Evaluation of Growth Performance, Biochemical Composition, and Polyhydroxyalkanoates Production of Four Cyanobacterial Species Grown in Cheese Whey

Large-scale cultivation of cyanobacteria is often limited by the high cost of synthetic culture medium and the environmental impact of nutrient consumption. Cheese whey, a major agro-industrial waste product, is rich in organic and inorganic nutrients, making it a promising low-cost alternative for microbial growth while addressing waste bioremediation. This study investigates the growth performance and the biochemical composition of four different cyanobacterial species (<i>Phormidium</i> sp., <i>Synechocystis</i> sp., <i>Chlorogloeopsis fritschii,</i> and <i>Arthrospira platensis</i>), cultivated in cheese whey (CW). Pretreated CW was used at 20% and 100% <i>v</i>/<i>v</i> concentrations. All species grew satisfactorily in both concentrations, reaching biomass above 4 g L^-1 (in 100% <i>v</i>/<i>v</i> CW) and 2 g L^-1 (in 20% <i>v</i>/<i>v</i> CW). The highest μ_max value (0.28 ± 0.02 d^-1) was presented by <i>Synechocystis</i> sp. grown in 20% CW. Waste bioremediation of both 20 and 100% <i>v</i>/<i>v</i> CW demonstrated effective nutrient removal, with COD removal exceeding 50% for most species, while total nitrogen (TN) and total phosphorus (TP) removals reached up to 33% and 32%, respectively. Biochemical composition analysis revealed high carbohydrate and protein content, while lipid content remained below 15% in all cases. Interestingly, <i>C. fritschii</i> accumulated 11% <i>w</i>/<i>w</i> polyhydroxyalkanoates (PHAs) during the last day of cultivation in 20% <i>v</i>/<i>v</i> CW. These findings highlight the potential of <i>C. fritschii</i> as a valuable candidate for integration into bioprocesses aimed at sustainable bioplastic production. Its ability to synthesize PHAs from agro-industrial waste not only enhances the economic viability of the process but also aligns with circular economy principles. This study is a primary step towards establishing a biorefinery concept for the cultivation of cyanobacterial species in cheese whey-based wastewater streams.