(510t) Evaluation of Galdieria Sulphuraria for the Bioremediation of Produced Water

Produced water (PW) is the largest volume of wastewater in oil and gas industries and accommodates 80% of the waste and residuals generated during oil and gas exploration. In the United States alone, onshore oil and gas extraction operations generate an estimated 24 billion barrels of PW annually, making it the largest waste stream associated with the upstream development of petroleum hydrocarbons. Produced water has a complex composition, containing inorganic and organic components as well as heavy metals, dissolved gases, treating chemicals, radionuclides, scaling products, and microorganisms. Currently, most of the PW is reinjected into disposal wells, which incurs transportation problems and induces seismicity issues. In its native state, PW is not considered usable for land applications due to environmental concerns. Moreover, the cost of treating one barrel of PW is $ 0.775 USD, whereas the reinjection cost is $ 0.75 – 8.00 USD per barrel. These facts act as the driving forces for the treatment of PW.

The utilization of PW as an algal growth medium has a great potential to eliminate chemicals from the PW and minimize the large volumes of freshwater needed for cultivation. Additionally, algae’s ability to utilize certain pollutants as nutrient sources has proven beneficial to remediate PW contaminated by petroleum hydrocarbons, complex organic chemicals, and solvents. However, significant dilution of PW is often required in algal-based systems due to complex chemical contaminants present in PW. In light of these facts, the current work has investigated the potential of cultivating Galdieria sulphuraria in PW using multiple dilutions; 0% PW, 5% PW, 10% PW, 20% PW, 50% PW, and 100% PW. The current results indicated that G. sulphuraria has a high potential of growth in up to 50% PW (total dissolved solids of up to 55 g L^-1) with a growth rate of 0.72 ± 0.05 g L^-1 d^-1 and can achieve a final biomass density of 4.28 ± 0.16 g L^-1 in seven days without the need for additional micronutrients. Additionally, the algal strain showed the potential of removing 99.6 ± 0.2% ammoniacal nitrogen and 74.2 ± 8.5% phosphate phosphorus from the PW. Overall, the current work highlights the PW bioremediation in an eco-friendly and low-cost approach using algae and brings attention to utilizing PW to grow biomass that can be processed to generate useful bioproducts.