Geothermal aquifers offer green potential but quality checks required

The aquifer thermal energy storage (ATES) system, which uses geothermal heat as a renewable energy source, is one of the solutions to reducing fuel consumption and carbon dioxide emission. This system stores heat underground in aquifers, using groundwater as a heat medium. The heat is then extracted as needed according to the season to efficiently heat and cool buildings.

Its use is mainly expanding in Europe, and its widespread introduction is expected in Japan. However, regular inspection is required to utilize these systems without faults.

This fact became evident when a research group led by Specially Appointed Professor Harue Masuda at the Osaka Metropolitan University Urban Resilience Research Center identified clogging that occurred in the plumbing pipe of an ATES well at a facility in Osaka. The findings are published in Geothermics.

In their findings, iron oxyhydroxide precipitation occurred after a vent was accidentally left open, allowing for air to enter the geothermal wells through plumbing pipes.

In turn, an oxygen-rich environment formed and iron oxyhydroxide spread through the piping, causing a clog, leak, and subsequent mixing of groundwater between two aquifers at different depths of each well. Fortunately, natural microbial activity resolved the clog and restored the groundwater.

Observation of this chain of events revealed that it is crucial to evaluate the water quality before the well is put into operation, and to continuously monitor for long-term use of the ATES system.

“The results of this research show that geochemical analysis of groundwater, which has not been emphasized in the engineering field until now, is effective and essential for the stable, widespread use of the ATES system,” stated Professor Masuda.

“We believe that by proposing a method for monitoring water quality as a guideline, we can establish the ATES system as a technology that can be used for the long term.”