Attached microalgae converting spent coffee ground into lipid for biodiesel production and sequestering atmospheric CO2 simultaneously

Abstract

The impacts of simultaneous exposures of arbitrary light intensities and photoperiods on attached Chlorella vulgaris microalgal growth onto spent coffee ground (SCG) were studied, and subsequently optimized using Response Surface Methodology (RSM) tool. The statistical analysis revealed the optimum light intensity and photoperiod were achieved at 100 μmol/m2s and 20:4 dark:light hours/cycle, respectively, producing microalgal density of 0.358 g/g and lipid productivity of 16.8 mg/Lday. The biodiesel yielded from the optimum condition possessed high cetane number and oxidative stability due to the high saturated fatty acid methyl esters (FAME) content of 63.7 %. In fact, the major FAME compositions ranged within C16 to C18 which were favourable for quality biodiesel production. Furthermore, the viability of SCG to serve as a carbon source was also evidenced by the high productivities of microalgal protein and carbohydrate at 94 and 168 mg/L day, respectively. The capability of attached microalgal cultivation in sequestering atmospheric CO2 was finally unveiled, with high CO2 capture rate being recorded at 9.38 mg/L h. Accordingly, growing attached microalgae onto SCG was recognized as an alternative approach for sustainable CO2 reduction, while producing green diesel to assuage the global warming phenomenon.