Geothermal power plant emissions are negligible compared to those of fossil fuel combustion-based power plants. Hydrogen sulfide and mercury are the main potential air pollutants associated with geothermal power generation employing flash or dry steam technologies. Carbon dioxide is present in the steam although its emission is also considered negligible compared to fossil fuel combustion sources.
Minor air emissions of hydrogen sulfide, mercury vapor, and sulfur dioxide may arise as fugitive emissions from the cooling tower if the condensation process involves direct contact of steam with cooling water. The significance of the hydrogen sulfide hazard may vary depending on the location and geological formation particular to the facility.
The presence and concentration of potential air pollutants may vary depending on the characteristics of the geothermal resource. Emissions may occur during well drilling and flow testing activities, and via the open contact condenser / cooling tower systems unless pumped out of the condenser and re-injected into the reservoir along with reject geothermal fluids.
Geothermal technologies do not produce a substantial amount of solid waste. Sulfur, silica, and carbonate precipitates are typically collected from cooling towers, air scrubber systems, turbines, and steam separators.
This sludge may be classified as hazardous depending on the concentration and potential for leaching of silica compounds, chlorides, arsenic, mercury, vanadium, nickel, and other heavy metals.
Spent geothermal fluids are typically re-injected to the host rock formation, resulting in minor effluent volumes involving reject waters. Although geothermal energy projects do not normally generate significant point source emissions during construction and operations, hydrogen sulfide emissions, or other types of emissions, should not result in ambient concentrations above nationally established air quality standards.
Environmental, health, and safety guidelines: Geothermal power generation – World Bank Group