Composites of high-density polyethylene and agave fibers coated with chitosan were used as adsorbent for Cr(VI). The adsorptions were made in batch and continuous systems. Different kinetic models were used to characterize the batch adsorption and to determine the adsorption capacity of the compound. To test the composite regeneration/reuse capability, the chromium content in the composite material was desorbed using different acids. The coated composites were characterized by scanning electron microscopy (SEM), attenuated total reflectance infrared spectroscopy (ATR-IR), and X-ray photoelectric spectroscopy (XPS). From the results it was found that the composite has a maximum adsorption capacity of 200 mg Cr(VI)/g of chitosan at pH 4. Sulfuric acid proved to be a good desorbent of Cr(VI), allowing the material to be reused while keeping its adsorption properties. Finally, the results showed that the continuous system has higher sorption capacity than the batch system; it was determined that the system needs a minimum retention time of 20 min in order to use the material in the treatment of contaminated effluents.
Wetland plant uptake of 14C-labeled phenanthrene and chlorobenzene was investigated in greenhouse studies using sediment prepared to contain only the desorption-resistant fraction of the contaminant. Measurements of contaminant distribution in the plants and root-contaminant partition coefficients were conducted as well as estimates of the transpiration stream concentration of chlorobenzene and phenanthrene. Plant uptake of desorption-resistant phenanthrene and chlorobenzene occurred primarily in the root zone with total uptake ranging from 3.8 to 5.7% of the initial concentration in the sediment. Observed uptake of the compounds was remarkably similar despite wide differences in contaminant properties. A biphasic sorption isotherm was combined with a simple translocation model to predict plant uptake from two processes: root sorption and translocation. The model predicted the observed uptake well and may serve as an important tool for estimating plant uptake in sediments containing a desorption-resistant fraction. The potential implications of the existence of a finite, desorption-resistant pool of contaminants on phytoremediation of sediments are discussed.
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