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The objective of this study was to determine the feasibility of using saline industrial streams as a culture medium to grow microalgae and cyanobacteria. Experiments were performed to determine the extent of the growth in artificial saline produced water and aquifer water supplemented with liquid digestate. Tests were performed in 96-wells microplates. Media were composed with different proportion of saline artificial produced water or aquifer water supplemented with 5% v/v liquid digestate (final concentrations: 149–195 mgN·L−1, 1.5–2.7 mgP·L−1). Media were completed to 100 % with artificial seawater, corresponding to final salinities of 40, 70 and 100 g·L−1. D. salina , N. oceanica and T. suecica showed the best growth rates. They were selected to perform mixed cultures in 80 mL tubes in the same culture media. Population evolutions were followed for 19 days. Depending on salinity and industrial effluent used, different species became predominant over the two others (N. oceanica , T. suecica and D. salina. at 40, 70 and 100 g·L−1, respectively). It appears that mixed culture is a good solution to have a biomass production during a culture process where the culture media will evolve in terms of salinity and composition. • Liquid digestate was used as a source of nutrient to support microalgae growth in saline produced water and aquifer water. • Six candidate strains were investigated at various saline effluent loads to identify the best performing ones. • N. oceanica , T. suecica and D. salina had the best growth performances at 40, 70 or 100 g·L−1, respectively. • According to the salinity, N. oceanica , T. suecica and D. salina became predominant over the two others during mixed culture. [ABSTRACT FROM AUTHOR]

This work investigates the feasibility of growing marine microalgae Nannochloropsis oculata in a mix of seawater and saline produced water obtained during oil & gas extraction, supplemented with liquid digestate from anaerobic digestion process as source of nutrients. In particular, three-stage cultures were conducted by varying the produced water loading in the culture media (from 0 up to 50% v/v), supplemented with 5% v/v of digestate and seawater. Growth parameters as well as nitrogen (ammonium) and organic carbon (expressed as chemical oxygen demand) removal efficiencies were monitored. Results revealed that N. oculata is perfectly able to grow in a seawater containing produced water from 10 up to 30% v/v. A slower growth was observed for 40 and 50% v/v of produced water, because of the salinity higher than 60 g·L−1. Maximal growth rates obtained were 0.35, 0.27 and 0.16 day−1, with a maximal optical density of 6.3, 5.2 and 3.2 for 10, 20 and 30% v/v of produced water, respectively. Nannochloropsis oculata showed better removal efficiencies for ammonium nitrogen (around 100%) than for organic carbon (approximately 40% after one step of acclimation), regardless of the produced water loading, most chemical oxygen demand being volatilized and/or degraded by bacteria during the first two days of a culture. Regardless of the loading, >90% of iron brought by produced water and digestate was precipitated and/or assimilated/adsorbed by N. oculata. • Produced water and liquid digestate as culture media instead of fresh water • Positive effect on microalgae productivity after three steps of acclimation • Nannochloropsis sp. as potential candidate to bioremediate produced water [ABSTRACT FROM AUTHOR]