Algal Bioremediation Strategies for the Removal of Heavy Metals, Dyes, and Hydrocarbons

Algal bioremediation leverages the metabolic and physicochemical properties of a diverse range of algae to remediate a broad spectrum of environmental pollutants, including heavy metals, synthetic dyes, and hydrocarbons. Algae remediate contaminants through a combination of complementary processes, including biosorption, bioaccumulation, enzymatic conversion, and synergistic systems with other related microorganisms. Functional groups are incorporated into the algal cell walls and extracellular polymeric substances (EPS), which generate large binding sites that promote the rapid accumulation of metals and dyes through ion exchange, complexation, electrostatic attraction, and hydrophobic interactions, particularly in the case of aromatic compounds. Since heavy metals are non-biodegradable, their removal is achieved by adsorption on the surface, immobilization, sequestration within the cell, and, in a few cases, a redox reaction, which decreases toxicity and allows for recovery. Synthetic dyes are mainly eliminated by adsorption and hydrogen bonding, whereas algal and microbial enzymes help to decolorate and partially transform complex dye molecules. Remediation of hydrocarbons by adsorption and emulsification through algal polymers and biosurfactants increases bioavailability and enzyme-mediated oxidation, which is usually catalyzed in algal-bacterial consortia to mineralize. This chapter describes the overall algal-based pollution reduction strategies and outlines the mechanisms of remediation for dyes, heavy metals, and hydrocarbons through microalgae, as well as identifies the major challenges and future opportunities for sustainable effluent treatment.