Biodiesel production from indigenous microalgae grown in wastewater

•Desmodesmus sp. and mixed culture of microalgae were cultivated in untreated wastewater.•We report effective nutrients and total coliform removal from wastewater by microalgal treatment.•Ozone-flotation was investigated for microalgae harvesting and microalgae cell wall treatment.•The lipid content and FAME conversion of different microalgae strains were compared.•The FAME obtained from ozone-treated microalgae biomass showed more oxidative stability. This paper describes a process for producing biodiesel sustainably from microalgae grown in wastewater, whilst significantly reducing the wastewater’s nutrients and total coliform. Furthermore, ozone-flotation harvesting of the resultant biomass was investigated, shown to be viable, and resulted in FAMEs of greater oxidation stability. Desmodesmus sp. and two mixed cultures were successfully grown on wastewater. Desmodesmus sp. grew rapidly, to a higher maximum biomass concentration of 0.58g/L. A native mixed culture dominated by Oscillatoria and Arthrospira, reached 0.45g/L and exhibited the highest lipid and FAME yield. The FAME obtained from ozone-flotation exhibited the greatest oxidative stability, as the degree of saturation was high. In principle ozone could therefore be used as a combined method of harvesting and reducing FAME unsaturation. During microalgae treatment, the total nitrogen in wastewater was reduced by 55.4–83.9%. More importantly, total coliform removal was as high as 99.8%.