**6. Types of biosorbents**

Identification of biosorbents for the process of biosorption is a major challenge. It is desirable to develop/obtain biosorbents with the capacity to bind/uptake metal ions with greater affinities [56]. A wide variety of materials available in nature can be used as biosorbents for the removal of metals from contaminated water resources. Any kind of plant, animal, and microbial biomass and their derivatives; plant, industrial and agriculture wastes; and byproducts discharged from various industries can be employed as biosorbents. It is important to select a biosorbent from the large spectrum of available materials. The desired characteristics of an ideal biosorbent are [56]:


**6.2. Agricultural waste materials**

**6.3. Microbial biosorbents**

biosorption of metal ions are given in **Table 4**.

*6.3.1. Algae as biosorbents*

A great deal of interest in the removal of pollutants from wastewaters has focused on the use of agricultural waste/byproducts as biosorbents. Agricultural wastes especially those with high percentage of cellulose and lignin contains polar functional groups like amino, carbonyl, alcoholic, phenolic, and ether groups having high potential for metal binding [66]. These groups donate a lone pair of electrons and form complexes with metal ions in the solution [67]. Due to their unique chemical composition (the presence of hemicellulose, lipids, lignin, water hydrocarbons, simple sugars, and starch having a variety of functional groups) and availability, the use of agro-wastes seems to be a viable option for heavy metal remediation. Grapefruit peel was reported to biosorb cadmium and nickel with a biosorption capacity of 42.09 and 46.13 mg/g from aqueous solutions. Equilibrium data showed the better fit with the Freundlich isotherm model with the ion exchange mechanism. FTIR analysis showed that the carboxyl and hydroxyl groups are mainly involved in the biosorption of metal ions [68]. The bark powder of *Acacia leucocephala* was used as a low-cost biosorbent for the removal of Cu (II), Cd (II), and Pb (II) with the biosorption capacity of 147.1, 167.7, 185.2 mg/g, respectively, from the aqueous solution. The biosorption mechanism involved is physico-chemical adsorption involving carboxyl, hydroxyl, and amine groups present on the surface of the biosorbent for biosorption. The Langmuir model shows the best fit than the Freundlich model [69]. **Table 3** summarizes the type of the biosorbent, biosorbate, and maximum biosorption capacity of the different agriculture wastes as biosorbents.

Application of Biosorption for Removal of Heavy Metals from Wastewater

http://dx.doi.org/10.5772/intechopen.77315

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Microorganisms capable of tolerating unfavorable conditions evolved their use as biosorbents in the removal of metal ions from wastewaters. They include bacteria, yeast, algae, and fungi. Experiments focused on the use of dead and or living microorganisms offer options for the type of remediation to perform [82]. However, the use of dead microbial biomass for the binding of metal ions has been preferred over living biomass because of the absence of the requirement of nutrients and monitoring BOD and COD in effluents. Hence, the use of dead biomass is economical [83]. These biosorbents can effectively sequester metal ions in the solution and decrease the concentration from the ppm to ppb level efficiently; therefore, they are considered as ideal candidates for the treatment of complex wastewaters with high volume and low concentration of metal ions [84]. A large quantity of materials of microbial origin has been investigated as biosorbents for the removal of metal ions extensively [85]. Reports do not include the use biomass of any pathogens for water treatment. Most of the microbial groups are composed of a large number of functional groups which indicate their potential as biosorbents. Some studies which identified the functional groups involved in the

The use of algae as a biosorbent has received focus due to the scarce requirement of nutrients, high sorption capacity, plentiful availability, high surface area to volume ratio, less volume of sludge to be disposed, and the potential for metal regeneration and recovery. They are considered as both economic and ecofriendly solutions for wastewater treatment [92]. Different groups of algae differ in the composition of the cell wall. The cell wall of brown algae mainly contains three components: cellulose (structural support), alginic acid (a polymer of mannuronic and

The use of different materials as biosorbents is explained in detail:
