Production of Chlorella pyrenoidosa biodiesel by heterotrophic pathway to improve CI engine output characteristics using statistical approaches

Abstract

An alarming rise in greenhouse gases originating from on-road vehicles and the rapid depletion of cultivable land for fuel feedstocks has led researchers to explore alternative means of biofuel production. In this context, the current study explores the heterotrophic cultivation of Chlorella pyrenoidosa microalgae by scaling-up using various combinations of stir-tank bioreactors for the sustainable synthesis of low-density biodiesel. Furthermore, statistical tools are employed to develop prediction models to incorporate 20% (vol/vol) of the low-density biodiesel with diesel fuel (CP20) to obtain optimal experimental outputs. From the study, it was found that the percentage dry cell weight of samples acquired from 100 L, 200 L and 300 L stir tank bioreactors achieved 44.1%, 46.7% and 41% of lipid content and biomass concentrations of 5.15 g/L, 4.24 g/L and 4.36 g/L on up-scaling. At an optimal reaction temperature and time of 37 °C and 12 h, the highest biodiesel conversion rate of 98% was achieved during enzymatic transesterification. The prediction engine models reveals that at the finest engine input parameter combinations, 0.74% improvement in brake thermal efficiency and a 50% drop in smoke emissions are achieved using the low-density CP20 blend. Also, superior combustion characteristics are delivered on operation as a trade-off for NOX emissions.