Biogeochemical processes in anoxic saline siliciclastic aquifers induced by Aquifer Thermal Energy Storage between 20°C and 80°C

Aquifer Thermal Energy Storage (ATES) is a promising technology for storing excess energy in urban environments, offering high energy storage capacity with a minimal surface area footprint. Despite its potential to support urban decarbonization efforts, the planning, approval, and implementation of ATES systems in Germany remains limited, partly due to uncertainties regarding long-term performance and environmental impacts within the subsurface. In particular, mineral precipitation and biofilm formation may clog wells and aquifers, thus posing operational challenges.

To assess temperature-dependent biogeochemical processes, sterile and non-sterile water-saturated column and batch experiments are performed at 20°C, 40°C, and 80°C. Natural siliciclastic sediment, derived from an ATES exploration drilling in Berlin, is used in the column experiments, while artificial siliciclastic sediment is applied as analog material in the batch experiments. All experiments are carried out using natural saline groundwater from a potentially ATES-suitable ~200 m deep saline aquifer in Berlin. The column experiments are conducted under an Ar/CO₂ atmosphere and focus on investigating dissolution and precipitation processes, (de-)sorption phenomena, (bio)clogging, microbial activity, and shifts in microbial community composition. The batch experiments examine the change of microbial abundance, activity and community composition, under four distinct gas atmospheres: N₂/CO₂, H₂/CO₂, Ar, and air.

Preliminary microbiological results indicate proliferation and higher microbial activity under anoxic compared to oxic conditions, and at low to moderate temperatures relative to high temperatures. The presence of microorganisms appears to induce changes in iron mineralogy.

The results will support the understanding and mitigation of mechanisms responsible for efficiency loss in ATES systems.