Moving Bed Biofilm Reactor in Municipal Used Water Purification

In the moving bed biofilm reactor process (MBBR) the sludge is growing as a biofilm on a mobile carrier, mostly made out of plastic material. The carrier is retained in its compartment using retention devices. Aeration and/or mixing ensure a homogeneous exposure of the outside biofilm to the bulk environment. MBBR allows for a higher biomass concentration in the reactor, thus reducing necessary reactor volume and footprint. The process is mostly diffusion limited and therefore diffusion of substrates through the biofilm is essential for understanding MBBR design. Since modeling of the process becomes complex and analytical solutions are not available, numerical solutions are required for precise design, even if approximate degradation rates are existing. Furthermore, hydraulics inside of MBBR are important to understand. When not correctly designed, carrier displacement toward the outlet retention devices occurs, which can lead to loss of process performance and/or clogging of the reactor. Finally, being a biofilm process, the MBBR process is more stable toward toxic shocks than activated sludge treatment. Especially slow growing bacteria will take advantage of the biofilm environment, which will enable an MBBR to treatment compounds that are normally nonbiodegradable or even toxic (aromatic compounds, endocrine disrupting substances, etc.).