Resumen
The energy available via microbial sulfate reduction was estimated for a Quaternary aquifer in northern Japan that is a candidate site for low temperature aquifer thermal energy storage. In evaluating whether microbial sulfate reduction proceeded or ceased, it was assumed that electron donor/acceptor concentrations were unchanged by temperature increase. The estimated energy availability via microbial sulfate reduction at 9 °C with no thermal disturbance was 37, 51, and 53 kJ·(mol SO42-)-1. The low estimate of 37 kJ·(mol SO42-)-1 was attributed to low concentration of SO42-. Excluding the sampling site with low concentration of electron acceptors, energy availability was estimated 52 and 54 kJ·(mol SO42-)-1 at 20 °C; 54 and 57 kJ·(mol SO42-)-1 at 40 °C; and 57 and 59 kJ·(mol SO42-)-1 at 60 °C. These results indicate that possible energy availability via microbial sulfate reduction at approximately 40?60 °C exceeded the range of available energy (compiled from previous studies) at which sulfate reduction would cease. Thus, microbial sulfate reduction at this site may proceed at approximately 40?60 °C.