Effects of cyclic temperature from geothermal heating on BTEX biodegradation in soil

Geothermal heating is a sustainable technique used for heating and cooling of buildings using geothermal heat pumps (GHPs). In this study, a novel idea is proposed to use the excess heat injected into the subsurface during geothermal heating as a temperature source to enhance the bioremediation of pollutants. Since in-situ bioremediation in the subsurface can be slow due to the low subsurface temperatures (10-15 °C), that limit microbial degradation activity, geothermal heating can provide optimum growth temperatures, proliferating microbial growth and enhancing bioremediation sustainably. In this paper, the effect of cyclic temperature fluctuations on a small scale has been studied in BTEX-contaminated soil using B. infantis, M. esteraromaticum and the microbial consortium. To understand the influence of the soil matrix, three different soil types- silty loam, fine sand, and coarse sand were studied in continuous soil column experiments. The results revealed that cyclic temperature of 5 °C to 40 °C (shallow low enthalpy geothermal temperature range) enhanced BTEX biodegradation in all soils but showed more promising results for silty loam soil (> 80%) in comparison to constant aquifer temperature (12 °C). Higher K_bio for all four compounds was observed above 25 °C in cyclic treatment for the three soil types compared to the isothermal 12 °C treatment. The study demonstrated that increased and cyclic temperatures facilitated enhanced microbial metabolism and simultaneous BTEX biodegradation, thereby promoting a cleaner approach to subsurface remediation.