Influence of Microbial Processes on the Operational Reliability in a Geothermal Heat Store – Results of Long-term Monitoring at a Full Scale Plant and First Studies in a Bypass System

Abstract This paper describes microbial metabolic processes that are considered to be relevant for the technical reliability of a geothermal heat store. The study reports on changes of the microbial community composition in geothermal well fluids of different temperatures and after plant downtimes monitored by genetic fingerprinting. Stagnant conditions favored the enrichment of bacteria, sulfate reducers (SRB), and sulfur oxidizers (SOB) in the well. Furthermore higher concentrations of DOC, SO 4 2- , H 2 S, and H 2 were detected in the first fluids produced after plant downtime. The increased abundance of SOB indicated oxygen ingress during plant downtime. The interaction of SRB and SOB might have further enhanced corrosion and scaling processes. A mobile bypass system installed at the site will help to understand the processes occurring in the well and to study biofilm formation and corrosion rates at different temperatures.