Analysis of fatty acid methyl esters and polyhydroxyalkanoates production along with wastewater contaminant removal using sewage sludge bacteria

Abstract

Environmental issues such as air pollution and climate change due to excessive fossil fuel burning; plastic pollution and wastewater contamination are a cause of global concern. Bacteria have the ability to not only utilize organic contaminants present in wastewater, but also to synthesize bioproducts such as fatty acid methyl esters (FAMEs), the primary molecules in biodiesel and Polyhydroxyalkanoates (PHAs) or bioplastics. The present study aims to investigate production of FAMEs and PHA along with biodegradation of wastewater contaminants by sewage sludge bacteria. Screening of sewage sludge bacteria was done for their lipid/PHA accumulation potential in filter sterilized wastewater by viable colony, fluorescence microscopy and spectrofluorometry methods using nile red staining. For characterization of bacterial FAME and PHA, cultures were subjected to in situ transesterification and analysed using gas chromatography mass spectrometry (GC-MS). A previously reported thermotolerant bacterial strain Bacillus sp. ISTVK1, that showed promising results was further tested for its the potential to produce FAME/PHA along with wastewater contaminant removal by performing physico-chemical analyses, scanning electron microscopy-energy dispersive X-ray (SEM-EDX) spectroscopy and transmission electron microscopy (TEM). The analysis showed the presence of C_{15 − 18} FAMEs such as Hexadecanoic acid, methyl ester and Tetradecanoic acid 12-methyl ester and PHA such as Pentanoic acid, 4-oxo, methyl ester. Physico-chemical analysis of culture supernatant revealed a 92% reduction in COD and the absence of contaminants such as Benzene, 1,1’-(2-pentene-1,5-diyl)bis (R.T.= 25.42) and 5-(1-Phenyl-cyclopentyl)- [1,3,4]oxadiazole-(R.T.=27.75) from post-treated samples. Results of SEM-EDX and TEM further confirmed bacterial lipid/PHA accumulation and contaminant reduction post-treatment. The potential of the thermotolerant Bacillus sp. ISTVK1 for biodiesel and biopolymer production along with wastewater contaminant removal, as revealed in this study could have future implications in various thermal and polymer industries and wastewater valorization technologies.