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Investigation of Environmental Effects of Geothermal Energy

Kamil B. VARINCA

Yildiz Technical University Environmental Engineering Department Davutpasa Campus, 34220, Istanbul, Türkiye

kvarinca@yidliz.edu.tr

ABSTRACT

Geothermal energy is a clean and sustainable energy source, but its development still has some impact on the environment. Geothermal utilization can cause surface disturbances, physical

effects due to fluid withdrawal, noise, thermal effects and discharge of chemicals as well as affect the communities concerned socially and economically. Geothermal energy, a relatively benign energy source when compared with other energy sources due to reduction in greenhouse gas

emissions, is used for electricity generation and direct utilization. This paper describes the potential environmental impacts associated with geothermal plants. Emissions abatement, water and land-

use, and other aspects are discussed for environmental controls. Keywords: Geothermal energy, environmental impacts.

1 INTRODUCTION

Geothermal energy, as natural steam and hot water, has been exploited for decades to generate

electricity, and both in space heating and industrial processes. The geothermal electrical installed capacity in the world is 7974 MWe (year 2000), and the electrical energy generated is 49.3 billion kWh/year, representing 0.3 % of the world total electrical energy which was 15,342 billion kWh in

2000 [1]. Problems with energy supply and use are related not only to global warming but also to such

environmental concerns as air pollution, acid precipitation, ozone depletion, forest destruction, the emission of radioactive substances, etc. These issues must be taken into consideration simultaneously if humanity is to achieve a bright energy future with minimal environmental

impacts. Much evidence exists that suggests the future will be negatively impacted if humans keep degrading the environment [2].

2 ENVIRONMENTAL IMPACTS

The environmental benefits of geothermal energy are felt locally, regionally and globally.

Geothermal energy can displace power from fossil fuel-powered plants, and thereby help to improve local air quality, mitigate regional effects such as acid rain, and reduce greenhouse gas

emissions globally. Power plants not only emit pollutants as a by-product of power generation, but also may account for further emissions in connection with plant construction, operation, and

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decommissioning. For example, the mining and transport of fuel are themselves energy-intensive activities, with associated emissions and environmental impacts. Geothermal energy compares favorably to traditional power generation on this metric as well. Lifecycle CO2 emissions per unit of

power produced by a geothermal power station are about 2.5% of that for coal plants and about 5.4% of that for natural gas facilities [3].

The main environmental issues involved in geothermal development are: Surface disturbances, Physical effects of fluid withdrawal, Noise, Thermal effects, Chemical pollution,

Biological effects, Protection of natural features.

Environmental effects from renewable energy sources are shown in Table 1. The major environmental effects considered, the rows of the table, are those effects these technologies have on Land, Water, and Air, together with Wastes, Working Fluids and Gases, General Effects, and

Catastrophes. Each major effect is then subdivided. To present the information in a comparative way, each box on the table is occupied by an L (large effect), M (medium effect), S (small effect) or 0 (not applicable).

Table 1 Environmental effects of geothermal energy source [4]

Environmental effects Hot dry

-rocks

Aquifers Environmental effects Hot dry

-rocks

Aquifer

s

Land Air

Land use/sterilization L S Aesthetics M S

Land erosion Acoustic noise S S

Construction S S Wastes working fluids and gases

Maintenance 0 0 Solid 0 0

Seismicity/subsidence S S Liquid M L

Water Gessoes S S

Water levels/flow

patterns/velocity/sediments

S S Industrial 0 0

Drainage S S Sewage 0 0

Salinity changes S S

2.1 Surface Disturbances and Physical effects of fluid withdrawal

Surface disturbances may occur during drilling, but will mostly disappear once drilling is

completed, the drill rigs have been removed, the ponds drained and the landscape reshaped. Surface disturbances caused by excavation, construction and the creation of new roads will accompany most new activities, but the area involved is relatively small. A drillsite usually covers 200–2500 m2 and

can be kept at a minimum by directional drilling of several wells from one site. As the source is normally utilized near the drill site there is no need for long pipelines. Space heating is an exception

to this general rule as the pipelines in this case could be quite long [5]. The weight of the rocks above a reservoir of groundwater, oil or geothermal fluids is borne in

part by the mineral skeleton of the reservoir rock, and in part by fluids in the rock pores. As fluids

are removed, pore pressure is reduced, and the ground tends to subside. Less subsidence is expected with harder reservoir rock. The scale of geothermal fluid extraction is comparable to large

agricultural groundwater withdrawals. A potential for subsidence is associated with geothermal development. Subsidence can be controlled or prevented by the reinjection of spent fluids [1].

Landslides are liable to occur in some places and may set constraints on the sites chosen for

construction. The scenery needs attention, as geothermal fields are often situated in places of outstanding beauty and touristic importance and may also be of historic interest. Fluid withdrawal

can effect changes to surface manifestations, causing hot springs or geysers to disappear or be transformed into fumaroles; the site of this type of activity could even shift to another area.

Untidiness can lead to unacceptable eyesores and it should be a feature of any monitoring program that the sites be inspected by an outside agency. Physical effects are induced by the fluid withdrawal

that accompanies the utilization of geothermal resources. Fluid withdrawal can cause land

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subsidence, lowering of the groundwater table and even induced seismicity. Subsidence takes place when fluid withdrawal exceeds the natural inflow. There is evidence in almost every utilized area, although the magnitude of this phenomenon can vary greatly. The natural seismicity may also be

changed by fluid withdrawal. Reinjection may also induce microseismicity [1, 5].

2.2 Noise

The noise brought on by geothermal utilization consists firstly of drilling noise, which is temporary and rarely exceeds 90 dB (75–90 dB through silencers); this is followed by the noise

from discharging boreholes, which may exceed 120 dB, the pain threshold ranging between 2000 and 4000 Hz. [1, 5].

2.3 Thermal Effects

Heat-thermal effects and even pollution will normally accompany production from geothermal fields. The heat efficiency of power production is low, so a considerable amount of

energy is wasted. Waste water causes problems for the environment. Excess heat emitted in the

form of steam may affect cloud formation and change the weather locally, and waste water piped into streams, rivers, lakes or local ground waters may seriously affect the biology and ecological

system [5].

2.4 Chemical pollution

Chemical pollution in geothermal utilization is a result of the discharge of chemicals into the

atmosphere via steam; the spent liquid may also contain dissolved chemicals of potential harm to the environment. Spray, which constitutes a problem mainly in the testing period, could damage

vegetation in the surrounding area. The main pollutant chemicals in the liquid fraction are hydrogen sulfide (H2S), arsenic (As), boron (B), mercury (Hg) and other heavy metals such as lead (Pb), cadmium (Cd), iron (Fe), zinc (Zn) and manganese (Mn). Lithium (Li) and ammonia (NH3), as well

as aluminum (Al), may also occur in harmful concentrations. Some geothermal fluids are brines, whose excessive salt concentrations can cause direct damage to the environment [5].

Air Pollution

Steam from major geothermal fields has a content of non-condensable gases (CO2 (21 g/kW

h), H2S, NH3, CH4 (0,059 g/kW h), N2 and H2) that ranges from 1.0 to 50 g/kg of steam. CO2 is the major component, but its emission into the atmosphere is well below the figures for natural gas, oil

or coal-fired power stations per kWh generated (Fig. 1) [1, 3]. All known geothermal systems contain aqueous CO2 species in solution, and when a steam phase separates from boiling water, CO2 is the dominant (over 90% by weight) noncondensible gas. In most geothermal systems,

noncondensible gases make up less than 5% by weight of the steam phase [6]. Hydrogen sulfide is the air pollutant of major concern in geothermal development. Its

emissions generally range between 0.5 and 6.8 g/kWh. H2S is oxidised to sulfur dioxide and then to sulfuric acid, and may cause acid rain. However a direct link between H2S emission and acid rain has not been established. Without abatement, the specific emissions of sulfur from geothermal

power plants are about half of those from coal-fired plants (Fig. 2) [1]. Geothermal plants do not emit nitrogen oxides, fossil fuel plants on the contrary exhaust these

toxic chemicals. Geothermal gases in steam may also contain ammonia (NH3), traces of mercury, (Hg), boron vapours (B), hydrocarbons such as methane (CH4), and radon (Rn) [1].

Boron, ammonia, and to a lesser extent mercury, are leached from the atmosphere by rain,

leading to soil and vegetation contamination. Boron, in particular, can have a serious impact on vegetation. These contaminants can also affect surface waters and impact aquatic life. Geothermal

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literature reports that mercury emissions from geothermal power plants range between 45 and 900 micrograms/kWh, and are comparable with mercury emissions from coal-fired power plants. Ammonia is discharged into the atmosphere in concentrations between 57 and 1938 mg/kWh, but

due to atmospheric processes it is dispersed rapidly. Radon (222Rn), a gaseous radioactive isotope naturally present in the Earth’s crust, is contained in the steam and discharged into the atmosphere

in concentrations of 3700–78,000 Becquerel/kWh [1].

Fig. 1. Comparison of carbon dioxide emissions

from geothermal and fossil fuel-fired power

plants [1]

Fig. 2. Comparison of sulfur emissions from geothermal and fossil fuel-fired power plants [1]

Water pollution

Water pollution of rivers and lakes is a potential hazard in power production and the management of spent geothermal fluids. In vapour-dominated reservoirs, most of the pollutants are

found in the vapour state, and the pollution of water bodies is more easily controlled than in water-dominated reservoirs. In the latter waste steam condensate (20% of the steam supply) must be added to the waste water. The water and the condensate generally carry a variety of toxic chemicals

in suspension and solution: arsenic, mercury, lead, zinc, boron and sulfur, together with significant amounts of carbonates, silica, sulfates and chlorides [1].

In water-dominated and in hot water reservoirs, water and steam (if present) are separated at the surface (the steam is used for the generation of electricity), and the volume of water to be disposed of (which may contain large quantities of salts, even above 300 g/kg of extracted fluid)

can be as much as 70 kg/kWh, more than four times the steam supply, and up to 400 kg/kWh in binary cycle plants [1].

2.5 Biological effects

As many geothermal areas are of unique beauty, of historical interest or are tourist attractions, their protection must be considered. Disturbance to the natural state of an area can cause

phenomena such as geysers, hot springs or pools, silica sinter terraces and mud pools, to deteriorate or disappear, along with special thermophilic vegetation such as algal mats, thermophilic plants and bacteria [5].

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2.6 Protection of natural features

Besides the environmental effects discussed here, which are mostly physical, there are also

social and economic effects. These may be considered in a positive or negative light, however,

according to the political viewpoint of the individual, as in the case of any large-scale engineering project. Generally there is a need for more public involvement in such issues as the construction of power plants, in order to resolve controversies, improves plans and takes mitigation measures [5].

3 CONCLUSION

Geothermal energy provides a clean, renewable energy source that could dramatically improve our environment, economy and energy security. Geothermal energy generates far less emissions than fossil fuels and decreases the reliance on imported energy. Today, in most ways,

geothermal energy has come of age; the technology has improved, the economics has become more appealing, and substantial progress has been achieved in reducing environmental impacts.

REFERENCES

[1] Barbier, E. (2002). Geothermal energy technology and current status: an overview . Renewable

and Sustainable Energy Reviews(6), 3-65. [2] Dincer, İ., Hepbasli, A., & Ozgener, L. (2007). Geothermal Energy Resources. In B. L.

Capehart (Ed.), Encyclopedia of Energy Engineering and Technology (pp. 744-752). CRC

Press. [3] Erdogdu, E. (2009). A snapshot of geothermal energy potential and utilization in Turkey.

Renewable and Sustainable Energy Reviews(13), 2535-2543. [4] Laughton, M. A. (Ed.). (1990). Renewable Energy Sources. CRC Press. [5] Kristmannsdottir, H., & Armannsson, H. (2003). Environmental aspects of geothermal energy

utilization. Geothermics(32), 451-461. [6] Renner, J. L., & Reed, M. J. (2007). Geothermal Energy. In D. Y. Goswami, & F. Kreith

(Eds.), Energy Conversion. CRC Press.

BIOGRAPHY

Kamil B. VARINCA (Ms.C.) was born Bayburt (Turkey) in 1981. He works as a research assistant

at Yıldız Technical University Environmental Engineering Department. Varınca received his BSc in Environmental Engineering in 2002 from İstanbul University, İstanbul, Turkey, and his MSc in

Environmental Engineering in 2006 from Yıldız Technical University, İstanbul, Turkey. He is still PhD student on Hazardous Waste Management at Yıldız Technical University Environmental Engineering Department. His main subject areas are Solid and Hazardous Waste Management and

Renewable Energy Mr. Varınca is a member of Chamber of Environmental Engineers (CEE) and Turkish National

Committee on Solid Wastes (TNCSW). He may be contacted at kvarinca@yildiz.edu.tr or kvarinca@gmail.com.