Cationic Dye Adsorption on Hydrochars of Winery and Citrus Juice Industries Residues: Performance, Mechanism, and Thermodynamics

Abstract

With the increasing needs of clean water supplies, the use of biomass wastes and residues for environmental remediation is essential for environmental sustainability. In this study, the residues from winery and citrus juice industries, namely grape skin and orange peel, respectively, were first converted to hydrochars by hydrothermal carbonization (HTC) and then a cationic dye (methylene blue) adsorption was studied on hydrochars. Hydrochars from both feedstocks were produced at three different temperatures (180, 220, and 250 °C) and a fixed residence time (1 h) to evaluate the hydrochar’s performance on the dye adsorption. The hydrochars were characterized in terms of their pH, pH at point of zero charge (pHPZC), surface functionalities, and surface area. A batch adsorption study of the dye was carried out with variable adsorbate concentration, pH, and temperature. Two adsorption isotherms namely Langmuir and Freundlich models were fitted at 4, 20, and 36 °C. The thermodynamic properties of adsorption (Gibbs free energy (ΔG), enthalpy (ΔH) and entropy (ΔS)) were evaluated from the isotherms fittings. Results showed that the dye adsorption on both hydrochars was significant and followed Langmuir isotherm. The maximum adsorption capacity on citrus waste hydrochar was higher than the winery waste hydrochar at any corresponding HTC temperature. Although hydrochars showed the lowest surface area (46.16 ± 0.11 and 34.08 ± 1.23 m2/g for citrus and winery wastes, respectively) at 180 °C, their adsorption was the highest, owing to their maximum density of total oxygen functional groups (23.24 ± 0.22 and 32.69 ± 1.39 µmol/m2 for citrus and winery wastes, respectively), which decreased with the increase in HTC temperature. This research shows a sustainable route for the production of highly effective adsorbent materials at lower HTC temperatures from citrus and winery wastes.

Mesoporous Carbon from Optimized Date Stone Hydrochar by Catalytic Hydrothermal Carbonization Using Response Surface Methodology: Application to Dyes Adsorption

“…e hydrochar optimized under the conditions X A � 200°C, X B � 120 min, and X C � 20 mg is characterized by a BET surface area of 60.75 m 2 /g and a pore volume of 0.14 cm 3 /g. ese results are similar to the results of [59] in the case of hazelnut shell and a little high compared to those reported by [39,60] in the case of residues from the wine industry and salacca peel, respectively. is finding can be explained by the type of raw material and the conditions of synthesis, including the introduction of citric acid as a catalyst in the hydrothermal reaction.…”

Kinetic and Isothermal Investigations of Cost-Effective Sorptive Elimination of Gentian Violet Dye from Water Using Haplophragma adenophyllum Biowaste

“…From all the abovementioned methods, the pH drift method was utilized as a reliable method. According to this method [48], pH of electrolyte, i.e., KCl, was set down by using KOH and HNO 3 in the range of 2-10 and after adding 0.1 g of HAB, it was agitated for 24 hours. Final pH was measured after 48 hours and a plot was drawn between initial and final pH and the point was chosen where initial and final pH become equal at the cutoff point.…”

Process Water Recirculation during Hydrothermal Carbonization of Waste Biomass: Current Knowledge and Challenges

“…For these reasons, wet thermochemical conversion technologies as hydrothermal processes gained increasingly more attention in the last decades, demonstrating to be very promising conversion routes for wet biomass wastes to energy dense bio-fuels and valuable materials. In particular, hydrothermal carbonization (HTC) was demonstrated to be efficient for very high moisture residues as sewage and agro-industrial sludge [12][13][14]. In hydrothermal processes, the organic residue is subjected to a thermal process at autogenous pressure of saturated steam in the presence of sub-critical or supercritical water [15].…”