Techno-economic evaluation of heterotrophic microalgal cultivation approaches

This work focuses the attention on the evaluation of different heterotrophic microalgal cultivation approaches, finding the best process solution to achieve the accumulation of high value-added metabolites, such as astaxanthin and polyunsaturated fatty acids (PUFA), trying also to use a wastewater as carbon source. Three different approaches are evaluated: 1) Classical batch cultivation in sterilized fermenter; 2) Impulse nutrient feeding without sterilizing the reactor; 3) Impulse nutrient approach coupled with wastewaters’ usage in two different parallel reactors. This latter strategy is the one adopted in the European Project MEWLIFE (MicroalgaE biomass from phototrophic-heterotrophic cultivation using olive oil Wastewaters) that aims to produce microalgal biomass in an integrated photo-heterotrophic cultivation system using preconcentrated (in a membrane filtration plant) olive oil mill wastewater (OOMWW) as carbon source for growing algae, thus contributing to waste reuse and valorisation. Thanks to the Aspen Custom Modeler software, it is possible to write codes to represent the fermentation units, which are normally not present in the databases of most common simulators. Finally, a technical-economic analysis is conducted to evaluate the most advantageous process. At present, the pulse technique represents an extremely promising strategy with margins of improvement, deserving thus further investigation.