The combination of aquifer thermal energy storage (ATES) and enhanced natural attenuation (ENA) appears attractive, as such integration between groundwater treatment and sustainable energy technology provides a promising solution for redevelopment of urban areas in terms of energy and environment. However, the concept currently is relatively far from mature applications, also suffering from lack of understanding on basic biogeochemical processes in aquifer under ATES-ENA conditions. Therefore, efforts are required for the investigation of these processes as a base for further assessing the feasibility of the combination in practice. The research regarding to this matter should then focus on finding the essential process factors involved, revealing possible drawbacks, and providing better understanding to design alternative options on better operation of the combined system. This thesis study aims to generate a more fundamental understanding of these processes and make use of laboratory experiments, modeling and conduct a small technological bench pilot test.