A modified method to determine biomass concentration as COD in pure cultures and in activated sludge systems

A simple technique to determine biomass concentration as chemical oxygen demand (COD) was developed as an alternative to the standard volatile suspended solid (VSS) method. The proposed technique for biomass measurement as COD is based on the determination of the biomass COD (COD B ) as the difference between total COD (COD T ) and the soluble COD (COD S ) of the sample. The obtained results show that this technique was quicker and simpler than the traditional VSS method. The validity of the proposed methods was tested with pure cultures of a filamentous micro-organisms (Sphaerotilus natans), a floc-forming bacteria and activated sludges. The method was also used for estimating the conversion factor (f CV ) from VSS to COD units. A modification of the standard VSS technique was also proposed using two membranes in the filtration device; this technique allowed the biomass determination in 1 μm size bacteria cultures that cannot be detected by the standard VSS method because cells are not retained by the 1.5 μm diameter pore glass-fibre filter.