MBBR (Moving Bed Biofilm Reactor) is a different type of wastewater treatment process which employs a physical medium such as rock, plastic, wood, or other natural or synthetic solid material that supports biomass on its surface and within its porous structure.

The main characteristic is the presence of bioelements called carriers that have a huge specific surface, due to their porosity where a biofilm can grow. The carriers are made of a material with a density close to the density of water (1 g/cm3). An example is high-density polyethylene (HDPE) which has a density close to 0.95 g/cm3., The growth of a biofilm on the carriers’ surface and pores is the result of the interaction between biological processes and transport processes; the biomass developed continuously exchanges oxygen and organic compounds with the external environment.

The carriers will be mixed in the tank by the aeration system and thus will have good contact between the substrate in the influent wastewater and the biomass on the carriers. To prevent the plastic carriers from escaping the aeration it is necessary to have a sieve on the outlet of the tank.

The first kind of fixed-film treatment process was born during the fiftyies with the first trickling filters It consists of a tank with a fixed bed made of rocks, coke, polyurethane foam, ceramic, or plastic media over which wastewater is spread through a hydraulic distribution device. Other types still used for small plants are the rotating biological contactor or biodiscs . The rotating packs of disks (known as the media) are contained in a tank and rotate very slowly (between 2 and 5 revolutions per minute). Commonly used materials for the media are polyethylene, PVC and expanded polystyrene. The rotating drum is aligned with the flow of wastewater so that the discs rotate at right angles to the flow and About 40% of the disc area is immersed in the wastewater. Biological growth is attached to the surface of the disc and forms a sludge layer.

The most recent technologies about this kind of process, called Moving Bed Biofilm Reactor (MBBR) was first invented in the late 1980s in Norway University of Science and Technology and was after commercialized by Kaldnes Miljöteknologi with a typical shape as you can see in the picture

Notice how the empty spaces of the media allow the rooting (mettere radici, attecchire) and growing ogf biomasses useful for the biological processes of oxidation-nitrification. The MBBR system consists of an aeration tank (similar to an activated sludge tank) with special plastic carriers that provide a surface where a biofilm can develop. The carriers are mixed in the tank by the aeration system thus having a good contact between the substrate in the influent wastewater and the biomass on the carriers. To avoid the plastic carriers escape, a small cage is put on the outlet of the tank.

According to recent survey and real-life experience the advantages of this process are:

1. Biofilm processes in general require less space than activated sludge systems because the biomass is more concentrated, and the efficiency of the system is less dependent on the final sludge separation;

2. The MBBR system is often installed as a revamping of existing activated sludge plants in order to increase the capacity of the existing treatment plant that can increase its treatment capacity without building new tanks or construction;

3. We can choose the degree of filling of carriers that can be adapted to the specific situation for example when constructing the filling degree can be set to 40% in the beginning, and later be increased to 70% by filling in more carriers. A typical situations can be a sudden population increase in a city.

4. Modular realization and simply to extend

5. Relative Lower sludge production;

6. Resilient to toxic shock;

7. Simply to maintain

8. Suitable for Chemical industries, Pulp & paper factory, Food & beverage factory.