Bioremediation and biomass harvesting of anaerobic digested cheese whey in microalgal-based systems for lipid production

•Anaerobic digested cheese whey is used for microalgal growth.•Increasing organic and nutrient load and shorten HRT enhance lipid productivity.•Flocculation induced by high pH is effective as a pre-concentrated step.•Efficiencies at pH up to 13.0 are similar regardless microalgal population.•Organic content influences flocculation efficiency in microalgal-bacterial broths.

Agro-industrial wastewaters are potential resources for production of microalgae biofuels. The aim of the present work was to determine the feasibility of a semi-continuously fed microalgal-based system for the treatment of anaerobic digested cheese whey (AD) and to evaluate biomass productivity and lipid accumulation for a period of 77 d. The effect of increasing ammonium loading rate (ALR) and decreasing hydraulic retention time (HRT) was evaluated. Maximum biomass productivity and lipid content were 12.0 g m−2 d−1 and 12.3%, respectively, achieved when operating at an ALR of 12.9 mg L−1 d−1 and at a HRT of 5 d. Under these conditions, soluble chemical oxygen demand (SCOD), ammonium and soluble phosphorous (SP) removal accounted for 94%, 92% and 20%, respectively. Additionally, the effectiveness of flocculation induced by increase pH to harvest produced biomass was investigated. Flocculation efficiencies up to 90% were obtained for a pH of 13.5 regardless culture broth characteristics, and therefore, this process can be used as a pre-concentrated step of microalgal-bacterial suspensions.