What waste is produced as a result of obtaining or using geothermal energy?
Using geothermal energy may cause emissions of gases into the atmosphere. The amount of gases emitted into the atmosphere depends on the technology used within a hydrothermal energy plant. Hydrothermal plants produce geothermal energy.
Geothermal energy is produced by heat energy stored within the Earth (“geo” = Earth, "thermal" = heat). Hydrothermal energy plants reside over or near locations where molten rock heats water that is close to the Earth’s crust. Although the technology used amongst various hydrothermal energy plants varies, most use this hot water to spin a turbine that generates energy.
Hydrothermal plants can have closed-loop or open-loop water systems. Closed-loop systems contain the water and steam that is extracted from the geothermal reservoir within steel casings. Therefore, closed-loop systems do not expose gases that are extracted from the reservoir to the atmosphere. Instead, the gases and water are returned back to the ground after the heat is used for energy.
Open-loop systems do not contain the water and steam as well. As a result, carbon dioxide, methane, boron, hydrogen sulfide, ammonia, and other gases are emitted into the atmosphere. Such emissions may contribute to global warming and/or acid rain.
Geothermal energy generation facilities operate by extracting hot water from the ground. The extracted water can contain large quantities of sulfur, salt, and a myriad of other chemicals. Generally, the system through which this is done also involves pumping the water, after having been utilized for energy generation, back into subterranean containment tanks. This is done to prevent any contamination of the surrounding grounds. Thus far, there have been no reported breaches of these containers, but it remains a possibility.
Additionally, water is required to cool the generators. This water is drawn from a reservoir, put to use as a coolant through which some of it is lost as steam and then finally recycled back into the original reservoir. The water contained in these reservoirs is not clean water, but no less does not contain any additional contaminants. In some cases these reservoirs use processed waste water.
As for atmospheric impacts, if a geothermal facility is using a closed loop system all gasses removed from the ground are returned, rendering no affect on the air. Other facilities release the extracted gas, after processing, directly into the air. This released gas contains a myriad of "not-so-great" substances, particularly sulfur dioxide. Scrubbers can be implemented to filter the expelled gas but this process produces a toxic mixture of water, mercury, nickel, arsenic and other metals. This toxic waste is disposed of at a dedicated waste containment facility.