As the human population is rising, the need for novel protein sources and a reduction of greenhouse gas emission is of utmost importance. An approach tackling both concerns at once, is given via microalgal cultivation. Microalgae can be cultivated on non-arable land and require less space than the production of currently established protein sources, such as meat and soy. Trying to implement circular economy, hydrolysates from abundantly available lignocellulosic waste streams could be used as substrates for heterotrophic and mixotrophic cultivations of Chlorella vulgaris. Even though hydrolysis is a powerful method to degrade oligomeric C5 and C6 sugars of these waste-streams, inhibitors will be formed as a by-product. Applying liquid hot water hydrolyzation to lignocellulosic biomasses, furfural and 5-Hydroxymethylfurfural (HMF) are formed in the process. Furfural and HMF are known fermentation inhibitors to a diverse set of microorganisms. In this presentation, I discuss the impact of furfural and HMF on the mixotrophic and heterotrophic cultivation of Chlorella vulgaris. Results demonstrate that substrates containing furfural and HMF are suitable for microalgal cultivation. Using mass spectrometry analysis, we identified two metabolites stemming from Chlorella vulgaris cultivated in media containing those inhibitors. Even though, metabolic pathways of these reactions are still unknown as of now, the two metabolites have not yet been described in any microalgal species. The conversions of these inhibitors might open up new future applications in microalgal cultivation.