Employment of wastewater to produce microalgal biomass as a biorefinery concept

Abstract

Microalgae have been proposed for use in the production of biodiesel because oil from microalgae has characteristics similar to those of vegetable oils. Nevertheless, the production of microalgal biomass only for oil is not economically feasible because its costs are higher than those of vegetable crops. One option to improve the economic balance of the process is a biorefinery concept that consists of the complete exploitation of the biomass and capitalization of all possible products. The biorefinery includes the employment of wastes such as wastewater, residues from food industries, or even residual wastes for biomass production. In particular, wastewaters have high amounts of nitrogen and phosphorus, and microalgae culture can remove them very quickly because both are essential biomass constituents. The employment of wastewater to grow microalgae reduces the risk of eutrophication of water bodies; in a biorefinery concept, it permits the reduction of the cost of nutrient addition, increasing the economic feasibility. The development of the biorefinery concept requires innovations in many steps of the biomass production process, such as cell disruption, biomass recuperation, and extraction techniques, in order to ensure the complete use of the biomass. The cost-effectiveness is not favorable if only the production of biomass is considered, but with the biorefinery concept, the possibility of obtaining high-value subproducts such as carotenoids, polyunsaturated fatty acids, or even active molecules permits a positive economic balance and drives the development of this type of process.