Comparison of Selective Culturing and Biochemical Techniques for Measuring Biological Activity in Geothermal Process Fluids

Abstract

For the past three years, scientists at the Idaho National Engineering and Environmental Laboratory have been conducting studies aimed at determining the presence and influence of bacteria found in geothermal plant cooling water systems. In particular, the efforts have been directed at understanding the conditions that lead to the growth and accumulation of biomass within these systems, reducing the operational and thermal efficiency. Initially, the methods selected were based upon the current practices used by the industry and included the collection of water quality parameters, the measurement of soluble carbon, and the use of selective medial for the determination of the number density of various types of organisms. This data has been collected on a seasonal basis at six different facilities located at the Geysers’ in Northern California. While this data is valuable in establishing biological growth trends in the facilities and providing an initial determination of upset or off-normal conditions, more detailed information about the biological activity is needed to determine what is triggering or sustaining the growth in these facilities in order to develop improved monitoring and treatment techniques. In recent years, new biochemical approaches, based upon the analyses of phospholipid fatty acids and DNA recovered from environmental samples, have been developed and commercialized. These techniques, in addition to allowing the determination of the quantity of biomass, also provide information on the community composition and the nutritional status of the organisms. During the past year, samples collected from the condenser effluents of four of the plants from The Geysers’ were analyzed using these methods and compared with the results obtained from selective culturing techniques. The purpose of this effort was to evaluate the cost-benefit of implementing these techniques for tracking microbial activity in the plant study, in place of the selective culturing analyses that are currently the industry standard.