Algal–bacterial symbiosis and its application in wastewater treatment

The potential of algae in the field of environmental application has been explored in recent years. Algal systems are simple, cost-effective biological treatment systems for industrial and domestic wastewater. Conventional treatments, mainly employing heterotrophic bacteria, are usually ineffective in the removal of nutrients and metals; on the contrary, algal systems are very effective for the uptake of nutrients and metals. A symbiotic algal–bacterial consortium, through exchange of metabolites, can overcome these disadvantages and result in the effective removal of organic matter as well as nutrients. In addition, symbiotic systems are reported to remove heavy metals, pharmaceuticals, and other persistent compounds from wastewater. This system will be a cost-effective and sustainable option for field-scale application due to the reduction in aeration costs, reduction in CO2 generation (i.e., greenhouse gas emission) and revenue generated from biomass. This chapter discusses (1) the symbiotic interaction between the two species, (2) reactors used in symbiotic systems, (3) removal of specific pollutants in different wastewater treatment systems, and (4) comparison of removal efficiency of symbiotic system with conventional systems. The potential for revenue generation and resource recovery is also explored. Finally, future scope and opportunities in this field will be discussed in this chapter.