A continuous adsorption study in a fixed-bed column was carried out using a chitosanglutaraldehyde biosorbent for the removal of the textile dye Direct Blue 71 from an aqueous solution. The biosorbent was prepared from shrimp shells and characterized by scanning electron microscopy, X-ray diffraction, and nuclear magnetic resonance spectroscopy. The effects of chitosan-glutaraldehyde bed height (3-12 cm), inlet Direct Blue 71 concentration (15-50 mg l À1), and feed flow rate (1-3 ml min À1) on the column performance were analyzed. The highest bed capacity of 343.59 mg Direct Blue 71 per gram of chitosan-glutaraldehyde adsorbent was obtained using 1 ml min À1 flow rate, 50 mg l À1 inlet Direct Blue 71 concentration, and 3 cm bed height. The breakthrough curve was analyzed using the Adams-Bohart, Thomas, and bed depth service time mathematical models. The behaviors of the breakthrough curves were defined by the Thomas model at different conditions. The bed depth service time model showed good agreement with the experimental data, and the high values of correlation coefficients (R 2 ! 0.9646) obtained indicate the validity of the bed depth service time model for the present column system.

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The present study was designed to evaluate the chitosan, which has been obtained by deacetylation of chitin, as a biosorbent. The chitin was isolated from fermented shrimp waste by an important local industrial food biopolymer. The aim of this work was the characterization of chitosan and preparation of cross-linked chitosan- tripolyphosphate (chitosan-TPP) beads for the removal of allura red food dye from aqueous solutions. Conditions of batch adsorption such as pH, time and adsorbent dose were examined. The effectiveness of cross-linked chitosan beads for dye removal was found to be higher for pH 2 (98%, percentage of dye removal) and tends to decrease at pHs of 3 to 11 (up to 49%). The values of percentage removal show that the adsorption capacity increases with time of contact and dosage of chitosan-TPP, but red dye adsorption is mainly influenced by pH level. The cross-linked chitosan-TPP beads can significantly adsorb allura red monoazo dye from aqueous solutions even at acidic pHs unlike raw chitosan beads that tend to dissolve in acidic solutions. Consequently, this modified chitosan has characteristics that allow minimization of environmental pollution and widening the valorization of shrimp waste.

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The purpose of this research was to analyze the adsorption behavior of Fe(II) and Fe(III) ions in aqueous solution onto beads of naturally derived chitosan cross-linked with tripolyphosphate in a batch system. Effects of solution pH, contact time and amount of adsorbent were regarded in the kinetic and equilibrium studies. The optimum conditions of adsorption for Fe(II) and Fe(III) were obtained as pH 5 and 3, amount of adsorbent 2 and 1.9 g and contact time 70 and 60 min, respectively. The kinetic and equilibrium experimental data were integrated into different models using the non-linear regression method. As a result, the pseudo-second-order and the Redlich-Peterson isotherm were the best evaluated models. The adsorption capacity, based on Langmuir, was 11.65 mg g À1 for Fe(II) and 13.72 mg g À1 for Fe(III). The beads of chitosan cross-linked with tripolyphosphate may be used as an effective bioadsorbent for the removal of Fe(II) and Fe(III) from an aqueous solution. This study confirms that the chitosan isolated from shrimp waste can be used to remove certain heavy metals in wastewater, without adversely affecting the ecosystem. NOMENCLATURE a R Redlich-Peterson isotherm constant, (L mg À1 ) g b Langmuir constant, L mg À1 C 0 Initial concentration of metal ions in the solution, mg L À1 C e Equilibrium concentration of metal ions in the solution, mg L À1 C f Final concentration of metal ions in the solution, mg L À1g Redlich-Peterson isotherm exponent K 1 Pseudo-first-order rate constant, min À1 K 2 Pseudo-second-order rate constant, g min À1 mg À1 K F Freundlich constant, (mg g À1 ) (L mg À1 ) 1/n K i Intra-particle diffusion rate constant, mg g À1 min À0.5 K R Redlich-Peterson isotherm constant, L g À1 m Dry mass of adsorbent, g n Freundlich constant Q 0 Maximum adsorption capacity, mg g À1 q e Equilibrium adsorption capacity of the adsorbent, mg g À1 q m Adsorption capacity obtained from the kinetic or isotherm models, mg g À1 q t Adsorption capacity of the adsorbent at time t, mg g À1 q Average of q e or q t , mg g À1 R L Separation factor t Time, min V Volume of solution, L α Elovich initial adsorption rate, mg g À1 min À1β Elovich desorption constant, g mg À1

This study focuses on the isolation and quantification of astaxanthin and its esters in the oils extracted from shrimp waste. The content of astaxanthin was determined by high performance liquid chromatography and ranged from 1.5 to 2.1 mg g -1 . The astaxanthin and its esters were isolated by thin layer chromatography in three fractions: free astaxanthin, monoester, and diester of astaxanthin, with percentages of 44, 32, and 26%, respectively. Oleic acid was the major fatty acid in the monoester fraction, while palmitic, oleic, and stearic acids were present predominantly in the diester fraction. Free radical-scavenging activity of the oils and the three fractions was evaluated. All oils showed an effect on the decrease in the absorbtion of 1,1-diphenyl-2-picrylhydrazyl solutions, while among the fractions no significant difference occurred. Pigmented oil from shrimp waste is an organic source of pigment and antioxidant astaxanthin, the esters, and fatty acids, such as eicosapentaenoic and docosahexaenoic.

Palabras clave: aguas ácidas, metales pesados, bioadsorbente, remoción RESUMEN La minería representa una de las actividades económicas más importantes para muchos países y México no es la excepción. Sin embargo, los residuos líquidos que genera esta actividad suponen un riesgo para el ambiente debido a que se caracterizan por su elevado contenido de iones metálicos y valores bajos de pH. Actualmente, la adsorción en quitosano constituye una alternativa a los tratamientos convencionales para la recuperación de metales pesados en solución acuosa. En este estudio se obtuvieron hidrogeles de quitosano puro y modificado a partir del exoesqueleto de camarón para llevar a cabo ensayos de adsorción de cobre en solución ácida, con particular referencia a los efectos del tiempo de contacto, pH de la solución, masa del adsorbente y concentración inicial de cobre. Los resultados experimentales mostraron que las condiciones óptimas de adsorción de cobre fueron a pH 4, con 4.5 g de adsorbente (quitosano puro) y 4 h de tiempo de contacto, con estas condiciones se alcanzó una remoción del 99.35 %. Adicionalmente, se llevaron a cabo ensayos de adsorción con 160, 250 y 416 ppm de concentración de cobre en solución ácida y se observó que, a menor concentración mayor porcentaje de remoción, con hasta 92 % de remoción para la concentración de 160 ppm, así como 72 y 67.3 % para las concentraciones de 250 y 416 ppm, respectivamente. Lo anterior sugiere que el hidrogel de quitosano puro en forma de perlas, puede ser usado como adsorbente efectivo en la remoción de cobre presente en lixiviados de minas.Key words: acidic waters, heavy metals, biosorbent, removal ABSTRACTMining is one of the most important economic activities for many countries and Mexico is not the exception. However, liquid wastes generated by this activity pose a risk to the environment because they are characterized by its high content of metal ions and low pH values. Currently, the adsorption process in chitosan is an alternative to conventional treatments in the recovery of heavy metals from aqueous solutions. In this study we obtained both, pure and modified chitosan hydrogels from shrimp shell to carry out adsorption tests of copper in acid solution.