Mass-Transfer-Limited Biodegradation at Low Concentrations—Evidence from Reactive Transport Modeling of Isotope Profiles in a Bench-Scale Aquifer

• DOI: 10.1021/acs.est.0c08566
• Publication Date: 2021-05-10T21:26:44Z
• Authors: Fengchao Sun; Adrian Mellage; Mehdi Gharasoo; Aileen Melsbach; Xin Cao; Ralf Zimmermann; Christian Griebler; Martin Thullner; Olaf A. Cirpka; Martin Elsner
• Keywords: Microcosm; Isotope Analysis; Field-Flow Fractionation

Organic contaminant degradation by suspended bacteria in chemostats has shown that isotope fractionation decreases dramatically when pollutant concentrations fall below the (half-saturation) Monod constant. This masked implies membrane transfer is slow relative to enzyme turnover at μg L–1 substrate levels. Analogous evidence of mass as a bottleneck for biodegradation aquifer settings, where microbes are attached sediment, lacking. A quasi-two-dimensional flow-through sediment microcosm/tank system enabled us study aerobic 2,6-dichlorobenzamide (BAM), while collecting sufficient samples outlet compound-specific analysis. By feeding an anoxic BAM solution through center inlet port and dissolved oxygen (DO) above below, strong transverse concentration cross-gradients DO yielded zones low (μg L–1) steady-state concentrations. We were able simulate profiles ratios plume using reactive transport model accounted mass-transfer limitation into bacterial cells, apparent enrichment factors *ε decreased strongly around 600 μg/L BAM. For organic micropollutants, cell emerges bottleneck, specifically Neglecting this effect interpreting field sites may lead significant underestimation biodegradation.