Microalgae cultivation in wastewater for simultaneous nutrients removal and biomass production

This study was based on the comparison for the cultivation of microalgae species Chlorella vulgaris in domestic wastewater and distilled water in order to reduce nutrients and simultaneously generate biomass to produce biodiesel. Microalgae reduces concentration of inorganic pollutants (nutrients), and it was observed that 41% (nitrates) and 37% (orthophosphates) were removed by cultivating microalgae in wastewater, while nitrate and orthophosphate removal efficiency was found to be 36% and 23%, respectively, with its cultivation in distilled water. It is worth mentioning that maximum microalgae biomass productivity was found to be higher at 6.768 mg/L with wastewater cultivation as compared to 3.308 mg/L in distilled water. The lipid extraction from the microalgal biomass produced using wastewater was found to be 25.2% by dry weight. The GC–MS fatty acids analysis of the microalgae lipids demonstrated the presence of myristic (C14:0), palmitic (C16:0), palmitoleic (C16:1), oleic acid (C18:1), linoleic (C18:1) and linolenic acids (C18:3), which are favourable to produce biodiesel with better fuel characteristics. FTIR peaks at 1361 cm⁻¹ and another at 1639 cm⁻¹ revealed the presence of ester linkages in microalgae, and a peak at 1000 cm⁻¹ denotes strong polysaccharide (C–O) bonding. Thus, FTIR analysis revealed well-formed microalgae with all characteristic peaks and distinct finger prints of lipid existence. The energy requirement for microalgae cultivation per litre for a 10 day cultivation period showed higher value with distilled water (1.539 kWh) as compared to its cultivation in wastewater (0.966 kWh). Current investigation suggests that microalgae cultivated using domestic wastewater can produce more biomass as compared to its cultivation in distilled water, with a benefit of freshwater conservation. It also treats wastewater by taking up the nutrients and helps in mitigating eutrophication if untreated wastewater is discharged directly into water bodies.