Application of microalgae in wastewater treatment: simultaneous nutrient removal and carbon dioxide bio-fixation for biofuel feedstock production

Abstract

The release of organic and inorganic pollutants generated from domestic, agricultural, and industrial water activities can have a serious impact on the environment. Conventional treatment processes (primary and secondary) have shown excellent efficiencies in removing the easily settled solids and oxidizing the organic matters present in wastewater. However, secondary effluents are loaded with nutrients (nitrogen and phosphorus), cause eutrophication, and more long-term environmental problems due to the presence of refractory organics and heavy metals that are discharged. Microalgae-based wastewater treatment systems are gaining popularity in recent years and offer a simple and cost-effective tertiary biotreatment process combined with the production of valuable biomass that can be utilized for several purposes. Microalgae include eukaryotic microalgae and prokaryotic cyanobacteria, which have high potential to grow in a harsh environment, can utilize inorganic carbon and nutrients, and are capable of photosynthesis. As a result, microalgae can be used to remove carbon, nitrogen, and phosphorus from wastewater and aid disinfection due to the increase in pH during photosynthesis. Oxygen produced by microalgae can support the biological treatment of wastewater by providing oxygen to the heterotrophic bacteria. In addition, microalgae hold amazing potential for the removal of heavy metals, as well as some toxic organic compounds, and can be used for CO2 biofixation from the air, without the production of secondary pollutants. The produced algae biomass can be used for the production of food, biofuels, and different chemicals. Algae can have a good capacity for the production of polymer, fatty acids, pharmaceuticals, and cosmochemical products. In this chapter, we will highlight the role of micro-algae in the treatment of wastewater.