The function of key microbial guilds in full-scale wastewater treatment reactors with aerobic granular sludge

Abstract

Aerobic Granular Sludge (AGS) is aggregated microbial growth in the form of granules. The use of AGS technology in wastewater treatment operations can significantly reduce land footprint, energy, and chemical consumption. The goal of the thesis was to study the performance of these aggregates under controlled environmental conditions. Batch activity tests were carried out to study the nitrification, denitrification, and polyphosphate accumulation process in mixed granules (a mixture of all granule sizes) and sieved granules (different granule sizes). It has been observed that performing experiments at relatively high sludge concentrations (15 g/L), and at pH 7.5±0.1, can provide favourable environmental conditions to study the PAO activity in terms of high P-release and P-released to acetate consumed ratio (P-release/C up-take). The PAO activity rate seems to be higher in relatively larger granules (>2mm) while nitrogen removal performance i.e. nitrification and denitrification appears to be more efficient in smaller granules (<2mm). The low P-release/C up-take during the anaerobic phase suggests presence and, in some cases, the dominance of GAO metabolism irrespective of granule sizes. DPAO activity seems to be suppressed or even absent in both the granule sizes. The strong correlation (>0.95) between co-release of cations and PO43−-P during the anaerobic phase suggests the breakage of poly-P reserves in PAOs to take up acetate from the solution.