Determination of heterotrophic active biomass concentrations in activated sludge systems

The heterotrophic biomass (X_H) was a key parameter in current steady state design and kinetic models for activated sludge systems, however, the parameter usually remained hypothetically within the current simulation procedure due to the lack of suitable and simple measurement method. The batch aerobic digestion method was applied for the determination of X_H concentrations in mixed liquor from aerobic tanks of a full-scale wastewater treatment plant (WWTP) with anaerobic/anoxic/aerobic (AAO) process and a pilot-scale anaerobic/aerobic (AO) process. The measured X_H concentrations were good in repeatability and in close agreement with those theoretical values calculated by the steady state design model, indicating the correctness of models and the experimental method. The percentages of measured X_H in volatile suspended solids in aerobic tanks were about 27.5% and 23.2% for the AAO process with sludge age of 10 days and the AO process with sludge age of 15 days, respectively. Furthermore, the decay rate constants of X_H could also be determined by the aerobic digestion method. Compared with the respirometric method containing external carbon sources, the aerobic digestion method was provided with good precision and accuracy, not inhibited by carbon sources and sludge age, and suitable for the X_H determination of urban WWTPs fed by wastewater with low COD concentrations.