In biological wastewater treatment systems, recent research has been focused on reducing the economic costs and increasing the efficiency of wastewater treatment plant design and operation. For this purpose, mathematical models, which can describe diverse and complex biological processes, have been developed. In such models, one of the most important parameters is the microbial concentration. The conventional methods to determine the biomass in wastewater and activated sludge are the measurement of total suspended solids (TSS) and volatile suspended solids (VSS). Such methods do not play any role in the treatment of wastewater. In order to accomplish better results from the mathematical modelling of wastewater treatment processes, it is essential to avoid the overestimation of microbial biomass. A new approach is introduced for the accurate estimation of biomass by measuring the protein content of the activated sludge. Proteins are essential parts of living cells and participate in every biological process. They are readily degraded when cell lysis occurs and easy to extract, purify and analyse. Such characteristics of proteins make them an alternative parameter for microbial concentration. In this study, biomass was determined with both conventional methods, which were mentioned before, and alos through measuring the protein content with the Modified Lowry Method. In order to investigate the relationship between activity and biomass concentration in terms of TSS, VSS and protein content, some starvation experiments were conducted. It was found that the protein fraction of VSS differs under different starvation conditions. The activity was measured as oxygen uptake rate. Results showed that under various conditions the correlation between activity and protein content is the only significant correlation.weiterlesen