Effects of fluctuating iron dosage on nitrification in integrated fixed film and conventional activated sludge processes.

An integrated fixed-film activated sludge (IFFAS) process with four media cells is operating in parallel with a conventional activated sludge (CAS) train at Lakeview Wastewater Treatment Plant (Ontario, Canada). During winter 2007, an intensive sampling campaign was conducted to monitor the temporal and spatial variations of the nitrification capacity within the two plug-flow reactors. At the beginning of the six-week study, the CAS train was partially nitrifying, whereas the IFFAS train was nitrifying completely using the first two IFFAS cells only. Within one week, the CAS train lost nitrification because of a drop in solids retention time and pH caused by the onset of iron overdosing. When the IFFAS train received an iron spike, the carriers at the injection point (first cell) became iron-coated and lost 80% of their nitrification capacity. However, this train maintained its total nitrification capacity using the reserve capacity in the three remaining cells.