of biological carriers mentioned in the article include AnoxKaldnes K1, K3, and K5, which are widely used. Other brands include Hydroxyl ActiveCell, Bio-Portz, and Siemens AGAR, which come in various shapes and sizes to suit different applications.

Moving Bed Biofilm Reactor (MBBR) Technology For Wastewater Treatment: Performance, Applications, and Advantages

By Hossein Jalalian

15 minutes read

Moving Bed Biofilm Reactor (MBBR) Technology For Wastewater Treatment: Performance, Applications, and Advantages

Due to the growing demand for freshwater all around the world, new and more advanced wastewater treatment technologies that can provide high-quality treated water, which will be suitable for domestic, industrial, and agricultural purposes should be established and used instead of old wastewater treatment technologies. It is estimated that around $38 million over 20 years will be saved by implementing the MBBR technology (Martin et al., 2009). Compact wastewater treatment plants that produce a high standard of effluent in the presence of a smaller footprint and minimize waste, have been a major concern in the world, especially in populated areas where there is limited space for the treatment plants (Barwal & Chaudhary, 2014).

In the last two decades, the Moving Bed Biofilm Reactor (MBBR) has been implemented as a compact and flexible technology for wastewater treatment. This approach is very promising in reducing pollution load and has obvious advantages over other systems. Since their design and operation have been developed, MBBRs have become an interesting and reliable alternative for wastewater treatment that can result in footprint reduction, minimal waste disposal, lower suspended solid production, and production of high-quality and reusable water (Rodgers & Zhan, 2003).

The basic purpose of this paper is to study the application and performance of MBBR technology. We also review the advantages of wastewater treatment using MBBR technology over other wastewater treatment systems.

Schematic diagram of a complete MBBR system, from influent to clarifier, showing the internal plastic biofilm carriers — Fig. 1. The Moving Bed Biofilm Reactor (MBBR) process, showing the biological reactor, carriers, and clarifier.

1. MBBR Technology Performance

In both pilot plant studies and full-scale plants, the MBBR technology has been widely used. The reactor could be applied for aerobic, anoxic, and anaerobic processes. Due to the agitation created by the air in the aerobic process, the biofilm carrier movement occurs. However, in the anoxic and anaerobic process, a mixer (horizontal or vertical shaft) is used to keep the carrier in suspension (Rusten et al., 2006).

A schematic showing two types of MBBR reactors: an aerobic reactor (A) using air bubbles for agitation and an anaerobic-anoxic reactor (B) with a mechanical mixer. — Fig. 2. The MBBR process for different reactor types: (A) Aerobic reactor using air for mixing and (B) Anaerobic/anoxic reactor using a mechanical mixer.

The MBBR process is carried out using a biological carrier as a media with a density close to water, so it can be kept in suspension, in which minimum mixing energy caused by aeration or mechanical mixing would be required (Henze et al., 2008). Therefore, the active biomass can grow into biofilm on the surface of these carriers when the suspended porous biofilm carriers are mixed in tanks. The MBBR system is a very effective and efficient method to retain slow-growing microorganisms like nitrifiers in the form of biofilm (Shrestha, 2013).

A schematic diagram illustrating a two-stage MBBR process with an anaerobic reactor (using a mixer) followed by an aerobic reactor (using process air). — Fig. 3. The schematic of the MBBR performance, showing the anaerobic reactor followed by the aerobic reactor.

1.1. Biofilm and Biological Carriers

Microorganism communities that grow on the surface are called biofilms (Das & Naga, 2011). These microorganisms require a surface to adhere and grow on, and the biological carrier in the MBBR system supports their growth as a media. Biofilms that grow within the internal structures of the biocarriers can degrade dissolved pollutants in the wastewater (Briones & Raskin, 2003).

A new, white plastic MBBR carrier shown side-by-side with a carrier covered in a dark, mature biofilm. — Fig. 4. The biological carrier and biofilm growth on the surface of the MBBR media.

A variety of biocarrier models are now available that have different shapes and sizes with a large specific surface area to colonize the bacteria and are made up of Polypropylene (PP), High-Density PolyEthylene (HDPE), and Polyethylene (PE). There are some brands in the market for this media but the original AnoxKaldnes K1 is mainly used for effluent treatment and K3 and K5 are normally used in new treatment plants. Biofilm Chip M is another type that is mostly used for slow-growing organisms like nitrifiers and Anammox bacteria (Haandel & Lubbe, 2012). Some of the popular models in the market are Hydroxyl ActiveCell, Bio-Portz, and Siemens AGAR.

A group of cylindrical black plastic MBBR filter media pieces with internal and external fins and crosses. — Fig. 5. Various models of MBBR filter media, which provide a surface for biofilm growth.

Table 1. Different models of biological carriers

Model	Company	Country	Specific surface area (m2m3)
K1	AnoxKaldnes	Sweden	500
K3	AnoxKaldnes	Sweden, USA	500
Biofilm Chip M	AnoxKaldnes	Sweden	500
FLOCOR-RMP	FLOCOR-Henderson Plastics Ltd	UK	260
BioSphere	Siemens	USA	800
ActiveCell 450	Hydroxyl Systems Inc.	USA	402
Bioportz™	-	USA	576
Bio-media	Fxsino	China	>550
Bee-Cell 2000	-	Iran	650
MB3	-	USA	604

1.2. Difference between MBBR Technology and Conventional Activated Sludge

One of the common suspended growth processes used for wastewater treatment is known to be the Conventional Activated Sludge (CAS). The CAS has been widely used in the past due to its cost-friendly characteristics. However, in recent years, overall performance has shown that the moving bed biofilm reactor has a higher rate of constituent removal efficiency compared to the conventional activated sludge in laboratory-based studies (Sidek et al., 2015).

Compared to conventional activated sludge, the MBBR technology does not require recirculation of sludge from the secondary clarifier, because the biofilm development occurs on carriers that can move freely in the reactor tank. However, it should be noted that if the system is not designed properly, some issues relating to the hydrodynamics like the formation of stagnant regions may happen. In addition, the MBBR technology has some benefits compared to the conventional activated sludge system or other fixed biofilm-based technologies. For Example, this system requires less space for its performance and implementation, it is more efficient in BOD and nutrient removal, and it is more compact (Bassin & Dezotti, 2018; McQuarrie & Boltz, 2011).

1.3. Factors Affecting the MBBR Performance

The performance of the MBBR technology depends on the percent of media provided in the reactor as well as the organic loading. The carrier filling fraction should normally vary from 60 to 70% (percentage of reactor volume occupied with carriers in an empty tank), to allow the free carrier suspension. Furthermore, mixing efficiency can be reduced when a greater proportion of filling is used (Weiss et al., 2005). Low-suspended biomass may reduce the MBBR removal efficiency since they are vital in enzymatic pyrolysis and bioflocculation in the reactor (Accinelli et al., 2012).

The biofilm area, which represents the effective carrier-specific area, is one of the important parameters in the MBBR performance and its design. In a small reactor volume, the high specific area of the carrier media allows very high biofilm concentration, which controls the system performance. The effective area of the MBBR carrier medium is reported to be 70% of the total surface area. The carrier surface properties like surface roughness and specific surface area, are one of the most important factors in the accumulation of biofilm (Bolton et al., 2006).

A detailed close-up shot of a white plastic MBBR carrier, showing its intricate honeycomb-like internal structure. — Fig. 6. The surface of a biological carrier, showing its intricate design to promote biofilm growth.

For efficient COD removal, the Dissolved Oxygen (DO) should be kept higher than 2 mg L-1 in a reactor. Moreover, the COD removal efficiency will be decreased when DO reduces from 2 to 1 mg L-1. With growing biofilm, DO concentration also reduces rapidly due to higher bacterial activity (Wang et al., 2006).

An overhead shot of various white and black plastic MBBR media pieces in different shapes and sizes on a blue background. — Fig. 7. Different biocarrier surfaces, showing a variety of designs for optimal biofilm growth.

Proper turbulence is ideal and desirable for the efficiency of system performance. To enable the transport of substrate and oxygen to the biofilm surface, the carrier requires the development of a very thin, evenly distributed, and smooth biofilm. Therefore, thick and fluffy biofilms are not suitable for this system. Generally, it is preferable to use biofilms of less than 100 μm thickness for full substrate penetration (Leiknes & Ødegaard, 2001).

A scanning electron micrograph showing a highly magnified view of a complex network of microorganisms forming a biofilm. — Fig. 8. A microscopic view of biofilm, showing the complex community of microorganisms that form on the MBBR carriers.

Various processes, including biofilm growth, thickness, adsorption and desorption of microorganisms to the solid surface, biofilm adhesion, and detachment to and from the solid surface or media can influence the development of biofilm. Some of the characteristics of the water medium, such as nutrient level, pH, ionic strength, and temperature, can also play a major role in the microbial attachment to the solid surface rate (Rodney, 2002).

A split image showing a beaker with a thermometer measuring cold water temperature and a hand testing a liquid's pH level. — Fig. 9. Key wastewater characteristics, including water temperature and pH level, which are crucial for MBBR performance.

2. MBBR Technology Application

MBBRs have been designed to comply with a broad range of effluent quality standards, including stringent nutrient limits, and this technology is applicable to a wide range of wastewater flows ranging from 10,000 to 150,000 m3 day-1. Currently, there are at least 400 large-scale wastewater treatment plants in 22 countries from all over the world that are based on this technology and it is obvious that its application in wastewater treatment has increased over the past decade (Kermani et al., 2008). Moving bed biofilm reactor technology has been successfully used for municipal and industrial wastewater, including pulp and paper industry wastewater, phenolic wastewater, poultry processing wastewater, dairy wastewater, pharmaceutical wastewater, aquaculture, refinery, and slaughterhouse waste, drinking water denitrification, and also in roughing, secondary, tertiary, and sidestream applications (Borghei & Hosseini, 2004; McQuarrie & Boltz, 2011).

A collage showing two applications for wastewater treatment: a municipal plant reactor tank and an illustration of pharmaceutical pollutants in water. — Fig. 10. MBBR technology can be used to treat both municipal wastewater and complex industrial wastewater containing emerging pollutants such as pharmaceuticals.

3. MBBR Technology Advantages

MBBR is one of the Biological treatment processes in wastewater that offers a compact treatment plant design to overcome the disadvantages of other technologies and produces higher-quality effluent in small footprints. MBBR technology has numerous advantages in the improvement of treatment facilities, which ultimately results in economic benefits by reducing the solid load of existing secondary clarifiers (Kim et al., 2011).

The MBBR process is extremely flexible and can be adapted to different sizes and shapes of a tank (Zimmerman et al., 2005). The moving bed biofilm reactor technology can also be used to upgrade trickling filters, overloaded activated sludge, and other processes. The MBBR technology operates constantly and is not influenced by clogging issues that need backwashing or maintenance work. The moving bed biofilm reactor technology has a much higher specific surface area for the biofilm than other systems (Bertino, 2010). Nitrification and denitrification may also be achieved successfully in biofilm-based processes because the nitrifiers (slow-growing microorganisms) are retained by the biofilm.

It is indicated that MBBR is very effective in removing up to 90% of chemical oxygen demand and 95% of biochemical oxygen demand with nutrients from the effluent stream at optimal conditions if there is enough retention time. Since this technology is efficient, compact, and easy to operate, it is a cost-effective way of upgrading existing wastewater treatment plants (Barwal & Chaudhary, 2014).

Consequently, the MBBR technology is approved to be an advanced wastewater treatment technology with high treatment efficiency, low capital, operational, maintenance, and replacement cost, and is a reliable and robust operation technology.

A conceptual diagram showing white plastic MBBR media floating in water, next to a list of its benefits: large surface area, high efficiency, and low energy consumption. — Fig. 11. An illustration highlighting the advantages of MBBR media, including a large surface area, high efficiency, and low energy consumption.

4. Conclusion

The implementation of the moving bed biofilm reactor technology in domestic sewage and industrial wastewater has increased worldwide. In comparison to conventional activated sludge, the MBBR technology offers numerous advantages such as high treatment efficiency, cost-effective implementation, and easy operation. This technology can also adapt to different sizes and spaces and is very suitable for nitrification and denitrification processes. Generally, the biofilm process indicates good efficiency for the removal of microorganisms in the wastewater. There are several biocarrier models available in the market and depending on the purpose, it is possible to select a proper type.