Valorisation of Lignocellulosic Wastes, the Case Study of Eucalypt Stumps Lignin as Bioadsorbent for the Removal of Cr(VI).

The main objective of this work was to assess Eucalyptus globulus lignin as an adsorbent and compare the results with kraft lignin, which has previously been demonstrated to be an effective adsorbent. Eucalypt lignin was extracted (by the dioxane technique), characterised, and its adsorption properties for Cr(VI) ions were evaluated. The monomeric composition of both types of lignin indicated a high content of guaiacyl (G) and syringyl (S) units but low content of p-hydroxyphenyl (H), with an H:G:S ratio of 1:50:146 (eucalypt lignin) and 1:16:26 (kraft lignin), as determined by Py-GC/MS. According to elemental analysis, sulphur (2%) and sodium (1%) were found in kraft lignin, but not in eucalypt lignin. The adsorption capacity of the eucalypt lignin was notably higher than the kraft lignin during the first 8 h, but practically all the ions had been absorbed by both the eucalypt and kraft lignin after 24 h (93.4% and 95%, respectively). Cr(VI) adsorption onto both lignins fitted well using the Langmuir adsorption isotherm model, with capacities of 256.4 and 303.0 mg/g, respectively, for eucalypt and kraft. The study's overall results demonstrate the great potential of eucalypt lignin as a biosorbent for Cr(VI) removal from aqueous solutions.

Modelling and efficiency evaluation of the continuous biosorption of Cu(II) and Cr(VI) from water by agricultural waste materials.

As a result of intensive anthropogenic activities, population growth and unplanned urbanization, enormous quantities of organic and inorganic pollutants are discharged into the environment every year. The primary hazardous substances of concern regarding their environmental load and health effects are heavy metals. Heavy metal pollution of aquatic ecosystems, including resources of drinking water and water intended for food processing, has been of increasing interest. Biosorption technology is a promising strategy, as it utilizes industrial or agricultural wastes to remove metals from aqueous media passively, and they represent efficient, cost-effective and environmentally friendly alternatives to traditional adsorbents such as activated carbon. In this paper, the efficiency of biosorption of copper and chromium ions was examined using different agricultural waste biomass - sugar beet shreds, poplar sawdust and wheat straw. The possibility of applying a parallel sigmoidal (PS) model to describe the biosorption process was investigated to confirm its applicability to different types of biomass and various kinds of heavy metal ions. The results showed that the biosorption of copper ions using poplar sawdust and wheat straw consist of two steps. The moiety of one step in the overall process, defined by the parameter p, was determined to be 0.85 for poplar sawdust and 0.86 for wheat straw. These values, being less than 1, clearly indicate that the process consists of two simultaneous, kinetically different steps that shift in their dominance over the process and thus could be successfully modelled by the PS model. These studies also deal with the phenomenological examination of an unusual breakthrough curve obtained for the chromium ions biosorption by sugar beet shreds, by the comparative view of the process flow and changing the pH of the effluent. The clarification of the appearance of a double curve with a negative trend in one part allows adjusting the biosorption conditions to avoid the initial blockage of chromium ion binding to the adsorbent and thus increase the adsorption process efficiency.

A new approach for modelling and optimization of Cu(II) biosorption from aqueous solutions using sugar beet shreds in a fixed-bed column.

The potential use of sugar beet shreds for copper ions removal from aqueous solution in a fixed-bed column was investigated. Experiments were performed using Box-Behnken experimental design on three levels and three variables: concentration of the inlet solution (50-150 mg L-1), adsorbent dosage (8-12 g) and pH of the inlet solution (4.0-5.0). The obtained breakthrough curves were fitted with two common empirical models, Bohart-Adams and dose-response. Observing the asymmetric shape of the breakthrough curves, the new mathematical model was proposed. The new model proposes the breakthrough curve composed of two parts, sum of which gives the asymmetrical S-shaped curve, accurately matching experimental data. Regarding the lowest SSer (7.8·10-4) and highest R2 (0.9998), new model exhibited the best fit comparing to the commonly used models. RSM and ANN modelling were employed for process variables evaluation and optimization. The most influential parameter exhibiting negative influence on target response (critical time) was concentration of the inlet solution, while the adsorbent dosage exhibited positive influence. Optimization procedure revealed that the highest critical time (341.4 min) was achieved at following conditions: C0 = 50 mg·L-1, ma = 12 g and pH 4.53 by ANN, while RSM considered pH as insignificant factor and obtained 314.8 min as the highest response.