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In this study, a full-scale pilot testing was performed with side-by-side operation of a conventional enhanced biological phosphorus removal (EBPR) process and a side-stream EBPR (S2EBPR) process. A comparison of the performance, activities and population dynamics of key functionally relevant populations between the two configurations were carried out. The results demonstrated that, with the same influent wastewater characteristics, S2EBPR configuration showed more effective and stable orthophosphate (PO4-P) removal performance (up to 94% with average effluent concentration down to 0.1 mg P/L) than conventional EBPR, especially when the mixers in side-stream reactor were operated intermittently. Mass balance analysis illustrated that both denitrification and EBPR performance have been enhanced in S2EBPR configuration through diverting primary effluent to anoxic zone and producing additional carbon (~40%) via fermentation in side-stream reactor. Microbial characterization showed that there was no significant difference in the relative abundances of Ca. Accumulibacter (~5.9%) and Tetrasphaera (~16%) putative polyphosphate-accumulating organisms (PAOs) between the two configurations. However, lower relative abundance of known GAOs was observed in S2EBPR configuration (1.1%) than the conventional one (2.7%). A relatively higher PAO activity and increased degree of dependence on glycolysis pathway than TCA cycle was observed in S2EBPR configuration using P release and uptake batch test. Adequate anaerobic solid retention time (SRT) and conditions that generate continuous and slow feeding/production of volatile fatty acid (VFA) with higher composition percentage of propionate in the side-stream reactor of S2EBPR process likely provide a competitive advantage for PAOs over GAOs.

The Upper Blue Sanitation District (UBSD) (formerly known as Breckenridge Sanitation District) was established in 1966 as a Colorado Special District to provide collection and treatment of wastewater to residents of Breckenridge and the upper Blue River watershed. The district has predicted build-out flows to be 25ML/d (6.6 MGD), leading to an annual average phosphorus limit of 0.03 mg/L. To ensure the technological expertise and operational reliability to meet this limit, the district has set a treatment goal of 0.02 mg/L total phosphorus. Multiple technologies are employed at two major facilities, including: Conventional activated sludge followed by tertiary stage Alum flocculation/sedimentation and mixed media filtration, and A/O Bio-P coupled with ballasted Alum flocculation/sedimentation and dynamic sand bed filtration. Additionally one plant wastes sludge into the other, providing a countercurrent dose of Alum. The district began examining molar chemical feed ratios in 2009.

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