Chitosan-macroalgae biocomposites as potential adsorbents of water-soluble hydrocarbons: Organic matter and ionic strength effects

Nowadays the recovery of low-molecular soluble aromatic hydrocarbons (HCs) released into natural bodies of water continues to be a challenging task. These contaminants bring sever consequences to the environment and to the human health. Biosorption on macroalgae (Ma) biomass seem to be a potential alternative due to low costs and high availability, but the low strength and density are important drawbacks to handle, start up and operate continuous biosorption units. In this study, chitosan (Ch) and pectin (Pe) were employed as precursors to synthesize a new Ma−Ch−Pe composite with regard to enhance the stability and applicability of macroalgae biomass towards the removal of soluble HCs pollutants. The biocomposite synthesis was based on a factorial design and a posterior response surface methodology. The optimized biocomposite (75.4%, 19.8 and 4.8% for macroalgae biomass, chitosan and pectin, respectively), was characterized and evaluated under different ionic strengths, pH values and organic load to determine their potential as biosorbents and to elucidate the adsorption mechanisms involved. Removal capacities were 58.68, 16.64 and 6.13 mg g−1 for benzene, toluene and naphthalene, respectively. The adsorption capacity was slightly influenced by the pH (3–9), and diminished with ionic strength values up to I > 0.6 M. The presence of dissolved organic matter (DOM) enhanced the removal of HCs by providing hydrophobic sites to the biosorbents. Moreover, the biosorption data was well-described by Sips adsorption isotherm, and the pseudo-second order equation represented the best fitting model for the biosorption kinetics. The biosorption mechanisms included hydrophobic effect by the algae fraction and London forces between the HC and the diverse of functional groups present offered by the precursors.