Caulerpa Species as Adsorbents for Pollutants

The high adsorption properties of preparations from Caulerpa species on dyes and heavy metals have recently attracted increasing interest. Caulerpa species are proposed as low-cost adsorbents in these studies. Several physicochemical characterisations such as determination of adsorption kinetics, equilibrium constants and thermodynamics of the adsorption process have been reported. Generally, pseudo-first-order and pseudo-second-order kinetic models are used to express adsorption kinetics. Langmuir, Freundlich and Dubinin-Radushkevich models are the most used isotherm models.

The first study on adsorptive properties of powdered Caulerpa lentillifera was carried out by Marungrueng and Pavasant (2006). The basic dye astrazon blue FGRL was adsorbed according to a pseudo-second-order model. The chemisorption occurs with a positive enthalpy value (Marungrueng and Pavasant, 2006). In a comparative investigation of adsorption properties of C. lentillifera and activated carbon, Marungrueng and Pavasant (2007) showed that the algal powder has about 1.75-fold higher adsorption capacity (417.19 mg/g) for methylene blue compared to activated carbon (238.12 mg/g).

Pavasant et al. (2006) investigated the affinity of dried and powdered C. lentillifera on metal ions such as Cu2+, Cd2+, Pb2+ and Zn2+. FT-IR analysis allowed the identification of the functional groups which are associated with the metal adsorption (O-H bending, N-H bending, N-H stretching, C-N stretching, C-O stretching, S=O stretching and S-O stretching). A low equilibrium time of 10-20 min was required for the adsorption of Cu2+, Cd2+, Pb2+ and Zn2+ onto C. lentillifera. The adsorption process obeyed the Langmuir isotherm; the maximum sorption capacities were confirmed in the order Pb2+ > Cu2+ > Cd2+ > Zn2+.

Sorption of copper, cadmium and lead ions in a binary component system prepared from the same macroalga was studied by Apiratikul and Pavasant (2006). The presence of a second ion reduces the adsorption capacity of the algal preparations. Pb2+ was the best sorbed species, followed by Cu2+ and Cd2+.

Apiratikul and Pavasant (2008) investigated the batch and column biosorption of the above-mentioned heavy metals by using preparations of the same macroalga C. lentillifera. The authors gave column properties and performances (effects of flow rate and bed depth) related to metal ions biosorption. The release of Ca(II), Mg(II) and Mn(II) from algal residue during the sorption was observed and it was proposed that column systems could be employed for the remediation of wastewaters.

Aravindhan et al. (2007a) studied biosorption of basic blue (Sandocryl blue C-RL), which is used in leather industry, onto Caulerpa scalpelliformis. They developed a two-stage treatment with this seaweed to obtain complete decolorisation. Aravindhan et al. (2007b) in another study investigated the factors that affected sorption of yellow dye (Sandocryl golden yellow C-2G) onto C. scalpelliformis. They reported a maximum uptake of 27 mg of dye/g seaweed.

Cengiz and Cavas (2008) studied methylene blue adsorption onto invasive C. racemosa and proposed an alternative use of biomass of this alga after possible eradication efforts that could be based on manual uprooting.

Punjongharn et al. (2008) studied the influence of particle size and salinity on the biosorption of basic dyes by C. lentillifera. The authors prepared three powders from C. lentillifera with average grain sizes of S (0.1-0.84 mm), M (0.84-2.0 mm) and L (larger than 2.0 mm). They found that S- algal powder had the highest adsorption capacity and increased salinity caused the decreased adsorption capacity.

C. racemosa powder was also used to remove malachite green from aqueous solutions by a physisorption process (Bekci et al., 2009). In another study, the same group showed the affinity of C. racemosa powder on boron in the form of borate. They proposed the removal of boron with dried and powdered biomass of C. racemosa (Ant-Bursali et al., 2009).

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