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In this work, six Tunisian local biomasses, namely ziziphus wood (ZW), almond shells (AS), olive stones (OS), vine stems (VS) and date palm leaflets (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 physico-chemical 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.

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${\cdot }$g$^{-1}$, 0.57 cm3${\cdot }$g$^{-1}$ and 0.25 cm3${\cdot }$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${\cdot }$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.

The transition from the use of fossil fuels to renewable and green energy is a worldwide challenge that must be seriously considered in order to ensure sustainable development and the preservation of the environment. The conversion of wet biomasses (i.e., sewage sludge) into energy through thermochemical processes in general and hydrothermal carbonization (HTC) in particular has been pointed out as an interesting and attractive approach for the energetic and agricultural valorization of the produced solid residues, named hydrochars. The success of such valorization options is highly dependent on these hydrochars' physico-chemical and energetic properties that are influenced not only by the type of the sludge (urban or industrial) and its nature (primary, secondary, or digested) but also by the HTC parameters, especially temperature, pressure, and residence time. This editorial provides a summary of the latest studies regarding the impact of the cited above parameters on the properties of the produced hydrochars. The economic and environmental feasibility of this process for sewage sludge management is also presented. [ABSTRACT FROM AUTHOR]

This paper presents an in-depth characterization of a raw industrial sludge (IS-R) and its KOH-activated biochar pyrolyzed at 750 °C (IS-KOH-B) followed by their application to remove a cationic dye from aqueous solution. Materials characterization shows that compared to the IS-R, the IS-KOH-B has improved structural, textural, and surface chemical properties. In particular, the IS-KOH-B's BET surface area and total pore volume are about 78 and 6 times higher than those found for the IS-R, respectively. The activated biochar efficiently retained the cationic dye under wide experimental conditions. Indeed, for an initial dye concentration of 50 mg L−1, removal yields were assessed to be more than 92.5%, 93.5%, and 97.8% for a large pH range (4–10), in the presence of high contents of competing cations (3000 mg L−1 of Ca2+, Mg2+, Na+, and K+), and a low used adsorbent dose (1 g L−1), respectively. The Langmuir's adsorption capacities were 48.5 and 65.9 mg g−1 for of IS-R and IS-KOH-B, respectively, which are higher than those reported for various adsorbents in the literature. The dye removal was found to be monolayer, spontaneous, and endothermic for both the adsorbents. Moreover, this removal process seems to be controlled by chemical reactions for IS-KOH-B whereas by both physico–chemical reactions for IS-R. This study demonstrates that the raw industrial sludge and especially its KOH-activated derived biochar could be considered as promising adsorbents for the removal of dyes from aqueous solutions. [ABSTRACT FROM AUTHOR]

Raw poultry manure (RPM) and its derived biochars at temperatures of 400 (B400) and 600 °C (B600) were physico-chemically characterized, and their ability to release nutrients was assessed under static conditions. The experimental results showed that RPM pyrolysis operation significantly affects its morphology, surface charges, and area, as well as its functional groups contents, which in turn influences its nutrient release ability. The batch experiments indicated that nutrient release from the RPM as well as biochars attains a pseudo-equilibrium state after a contact time of about 48 h. RPM pyrolysis increased phosphorus stability in residual biochars and, in contrast, transformed potassium to a more leachable form. For instance, at this contact time, P- and K-released amounts passed from 5.1 and 25.6 mg g−1 for RPM to only 3.8 and more than 43.3 mg g−1 for B400, respectively. On the other hand, six successive leaching batch experiments with a duration of 48 h each showed that P and K release from the produced biochars was a very slow process since negligible amounts continued to be released even after a total duration of 12 days. All these results suggest that RPM-derived biochars have specific physico-chemical characteristics allowing them to be used in agriculture as low-cost and slow-release fertilizers. [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]

Hydrothermal carbonization (HTC) is considered as a promising technique for wastes conversion into carbon rich materials for various energetic, environmental and agricultural applications. In this work, the HTC of olive mill wastewater (OMWW) was investigated at different temperatures (180–220 °C) and both, the solid (i.e., hydrochars) and the final process liquid derived from the thermal conversion process were deeply analyzed. Results showed that the solid yield was affected by the temperature, i.e., decrease from 57% to 25% for temperatures of 180 °C and 220 °C, respectively. Furthermore, the hydrochars presented an increasing fixed carbon percentage with the increase of the carbonization temperature, suggesting that decarboxylation is the main reaction driving the HTC process. The decrease in the O/C ratio promoted an increase of the high heating value (HHV) by 32% for hydrochar prepared at 220 °C. The process liquids were sampled and their organic contents were analyzed using GC–MS technique. Acids, alcohols, phenols and sugar derivatives were detected and their concentrations varied with carbonization temperatures. The assessment of the physico-chemical properties of the generated HTC by-products suggested the possible application of the hydrochars for energetic insights while the liquid fraction could be practical for in agricultural field. Unlabelled Image • Valorization of olive mill wastewater was studied using hydrothermal carbonization. • Characterization of the produced hydrochars was assessed by multiple techniques. • Carbonization process of the precursor was governed by decarboxylation mechanism. • Produced hydrochars presented a high calorific content (35.01 MJ/kg). • Final liquid fractions exhibited interesting organic compounds for agricultural use. [ABSTRACT FROM AUTHOR]

• Raw kenaf stems and its pyrolytic char are fully characterized. • Thermal properties of kenaf stems are more interesting than many other usual crops. • Kenaf stem derived char is very promising for pollutants removal or gas storage. • Kenaf derived char is suitable for soil amendments. • High SSA of the 500 °C-chars incite to activation process to get excellent AC. Kenaf stems are characterized in this present investigation in order to assess their suitability in energy recovery through a pyrolysis process and to identify sustainable applications of the generated biochar. In particular, the raw biomass properties are analyzed using numerous analytical techniques such as thermogravimetric analyses (TGA/DTG), X-Ray Fluorescence (XRF) and Scanning Electronic Microscopy (SEM). First, the thermogravimetric analyses monitor the pyrolysis parameters, control the proportion of its outputs and allow to extract the kinetic parameters. The latter is determined using Friedman, Flynn-Wall-Ozawa (FWO) and Kissinger-Akahira-Sunose (KAS) models. In a second step, Kenaf derived chars are produced at different pyrolysis temperatures and their physicochemical, morphological, textural and structural properties are determined using different techniques such as CO 2 adsorption, Raman Spectroscopy, and DRIFT Spectroscopy. The main results confirm the Kenaf potential for energy applications as its thermal properties are more interesting compared to other usual crops. The Kenaf stem derived char is also very promising for pollutants removal or gas storage as its surface area as well as its microporous structure are interestingly developed when increasing the pyrolysis temperature. Kenaf char could be also chemically or physically activated in order to be used for pollutants removal from gaseous and aqueous effluents. Finally, the XRF analysis indicated that contents in K and P elements are high. Ca and Mg are also major mineral species in the char. These contents indicate that Kenaf derived char could be also suitable for agricultural soil amendments. [ABSTRACT FROM AUTHOR]