Removal of paraquat from drinking water by activated carbon prepared from waste wood

In this study, activated carbon was produced from the chips of two wood species, namely Ayous (Triplochiton schleroxylon) and Sapelli (Entandrophragma cylindricum) and characterized for its texture by scanning electron microscopy, granulometry using a master sizer, and the structure by determining the iodine and methylene blue indices. The obtained carbon was used to study the adsorption of paraquat in aqueous solution. Results from the characterization of carbon revealed that it consist essentially of micropores and mesopores, a tubular structure, and a fine coating of very small granules on the surface (Ayous) and elongated fibers (Sapelli). The adsorption kinetics of paraquat in solution followed a maximum exponential growth model with three stages: the first, which corresponds to an increase adsorption of the molecule on sites located on the outer surface of the carbon, the second phase, which correspond to the diffusion of the molecules on the internal pores, and the third constant phase corresponding to the adsorption equilibrium. The equilibrium time obtained was 10 min for Ayous with 87% of paraquat adsorbed and 20min for Sapelli with 90% of paraquat adsorbed. The biosorption kinetics of paraquat in the solution followed a pseudo-first order and intra-particle diffusion model. Result from the influence of paraquat concentration and mass of carbon showed that, an increase in concentration and mass of the adsorbent impel respectively in the amount of the paraquat molecule adsorbed. Change of solution pH does not affect the amount of paraquat adsorbed whatever the type of carbon. The adsorbed amounts of paraquat decreased (from 88 to 60 mg g−1) as the ionic strength increased from 5 × 10−3 to 5 × 10−2 M. This study shows that activated carbon products obtained from Sapelli and Ayous wood chips, which are wastes released into the environment, can be used as low-cost biosorbents for the removal of organic micropollutants in drinking water.