Integrating Cyanobacterial Biomass, Biodiesel, and Bioethanol Production During Municipal Wastewater Treatment Towards a Cleaner and Greener Approach

This study assesses the aptitude of heterocystous cyanobacterial strain Dolichospermum spiroides MBDU 903 in integrated wastewater treatment and biofuel production at a laboratory scale. The efficiency of the strain was assessed based on pigment accumulation, growth kinetics, nutrient remediation efficiency, and biodiesel fuel quality. The results demonstrated that the biomass productivity of D. spiroides MBDU 903 ranged from 69.27 to 167.08 mg L−1 day−1 across various nutrient regimes, achieving a maximum lipid content of 31% (w/w). Cultivation in municipal wastewater with BG11+ (50% v/v) yielded the highest pigment production biomass. The physicochemical properties of the derived biodiesel were estimated from gas chromatography-derived fatty acid methyl ester (FAME) profiles. Furthermore, the biorefinery potential was explored as a proof-of-concept by fermenting the post-transesterification residual biomass with Saccharomyces cerevisiae, yielding 14.5 mg/g of bioethanol from the pretreated residue. While a 10 L pilot-scale trial was conducted, significant productivity drops suggest that further optimization is required to bridge the gap between laboratory results and practical application. This study provides a baseline evaluation of the dual-fuel potential of a heterocystous cyanobacterium under wastewater-integrated conditions.