Growing Microalgae on Hydraulic Fracturing Return Water for the Combined Benefit of Bioremediation and Biodiesel Production

Van Aken, Benoit; Ranjbar Kolachaie, Sibia

Natural gas extraction by hydraulic fracturing requires large amount of water of which about 50% to 90% returns to the surface during gas production, carrying naturally-occurring underground contaminants (salts, heavy metals) and fracturing chemicals (biocides, corrosion inhibitors). When reaching the surface, fracturing return water is frequently stored in open ponds that may leak or overflow and constitute a threat for the environment.

Some microalgae have high salinity tolerance and they are promising candidates for bioremediation of fracturing wastewater. Microalgae have been shown to tolerate and efficiently remove inorganic contaminants, including heavy metals. In addition, certain algal strains accumulate high level of lipid when cultivated in hypersaline media and they are therefore attractive for biodiesel production. However the capability of microalgae to grow in fracturing return water has not been investigated.

The objective of this research is to test the potential of cultivating the hyperhalophilic microalga, Dunaliella Salina, on fracturing return water for the combined benefit of bioremediation and biodiesel production.

In the first experiment, we tested the ability of D. salina to grow on two samples of fracturing return water from natural gas extraction. Different dilutions of return water samples were introduced into 125-mL conical flasks, supplemented with essential algal nutrients, and sterilized. The flasks were then inoculated with pure culture of D. salina and incubated on an orbital shaking under constant lighting. In addition similar experiments were conducted with the same return water samples but without supplemental salts and without sterilization.

Surprisingly, the highest algal growth was recorded in flasks containing the original fracturing return water without dilution. Dilution of the samples consistently resulted in lower growth and no growth was recorded in samples diluted 64 times. Experiments conducted without addition of supplemental salts resulted in growth inhibition in one of the two samples. In the same sample, the absence of sterilization also resulted in growth inhibition, presumably because of the presence of antagonist microorganisms.

Our results provide proof-of-concept that fracturing return water can support the growth of halophilic microalgae. Further experiments are conducted to determine the potential of D. Salina for bioremediation of return water and for biodiesel production.

AAPG Search and Discovery Article #90163©2013AAPG 2013 Annual Convention and Exhibition, Pittsburgh, Pennsylvania, May 19-22, 2013