Nutrients utilization and contaminants removal. A review of two approaches of algae and cyanobacteria in wastewater

The detection of new pollutants, stricter environmental regulations, and advancements in treatment technologies are driving improvements in bioprocesses for treating wastewater. Specifically, special concern is being placed on phosphorus and nitrogen forms, which spur eutrophication of water bodies, and emerging micropollutants such as pharmaceuticals and person-care products. Algae and cyanobacteria cultivation requirements include water and nutrient sources that currently are supplied by fertilizers, which provide poor sustainability and economics. Using wastewater as a source of nitrogen and phosphorus represents an attractive option to cultivate microalgae simultaneous with contaminant removal. Phycoremediation refers to the assimilation or disintegration of organic and inorganic compounds (carbon, nitrogen, or phosphorus), metals, and emerging contaminants in wastewater by microalgae - algae and cyanobacteria. In addition, added value comes when the microalgae are harvested to become feedstock for biofuels such as biogas. Although promising studies have been published for algal growth in wastewater while simultaneously removing contaminants, limitations in the scale-up process still have to be addressed. In this work, we summarize biological mechanisms by which nutrients and contaminants are removed by microalgae. We specifically address the interactions that the microalgae have with other microorganisms and the production of extracellular polymeric substances, a mechanism well known in the literature, but hardly studied in microalgae. Finally, we discuss different strategies reported to improve the scale up of microalgae cultivation in wastewater.