RESUMO
Microalgae have demonstrated a large potential in biotechnology as a source of various macromolecules (proteins, carbohydrates, and lipids) and high-added value products (pigments, poly-unsaturated fatty acids, peptides, exo-polysaccharides, etc.). The production of biomass at a large scale becomes more economically feasible when it is part of a biorefinery designed within the circular economy concept. Thus, the aim of this critical review is to highlight and discuss challenges and future trends related to the multi-product microalgae-based biorefineries, including both phototrophic and mixotrophic cultures treating wastewater and the recovery of biomass as a source of valuable macromolecules and high-added and low-value products (biofertilizers and biostimulants). The therapeutic properties of some microalgae-bioactive compounds are also discussed. Novel trends such as the screening of species for antimicrobial compounds, the production of bioplastics using wastewater, the circular economy strategy, and the need for more Life Cycle Assessment studies (LCA) are suggested as some of the future research lines.
RESUMO
Phytofiltration lagoons are phytoremediation technologies suitable for tropical and sub-tropical regions requiring cost-effective and echo-friendly technologies. A biorefinery of fourth generation has been implemented at pilot plant level in Xalapa, Mexico, and the phytofiltration lagoon, being the first module for provision of treated water and plant biomass for biofuel production plays a key role. The aim of this work was to evaluate the performance of such phytofiltration lagoon with a working volume of 13,000 L for the removal of nutrients from an urban river polluted with domestic wastewater and the biomass productivity of the macrophyte Pistia stratiotes, during five different experimental periods, comprising 42 days each one. The maximum absolute growth rates (AGR, gdwday-1) registered for P. stratiotes during the Aug-Oct '15 and the March-Apr '16 and Apr-May '16 period were in the range of 13.51±2.66 to 16.54±2.02gdwday-1. The average biomass productivity was 5.808gdwm-2day-1. Productivities were similar during the periods of Aug-Oct '15, Mar-Apr '16 and Apr-May '16 and significantly higher (p<0.05) than those registered in Oct-Nov '15 and Jan-Feb '16. Removal percentages of COD and nutrients varied according to the season. COD was in the range of 47.82±39.3% to 88.00±15.0%. Ammonium N was in the range of 76.78±21% to 98.79±0.9%. Nitrates were removed in the range of 16.92±64%. to 97.14±4.5%. Finally, phosphates were removed very effectively, from 73.72±18.5% to 92.89±4.3%. A hydraulic retention time of 7 days was enough for the effective treatment of the water from the polluted river. It was concluded that the phytofiltration lagoon with P. stratiotes is very feasible within the biorefinery for providing biomass year-round and for treating the polluted water very effectively.