Contrasting the Benefits of Primary Clarification versus Prefermentation in Activated Sludge Biological Nutrient Removal Systems

Abstract

The potential benefits prefermentation can provide to biological nutrient removal are measured and compared to the costs of excess oxygen consumption and sludge production incurred by an activated sludge system that utilizes prefermentation, instead of primary clarification. Prefermentation was found to produce superior performance in regards to enhanced biological phosphorus removal. A lower soluble orthophosphorus effluent value ͓3.2 mg/ L for the prefermented activated sludge ͑PAS͒ train versus 4.6 mg/ L for the control train with primary clarification ͑PCAS͔͒ and a higher percent phosphorus ͑% P͒ content of the biomass ͑9.0% for the PAS train versus 7.8% for the PCAS train͒ were both found to be statistically significant ͑P values of 4.26ϫ 10 −5 and 0.0082, respectively͒. In addition statistically significant improvements in denitrification rates and reduced observed yields were observed due to prefermentation. However statistically significant increases in solids inventory and in particular oxygen uptake rates offset these improvements. Waste activated sludge production was slightly higher in the PAS train but was not found to be statistically significant.

The effect of flow equalisation and prefermentation on the sludge production and sludge characteristics in a BNR plant

“…COD (RBCOD) and in particular the VFA fraction of the RBCOD has been established in several studies (Brinch et al 1994;Gonç alves et al 1994;Pitman 1999). Prefermentation has proved to be a good option for the production of VFA by using wastewater's own internal carbon sources, but recent studies have reported that prefermentation significantly increases the oxygen requirements (McCue et al 2006).…”