Hypothesis
Pre-exposing an activated-sludge community to metformin in a chemostat should enrich its degraders and so raise biodegradation of metformin and its transformation product in ready biodegradability tests.
What failed
Fresh sludge removed 15 mg/l metformin and the guanylurea formed from it completely, but after three and nine months in the chemostat removal fell; the single metformin-degrading Aminobacter isolate consumed 15 mg/l within three days on its own, yet its abundance in the community stayed under 1% and did not track the community’s fluctuating degradation capacity.
Broken assumption
A chemostat reproduces the conditions that keep a pollutant-degrading community competent.
Why
The authors conclude the capacity rests on environmental exposure plus conditions that the laboratory chemostat could not reproduce.
From the published paper: Poursat et al. Ecotoxicology and Environmental Safety, 2019. ↗CC BY