Phytoremediation of Metal-Contaminated Soils Using Organic Amendments

Activated carbon contains carbonaceous material derived from charcoal. Activated carbon is produced by pyrolysis of organic materials of plant origin. These materials include coal, coconut shells and wood, sugarcane bagasse, soybean hulls and nutshell (Dias et al., 2007; Paraskeva et al., 2008). On a limited scale, animal manures are also used for the production of activated carbon. Use of activated carbon is common to remove metals from waste waters, but its use for metal immobilization is not common in contaminated soils (Gerçel and Gerçel, 2007; Lima and Marshall, 2005b). Poultry manure derived activated carbon had excellent metal binding capacity (Lima and Marshall, 2005a). Activated carbon is often used for remediation of pollutants in soil and water due to porous structure, large surface area and high adsorption capacity (Üçer et al., 2006). Activated carbon removes metals (Ni, Cu, Fe, Co, Cr) from solution through precipitation as metal hydroxide, adsorption on activated carbon (Lyubchik et al., 2004). Almond husk derived AC effectively removed Ni from waste waters with and without H₂SO₄ treatment (Hasar, 2003).

Recently, biochar has been used as a soil amendment due to its beneficial effects on different soil physical and chemical properties (Beesley et al., 2010). Biochar contains very high contents (up to 90%) depending upon the parent material (Chan and Xu, 2009). Addition of biochar improves the adsorption of dissolved organic carbon, soil pH, decreases metals in the leachates and supplement macro nutrients (Novak et al., 2009; Pietikäinen et al., 2000). Long term persistence of biochar in soil decreases input of metals through repeated application of other amendments (Lehmann and Joseph, 2009). Beesley et al. (2010) concluded that biochar decreased water soluble Cd and Zn in the soils due to increase in organic carbon and pH. Activated carbon decreased metal concentration (Ni, Cu, Mn, Zn) in shoots of maize plants grown in contaminated soils compared to the un-amended soil (Sabir et al., 2013). Biochar decreased high concentrations of soluble Cd and Zn in a contaminated soil (Beesley and Marmiroli, 2011). They concluded that sorption is an important mechanism for retention of metals by soils. Biochar decreased concentration of Cd and Zn to a 300- and 45-fold decrease in their leachate concentrations, respectively (Beesley and Marmiroli, 2011).