Purple nonsulfur bacteria biomass as a potential biofuel source: A study of lipid characterization methods using gas chromatography

Wastewater treatment with purple nonsulfur bacteria (PNSB) is an emerging biotechnology for sustainable wastewater management and resource recovery. Previous studies in this field have concentrated on microbial protein potential; however, this study examines the lipid recovery potential of PNSB-dominated mixed culture biomass derived from gas-to-liquid wastewater treatment. Lipid characterization employed gas chromatography, focusing on the efficacy of esterification processes and solvent selection. The PNSB biomass showed approximately 34.4 ± 4.7% and 33 ± 2.4% lipid content under dim and full light conditions, respectively. Full light conditions enhanced biomass production, resulting in a higher lipid productivity rate (0.145 ± 0.018 gL^–1day^–1) than dim light conditions (0.068 ± 0.010 gL^–1day^–1); however, the choice between these conditions presents a tradeoff between maximizing lipid yield and minimizing energy input. Initial attempts using hexane for fatty acid methyl ester (FAME) characterization were ineffective. However, solvents with higher polarity indices, like dichloromethane (DCM) and diethyl ether (DEE), yielded more comprehensive FAME profiles, especially with continuous mixing during esterification. This highlighted the influence of solvent polarity on lipid analysis. Solvent mixtures like DCM–hexane and DEE–hexane further enhanced the FAME profile. Dominant FAME peaks included 11-octadecenoic acid, hexadecenoic acid, methyl stearate, and 9-octadecenoic acid. Terpenes like citronellol and phytol were also present. With a FAME profile similar to that of microalgae, PNSB biomass holds potential for biodiesel production and applications in nutrition, therapeutics, and agriculture.