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Protozoa grazing of nitrifiers is important process in activated sludge process that leads to decrease of mass of active bacteria. In classical models this process is included in decay processes. Such approach makes modelling of influence of protozoa grazing on nitrifiers impossible. In cases when maximization of nitrifiers growth is important (such as nitrifiers cultivation for bioaugmentation) this simplification becomes major drawback. This paper presents extended version of ASM3 model that includes protozoa grazing as well as results of calibration of protozoa grazing process on experimental data. Additionally new approach for analysis of decay rate is proposed. This approach includes calculation of new parameters: substitute decay rate which is sum of ASM3 base decay rate and excluded predation process.

Sludge drying leads to volatisation and removal of part of nitrogen contained in sludge. Removed nitrogen is usually condensed and recirculated to activated sludge process. It is assumed that mass of volatised nitrogen is equal to mass of soluble nitrogen in sludge. However results obtained from full-scale drying facility shows that mass of volatised nitrogen is 100% higher than mass of soluble nitrogen. It is suspected that nitrogen mineralization occurs due to high temperature maintained in dryers (> 220°C). These results are important as higher mass of nitrogen in condensate makes its removal economically reasonable. This paper shows results of nitrogen mass balance of full-scale drying facility.