Highly Wet Chlorella minutissima Biomass for In Situ Biodiesel Production and Residual Biomass Rich in Labile Carbohydrates

Abstract

This study evaluated the use of biomass of Chlorella minutissima grown in 40-L photobioreactors using a Guillard f/2 biomass at over 80% moisture content as feedstock to produce ethyl esters. The study design investigated the influence of acid catalyst type (HCl or H2SO4) and concentration (0.3 or 0.6 mol L−1), co-solvent to ethanol ratio (1:10 or 1:5 v/v), and acyl acceptor to biomass ratio (25 mL g−1 or 50 mL g−1) on ester yield and conversion. An L8 Taguchi design was used to evaluate the influence of the factors, demonstrating a range of conversion ranging from 37 to 98%. Furthermore, the effects of reaction conditions on the residual biomass were assessed by measuring the concentration of acid-labile carbohydrates, which could be utilized in integrated sugar- and lipid-based algal refineries. It was found that in situ transesterification using HCl can provide easily accessible and fermentable carbohydrates at concentrations of about 32 wt% in residual biomass. In this sense, the findings of this study demonstrate a further step in the integration of microalgae biomass in the development of liquid-fuel biorefineries. Graphical abstract: [Figure not available: see fulltext.]