Performance of IFAS wastewater treatment processes for biological phosphorus removal

Abstract

Integrated fixed film activated sludge (IFAS) is a promising process for the enhancement of nitrification and denitrification in conventional activated sludge systems that need to be upgraded for biological nutrient removal (BNR), particularly when they have space limitations or need modifications that will require large monetary expenses. Several studies have reported successful implementations of IFAS at temperate zone wastewater treatment facilities, typically by placement of fixed film media into aerobic zones. However, nearly all of the implementations have not included enhanced biological phosphorus removal (EBPR) in the upgraded systems. This is possibly because the treatment plants have been operated at low mixed liquor mean cell residence times (MCRTs), and EBPR would wash out of the systems at the low temperatures encountered, making it difficult to maintain EBPR. The primary objective of this study was to investigate the incorporation of EBPR into IFAS systems, and study the interactions between the fixed biomass and the mixed liquor suspended solids with respect to substrate competition and nutrient removal efficiencies. Three pilot-scale UCT/VIP configuration systems were used, one as a control and the other two with Bioweb ® media integrated into some of the anoxic and aerobic reactors. The systems were operated at different MCRTs, and influent COD/TP ratios, and with split influent flows. The experimental results confirmed that EBPR could be incorporated successfully into IFAS systems, but the redistribution of biomass resulting from the integration of fixed film media, and the competition of organic substrate between EBPR and denitrification would affect performances. Also, the integration of fixed film media into the anoxic reactors affected performances differently from media in aerobic reactors.