A temporal analysis of microbiome dynamics in activated sewage sludge aerated for 14 days in OECD 301 biodegradation tests

SETAC Europe 2026 -- Microbial consortia in activated sewage sludge undergo temporal succession: early-stage communities are dominated by fast-growing heterotrophs utilising readily available substrates. Later stages shift toward specialised degraders (slower growers) metabolising more recalcitrant compounds. Extended aeration can cause gradual replacement of sensitive taxa by oxygen-tolerant or facultative aerobic species. Temporal changes in enzyme expression (oxygenases, hydrolases, dehydrogenases) reflect shifts in dominant taxa. The microbiome may increase catabolic versatility over time by inducing stress-response genes or co-metabolism pathways as substrates become scarce. Protozoan grazing and phage dynamics exert top-down control, reshaping bacterial composition across time. These interactions maintain diversity by preventing dominance of single bacterial taxa, which stabilises biodegradation functions. Biodegradation potential is not a static measurement, but a function of time-dependent microbial adaptation. Temporal profiling (e.g., by 16S rRNA sequencing) could refine test interpretation and reproducibility. OECD ready biodegradability tests rely on microbial diversity to supply numerous enzymatic pathways to degrade test items.