Use of Non-Condensable Geothermal Gas and Geothermal Seawater to Grow Biomass

Abstract

The geothermal aquifer Blue Lagoon formed roughly four decades ago in a lava field on Reykjanes peninsula in Iceland due to activity of a nearby geothermal power plant. The geothermal fluid of the Blue Lagoon is composed of 2/3 seawater and 1/3 meteoric water (referred to as geothermal fluid), discharged at 240°C from geothermal wells to depths of up to 2000 m. Because of this origin, the BL-geothermal seawater is rich in minerals and salts. Exploitation of the geothermal resources also involve considerable emission of non-condensable gases (NCG), mainly composed of CO2 ( more than 90%) and H2S (~2%). A unique blue-green microalgae species, found in the Blue Lagoon´s ecosystem is being cultivated in a photobioreactor at the Blue Lagoon R&D center, for use as an active ingredient in the Blue Lagoon Iceland skin care products. Being a photosynthetic organism, the microalgae uses light-energy to convert CO2 into biomass. Originally, the algae were fed on bottled pure CO2 in a liquid media of geothermal fluid and commercially available nutrient. Three years ago, with aims towards increased sustainability and lower carbon footprint, the high-purity CO2 was fully substituted by un-purified NCG emitted from the geothermal power plant. In this study, the microalgae´s growth rate was measured in an expanded volume of photobioreactor (3.5 m3) for a continuous time-span of 5 weeks, using only NCG and geothermal fluid as nutrient sources (in contrast to our previous study where commercial nutrient was added and smaller volume of photobioreactor). A steady growth rate was obtained, indicating that biomass could be sustainably produced using only geothermal resources.