Removal of Phenolic Compounds from Olive Mill Wastewater by Microalgae Grown Under Dark and Light Conditions

Phenolic compounds in olive mill wastewater (OMW) are considered an environmental threat due to their antimicrobial properties. Because of the metabolic versatility of microalgae, a biotic removal of these compounds seems a suitable approach. To investigate the biotic removal of phenolic compounds, the three microalgae species Chlorella vulgaris, Acutodesmus obliquus and Monoraphidium braunii were cultivated in flasks under constant light (50 µmol/m2s) and dark (1 g/L glucose) conditions in presence of different concentrations of OMW. Addition of 1% (v/v) OMW to the culture medium was shown to be non-inhibitory or even growth enhancing, and phenolic compounds were removed by 7–21% by all tested species. Cultivations with 6% (v/v) OMW resulted in a few exceptional experiments in fast growth (C. vulgaris under light, M. braunii under dark conditions) and removal of phenolic compounds (M. braunii, dark). Higher percentages (12 and 25%, v/v) of OMW were inhibitory. Under dark conditions microalgae first consumed glucose and removed phenolic compounds in a diauxic process. Removal of phenolic compounds was favoured under light conditions. Results of this study reveal the opportunities and the challenges of a microalgae-based removal of phenolic compounds and valorization of toxic OMW. Graphic abstract