Stabilization of a geothermal power plant operation by repressing of sulfur bacteria in the cooling water system

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The purpose of this study is to reduce the amount of sulfur scale formation in the cooling water system of a geothermal power plant by repressing sulfur bacteria.At Uenotai geothermal power plant, 10% of hydrogen sulfide derived from production well was oxidized to sulfuric acid, and 2% was converted to elemental sulfur. These changes were mainly occurred in the cooling tower. Many strains of sulfur oxidizing bacteria were isolated from sulfur scale sampled from the cooling tower, the condenser and pipelines. Also, some kind of bacteria was isolated from the river sludge. This river water is used for the cooling water of the power plant. The 16S ribosomal DNA analysis indicates that the sulfur oxidizing bacteria isolated from inside of the power plant are dominant in the equipments and derived from the river. Sulfate reducing bacteria were also isolated from bottoms of the cooling tower and the condenser. In these equipments, microbial sulfur oxidation and reduction occur simultaneously.To minimize the formation of sulfur scale, glutaraldehyde and cationic surfactant (G-50) were added to the cooling water of Uenotai geothermal power plant. About 25% of the scale formation was reduced for one year operation.