**1. Introduction**

Nature has gifted our earth with four spheres; biosphere, lithosphere, hydrosphere, and atmosphere. Together these spheres are important for maintaining a balanced ecosystem [1]. The industrial revolution in the past five decades is remarkable. Due to anthropogenic activities, increasing population, industrialization and urbanization, all spheres have become polluted [2–7]. There are two main sources of introduction of heavy metals in the environment (1) natural sources which includes volcanic emissions, forest fires, deep-sea vents, and geysers [8] and (2) anthropogenic sources which includes mining and smelting sites, metalmanufacturing plants, painting- and coating-industries and tanneries. These heavy metals are

Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. © 2018 The Author(s). Licensee IntechOpen. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

© 2016 The Author(s). Licensee InTech. This chapter is distributed under the terms of the Creative Commons

released directly into the environment. Metals exhibit health issues [9] if their concentrations exceed allowable limits. Even when the concentration of metals does not exceed these limits, there is still a potential for bioaccumulation and associated chronic toxicity as heavy metals are known to be accumulative within biological systems [10]. These metals include arsenic, cadmium, chromium, copper, lead, mercury, nickel, and zinc [4, 11]. Industrial effluents are known to contain heavy metals which originate from metal plating, mining activities, smelting, battery manufacture, tanneries, petroleum refining, paint manufacture, pesticides, pigment manufacture, and printing and photographic industries [1, 11–14].

in the cells, due to which they form complex compounds [15, 18]. Microorganisms acquire resistance to these toxic metals by lateral gene transfer [20]. The interaction of microorganism with metal ions depends on factors like oxidation state of the metal ion, chemical/physical

Biosorption of Heavy Metals

23

http://dx.doi.org/10.5772/intechopen.72099

Since last many decades, various physical and chemical methods were employed to remove

**Chemicals methods**: Chemical precipitation, electrochemical treatment, oxidation/reduction. **Physical methods**: Ion exchange, membrane technology, reverse osmosis, and evaporation

However, these strategies were not the first choice as they are expensive, inefficient, laborintensive, or the treatment process lacks selectivity [25, 26]. The research on bioremediation or biosorption-based remediation techniques in the past decades has concluded that bioreme-

Biosorption is defined as "ability of biological materials to accumulate heavy metals from wastewater through metabolically mediated (by the use of ATP) or spontaneous physicochemical pathways of uptake (not at the cost of ATP), or as a property of certain types of inactive, non-living microbial biomass which bind and concentrate heavy metals from even very dilute aqueous solutions" [1, 5, 32]. It is a complex process that depends on differentfactors like cell physiology, physicochemical factors such as pH, temperature, contact time, ionic strength, and metal concentration, chemistry of the metal ions, cell wall composition of microorganisms [5, 33, 34]. Biosorption of different heavy metals e.g. cadmium, silver, lead, nickel etc. by using microorganisms like fungi, algae or bacteria was studied by different

Bioremediation offer different advantages such as low operating cost, minimum ratio of disposable sludge volume, high efficiency in detoxifying very dilute effluents and even *in situ* remediation [30, 43, 44]. Bacteria detoxify heavy metals in a variety of different ways [45]. Although various types of tolerance mechanisms have been reported in bacteria for heavy metal stress, Cd detoxification has only been restricted to efflux pumps. The plasmid encoded *cad* systems in (*Staphylococcus aureus*) and the *czc* system (*Alcaligenes eutrophus*) are

nature of metals, growth phase of microorganism etc. [21].

metals from environment. The list is given below [5, 13, 14, 22–24].

**Biological methods**: Microorganisms including bacteria, fungi or algae.

diation is a natural process and cost effective [4, 27–31].

**3. Methods for removal of heavy metals**

recovery, filtration.

**4. Biosorption**

groups [34–42].

**4.1. Significance**
