InterPore2026

Characterization of NAPL biodegradation by microfluidic imaging and spectral induced polarization (SIP) measurements

22 May 2026, 11:50

15m

Oral Presentation (MS02) Environmental Porous Media: Water, Agriculture, and Remediation MS02

Speaker

Dr Shuo Yang (Univ. Rennes, CNRS, Géosciences Rennes, UMR6118, 35042 Rennes, France)

Description

One of the dominant classes of subsurface pollutants in soils and aquifers is that of non-aqueous phase liquids (NAPL), and in particular petroleum products, which arise from leaks during petroleum production and storage. In situ bioremediation has emerged as a preferred strategy for treating such hydrocarbon contamination, owing to its sustainability and cost-effectiveness[1]. Compared with direct sampling approaches, spectral induced polarization (SIP) has shown strong potential for non-invasive monitoring of hydrocarbon biodegradation, on the field[2] and in column experiments[3]. However, the opacity of subsurface materials prevents observation of the biodegradation processes within them at a sufficiently small scale to provide a mechanistic explanation of the SIP response[4]. Microfluidic technology enables the observation of bio-physico-chemical processes at microscale[5], making it a promising solution to this challenge.

In this study, we present, for the first time, an integrated microfluidic platform that combines fluorescent imaging with spectral induced polarization (SIP) measurements to investigate biodegradation processes at the microscale. Platinum electrodes were deposited onto glass slides using metal deposition techniques. Then a microchannel featuring a dead-end structure was fabricated with NOA adhesive (using a silicon wafer mold) on the glass slides. First, toluene was trapped within the dead-end structure by displacement with culture medium. Rhodococcus wratislaviensis (RW) bacteria were then introduced and fresh culture medium without carbon sources was continuously circulated to supply oxygen, while the biodegradation process was monitored in situ using fluorescence microscopy. Simultaneously, a sinusoidal electrical current was injected through the current electrodes, and the resulting impedance amplitude and phase shift were recorded through the potential electrodes, enabling time-resolved SIP pore-scale characterization of the biodegradation process. For comparison, two control groups: one without medium circulation (with reaction and diffusion, labeled Case-RW-noflow); one without bacteria (with diffusion and advection, labelled Case-noRW-flow), and Case-RW-flow were collected.

Microscopic imaging shows that bacteria don't penetrate directly into toluene as toluene is toxic to them, but they can consume the dissolved toluene in the liquid phase (Solubility: 0.53 g/L). The toluene volume decreases linearly with time in three cases, with Case-RW-flow exhibiting the highest decrease rate and the largest toluene dissolution flux across the interface. This behavior arises from the combined advection and biodegradation, which persistently refresh the dissolved toluene’s concentration near the interface, thereby accelerating toluene dissolution. Based on the toluene consumption mechanisms, theoretical models were derived from diffusion–reaction equations for the three cases, accounting for their distinct boundary conditions. Analytical solutions accurately predict the experimental results. Next, particle-tracking analysis was employed to characterize bacterial motility near the toluene interface. The results indicate that bacteria gradually migrate toward the interface by crawling along the glass surface. Finally, SIP measurements reveal a pronounced decrease in impedance magnitude and phase shift at high frequencies (10²–10⁴ Hz) in Case-RW-flow compared to Case-noRW-flow. This is primarily attributed to microscale interfacial polarization, including Maxwell–Wagner–type polarization associated with bacteria membranes, and enhanced bulk conductivity resulting from microbial metabolic activity. These findings provide a basis for developing a quantitative model that explicitly links SIP signatures to the bio-physico-chemical processes governing hydrocarbon biodegradation.