Characterization and optimization of Rhodotorula toruloides and Ankistrodesmus falcatus co-culture in palm oil mill effluent for efficient COD removal and lipid production

Palm oil mill effluent (POME) with high COD can be utilized as a growth medium for microbial oil production, enabling simultaneous lipid production and effective green waste management. Thus, this study aimed to investigate the potential of co-cultivation of R. toruloides and A. falcatus to produce lipid and reduce COD in POME. The individual growth profiles of both cultures were assessed in POME and standard media. The cultures were co-cultivated in POME, and their lipid production, biomass growth, and COD removal were monitored. Response surface methodology (RSM) was used to determine the optimal POME concentration, yeast-to-microalgae ratio, and cocultivation duration for the co-cultivation. The results demonstrated that co-cultivating the yeast and microalga in POME led to a significant increase in COD reduction and remarkable lipid production compared to pure cultures, resulting in fold increases of 2 and 1, respectively. The optimum conditions for achieving optimum COD removal and lipid production were obtained using a POME concentration of 59.88%, a yeast-to-microalgae ratio of 9:25, and a growth duration of 18 days, yielding 72.27% COD reduction, and 0.012 mg/L/d lipid productivity. This study highlights the potential of co-cultivating oleaginous yeast and microalga as a promising strategy for eco-friendly waste management in the oil palm industry and sustainable integrated biofuel production.