Removal of methylene blue from aqueous solutions using a solid residue of the apple juice industry: full factorial design, equilibrium, thermodynamics and kinetics aspects

International audienceThe use of adsorbent materials derived from agro-industrial residues represents a simple, easy and low-cost process for the removal of dyes from aqueous solutions. In this context, this study aimed to evaluate the use of a solid residue from the apple juice industry in the removal of methylene blue (MB) dye. Several different analytical techniques, including elemental analysis, Fourier transform infrared spectroscopy, solid-state 13C nuclear magnetic resonance, nitrogen adsorption/desorption and determination of pH at zero-point charge, were used to investigate the physico-chemical properties of the apple pomace. Conventional bath experiments were carried out by simultaneously optimizing five variables (initial MB concentration, amount of adsorbent, pH, stirring frequency and temperature) using a full 2k factorial design with central point. In general, the characterization analyses evidenced the presence of several types of oxygenated functional groups in the adsorbent chemical structure and a favorable morphology for dye removal. Furthermore, the initial MB concentration, the amount of adsorbent and the pH of the medium had the strongest effect on the response variables, including their interactions and quadratic terms. In terms of equilibrium, it was found that the Langmuir model gave a good fit to the data, while the thermodynamic parameters indicated that the process was spontaneous and exothermic in nature. Moreover, kinetic studies revealed that the MB removal rate followed a pseudo-second-order model, suggesting an adsorption controlled by either diffusion on the stagnant film covering the adsorbent particles or intraparticle diffusion. Finally, the data acquired in this study also emphasized the interest to use materials derived from agro-industrial residues as potential adsorbents in the light of its properties for the removal of basic dyes, including MB

Highly efficient adsorption of antibiotics by spent brewery grains-based activated carbon

This work was developed inside the scope of the project CICECO -Aveiro Institute of Materials (UIDB/50011/2020 & UIDP/50011/2020 & LA/P/0006/2020). We acknowledge financial support to CESAM by FCT/MCTES (UIDP/ 50017/2020+UIDB/50017/2020+LA/P/0094/2020), through national funds. Érika M.L. Sousa thanks to Fundação para a Ciência e Tecnologia (FCT) for her PhD grant (2020.05390.BD). Paula Ferreira is thankful to FCT for the Investigator Program (IF/00300/2015). María V. Gil acknowledges support from a Ramón y Cajal grant (RYC-2017-21937) of the Spanish government and the Spanish State Research Agency, co-financed by the European Social Fund (ESF)

Structural description of humic substances from subtropical coastal environments using elemental analysis, FT-IR and 13C-solid state NMR data

Elemental composition and spectroscopic properties (FT-IR and CP/MAS 13C-NMR) of sedimentary humic substances (HS) from aquatic subtropical environments (a lake, an estuary and two marine sites) are investigated. Humic acids (HA) are relatively richer in nitrogen and in aliphatic chains than fulvic acids (FA) from the same sediments. Conversely, FA are richer in carboxylic groups and in ring polysaccharides than HA. Nitrogen is mostly present as amide groups and for lake and marine HS the FT-IR peaks around 1640 cm-1 and 1540 cm-1 identify polypeptides. Estuarine HS exhibit mixed continental-marine influences, these being highly influenced by site location. Overall, the data suggest that aquatic and mixed HS are more aliphatic than has been proposed in current models and also that amide linkages form an important part of their structural configuration

Kinetics of the PO4-P adsorption onto soils and sediments from the Mondego estuary (Portugal)

In order to assess the status of a North Atlantic Ocean Ecoregion (Mondego system, Portugal) after the implementation of a management programme, a study on PO4-P sorption was carried out. Considering that sorption velocity markedly determines the systems promptness to phosphorus external loading, the kinetics of the sorption of PO4-P onto estuarine sediments and the upstream agricultural soils was studied. The pseudo-second order kinetic equation gave an appropriate description of PO4-P sorption onto these soils and sediments, allowing for a quantitative comparison. For soils, the kinetic constants (k 2, lg 1 g h 1) ranged between 0.007 and 0.017 lg 1 g h 1 while, in the case of sediments these ranged between 0.008 and 0.012 lg 1 g h 1. Results showed that the reduction of water residence time after the management action was relevant for the system status, affecting its reaction capacity to phosphorus loading.The authors want to acknowledge financial support from FCT (Fundação para a Ciência e a Tecnologia) to CESAM (Centre for Environmental and Marine Studies) and to IMAR (Institute of Marine Research). The Post-Doc grant SFRH/BPD/48449/2008 (P. Coelho) funded by FCT is also acknowledged