Effects of substrate composition on the denitrifying polyphosphate-accumulating microbial community in aerobic granular sludge systems, with specific focus on the nitrous oxide (N2O) formation and reduction dynamics.

Aerobic granular sludge (AGS) is a revolutionary biological wastewater treatment system, with significant advantages in comparison to conventional activated sludge. A very interesting feature of AGS is the potential for simultaneous biological nitrogen (N) and phosphorus (P) removal from wastewater. This reaction relies on the specific storage metabolism of denitrifying polyphosphate-accumulating organisms (dPAO). Biological N-removal is however also linked to the formation of the potent greenhouse gas nitrous oxide (N2O). Specifically in AGS, unbalanced denitrification may lead to accumulation of the intermediate N2O, due to the slow consumption of storage polymers by dPAO. The most intensively studied (d)PAO in AGS are Accumulibacter species, but these bacteria have a substrate range limited to the volatile fatty acids (VFA) acetate and propionate. Other putative dPAO using broader substrate ranges have been identified in (conventional) biological wastewater treatment systems, but their role in granulation and N2O formation/reduction dynamics remains unexplored. The main objectives of the current proposal are to investigate (1) the formation of AGS, and (2) the dynamics of P-removal coupled to denitrification and N2O formation/reduction in AGS, in well-defined enrichments of putative dPAO, by applying single and mixed carbon substrates (i.e. VFA, amino acids, glucose). The long-term enrichments are supported by (1) short-term batch experiments to investigate microbial activities, (2) microbial analyses (using quantitative PCR and 16S rRNA gene amplicon sequencing analysis) to monitor the taxonomic composition of the enriched microbial communities, and (3) analyses of gene expression of the key denitrification genes. The knowledge gained will (1) increase our insight in the complex reactions in granular systems, offering opportunities (2) to optimize nutrient cycling in AGS reactors, and (3) to define much-needed strategies to limit and mitigate N2O emissions from these innovative wastewater treatment plants

Keywords:NITROGEN CYCLE, WASTEWATER TREATMENT, SEQUENCING, PHOSPHORUS

Disciplines:(Waste)water treatment processes