Assessing Oil Content of Microalgae Grown in Industrial Energetic-Laden Wastewater

Abstract

Industrial ammunition facilities generate wastewater containing different energetic compounds and nitrogen species. Our previous studies showed that some of these untreated wastewater streams can be mixed at a specific ratio to grow microalgae. In this study, four different untreated wastewater samples from an industrial ammunition facility were mixed and used as a culture media for microalgae, Scenedesmus obliquus ATCC®11477, in 100 L raceway reactors. The main objective of the study was to test the effect of growth parameters (light penetration, nutrient availability and retention times) on the oil content of microalgae in a semi-continuous setting. The raceway reactors were operated under 68–95 μmol/m2/s of light intensity for a 14:10 h light:dark photoperiod, and 60 rpm mixing paddle speed. Continuous monitoring of pH and temperature of the growth medium, periodic analysis of cell density and dry weight of microalgae, and analysis of the medium’s nutrient contents were performed. Biomass harvesting from the raceway reactors was conducted weekly, and the harvested algal biomass was tested for its oil content using an ethanol extraction method. Results showed that nitrogen starvation increased the oil production from 13% to 29% of oil based on the dry weight of biomass, whereas no increment in oil or biomass production was evidenced with the increase of light penetration for the two different retention times tested. This study provided significant information towards microalgae growth in energetic-laden wastewater streams. This study also showed that wastewaters from industrial ammunition facilities can be reused for culturing microalgae, which can be utilized for renewable energy production.