Bioaccumulation and Biosorption of heavy metals

PLAZA CAZÓN JOSEFINA; SEGRETÍN ANA; DONATI EDGARDO

Heavy Metals in the Environment: Microorganisms and Bioremediation

CRC Press

Año: 2018; p. 93 - 112

Metals can enter the environment through different pathways, ofwhich, anthropogenic sources play a significant role in increasing metalconcentrations. Wastewaters from industries are often disposed directly intothe rivers or other nearby water sources without any treatment procedure. Thisentails a high ecological risk as these water sources are usually considered tobe the basis for drinking water (Vijayaraghavan and Balasubramanian, 2015).Several remediation techniques to remove metal ions from aqueous solutionsare available ranging from traditional physicochemical methods to emergingbiotechnological techniques as biosorption and bioaccumulation (Chojnacka,2010). The main advantages of these biological methods are low operatingcosts, selectivity for specific metal remediation, minimization of the volume ofchemical and biological sludge, and high efficiency in detoxifying very diluteeffluents. Both processes mentioned involve interactions and concentrationof toxic metals either on living (bioaccumulation) or non-living (biosorption)biomass. Two of the most notable differences between both processes aretheir kinetics and values of activation energy (Chojnacka, 2010; Chojnackaet al., 2005). While biosorption is a fast process independent of the presenceof specific nutrients, bioaccumulation is slow and nutrient dependent. Inbiosorption, there is no danger of toxicity by sorbate to the sorbent but inbioaccumulation such danger exists (Chojnacka, 2010). Biosorption, alsoknown as passive metal uptake, is the metabolism-independent uptake ofmetals by non-living biomass. Mechanisms of cell surface sorption are basedon physicochemical interactions between metal and functional groups ofthe cell wall (Veglio et al., 2003; Schiewer and Volesky, 2000). Conversely,bioaccumulation comprises intracellular metal accumulation which occursin two-stages: the first, identical to biosorption which is fast and thesubsequent is slower and includes transport of sorbate inside the living cells,most frequently using active transport systems. Bioaccumulation is a nonequilibriumprocess, more complex than biosorption itself. Several livingorganisms (yeast, fungi, algae, and bacteria) have been reported with theability to capture large quantities of heavy metals (Wang and Chen, 2009).Particularly, algae have been extensively studied for heavy metal removalfrom wastewater due to their ubiquitous occurrence in nature. A numberof microalgal strains (Chlorella vulgaris, Chlorella fuscas, Spirogyra species,Spirulina sp., Chaetophora elegans, Cladophora fascicularis, Cladophora sp., andEnteromorpha sp.), potentially suitable for heavy metal removal in aqueoussolution, were used in several studies showing varying removal efficiencies. However, comparisonbetween bioaccumulation and biosorption of heavy metals by algae cells isvery limited on literature