The activated sludge simulator system
The system was operated under conventional conditions for 36 days to attain stable operation before switching to FFO mode, during which the two aeration columns were operated at different hydraulic retention times (HRT), return sludge rates and MLSS concentrations, resulting in relatively high and low F/M ratios. The simulator system was operated in an air-conditioned laboratory at the temperature of 25 ± 1 °C.