Biomass granulation in an aerobic:anaerobic-enhanced biological phosphorus removal process in a sequencing batch reactor with varying pH

Abstract

Long-term influences of different steady-state pH conditions on microbial community composition were determined by fluorescence in situ hybridization (FISH) in a laboratory scale reactor configured for enhanced biological phosphorus removal (EBPR). Chemical profiles were consistent with shifts in populations from polyphosphate-accumulating organisms (PAO) to glycogen-accumulating organisms (GAO) when pH fell from pH 7.5 to 7.0 and then to 6.5. While biomass was both dispersed and flocculated at pH 7.5, almost complete granulation occurred gradually after pH was dropped to 7.0, and these granules increased in size as the pH was reduced further to 6.5. Reverting back to pH 7.5 led to granule breakdown and corresponding increases in anaerobic phosphate release. Granules consisted almost entirely of Accumulibacter PAO cells, while putative GAO populations were always present in small numbers. Results suggest that low pH may contribute to granulation under these operational conditions. While chemical profiles suggested the PAO:GAO balance was changing as pH fell, FISH failed to reveal any marked corresponding increase in GAO abundances. Instead, TEM evidence suggested the Accumulibacter PAO phenotype was becoming more like that of a GAO. These data show how metabolically adaptable the Accumulibacter PAO can be under anaerobic:aerobic conditions in being able to cope with marked changes in plant conditions. They suggest that decreases in EBPR capacity may not necessarily reflect shifts in community composition, but in the existing population metabolism.

An Observation on Sludge Granulation in an Enhanced Biological Phosphorus Removal Process

“…This study contributes to the evidence of sludge granule formation in EBPR processes, which is consistent to reports by other researchers (Ahn et al, 2009;Dulekgurgen et al, 2003;Lin et al, 2003;Wu et al, 2010). Ail of the studies observed sludge granulation in a laboratory-scale SBR seeded with flocculated sludge and fed with synthetic wastewater.…”

“…Ail of the studies observed sludge granulation in a laboratory-scale SBR seeded with flocculated sludge and fed with synthetic wastewater. The main carbon source in the synthetic wastewater was contributed by acetate in the study conducted by Lin et al (2003), Ahn et al (2009), and in the present work; Dulekgurgen et al (2003) worked solely on acetate-based; and Wu et al (2010) worked solely on propionate-based. The SBR operated in this study was comparable with the one run by Ahn et al (2009) because both SBRs incorporated a six-blade Rushton turbine for mixing purposes.…”

The effects of carbon/phosphorus ratio on polyphosphate- and glycogen-accumulating organisms in aerobic granular sludge

“…A significant percentage (up to 16 %) of Tetrasphaera was also detected in a laboratoryscale GSBR fed with acetate, but abundance of this putative PAOs progressively decreased to less than 5 % when propionate was used alone or in mixture with acetate (Weissbrodt et al 2013). Ahn et al (2009) detected Tetrasphaera-related PAOs with Actino-658 probe after starting GSBR only, which was inoculated with activated sludge from full-scale WWTP. Those PAOs were rarely seen in subsequent samples, probably due to inability of Actino-658-targeted Tetrasphaera to utilize acetate.…”

“…The settling properties improved, and SVI decreased from 140 ml/g (seeding sludge) to below 30 ml/g on day 171. Ahn et al (2009) showed that dimensions and structure of aerobic granules in a laboratory-scale anaerobic-aerobic GSBR strictly depended on pH value. When pH fell from 7.5 to 6.5, the granules increased in size from 200 to 2000-3000 lm and were regularly spherical with smooth outer surfaces.…”

“…COD/P ratio affects the structure of bacterial communities involved in EBPR; however, majority of studies on PAO-GAO selection have been carried out on flocculent activated sludge as reviewed by Oehmen et al (2007). Very little knowledge is available on the PAO-GAO competition in AGS (de Kreuk and van Loosdrecht 2004;Lemaire et al 2008;Ahn et al 2009;Winkler et al 2011;Weissbrodt et al 2013). Lots of surveys focused on factors that influence granule formation and stability (Lee et al 2010).…”