The Treatment of Wastewater with Microalgae

Good Essays
2.1 Wastewater Treatment with Microalgae
Microalgae have a great potential to solve energy and environmental challenges around the world. Wastewater treatment with microalgae is a more environmental sound approach to reduce nitrogen and phosphorus and to remove heavy metals from wastewater. Microalgae can absorb significant amount of nutrients because they need large amounts of nitrogen and phosphorus for proteins (45-60% microalgae dry weight) and metals as micronutrients for their growth. William Oswald first developed the idea of treating wastewater using microalgae and performed photosynthesis in sewage treatment [29]. Figure 2.1 briefly depicts the process involved in high rate algal pond in which algae plays a dual role by assimilating nutrients from wastewater and supplying oxygen to bacteria. The bacteria take up the oxygen and degrade organic material in the wastewater, the same process which is used in activated sludge treatment [29].

Figure 2.1. Process involved in a high rate algal pond [29].

The selection of algae strain to be used in wastewater treatment is determined by their robustness against wastewater and by their ability to grow in and to assimilate nutrients from wastewater [30]. Chlorella, Scenedesmus, Neochloris and Spirulina are the widely used algae species in experimental studies of wastewater treatment. The major advantages of using microalgae over conventional methods as summarized by De la Noüe (1992) [31] are: (a) nutrients can be removed more efficiently; (b) no generation of toxic by-product (sludge) (c) biofuels can be produced from biomass harvested (energy efficient); (d) cost–effective.
2.2 Mechanisms of nutrient and heavy metal removal
Nutrient removal by algae involve...

... middle of paper ...

...l density. The major advantage of autotrophic growth condition is that it can reduce carbon dioxide to make useful organic compounds. However, the limitation is that light penetration is inversely proportional to the algal density. As the density of algae increases, the light exposure to algae cell decreases resulting in limitation of nutrient removal from wastewater.
During heterotrophic growth, no light is required and organic carbon source such as glucose or glycerol acts as source of carbon. Algae uses this organic carbon for growth.
High algal densities can be obtained in heterotrophic growth as the growth is not limited by the light. Mixotrophic growth is a combination of heterotrophic and autotrophic growth, where carbon dioxide and organic carbon are simultaneously assimilated and both respiratory and photosynthetic metabolism operates concurrently [49, 50].
Get Access