**Bioremediation of Waters Contaminated with Heavy Metals Using** *Moringa oleifera* **Seeds as Biosorbent**

Cleide S. T. Araújo, Dayene C. Carvalho, Helen C. Rezende, Ione L. S. Almeida, Luciana M. Coelho, Nívia M. M. Coelho, Thiago L. Marques and Vanessa N. Alves

Additional information is available at the end of the chapter

http://dx.doi.org/10.5772/56157

**1. Introduction**

[46] Jeyasingh, J. and Philip, L. Bioremediation of chromium contaminated soil: optimiza‐ tion of operating parameters under laboratory conditions. Journal of Hazardous Ma‐

[47] Krishna, K.R. and Philip, L. Bioremediation of Cr (VI) in contaminated soils. Journal

[48] Tokunaga, T.K., Wan, J., Firestone, M.K., Hazen, T.C., Olson, K.R., Donald, J. Her‐ man, D.J. Sutton, S.R. and Lanzirotti, A. Bioremediation and Biodegradation. In situ reduction of chromium (VI) in heavily contaminated soils through organic carbon

[49] Oliver, D.S., Brockman, F.J., Bowman, R.S., Thomas L. and Kieft, T.L. Microbial re‐ duction of hexavalent chromium under vadose zone conditions. Journal of Environ‐

[50] Lee, K. L., Buckley, M. R., Campbell, C. An amino acid liquid synthetic medium for development of mycelia and yeast forms of *Candida albicans.* Sabouraudia 1975; 13,

[51] Singh, K.K., Hasan, S.H., Talat, M., Singh, V.K. and Gangwar, S.K. Removal of Cr (VI) from aqueous solutions using wheat bran. Chemical Engineering Journal 2009;

[52] Wang, X.S., Tang, Y.P. and Tao, S.R. Kinetics, equilibrium and thermodynamic study on removal of Cr (VI) from aqueous solutions using low-cost adsorbent Alligator

weed. Chemical Engineering Journal 2009; 148, 217- 225.

amendment. Journal of Environmental Quality 2003; 32(5), 1641-1649.

terials 2005; 118(1-3), 113-120.

224 Applied Bioremediation - Active and Passive Approaches

mental Quality 2003; 32(1), 317-324.

148-153.

151, 113-121.

of Hazardous Materials 2005; 121 (1-3), 109-117.

Water is not only a resource, it is a life source. It is well established that water is important for life. Water is useful for several purposes including agricultural, industrial, household, recreational and environmental activities. Despite its extensive use, in most parts of the world water is a scarce resource. Ninety percent of the water on earth is seawater in the oceans, only three percent is fresh water and just over two thirds of this is frozen in glaciers and polar ice caps. The remaining unfrozen freshwater is found mainly as groundwater, with only a small fraction present above ground or in the air. Thus, almost all of the fresh water that is available for human use is either contained in soils and rocks below the surface, called groundwater, or in rivers and lakes.

The contamination of soil and water resources with environmentally harmful chemicals represents a problem of great concern not only in relation to the biota in the receiving envi‐ ronment, but also to humans. The continuing growth in industrialization and urbanization has led to the natural environment being exposed to ever increasing levels of toxic elements, such as heavy metals. Approximately 10% of the wastes produced by developed countries contain heavy metals. Figure 1 gives some indication of the amounts of metal-containing waste produced in developed countries. Much of the discharge of metals to the environment comes from mining, followed by agriculture activities.

© 2013 Araújo et al.; licensee InTech. This is an open access article 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.

**Figure 1.** Waste containing heavy metals produced in developed countries [1].

Many different definitions have been proposed for heavy metals, some based on density, some on atomic number or atomic weight, and others on chemical properties or toxicity, which are not necessarily appropriate. For example, cobalt, iron, copper, manganese, molybdenium, vanadium, strontium and zinc are required to perform vital functions in the body and therefore cannot be considered as compounds with high toxicity or ecotoxic properties. Regarding the meaning of the term "heavy metal" it was found that there can be misinterpretation due to the contradictory definitions and lack of a coherent scientific basis [2].

In conventional usage "heavy" implies high density and "metal" refers to the pure element or an alloy of metallic elements. According to Duffus [2], a new classification should reflect our understanding of the chemical basis of toxicity and allow toxic effects to be predicted. Various publications have used the term "heavy metals" related to chemical hazards and this definition will also be used herein. Among the classes of contaminants, heavy metals deserve greater concern because of their high toxicity, accumulation and retention in the human body. Moreover, heavy metals do not degrade to harmless end products [3, 4]. It is well established that the presence of heavy metals in the environment, even in moderate concentrations, is responsible for producing a variety of illnesses of the central nervous system (manganese, mercury, lead, arsenic), the kidneys or liver (mercury, lead, cadmium, copper) and skin, bones, or teeth (nickel, cadmium, copper, chromium) [5].

**Process Disadvantages Advantages**

**Table 1.** Maximum acceptable concentrations of metals in drinking water according to the US EPA [6].

Separation difficult Not very effective Produces sludge

conversion rate is slow and susceptible to adverse weather conditions

**Element US EPA Limit (mg L-1)**

Bioremediation of Waters Contaminated with Heavy Metals Using *Moringa oleifera* Seeds as Biosorbent

Antimony 0.006 Arsenic 0.010 Beryllium 0.004

Chromium (total) 0.1

Cadmium 0.005 Cupper 1.3 Lead 0.015 Mercury 0.002 Selenium 0.05 Silver 0.1

Applied to high concentrations

Adsorption Not effective for some metals Conventional sorbents (coal)

Simple Low cost

Low cost

Effective

Mineralization Enables metal recovery

Pure effluent (for recycling)

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Enables metal recovery

Pure effluent obtained

Precipitation and filtration For high concentrations

Chemical oxidation and reduction Requires chemicals

Reverse osmosis High pressures

Biological oxidation and reduction When biological systems are used the

Expensive

Expensive

Expensive Produces sludge

Resins of high cost

**Table 2.** Traditional process used in wastewater treatment: advantages and disadvantages [10].

Ion exchange Responsive to the presence of particles

Evaporation Requires an energy source

Due to its properties, water is particularly vulnerable to contamination with heavy metals. Table 1 shows the maximum limits for some metals in drinking water, according to the US Environmental Protection Agency (US EPA) [6]. The US EPA requires that lead, cadmium and total chromium levels in drinking water do not to exceed 0.015, 0.005 and 0.1 mg L-1, respec‐ tively. Corresponding values for other metals are presented in Table 1.

Within this context, and considering that heavy metals do not decay and are toxic even at low concentrations, it is necessary to remove them from various types of water samples. Of the conventional treatments used for the removal of metals from liquid waste, chemical precipi‐ tation and ion exchange are the predominant methods. However, they have some limitations since they are uneconomical and do not completely remove metal ions, and thus new removal processes are required [7-9]. Table 2 illustrates in more detail the advantages and limitations of the traditional methods applied to treat effluents.

Bioremediation of Waters Contaminated with Heavy Metals Using *Moringa oleifera* Seeds as Biosorbent http://dx.doi.org/10.5772/56157 227


**Table 1.** Maximum acceptable concentrations of metals in drinking water according to the US EPA [6].

Mining Agricuture Wastewater Industry Urban

**Figure 1.** Waste containing heavy metals produced in developed countries [1].

226 Applied Bioremediation - Active and Passive Approaches

contradictory definitions and lack of a coherent scientific basis [2].

tively. Corresponding values for other metals are presented in Table 1.

or teeth (nickel, cadmium, copper, chromium) [5].

of the traditional methods applied to treat effluents.

Many different definitions have been proposed for heavy metals, some based on density, some on atomic number or atomic weight, and others on chemical properties or toxicity, which are not necessarily appropriate. For example, cobalt, iron, copper, manganese, molybdenium, vanadium, strontium and zinc are required to perform vital functions in the body and therefore cannot be considered as compounds with high toxicity or ecotoxic properties. Regarding the meaning of the term "heavy metal" it was found that there can be misinterpretation due to the

In conventional usage "heavy" implies high density and "metal" refers to the pure element or an alloy of metallic elements. According to Duffus [2], a new classification should reflect our understanding of the chemical basis of toxicity and allow toxic effects to be predicted. Various publications have used the term "heavy metals" related to chemical hazards and this definition will also be used herein. Among the classes of contaminants, heavy metals deserve greater concern because of their high toxicity, accumulation and retention in the human body. Moreover, heavy metals do not degrade to harmless end products [3, 4]. It is well established that the presence of heavy metals in the environment, even in moderate concentrations, is responsible for producing a variety of illnesses of the central nervous system (manganese, mercury, lead, arsenic), the kidneys or liver (mercury, lead, cadmium, copper) and skin, bones,

Due to its properties, water is particularly vulnerable to contamination with heavy metals. Table 1 shows the maximum limits for some metals in drinking water, according to the US Environmental Protection Agency (US EPA) [6]. The US EPA requires that lead, cadmium and total chromium levels in drinking water do not to exceed 0.015, 0.005 and 0.1 mg L-1, respec‐

Within this context, and considering that heavy metals do not decay and are toxic even at low concentrations, it is necessary to remove them from various types of water samples. Of the conventional treatments used for the removal of metals from liquid waste, chemical precipi‐ tation and ion exchange are the predominant methods. However, they have some limitations since they are uneconomical and do not completely remove metal ions, and thus new removal processes are required [7-9]. Table 2 illustrates in more detail the advantages and limitations


**Table 2.** Traditional process used in wastewater treatment: advantages and disadvantages [10].

For these reasons, alternative technologies that are practical, efficient and cost effective for low metal concentrations are being investigated. Biosorption in the removal of toxic heavy metals is especially suited as a 'nonpolluted ' wastewater treatment step because it can produce close to drinking water quality from initial metal concentrations of 1-100 mg L-1, providing final concentrations of < 0.01-0.1 mg L-1 [11]. Biosorption has been defined as the ability of certain biomolecules or types of biomass to bind and concentrate selected ions or other molecules from aqueous solutions. It should to be distinguished from bioaccumulation which is based on active metabolic transport; biosorption by dead biomass is a passive process based mainly on the affinity between the biosorbent and the sorbate [12]. The biosorption of heavy metals by non-living biomass of plant origin is an innovative and alternative technology for the removal of these pollutants from aqueous solution and offers several advantages such as low-cost biosorbents, high efficiency, minimization of chemical and/or biological sludge, and regener‐ ation of the biosorbent [13].

Recently, natural adsorbents have been proposed for removing metal ions due to their good adsorption capacity. Technologies based on the use of such materials offer a good alternative to conventional technologies for metal recovery. In this context, *Moringa oleifera* represents an alternative material for this purpose [14-16].

**Figure 2.** Tree of *Moringa oleifera* species [18].

Bioremediation of Waters Contaminated with Heavy Metals Using *Moringa oleifera* Seeds as Biosorbent

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**Figure 3.** Pods of *Moringa oleifera* [18]*.*
