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Bioremediation of produced waters has been widely investigated in the last decades. More recently, microalgae-based treatments have been developed to produce biomass. The objective of this study was to determine, at lab scale, the remediation efficiency of three origin of microorganisms: a consortium of three halotolerant and halophilic microalgae and their associated bacteria, bacteria from liquid digestate, and aromatic-degrading bacteria selected to perform bioaugmentation. The medium was composed of artificial oil-produced water and seawater, and contained nutrients from liquid digestate. In order to identify what plays a role in nitrogen, chemical oxygen demand, and aromatics compounds elimination, and to determine the effectiveness of bioaugmentation to treat this mix of waters, 16S rRNA analyses were performed. Combination of microorganisms from different origins with the selected aromatic-degrading bacteria were also realized, to determine the effectiveness of bioaugmentation to treat these waters. Each population of microorganisms achieved similar percentage of removal during the biological treatment, with 43–76%, 59–77%, and 86–93% of elimination for ammonium, chemical oxygen demand, and aromatic compounds (with 50% of volatilization), respectively, after 7 days, and up to with 100%, 77%, and 99% after 23 days, demonstrating that in the case of this produced water, bioaugmentation with the specialized aromatic-degrading bacteria had no significant impact on the treatment. Regarding in detail the populations present and active during the tests, those from genus Marinobacter always appeared among the most active microorganisms, with some strains of this genus being known to degrade aromatic compounds. [ABSTRACT FROM AUTHOR]

This work evaluates the impact of salinity and the toxicity of some metals and organic compounds commonly found in produced waters on the growth of model photosynthetic organisms. Five strains of marine microalgae and one cyanobacteria (i.e. Dunaliella salina , Nannochloropsis oceanica , Tetraselmis suecica , Picochlorum costavermella , Coccomyxa simplex and Synechococcus rubescens) were tested in microplates as well as the freshwater Chlorella vulgaris selected as reference. Results revealed that D.salina was able to growth at high salinity (up to 135 g·L−1). Copper was the most toxic metal for all strains (half maximal effective concentration between 0.1 and 10 mg·L−1) except for D.salina and C.simplex. These two strains were the most resistant to all metals tested. All organic compounds presented half maximal effective concentration above 10 mg·L−1, none of them being very toxic for the studied microorganisms. P.costavermella and C.simplex were the most resistant strains to organic compounds. Looking at tolerance to salinity, metals and organic compounds, D.salina appeared to be the best choice for biomass production in produced waters. In addition, growths in 80% artificial produced water supplemented with f medium confirm the feasibility to use this medium to produce biomass. [Display omitted] • Salinity, six metals and four organic compounds were tested on six strains of halotolerant microalgae and cyanobacteria. • Among the tested strains, Dunaliella salina grows at the highest tested salinities (up to 135 g·L−1). • Copper is the most toxic metal for all strains tested, whereas none of the organic compounds tested are highly toxic. • Dunaliella salina is the best choice for biomass production in produced waters. • Artificial produced water shows biostimulating effects on the different strains. [ABSTRACT FROM AUTHOR]