Moving Bed Bio Reactor - MBBR
This reactor can have any shape and different loads in a reactor volume depending on carrier filling.
Design of the reactor is based on the actual wastewater characteristics and local conditions. MBBR units are placed in series based on the load entering each reactor. Neutralized and settled wastewater passes through MBBR for reduction in BOD/COD. Most of the MBBR plants are provided with vertically or horizontally mounted rectangular mesh sieves or cylindrical bar sieves. Biofilm carriers are made up of high density (0.95 g/cm3) polyethylene. These are normally shaped as small cylinders with a cross inside and fin outside. The standard filling of carrier is below 70% with a maximum specific area not more than 465 m2/m3.
Generally, design load for COD‐BOD removal is 20 g COD / m2d. Smaller carriers need smaller reactor volume at a given loading rate (as g/m2d) when the carrier filling is same. HRT of the reactor is about 3 – 4 hours for effective BOD and nitrogen removal. It is advisable to use MBBR in combination with a septic tank or a pre‐coagulation step as a pre‐treatment unit, depending on the local conditions and input characteristics. It is a very robust and compact alternative for secondary treatment of municipal wastewater, having removal efficiency for BOD 90 – 95% (low rate) and that of 75 – 80% for high rate. Average nitrogen removal is about 85%. There is no need for sludge recirculation. Phosphorus and faecal coli form reduction is feasible with additional passive (non‐mechanical) or active (mechanical) system components.
MBBR Operation and Maintenance
A constantly operating MBBR does not require backwashing or return sludge flows. It has minimal headloss. Coarse bubble aeration in the aeration zone in the wastewater treatment tank provides ease of operation at low-cost. Agitation continuously moves the carrier elements over the surface of the screen thus preventing clogging. Maintenance of MBBR system includes screening, influent equalization, clarifier system, sludge handling and integrated control system. There is no need to maintain f/M ratio as there is self‐maintenance of an optimum level of productive biofilm. Skilled labor is required for routine monitoring and operations of pumps and blowers.
