Biotechnological potential of Oscillatoria sp. for acid cheese whey remediation: insights into mixotrophic metabolism and nutrient removal

Abstract

Background: The unsafe disposal of milk processing effluents has a negative impact on the environment due to their high content of nutrients and organic matter. Green alternatives can be applied to effectively manage and valorize these effluents, reducing their environmental footprint. Methods: The ability of the free-living cyanobacterium Oscillatoria sp. to grow in real cheese whey was evaluated as a potential strategy for integrating dairy wastewater treatment with biomass valorization. Autotrophic and mixotrophic cultures were maintained under controlled laboratory conditions and monitored over 28 days for growth, cell viability, biomass, pigment content, and physicochemical parameters, including pH, protein, carbohydrate, and chemical oxygen demand (COD). Results: Oscillatoria sp. successfully adapted to the initial acidic conditions of the effluent (pH 2.8–2.9), increasing the pH of the treated whey to levels suitable for industrial wastewater disposal (pH 6.0–9.0). A 5-fold increase in dehydrogenase activity was observed after a 28-day culture, with no signs of oxidative damage. Cyanobacterial biomass cultivated under mixotrophic conditions displayed a significant reduction (∼55%) in photosynthetic pigments, including chlorophyll a and total carotenoids, compared to autotrophic cultures. Notably, Oscillatoria sp. biomass increased by 2.3-fold under mixotrophy, compared to the autotrophic control. The higher biomass production was accompanied by a significant reduction in the whey COD from 35,250 mg/L to 8500 mg/L, along with a 65% and 80% decrease in protein and carbohydrate content, respectively. Conclusions: These findings provide new insights into the metabolic behavior of Oscillatoria sp. during cheese whey bioremediation, highlighting the potential of mixotrophic cyanobacteria for managing dairy wastewater management.