Nitrification Potential Removal in an Autotrophic Membrane Bioreactor

Membrane bioreactor (MBR) process has now become an attractive option for the treatment and reuse of industrial and municipal wastewaters, as evidenced by their constantly rising numbers and capacity. However a good water effluent quality hides a very complex biological system involving particulate and soluble components. The efficiency of this system is mainly dependent on the nature of the bacterial communities in the MBR. For many decades the most common factor used to express all parameters needed for describing the biological reaction rate was the volatile suspended solids concentration (VSS). Different reaction rates’ data, expressed in terms of mgN g-1MVS h-1 are reported in literature. However, it is quite obvious that the VSS measurement is not an adequate indicator of the active biomass. Indeed it contains, besides active microorganisms, biodegradable and inert particulate substrate as well as the residue of bacterial death and lyses. This was perhaps the major cause of the reported nitrification rates discrepancies between the researchers. The idea in our study was to find a new way of expressing the nitrification potential through a new standard unit which is mgN gCOD-1biomass h-1. The challenge was then how to find a new and easy method to reach the active biomass in the membrane bioreactor regardless of the operating conditions. Four runs were conducted under different conditions; the identification of active biomass was done using the respirometric tools. The nitrification rates obtained were 14.59, 14.5, 21.25 and 18.16 g N gVSS-1h-1, but when expressed in terms of the active biomass we found approximately the same nitrification rate with values of 0.553, 0.551, 0.587 and 0.557 gN/g COD biomass/h respectively.