InterPore2025

Study of biofilm in porous media in low-temperature geothermal energy context: development and remediation by biocide injection

20 May 2025, 12:35

15m

Oral Presentation (MS05) Microbial Dynamics in Porous Media: Advances in Biofilms, Biogeochemistry, and Biotechnology MS05

Speaker

Alexis Vindret (IFPEN)

Description

Geothermal power is a promising technology for producing heat and electricity, supporting global decarbonisation efforts. However, this technology can be affected by several operational problems that reduce both profitability and long-term operability. Among them, the development of biofilms in pipes and porosity of reservoir rocks, known as bioclogging, accounts for almost 15% of injectivity problems(1). To counter the growth and spread of biofilms in geothermal installations, remediation methods involving the injection of biocides are commonly employed. However, these treatments are based on tests conducted under non-representative conditions, resulting in unrationalised concentrations and injection protocols. During treatment, only the effectiveness on clogging can be observed, and the exact bactericidal/bacteriostatic effect is not monitored in situ. This study provides an experimental system and experiments aiming toward a more detailed understanding of this phenomenon under representative conditions.

We elaborated a protocol to study the development of biofilms in porous media and their remediation by the injection of biocides. Flow takes place in anoxic conditions in a cylindrical porous medium with a diameter of 3 cm and a length of 13 cm, constituted of 100 µm Fontainebleau sand, at 30°C and 5 bar. The model bacterial strain, Shewanella oneidensis MR-1, was chosen for its ability to form biofilms and its metabolic versatility. In three experiments, sterile supplemented TS growth medium is injected at 5 mL/h in a pore volume of 32,7±1,6 mL. For the biocide efficiency assay, benzalkonium chloride (ADBAC) is added to a concentration of 100 ppm, followed by a treatment of HClO- 2000 ppm in water. Biofilm development kinetics were monitored by measuring the differential pressure across the porous medium. Biofilm growth and sloughing were estimated by plating and measuring the OD600 of the effluent. A dissolved CO2 probe measures in operando bacterial metabolism, and coupled with metabolites concentrations in the effluent (via HPLC) allowed the estimation of the metabolic activity.

For the three experiments, after a stagnation phase of 24-72 h, a biofilm develops and stabilizes over 96-192 h of injection. Bioclogging was variable, with differential pressure increases of 200-1500 mbar, a bacterial population in the effluent ranging from 108-1010 UFC/mL, along with an increase in OD600 between 0.04 and 1. It is also linked with the consumption of ~95% of lactate/fumarate, and production of succinate/acetate up to ~95% of theoretical stoichiometry. When treated with ADBAC 100 ppm, metabolic activity is reduced by ~95%, bacterial concentration in the effluent is reduced by 100 to 1000-fold over 143 to 190 h and OD600 reaches zero after 70-183 h. However, permeability is not regenerated and remained between 140 and 1100 mbar. HClO- 2000 ppm treatment restored ΔP to 14-17 mbar in 67 hours.

Biofilm in a porous medium was formed and both physical and biochemical characteristics were followed. While ADBAC significantly reduced bacterial viability, bioclogging required a strong oxidising solutions to be eliminated. Future experiments will study the effectiveness of another widely used biocide in geothermal energy, glutaraldehyde, and compare it to ADBAC for a more responsible use in industrial conditions.