Kenya is actively developing its geothermal resources, particularly in regions like the Menengai Geothermal Project in Nakuru. Historically, direct uses of geothermal heat in Kenya date back decades, with local settlers in Eburru using it for drying pyrethrum, and communities in Eburru, Suswa, and Narok condensing steam from natural fumaroles for domestic purposes.
More recently, the Geothermal Development Company (GDC) has championed the direct use of geothermal energy. Oserian Development Company, for instance, has utilised geothermally heated water for rose flower greenhouses and even enriched CO2 levels in the greenhouses to enhance plant growth. At the Menengai project, GDC has rolled out five pilot direct-use projects, showcasing the versatility of this resource for applications such as milk pasteurisation, aquaculture ponds, greenhouses for horticulture (like capsicum, tomatoes, and kales), laundromats, and grain drying. These projects often leverage heat from “low enthalpy wells,” which are typically unsuitable for large-scale electricity generation, thereby improving the overall economics of geothermal development. Another notable example of utilisation in Kenya is the Olkaria Geothermal Spa, operated by KenGen, which harnesses warm geothermal water for therapeutic and recreational purposes.
The Challenge of “Waste” Brine
While geothermal energy is celebrated as a clean and sustainable resource, the extraction and utilisation of geothermal fluids inevitably generate liquid and solid by-products, collectively termed “geothermal waste.” The sheer volume of brine produced can be substantial. For example, in desalination processes, approximately 1.5 litres of concentrated brine are generated for every litre of fresh water produced, leading to billions of litres daily globally. Similarly, major geothermal fields, such as the Salton Sea in California, produce over 120 million metric tons of brine annually.
In Kenya, operators like KenGen in Olkaria actively reinject cooled brine back into the subsurface reservoirs. This is a crucial practice for maintaining reservoir pressure and preventing environmental contamination. Historically, much of this post-production brine was simply reinjected underground without extracting any valuable minerals it might contain. However, due to the immense quantities of brine produced, even with reinjection, the volume remains significant, often leading to large quantities of what is effectively a waste product on the surface or requiring extensive management.
The complex chemistry of geothermal brine presents significant operational and environmental challenges:
- Scaling and Corrosion: As the hot brine cools and pressure changes during energy extraction, dissolved minerals like silica, calcium carbonate, and various metal salts can precipitate out, forming tenacious deposits known as “scaling.” This scaling clogs pipes and equipment, reducing efficiency, increasing maintenance costs, and potentially leading to plant shutdowns. The low pH and presence of dissolved gases like carbon dioxide and hydrogen sulphide also contribute to the corrosivity of the brine, degrading equipment and well casings.
- Environmental Contamination: Improper disposal of brines can contaminate surface and groundwater resources, harm aquatic ecosystems, and render water unsuitable for drinking or irrigation due to high salinity and heavy metal content.
- Air Emissions: While generally lower than fossil fuels, geothermal operations, particularly open-loop systems, can release non-condensable gases (NCGs) such as hydrogen sulphide (H2S), carbon dioxide (CO2), ammonia, methane, and radon into the atmosphere. Hydrogen sulphide, with its characteristic “rotten egg” smell, can contribute to acid rain and respiratory issues.
- Water Consumption: Geothermal power plants, especially those with cooling towers, can consume substantial amounts of water, potentially creating conflicts in water-scarce regions.
- Land Use and Subsidence: Although geothermal plants have a relatively small land footprint, the removal of large volumes of water from reservoirs can sometimes lead to land subsidence, where the ground surface sinks.
- Induced Seismicity: Fluid injection and pressure changes within the subsurface, particularly in Enhanced Geothermal Systems (EGS), can sometimes induce small earthquakes.
Brine Utilisation
The paradigm is shifting from viewing geothermal brine as a waste product to recognising it as a valuable resource. This transformation is driven by innovative management strategies and emerging technologies aimed at maximising resource utilisation and minimising environmental impact.
- Reinjection: The most fundamental and crucial management strategy is the reinjection of cooled brine back into the subsurface reservoir. This practice is vital for preventing surface and groundwater contamination, maintaining reservoir pressure, and ensuring the long-term sustainability and replenishment of the geothermal resource.
- Brine Treatment: Advanced treatment processes are employed to manage harmful components and prevent operational issues. Technologies like the crystalliser/clarifier process and pH modification (e.g., adding hydrochloric acid) are used to prevent silica scaling, either by forcing minerals to remain in solution or by precipitating them as manageable sludge.
- Critical Mineral Recovery (Brine Valorisation): This is perhaps the most transformative approach. Geothermal brines are increasingly recognised as a significant and sustainable source of critical minerals, creating an opportunity for “dual-purpose” operations that combine energy production with valuable material recovery.
- Lithium Extraction: Geothermal brines, particularly those from regions like California’s Salton Sea, are estimated to hold vast quantities of lithium, a crucial component for batteries. Direct Lithium Extraction (DLE) technologies offer substantial environmental advantages over conventional mining, including no new land use, minimal water consumption (operating in closed-loop systems), lower carbon footprints, and faster time-to-market. Various DLE technologies are being developed, including adsorption, ion exchange, solvent extraction, and membrane separation.
- Other Valuable Minerals: Beyond lithium, brines can yield silica (which also helps mitigate scaling), zinc, manganese, rare earth elements, strontium, and even precious metals like silver and gold.
- CO2 Co-injection: An innovative approach involves injecting captured CO2 along with geothermal brine into rock formations. This not only sequesters carbon by forming stable carbonate minerals but also acts as a natural anti-scalant, preventing silica precipitation and improving operational efficiency.
- Closed-Loop Systems: The adoption of closed-loop systems in geothermal power plants minimises the exposure of gases and fluids to the atmosphere, significantly reducing air emissions and water consumption compared to open-loop systems.
- Cascading Use: This principle optimises the economic value of geothermal heat. Higher-temperature heat is first used for power generation, and the residual, lower-temperature heat from the cooled brine is then sequentially cascaded to direct-use applications like space heating, agriculture, and industrial processes. This transforms “waste heat” into valuable energy streams.
Global Examples of Brine Utilisation
Across the globe, various projects demonstrate the evolving utility of geothermal brine:
- United States: The Salton Sea region in California is a prime example, generating 248 megawatts of baseload power from seven plants, while simultaneously being a vast domestic source of lithium, zinc, and manganese. Boise, Idaho, successfully operates four geothermal district heating systems, serving 366 buildings, including the Idaho State Capitol Building. Chena Hot Springs, Alaska, uses binary power plant technology to generate electricity from geothermal fluids below boiling point, and also provides heating for outdoor baths, swimming pools, and refrigeration for an ice museum. Klamath Falls, Oregon, employs geothermal energy for district heating and even for snow melting on roads and sidewalks. Geothermal heat is also used for aquaculture (e.g., alligators in Idaho/Colorado, tilapia/catfish in Salton Sea/Idaho) and food dehydration (e.g., onions and garlic in Empire, Nevada).
- Iceland: A global leader, Iceland meets approximately 90% of its central heating needs with geothermal energy. Its geothermal power plants contribute significantly to the national electricity grid. The renowned Blue Lagoon is a testament to balneology, using geothermal water for therapeutic bathing. Geothermal energy is also used for salt production, heating seawater for evaporation and drying salt flakes, and holds significant potential for green hydrogen production.
- New Zealand: With a long history of geothermal power generation (e.g., Wairakei since 1958), New Zealand has actively pursued mineral extraction research through programs like “From Waste to Wealth,” focusing on recovering valuable minerals such as silica, lithium, boron, rubidium, and caesium from geothermal brines.
- Indonesia: Research has explored using geothermal brine for milk pasteurisation and developing binary cycle power plants to recover waste heat from conventional geothermal operations. Geothermal energy is also applied for agricultural drying of various products like chilli, corn, vanilla, copra, and wood.
These global examples underscore a clear trend: geothermal brine is no longer just a source of heat, but a multi-faceted resource capable of driving sustainable development, supporting critical mineral supply chains, and contributing to a circular economy. The ongoing innovation and strategic investments in this field promise to unlock its full potential for a cleaner, more resilient future.
