Temperature-driven dynamics in prokaryotic and eukaryotic communities of an aerobic granular sludge lab-scale reactor

Faecal sludge from on-site sanitation systems often enters centralised wastewater treatment with minimal pre-processing, creating operational challenges. Aerobic granular sludge (AGS) offers a promising solution for co-treating domestic wastewater and faecal sludge, yet its performance under elevated temperatures remains underexplored. This study evaluated microbial succession and process stability in two lab-scale sequencing batch reactors (2.9 L) treating synthetic municipal wastewater with 4% v/v synthetic faecal sludge at 20 °C (AGS_20) and 30 °C (AGS_30). Chemical oxygen demand (COD) uptake was faster at 30 °C, but both systems achieved comparable removal of organic matter, nitrogen, and phosphorus. Phosphorus removal remained consistently high due to PAO enrichment, while nitrogen pathways were more dependent on operational stability than temperature. Prokaryotic communities converged toward specialised taxa, with Candidatus Competibacter dominating across samples, whereas Accumulibacter and Dechloromonas were more abundant in AGS_20. In contrast, AGS_30 showed fewer stable communities, with episodic dominance of Kouleothrix and Aeromonas. Eukaryotic assemblages acted as ecological drivers, with amoebae promoting granule compaction at 20 °C and ciliates regulating biomass at 30 °C. Fungal enrichment at higher temperatures further contributed to the degradation of organic matter and to cross-kingdom interactions. AGS consortia proved resilient, consistently removing nutrients under faecal sludge co-treatment, while bacterial and eukaryotic communities jointly reinforced stability across thermal regimes.