The secret to achieving reliable biological phosphorus removal

Abstract

The enhanced biological phosphorus removal (bio-P) activated sludge process has a reputation for variable performance. A significant factor contributing to variability in bio-P was found to be related to microbial population dynamics involving the competitive growth of polyphosphate accumulating organisms (PAOs) and glycogen accumulating organisms (GAOs). It was found that the key factor in their competitive growth was the specific type of VFA in the influent to the bioreactor. The PAOs seem to have a competitive advantage to use propionate, whereas the GAOs have a competitive advantage to use acetate. Therefore, the secret to achieving reliable biological phosphorus removal was to ensure an adequate supply of propionate, or an alternative substrate such as molasses that can be readily fermented to propionate.When Noosa WWTP was commissioned in Nov 1997, and for several years afterwards, the bio-P performance was found to be variable. This paper outlines the findings of the research and optimisation program that was carried out, which identified the cause of the variability in bio-P and subsequently lead to implementation of an improved operating strategy. The recent long-term results demonstrate that reliable bio-P can be achieved in full-scale wastewater treatment plants without dosing metal salts. The effluent total phosphorus has been maintained below 0.5 mg/L since Jul 2001 and the 50 percentile result for the last 12 months was 0.2 mg/L.

Research Advances and Challenges in the Microbiology of Enhanced Biological Phosphorus Removal—A Critical Review

“…Since the findings of Cech and Hartman (1993) concerning the G-bacteria, a major focus of EBPR microbiological research has been competition between PAOs and GAOs. While some operational parameters are known to cause upset and deterioration of EBPR (Scruggs et al, 2003;Stephens and Stensel, 1998;Thomas et al, 2003), GAO proliferation has been blamed primarily for impairment of the EBPR process (Thomas, 2008;Vaboliene and Brazenaite, 2009). Thus, understanding the mechanisms of how PAOs and GAOs compete and the circumstances that favor GAO growth have become increasingly important.…”

“…A strategy of alternating feed between acetate and propionate has been used in a number laboratory studies to obtain highly enriched PAO cultures (Saunders et al, 2007;Zhang et al, 2007;Zhou et al, 2008). Based on chemical measurements, Thomas (2008) reported increased stability of a full-scale plant in Australia when an adequate supply of propionate relative to acetate was provided. However, this strategy has been contradicted by many studies of full-scale EBPR plants.…”

Enhanced biological phosphorus removal and its modeling for the activated sludge and membrane bioreactor processes

“…Thomas (2008) The COD must have a sufficient portion of VFAs. Increasing pH could give an advantage to PAOs, while alkaline conditions inhibited GAO proliferation without affecting PAO metabolism.…”

Anaerobic Transformations of Wastewater Organic Matter in Sewer Systems

“…VFAs and in particular acetic acid has long been regarded crucial for successful operation of enhanced biological phosphorus removal in WWTPs as they are key substrates for several phosphorus accumulating organisms (PAO). In addition, recent investigations have shown that the presence of propionic acid may be important for PAOs to gain a competitive advantage over glycogen accumulating organisms (GAOs) (Thomas, 2008). Figure 4 shows total VFA concentrations, measured during the 9 experiments in reactor R6, where 48 hours of anaerobic conditions were maintained.…”