Effects of anaerobic HRT and VFA loading on the kinetics and stoichiometry of enhanced biological phosphorus removal
Erik R. Coats, Brent Deyo, Nicole Brower, Cynthia K. Brinkman
Abstract
Abstract Enhanced biological phosphorus removal (EBPR) can recover significant quantities of wastewater phosphorus. However, this resource recovery process realizes limited use largely due to process stability concerns. The research evaluated the effects of anaerobic HRT (τ AN ) and VFA concentration—critical operational parameters that can be externally controlled—on EBPR performance. Evaluated alone, τ AN (1–4 h) exhibited no statistical effect on effluent phosphorus. However, PHA increased with VFA loading and biomass accumulated more phosphorus. Regarding resiliency, under increasing VFA loads PAOs hydrolyzed more phosphorus to uptake/catabolize VFAs; moreover, PHA synthesis normalized to VFA loading increased with τ AN , suggesting fermentation. Kinetically, PAOs exhibited a Monod‐like relationships for qPHA AN and qVFA AN as a function of anaerobic P release; additionally, qP AE exhibited a Monod‐like relationship with end‐anaerobic PHA concentration. A culminating analysis affirmed the relationship between enhanced aerobic P uptake, and net P removal, with a parameter (phosphorus removal propensity factor) that combines influent VFA concentration with τ AN . Practitioner points Evaluated alone τ AN exhibits no statistical effect on effluent phosphorus in an EBPR configuration. Increased PHA synthesis, associated with increased VFAs and/or extended τ AN, enhances aerobic phosphorus removal. PHA synthesis normalized to VFA loading increased with τ AN , suggesting fermentation in the EBPR anaerobic zone. Aerobic phosphorus uptake increases linearly with anaerobic phosphorus release, with the slope exceeding unity. Increased VFAs can be substituted for shorter anaerobic HRTs, and vice versa, to enhance EBPR performance.