Win-win wastewater phycoremediation: Coupled carbon sequestration and heavy metal removal

Abstract Heavy metals (HMs) are non-biodegradable and persistent contaminants generated from diverse anthropogenic activities and discharged into the environment often via wastewater. HMs can cause toxicity to living organisms including human beings. The conventional environmental technologies such as electrolytic technologies, ion exchange, precipitation, chemical extraction, hydrolysis, polymer microencapsulation used for removal of HMs from wastewater are considered energy intensive and costly. Since several microalgae are endowed with the capability of removing HMs, they are considered as efficient biological agents for their environmental clean-up. Additionally, several microalgae show excellent ability of carbon sequestration, which draws attention of the scientists in reducing carbon dioxide concentration in the environment, and thereby combating global warming and climate change. Biological carbon sequestration using microalgae can offer a sustainable, ecofriendly and cost-effective approach, which has significant advantages over physical, chemical, and geoengineering approaches such as biomass burial, artificial capture, and sequestration of industrially produced CO2 using subsurface saline aquifers, reservoirs, ocean storage, underground storage in depleted oil and gas reservoirs, saline formations or deep, unminable coal beds, stratospheric aerosol injection, marine cloud brightening, cirrus cloud thinning, ground-based albedo modification for managing solar radiation. In this situation, phycoremediation technologies are seen as the most ecofriendly, efficient and suitable technologies for HM removal from wastewater. Numerous photosynthetic microalgae are not only able to remediate the toxic contaminants but also serve as agents of carbon capture from the environment. The present book chapter will deal with the unique potential of some microalgae like Scenedesmus spp., Chlorella spp., and Spirulina spp. for multiple environmental remediations based on coupled carbon sequestration and HM removal processes.