Membrane bioreactor

MBR (Membrane Biological Reactor) FOR THE BIOLOGICAL PURIFICATION OF WASTEWATERS

In Italy, the enforcement of Legislative Decree 258/00, assimilating EU Directives 271/91 and 676/91 and the recent Decree issued by the Ministry of the Environment and the Protection of Land and Sea No 185 of 12 June 2003, establishing the technical standards for reuse of waste water, has led to the introduction of more stringent regulatory limits regarding the removal of nutrients from effluents. In particular, the concept of a 'sensitive area', conceived as a receiving body of water exposed to the risk of eutrophication, boosted the need for revamping existing water treatment plants, often characterized solely by compartments for the biological oxidation of organic compounds. 

However, this need for enhancement tends to clash with lack of availability of surface areas for the execution of conventional activated sludge purification processes, encouraging a growing interest on the part of operators in treatments capable of rendering the volumetric characteristics of processes more compact and of optimizing the quality of purified water, at the same time simplifying plant management.

Membrane biological reactors (MBR) derive from the combination of traditional suspended biomass processes with filtration processes on microporous or ultraporous membranes, depending on the nominal size of the pores. The major advantages deriving from this technology are to be found in the possibility of eliminating the sedimentation unit downstream biological compartment and all management and operational constraints related to it.

The replacement of the sedimentation compartment with a membrane filtration compartment involves:

• a considerable reduction in the planimetric layout of the purification system due to both the disappearance of the clarifier and to the increase in the concentration of sludge in the biological reactor;
• the possibility of managing the biological process in a manner totally independent from fluctuations of the hydraulic load (the cell residence time and hydraulic retention time are entirely unrelated);
• the reduction of excess sludge associated with the highest values ?of sludge age;
• the elimination of problems relating to the sedimentation capacity of sludge common in traditional actiated sludge systems.
• the significant improvement of the qualitative characteristics of the effluent compatible with the potential re-use of purified water.

reverse osmosis system for washout water treatment