G. Markou, L. Wang, J. Ye and A. Unc, In: Application of Microalgae in Wastewater Treatment: Volume 2: Biorefinery Approaches of Wastewater Treatment, edited by S. K. Gupta and F. Bux, Springer International Publishing 2019, https://doi.org/10.1007/978-3-030-13909-4_7
Anaerobic digestion (AD) is a widely used technology for the treatment of organic wastes and by-products. Through AD, the organic matter is degraded producing a gaseous stream (biogas, which is a mixture of mainly methane and carbon dioxide) and a liquid/slurry stream (digestates) that contains most of the mineralized elements originating in the feedstock. Digestates are a very interesting source of nutrients for growing microalgae to produce valuable biomass with a simultaneous further treatment of the digestates. The performance of microalgae grown using digestates is influenced by various cultivation parameters, such as the physicochemical characteristics of the digestates (nutrient profile, content of inhibitory compounds, etc.), light penetration (turbidity and colored dissolved compounds), mixing regime, and hydraulic retention time (HRT). Digestates are characterized by their high content in ammoniacal nitrogen, suspended solids, and several inhibitors that might limit growth, and therefore pretreatment of digestates is likely to have a positive effect on biomass production. Microalgal cultivation is proven as an efficient technology for the removal of nitrogen, phosphorus, organic load, and other contaminants (heavy metals, pathogens). The produced biomass could be used as feedstock for the production of various commodities (biofuels, feed, etc.); however there are some concerns about the potential contamination of microalgal biomass with unwanted hazardous pollutants. This book chapter aims to give an overview on the cultivation of microalgae utilizing digestates derived from agro-industrial wastes and by-products, discussing the potentials and the drawbacks of such an approach.
