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The sustainable management of loaded adsorbents with organic pollutants represents an important environmental challenge. The current research work investigates the regeneration process optimization of raw orange tree sawdust (ROS) loaded with methylene blue (MB) by using NaCl solutions as eluent. The MB desorption was assessed in static mode under different process variables, notably the desorbing NaCl solution’s pH and concentration and the MB-loaded biomass dose. A full factorial design composed of 24 experiments was employed to apprehend the statistical significance of each followed parameter. Experimental results showed that the maximum desorption yield was estimated to be about 82.4% for the following parameter’s values: aqueous pH = 3, [NaCl] = 0.2 M and MB-loaded-ROS dosage in the desorbing solution = 1 g·L −1 . The statistical study confirmed the good fit of the experimental data with the statistical model used as well as regression and adjusted regression coefficients of about 99.0% and 96.6%, respectively. Moreover, the ranking of the effect of each studied parameter in terms of standardized effect on the desorption efficiency of MB from ROS was assessed through ANOVA test. The desorption mechanisms involved were explored by using multiple analysis techniques. It appears that the MB molecules’ desorption from ROS’s particles is mainly driven by a counter chemisorption process based on cationic exchange with the sodium and hydronium ions present in the desorbing solutions [ABSTRACT FROM AUTHOR]

Lignite, as an abundant and low-cost material, was tested for lead (Pb(II)) removal from aqueous solutions under various experimental conditions for both static (batch) and dynamic (column) experiments. Static assays showed that Pb(II) removal efficiency increases with rising in its initial concentration, aqueous pH, and adsorbent dosage values. Adsorption kinetic and isothermal data were well fitted with the pseudo-second-order and Freundlich models, respectively, suggesting that lead removal by lignite is mainly governed by chemical processes and occurs heterogeneously on multilayer surfaces. The maximum Langmuir’s adsorption capacity was equal to 61.4 mg·g −1, which is high in comparison to various natural materials. The laboratory column experiments showed that Pb(II) breakthrough curves and subsequent lignite adsorption efficiency is highly dependent on the bed height. Due to the short time contact between Pb(II) and lignite particles inside the column, the highest adsorption capacity was about 21%, which is lower than the one found in the batch mode. Even under dynamic conditions, lignite exhibits a high adsorption capacity compared to other adsorbents, which promotes its use as a low-cost and efficient material for Pb(II) and the removal of other heavy metals from wastewaters. [ABSTRACT FROM AUTHOR]

Studies on the removal of methylene blue (MB) from aqueous solutions by anodic oxidation (AO) using a boron-doped diamond (BDD) electrode, adsorption onto sawdust, and combined treatment have been undertaken. The results proved that AO presents a high efficiency in removing both color and COD in a wide pH interval. The total mineralization of the dye solution was performed in 6 h, which corresponds to relatively high-energy consumption. On the other hand, high sawdust dosage (12 g·L −1 ) was needed to ensure 98% of color and 81% of COD removal. Combining AO and adsorption onto sawdust constitute a very interesting technology. For instance, AO for 1 h followed by sorption permits a reduction in energy consumption by 80 W·h·g COD −1 , a reduction of more than 24 times the adsorbent dose and an enhancement of color and COD removal, indicating that sawdust is efficient in removing not only the MB initial molecules but also the electrogenerated by-products. [ABSTRACT FROM AUTHOR]

Phosphorus removal from synthetic solutions by raw and calcined powdered marble wastes (RPMW and CPMW) has been investigated in batch mode under different experimental conditions. The results showed that RPMW and CPMW have high removal efficiencies, especially in acidic media. The maximum phosphorus removal capacities were evaluated to 103.9 and 181.2 mg·g −1 at an initial pH and an aqueous concentration of 5 and 350 mg·L −1 , respectively. Phosphorus removal by RPMW occurred mainly through adsorption. However, for CPMW, phosphorus was removed not only by adsorption, but also by precipitation as calcium phosphate complexes. Specific analyses using scanning electron microscopy, energy dispersive spectroscopy, X-ray diffraction and Fourier transform infrared spectroscopy confirmed that this precipitate is most probably hydroxyapatite. On the other hand, CPMW have demonstrated an important ability in removing phosphorus from highly concentrated dairy wastewater ( C 0,P = 1000 mg·L −1 ) since only one dosage of 10 g·L −1 was enough to ensure more than 97% of phosphorus removal. [ABSTRACT FROM AUTHOR]

This work aimed to study petiole palm tree wastes (PTW) efficiency in removing two basic dyes: Rhodamine B (RB) and Victoria blue B (VBB) from aqueous solutions in single and binary systems under various experimental conditions including the effect of contact time, pH, initial concentration, and temperature. The PTW characterization shows that the PTW is a lingo-cellulosic material. The experimental results indicate that the removal of both dyes was relatively fast, spontaneous, exothermic and occurred on monolayers. Moreover, the adsorption competition between these two dyes on the adsorbent particles surface was important since the Langmuir's adsorption capacities were evaluated to 260.1; 440.1; 168.0; and 417.4 mg/g for RB and VBB in single and binary systems, respectively. These adsorption capacities, even in binary systems, are interesting compared to other raw materials and prove that this abundant agricultural waste can be considered as a promising material for an efficient dyes removal from aqueous effluents. [ABSTRACT FROM AUTHOR]

In this work, six Tunisian local biomasses, namely ziziphus wood (ZW), almond shells (AS), olive stones (OS), vine stems (VS) and date palmleaflets (DPL) and trunks (DPT)were slowly pyrolyzed under inert atmosphere at a heating rate of 5 °C/min through thermogravimetric (TG) analyses. The thermal degradation of samples involves the interaction in a porous media of heat, mass and momentum transfer with chemical reactions. Heat is transported by conduction, convection and radiation and, mass transfer is driven by pressure and concentration gradients. Thermal degradation curves have been studied with minute details for each degradation step. The Coats-Redfern model was used to extract the kinetic parameters from the TG data, then the kinetic parameters such as the activation energy, the pre-exponential factor and the order of the reaction were calculated. Results showed that the total mass losses amounts and kinetics are dependent on the type of the used biomass. Moreover, the devolatilization could be described by the first order model, while the char formation stage was better described by the second and third order reactions model. The physicochemical characteristics of these samples were also determined. The volatile matter (VM) content varies considerably, with values ranging from 67.19% for AS to 77.4% for ZW. The maximum values were obtained for ZW and VS with values of 77.4% and 71.9%, respectively. The lowest value (67.19%) was determined for AS. In addition, the ash contents vary between 0.8% for OS and 5.66% for DPT. The ashes vary significantly from one sample to another, with the values being even lower than 1% for OS, whereas the higher values in the DPT is 5.66%. Further, activation energies corresponding to main devolatilization regions were 59.5, 47.0, 55.8, 41.1, 89.1, 45.2 kJ/mol for ZW, AS, OS, VS, DPL, and DPT respectively. Among all the tested biomasses, the ZW and VS appear to have an important potential to be used for energy production. [ABSTRACT FROM AUTHOR]

In this work, four activated carbons were synthetized from natural olive stone (NOS) wastes using ZnCl2 as an activating agent. These activated carbons (OSAC) were synthetized for a constant mass ratio of ZnCl2: NOS of 2:1, a contact time of 2 h and four different heating temperatures (300, 400, 450 and 500 °C). The physicochemical characterization of these activated carbons by various analyses including N2 adsorption–desorption measurements, surface charge evolution versus pH, Boehm titration, Fourier transform(FTIR) and scanning electron microscopy (SEM) showed that the activated carbon produced at a temperature of 400 °C (OSAC 400 °C) exhibited the best properties. Indeed, it has the highest BET surface area, total pore and micropore volumes with values of 740 m2·g-1, 0.57 cm³·g-1 and 0.25 cm³·g-1, respectively. Moreover, it is rich in various acidic and basic functional groups that could react with various common adsorbents. The test of these activated carbons, for the adsorption of a cationic (methylene blue (MB)) and anionic (methyl orange (MO)) dye under various experimental conditions, showed that OSAC 400 °C could be considered as an effective, attractive and promising adsorbent for both the tested dyes. The Langmuir’s adsorption capacities of this adsorbent were assessed to 303.0 and 277.8 mg·g-1 for MB and MO, respectively, which are significantly high compared to other various activated carbons. The retention of the pollutants is mainly chemical including hydrogen bond and electrostatic attraction between the dyes and the activated carbon surface. [ABSTRACT FROM AUTHOR]

In this study, we assessed the transformation of raw olive pomace into carbon-richmaterial using olive mill wastewater (OMWW) as the liquid medium for the hydrothermal carbonization (HTC) process. The findings were compared accordingly with the use of distilled water (DW), which is the conventional practice. The use ofOMWWas a liquidmatrix enhanced the hydrochar yield, but volatile matter, fixed carbon content, and O/C and H/C ratios followed a decreasing trend. Furthermore, for an HTC temperature of 220 °C, the use ofOMWWconsiderably increased the high heating value of the hydrochars from approximately 24.2 MJ/kg to 31.6 MJ/kg. According to the van Krevelen diagram of feedstock and derived hydrochars, dehydration was the predominant carbonization reaction for both liquid sources. Morphological characterization of both sets of hydrochars indicated the generation of specific carbon nuclei when using DW while OMWW led to the creation of hydrochar with a less homogeneous surface. Structural analysis revealed the heterogeneous aspect of the hydrochar surface with an abundance of crystallized metal-based inorganic salts. [ABSTRACT FROM AUTHOR]