Low-current electrostimulation boosts Dunaliella salina growth on hypersaline produced water

The oil industry generates vast volumes of produced water (PW), a hypersaline effluent containing toxic compounds, posing significant environmental and economic challenges. This study investigates the effects of low-alternating electric currents (50, 750 and 990 μA) on Dunaliella salina cultivated in PW versus synthetic media (both 8.5 % salinity). Algal cultures were first tested with 30 min electrical stimulation every 24 h, but in a second group of experiments cultures were tested with 30 min every 12 h (twice daily). Key findings reveal that electric stimulation extended the exponential growth phase across all treatments, but 990 μA currents increasing total biomass by 80 % in synthetic media. Notably, 50 μA once-daily increased total biomass by 23 % and lipid ratios by 36 % in PW, yielding a net 69 % rise in total lipids. Pigment analysis also showed medium-dependent responses as chlorophyll-α declined in synthetic media but increased in PW under low currents. This work advances sustainable aquaculture by valorizing PW as a microalgal growth medium, reducing freshwater demand, and optimizing lipid-rich biomass production. Estimations show that for reproducing this experiment using a 1000 m³ photobioreactor would require the maximum of 0.0124 kWh/day, with maximum annual energy cost of €0.91 per treatment (assuming €0.20/kWh).