The objective of this NSF sponsored research was to provide a controlled comparison of identical continuous flow biological nutrient removal (BNR) processes both with and without prefermentation in order to provide a stronger, more quantitative, technical basis for design engineers to determine the potential benefits of prefermentation to EBPR in treating domestic wastewater. Specifically, this paper focused upon the potential impacts of primary influent prefermentation upon BNR processes treating septic domestic wastewater. This study can be divided into two distinct phases--an initial bench-scale phase which treated septic P-limited (TCOD:TP>40) wastewater and a subsequent pilot-scale phase which treated septic COD-limited (TCOD:TP<40) wastewater. The following conclusions can be drawn from the results obtained to date. Prefermentation increased both RBCOD, SBCOD and VFA content of septic domestic wastewater. Prefermentation resulted in increased biological P removal for a highly septic, non-P limited (TCOD:TP<40:1) wastewater. However, in septic, P-limited (TCOD:TP>40:1) wastewater, changes in net P removal due to prefermentation were suppressed by limited P availability, even though P release and PHA content were affected. Prefermentation increased specific anoxic denitrification rates for both COD and P-limited wastewaters, and in the pilot (COD-limited) study also coincided with greater system N removal.
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.
IntroductionThe ability of a prefermenter to enhance EBPR performance in BNR systems through increased VFA is well established in the literature (WEF, 1998; McCue et al., 2003; McCue et al., 2004). Less well understood are other potential benefits of prefermentation upon BNR performance. This study focused upon changes in wastewater and biokinetic parameters due to prefermentation, including RBCOD, the maximum specific growth rate for autotrophs (μ Amax ), and inert COD fractions. Using these experimentally determined values changes in BNR performance with and without prefermentation were modeled using Biowin by replacing standard default values rather than using included prefermentation modules or other existing prefermentation software. Later results will be compared to existing modules.
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