Cultivation of hydrocarbon-tolerant microalgae in flowback wastewaters produced during hydrofracking of impermeable rocks

Abstract

Huge amounts of Wastewaters (WWs) are produced yearly by the hydrofracking of impermeable rock formations for the extraction of oil or natural gas. Flowback Wastewaters (FWs) are characterized by high contents of inorganic contaminants and hydrocarbons thus representing a relevant threat for the environment. In this work three hydrocarbon-tolerant microalgae have been cultivated in flowback water generated during hydraulic fracturing to investigate their growth kinetics. All three strains could grow in FWs irrespective of the presence of oil hydrocarbons. Biomass productivity varied significantly among the strains. Ochromonas danica achieved a specific growth rate equal to 0.386 day-1 during the exponential phase and a maximum biomass productivity equal to 39 mg L-1 day-1 after 11 days of batch cultivation. Scenedesmus dimorphus was capable to grow in the FWs by achieving a biomass concentration equal to 0.5 g L-1 after about 25 days of cultivation. On the contrary, Prototheca zopfii was strongly affected by the contaminants of FWs. Ultimately, this study demonstrated that specific strains of microalgae could thrive in FWs and thus represent suitable candidates to future research activity aimed to verify the possibility to bio-remediate these harmful WWs.