Metal uptake by microalgae: Underlying mechanisms and practical applications

Abstract

Metal contamination of a few aquatic, atmospheric, and soil ecosystems has increased ever since the industrial revolution, owing to discharge of such elements via the effluents of some industrial facilities. Their presence to excessive levels in the environment will eventually lead to serious health problems in higher animals owing to accumulation throughout the food web. Current physicochemical methods available for recovery of metal pollutants (e.g., chemical precipitation, oxidation/reduction, or physical ion exchange) are either expensive or inefficient when they are present at very low concentrations. Consequently, removal of toxic metals by microorganisms has emerged as a potentially more economical alternative. Microalgae (in terms of both living and nonliving biomass) are an example of microorganisms suitable to recover metals and able to attain noteworthy percent removals. Their relatively high metal-binding capacities arise from the intrinsic composition of their cell walls, which contain negatively charged functional groups. Consequently, microalgal cells are particularly efficient in uptake of those contaminants when at low levels. Self-defense mechanisms developed by microalgal cells to survive in metal-containing media and environmental factors that affect their removal (e.g., pH, temperature, and biomass concentration) are reviewed here in a comprehensive way and further discussed in attempts to rationalize this form of remediation vis-a-vis with conventional nonbiological alternatives.

Microalgae – A promising tool for heavy metal remediation

“…The benefits include: rapid metal uptake capability, time and energy saving, eco-friendly, user-friendly, year round occurrence, ease of handling, recyclable/ reusable, lowcost, faster growth rate (as compared to higher plants), high efficiency, large surface to volume ratio, ability to bind upto 10% of their biomass, with high selectivity (which enhances their performance), no toxic waste generation, no synthesis required, useful in both batch and continuous systems, and, applicability to waters containing high metal concentrations or relatively low contaminant levels (Monteiro et al, 2012). Monteiro et al (2012) particularly justify the worthiness of microalgae (living and non-living biomass) by disclosing that they aid in noteworthy removal of metals even at low contaminant levels. Apart from possessing greater HM remediation efficacy, microalgae enable easy recovery of HMs involving a few simple desorption chemicals.…”

Prediction of phycoremediation of As(III) and As(V) from synthetic wastewater by Chlorella pyrenoidosa using artificial neural network

“…Chojnacka et al (2005) and Monteiro et al (2012) stated that the microalgal cell wall consisted mainly of peptidoglycan, polysaccharides, proteins, teichoic acid, and teichuronic acid, and lipids which offer various functional groups, like hydroxyl, carboxyl, sulfydryl, amine, or phosphate. Microalgae play an important role in controlling heavy metals concentration, since their functional groups that located on the cell wall, are capable to bound ionic metal (Volesky 2007;Kumar et al 2015); sink or remove it by accumulation, biosorption or metabolization into substantial level (Priyadarshani et al 2011).…”

Heavy metal migration and risk transference associated with cyanobacterial blooms in eutrophic freshwater

“…The results indicated the percentage of extracellular metals was increased during Microcystis blooms-forming period. The process of heavy-metal accumulation by biologically active algae could be divided into two principal steps: rapid (passive) uptake by surface adsorption followed by much slower one that occurs inside the cell (Monteiro et al, 2012). The first process (i.e., the passive uptake), is non-metabolic, rapid, and essentially reversible (Kumar et al, 2015).…”