Uptake of copper from acid mine drainage by the microalgae Nannochloropsis oculata.

The removal of heavy metals from acid mine drainage is a key factor for avoiding damage to the environment. The microalga Nannochloropsis oculata was cultured in an algal medium with 0.05, 0.1, 0.15, 0.2, and 0.25 mM copper under completely defined conditions to assess its removal capacity; the effects of copper on the cell density and lipid productivity of N. oculata were also evaluated. The results showed that N. oculata was able to remove up to 99.92 ± 0.04% of the copper content in the culture medium. A total of 89.29 ± 1.92% was eliminated through metabolism, and 10.70 ± 1.92% was removed by adsorption. These findings are favorable because they indicate that a large amount of copper was extracted due to the ability of the microalga to metabolize copper ions. The cell density, growth rate, and lipid content decreased with increased concentrations of copper in the culture medium. A positive effect on the fatty acid profile was found, as the saturated fatty acid (SFA) and monounsaturated fatty acid (MUFA) content improved when the copper concentration was higher than 0.1 mmol L-1, which can potentiate the production of high-quality biodiesel. N. oculata is a good option for the treatment of acid mine drainage due to its ability to eliminate a substantial percentage of the copper present. Moreover, combining different culture systems such that heavy metals are removed to non-toxic levels in the first stage and high cell densities, which promote lipid production, is obtained in the second stage would be an advantageous strategy.

Modeling of breakthrough curves for aqueous iron (III) adsorption on chitosan-sodium tripolyphosphate.

A fixed bed column packed with chitosan-sodium tripolyphosphate (CTPP) beads was used to remove aqueous Fe (III) ions. The adsorption of Fe (III) ions on CTPP beads was found to be dependent on operating conditions, such as the flow rate, adsorbent bed length, and feed concentration. The experimental data were assessed with Thomas, Adams-Bohart and Yoon-Nelson models to predict the breakthrough curves using linear regression. The breakthrough curves were better fitted with the Thomas and Yoon-Nelson models when the flow rate was varied and the feed concentration and the bed height of the column were fixed. Therefore, chemical adsorption may be the limiting step that controls the continuous adsorption process. The Adams-Bohart model presented a good fit to the experimental data, showing that external mass transfer was controlling the adsorption process in the initial part of the breakthrough curves. The parameters obtained from the continuous adsorption assays may be used as a basis for designing columns packed with CTPP beads for the removal of Fe (III) ions.

Adsorption of allura red dye by cross-linked chitosan from shrimp waste.

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.