Handbook of Microalgae-Based Processes and Products: Chapter 7 - Wastewater Treatment Based in Microalgae

Wastewater (WW) treatment comprises elimination of different contaminants, such as organic matter, nitrogen, and phosphorus. Moreover, WW can contain other types of pollutants such as heavy metals, colorants, antibiotics, hormones, and drugs. Because of the diversity of the contaminants, many biological processes for removal/degradation of these pollutants have been developed. These processes include the use of physical, chemical, or even biological strategies to remove or degrade the contaminants. Microalgae have been primarily used for the treatment of domestic and agro-industrial WW as it contains high amounts of nitrogen (N) and phosphorus (P), and this favors the growth of microalgae. The removal of both these contaminants is not the sole benefit of using microalgae in WW treatment; some of the other benefits are the reduction of eutrophication potential, oxygenation of the effluent, and reduction of pathogens.

Microalgae can eliminate other contaminants such as heavy metals, colorants, or drugs from industrial WW. Heavy metals are not degradable, but their removal is feasible by microalgal biomass because the cell wall functional groups interact with the metal ions and adsorb them. This process is rapid and can occur in just minutes. If the biomass remains viable, the metals can cross the cell membrane and get accumulated inside the cell, thus initiating different metabolic mechanisms in the cell to neutralize the heavy metals. In the case of recalcitrant molecules, such as colorants or the so-called emergent pollutants, normally biotransformation is performed and mineralization of the molecule is not so common. In this chapter, the processes of elimination of different pollutants by employing microalgal biomass, efficiencies achieved, and mechanisms involved in these processes have been analyzed.