The role of carbon storage in biological phosphate removal from wastewater
Creators: name: Comeau, Yves
Publisher: name: University of British Columbia
Year: 2010

description: The objective of this research was to define the importance and role of carbon storage in biological excess phosphorus (bio-P) removal. For that purpose, a sensitive GC technique was developed for poly-β-hydroxybutyrate (PHB) quantification. This technique also allowed the determination of poly-β-hydroxyvalerate (PHV). Both PHB and PHV are referred to as poly-β-hydroxyalkanoates (PHA). Characterization of bio-P sludges obtained from an experimental pilot plant was performed in a number of batch experiments. The effect of anaerobic substrate addition was investigated with the following compounds: formate, acetate, propionate, butyrate, iso-butyrate, valerate, iso-valerate, hexanoate, lactate, β-hydroxybutyrate, succinate, citrate, glucose, glycine and ethanol. In almost all cases, a direct relationship was observed between phosphate (Pi) release/uptake and PHA storage/consumption. These observations supported the concept that anaerobic polyP degradation was used for PHA storage, and that aerobic PHA consumption was used for polyP storage. It was also shown that nitrate, but not nitrite, could be used for Pi uptake and PHA consumption. For the sludge used in this research, acetate and propionate were found to be the two most favorable substrates to induce anaerobic PHA storage. Other substrates also triggered such storage, but at slower rates. The respective proportions of PHB and PHV storage indicated that, in general, substrates composed of an even number of carbons (e.g. acetate, butyrate, β-hydroxybutyrate) favored PHB formation, - whereas substrates composed of an odd number of carbons (e.g. propionate, valerate, lactate) favored PHV formation. The response of the pilot plant sludge to the anaerobic addition of toxicants (2,4-DNP, high pH, low pH, cyanide, fluoride, CO₂, H₂S) was also tested to help postulate biochemical mechanisms for bio-P removal. Anaerobic Pi release was significantly stimulated by the addition of 2,4-DNP, a high pH or cyanide; in these cases, however, minimal PHA storage was observed. It was proposed that polyP degradation could be regulated by a pH-gradient sensitive enzyme that could be used to expel protons, which, in turn, would assist bio-P bacteria in maintaining a constant proton motive force. Molar ratios calculated between metallic cations and Pi, indicated that potassium, magnesium and calcium were probably co-transported with Pi both for export and import into bio-P bacteria. At lab-scale, four sequencing batch reactors (SBR) were operated in parallel to develop bio-P sludges acclimated to different levels of acetate addition. PHA were also quantified in bio-P sludges taken from an experimental pilot plant at UBC over a five months period, and from the Kelowna full-scale treatment plant on two consecutive days. These continuous systems confirmed the role of PHA in bio-P removal. From the results obtained, a biochemical model was proposed to describe the activity of bio-P bacteria under anaerobic, anoxic and aerobic conditions. A summary of microbial activity in a bio-P biomass was presented. This research indicated that carbon storage as PHA played a central role in explaining bio-P removal mechanisms. It was proposed that to maximize bio-P removal, it is important to maximize anaerobic PHA storage by maximizing the addition of certain simple substrates and minimizing the addition of electron acceptors, such as nitrate or oxygen, into the anaerobic zone of a bio-P process.