Enhancement of biomass production and some biochemical compound of Dunaliella salina cultivated in dairy wastewater by plant growth regulators

One of the main limitations to the use of microalgae in various fields is the high production cost and low amount of biomass produced. In this study, the utilization of dairy wastewater as a culture medium to lower costs and the application of growth stimulants, gibberellic acid (GA₃) and indole-3-acetic acid (IAA) to enhance biomass production in Dunaliella salina was investigated. The amount of fresh and dry weight, chlorophyll, carotenoid, protein and soluble sugar obtained from D. salina cultivation in wastewater was higher than in Artificial Seawater medium. An approximately 2-fold increase in fresh and dry weight was observed in microalgae treated with 1 µM GA₃. Also, the lowest concentration of GA₃ (1 µM) increased the amount of chlorophyll a, b and carotenoid by 2.24, 3 and 2.4 times, respectively, compared to untreated wastewater. IAA at 100 µM concentration caused a 1.6 and 1.8-fold increase in fresh and dry weight, respectively. The amount of chlorophyll a, b and carotenoids in microalgae treated with 100 µM IAA increased by 4, 2 and 5.6 times, respectively. The rate of increase in protein and soluble sugar was 33 and 48% respectively compared to untreated wastewater. In simultaneous treatment only the amount of fresh and dry weight, chlorophyll b and soluble sugar increased at highest concentration of both phytohormones. The results of this research showed that the use of phytohormones to increase the growth of microalgae in the wastewater environment in order to obtain more biomass and thus increase the performance of algae in wastewater treatment, could be a suitable solution.