**1. Introduction**

The generation of large quantities of agro/food wastes by various means of food processing industries and the release of high amount of heavy metals into the environment through various industrial activities such as refining ores, metal plating, fertilizer industries, batteries, mining, and tanneries, etc. are very serious increasing problems of the society as well as they are grave threats to the environment [1–3]. It is estimated that worldwide, around 39% of food is wasted in the food manufacturing industries and this is expected to rise to about 126 million tonnes by 2020 if proper prevention polices are not put in place [2, 4]. Similarly in India a large amount of agro/food wastes are generated every year. Nearby about 20% of the produced fruits and vegetables are wasted because, India is the second largest producer of fruits, vegetables, groundnut, sugarcane, rice, wheat and cotton.

As the production increased, it also increased the percentage of wastes generated from them [5, 6]. This readily available, cheap, and large amount of waste could be utilized for the removal of heavy metals from the effluents as bioadsorbents either in their natural form or in modified form. So the idea of utilization of agro/food wastes for the removal of heavy metals can suppress both the aforementioned problems to a great extent. Some of the industries such as paper, electroplating, metallurgy, textiles, batteries, metal plating, dyes, pesticides, and fertilizers, etc. are the major contributors of heavy metals into the wastewater [7]. These industries directly or indirectly discharge the heavy metals into the environment, especially in developing countries. The discharge of heavy metals like mercury (Hg), iron (Fe), chromium (Cr), lead (Pb), nickel (Ni), cadmium (Cd), cobalt (Co), zinc (Zn), copper (Cu), arsenic (As) etc. from industries is hazardous to humans [8]. These heavy and toxic metals are a serious concern and are threats to environment due to their toxicity, persistence in nature, and bio-accumulation tendency [9]. Several reputed and standard organizations have set the limits for the release of toxic metals into the water streams. But the addition of heavy metals into the aquatic stream at a higher concentration is increasing day by day by the various industrial activities, thus it increases the human health hazards and environmental pollution. Two tragedies namely, Minamata and Itai-Itai (Jintsu River) occurred in Japan because of the contamination of methyl-mercury and cadmium in aquatic streams [3, 10].

In the past several years various conventional techniques have been used for the eradication of toxic metal ions such as ultrafiltration, reverse osmosis, oxidation, ion exchange, chemical precipitation, reduction, and electrodialysis [11]. But these conventional methods are mainly associated with certain limitations, such as they produce large amount of sludge, are less efficient, are sensitive in operating conditions and are of costly disposal [12]. Thus, the use of agro/food wastes material and by-products of fruits and vegetables such peel, pomace and seeds as a bioadsorbents for the eradication of toxic metals is an emerging and potentially alternative method and in the recent years this method has gained much attention. This technique has several advantages over the conventional method such as low cost, high efficiency, produces less sludge, and regenerates biosorbents [13]. Various types of agro/food waste materials such as sugarcane bagasse, wheat bran, rice bran, rice husk, orange peels, coffee beans, hazelnut shells, groundnut shells, wheat husk, waste tea leaves, maize corn cob, apple peels, banana peels, coconut shells, sugar beet pulp, soybean hulls, cotton stalks etc. have been tried by several researchers for the eradication of heavy metals [14–16]. The agro/food waste materials, especially those containing cellulose, show a high biosorption capacity. Their components such as lignin, hemicellulose, starch, lipids, proteins, hydrocarbons and other functional groups expedite metal complexation that helps in the removal of heavy metals [17]. Because of the several advantages that are associated with the agricultural waste as mentioned above it seems to be a viable option for the removal of heavy metals. These readily available, low cost, promising agro/food waste materials can be effectively utilized for the eradication of various toxic metal ions either in their natural form or after some modifications [18].

#### **2. Conventional methods for the eradication of toxic metal ions**

Several conventional methods are readily available for the removal of heavy metal ions present in effluents that come from different sources. These conventional methods can be classified as physical, chemical, and biological [19]. In the past several years, various industries were extensively using physical and chemical methods, but nowadays, they do not prefer these traditional methods due to

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*Potential Use of Agro/Food Wastes as Biosorbents in the Removal of Heavy Metals*

several reasons associated with them such as high cost and disposal problems. Membrane filtration, gravity concentration, adsorption, flotation, mechanical screening, and magnetic separation are some of the physical methods. Membrane filtration can be further classified as electrodialysis, reverse osmosis, ultrafiltration, and nanofiltration. In comparison to membrane filtration and adsorption, adsorption has been considered the appropriate and effective method for the removal of heavy metals because most of the times membrane separation is associated with several problems such as fouling. Chemical methods include electrochemical processes, coagulation, electro kinetic coagulation, irradiation, and electroflotation [20]. These chemical methods are efficient for removing the heavy metals from the effluent but they are very expensive and commercially unattractive. Like physical methods, these chemical methods are also associated with several limitations such as; they require high energy and high consumption of chemical reagents. Several studies have reported that both the physical and chemical methods are not much effective and economical towards the removal of heavy metals especially when the metals are present in low concentration [21, 22]. Some of the researchers have also used metal and metal oxide nanoparticles for water decontamination and purification [23]. Biological methods or bio removal is one of the alternative methods which can effectively reduce the concentration of heavy metals to environmentally tolerable levels at a reasonable cost [24]. In the past several years a large number of studies were conducted for the eradication of toxic metal ions from the waste water by utilizing the various products and by-products of plants [18, 25, 26]. They have also confirmed the efficacy of agricultural products or by-products as sorbents for the removal of metals. Further, they have recommended that this process is a good and efficient alternative for the removal of heavy metal but only if the adsorbents are inexpensive and do not require any pre-treatment before the application. Besides the several advantages of biological method, various other authors have also highlighted its drawbacks such as, it requires large area and has less design flexibility and lesser modes of operation. Further, it has also been recommended that this process is not favourable for the handling of large amount of effluent [27]. In order to overcome the drawbacks associated with the above mentioned techniques, several researchers have recommended the biosorption method as an economical and environmental friendly method. Biosorption is not only a method for the eradication of heavy metals but it is also an example of the potential use of bio waste (agro/food waste). Formation of adsorbent by using agro/food waste is a cheap, economical, environmental friendly, and simple to design method and moreover it does not

*DOI: http://dx.doi.org/10.5772/intechopen.94175*

produce any toxic and dangerous material [18].

It is a process that utilizes the biological material or components as adsorbents

for the eradication of toxic metal and non-metal ions, and small particulates from the wastewater, which come from numerous industries such as ore refining, metallurgic, fertilizer, paper, batteries, etc. The biological materials that are used as adsorbents in the process of biosorption are called as biosorbents. They can be classified as natural, biological, and waste oriented as shown in **Figure 1**. Some of the natural adsorbents that are having the good properties of an adsorbent are clay, zeolite, and siliceous material and they are easily available in the ecosystem [28]. Most of the biological adsorbents emanate from microorganisms which include bacteria, fungi, algae, and yeast [20]. Other than these, some of the biological adsorbents obtained from biological sources such as chitin and chitosan, peat, and

**3. Biosorption and its classification**

#### *Potential Use of Agro/Food Wastes as Biosorbents in the Removal of Heavy Metals DOI: http://dx.doi.org/10.5772/intechopen.94175*

several reasons associated with them such as high cost and disposal problems. Membrane filtration, gravity concentration, adsorption, flotation, mechanical screening, and magnetic separation are some of the physical methods. Membrane filtration can be further classified as electrodialysis, reverse osmosis, ultrafiltration, and nanofiltration. In comparison to membrane filtration and adsorption, adsorption has been considered the appropriate and effective method for the removal of heavy metals because most of the times membrane separation is associated with several problems such as fouling. Chemical methods include electrochemical processes, coagulation, electro kinetic coagulation, irradiation, and electroflotation [20]. These chemical methods are efficient for removing the heavy metals from the effluent but they are very expensive and commercially unattractive. Like physical methods, these chemical methods are also associated with several limitations such as; they require high energy and high consumption of chemical reagents. Several studies have reported that both the physical and chemical methods are not much effective and economical towards the removal of heavy metals especially when the metals are present in low concentration [21, 22]. Some of the researchers have also used metal and metal oxide nanoparticles for water decontamination and purification [23]. Biological methods or bio removal is one of the alternative methods which can effectively reduce the concentration of heavy metals to environmentally tolerable levels at a reasonable cost [24]. In the past several years a large number of studies were conducted for the eradication of toxic metal ions from the waste water by utilizing the various products and by-products of plants [18, 25, 26]. They have also confirmed the efficacy of agricultural products or by-products as sorbents for the removal of metals. Further, they have recommended that this process is a good and efficient alternative for the removal of heavy metal but only if the adsorbents are inexpensive and do not require any pre-treatment before the application. Besides the several advantages of biological method, various other authors have also highlighted its drawbacks such as, it requires large area and has less design flexibility and lesser modes of operation. Further, it has also been recommended that this process is not favourable for the handling of large amount of effluent [27]. In order to overcome the drawbacks associated with the above mentioned techniques, several researchers have recommended the biosorption method as an economical and environmental friendly method. Biosorption is not only a method for the eradication of heavy metals but it is also an example of the potential use of bio waste (agro/food waste). Formation of adsorbent by using agro/food waste is a cheap, economical, environmental friendly, and simple to design method and moreover it does not produce any toxic and dangerous material [18].
