Growth of microalgae in spectrum-neutral, volume-distributed light restriction as the baseline of wastewater exploitation

Producing culture media for microalgae from wastewaters may help reduce the culture management and wastewater treatment costs, but concomitant light limitation, nutrient restriction, toxic and growth-promoting effects complicate the preliminary data analysis and their subsequent exploitation. Post-treating the experimental data with a light-centred growth model would warrant the process developer with a powerful tool, but also a difficult one to validate in the absence of an accurate description of the microalgal growth behaviour in a purely radiative (i.e., non toxic) light restriction condition. Furthermore, purely radiative light restriction cannot be obtained by simply adjusting the external irradiance since in this latter case local irradiance and biomass growth cannot be decoupled. Aim of this work is, thus, carrying out an experimental investigation on the influence of purely radiative, chromatically neutral (grey), and volume-distributed light restriction on the observed growth rate of a microalgal culture. Semi-continuous cultures of the microalga Scenedesmus dimorphus (UTEX strain 1237) were realized in a synthetic culture media, with the addition of a non metabolised and non toxic black dye at different dilutions obtaining an array of equally spaced absorbances, ultimately yielding to a tailored light limitation. The cultures were grown in cylindrical and flat panel photobioreactors under artificial light. The experimental results were analysed with a simple (Lambert-Beer + Monod) growth model to investigate the exploitation criteria for wastewaters as culture media for microalgae.