Abstract
Here, we propose a low-cost, sustainable, and viable adsorbent (pine tree-derived biochar) to remove acid dyes such as acid violet 17 (AV), which is used in the silk dyeing industry. As a case study, the AV removal process was demonstrated using synthetic effluent and further as a proof of concept using real dye effluent produced from the Sirumugai textile unit in India. The pine tree-derived biochar was selected for removal of aqueous AV dye in batch and fixed-bed column studies. The adsorbent material was characterized for crystallinity (XRD), surface area (BET), surface morphology and elemental compositions (SEM–EDX), thermal stability (TGA), weight loss (DGA), and functional groups (FTIR). Batch sorption studies were performed to evaluate (i) adsorption at various pH values (at pH 2 to 7), (ii) isotherms (at 10, 25, and 35 °C) to assess the temperature effect on the sorption efficiency, and (iii) kinetics to reveal the effect of time, adsorbent dose, and initial concentration on the reaction rate. After systematic evaluation, 2 g/L biochar, 25 mg/L AV, pH 3, 40 °C, and 40 and 360 min in a completely mixed batch study resulted in 50 and 90% dye removal, respectively. The isoelectric point at pH 3.7 ± 0.2 results in maximum dye removal, therefore suggesting that monitoring the ratio of different effluent (acid/wash/dye) can improve the colorant removal efficiency. The Langmuir isotherm best fits with the sorption of AV to biochar, provided a maximal dye uptake of 29 mg/g at 40 °C, showing that adsorption was endothermic. Fixed-bed studies were conducted at room temperature with an initial dye concentration of 25 and 50 mg/L. The glass columns were packed with biochar (bed depth 20 cm, pore volume = 14 mL) at an initial pH of 5.0 and a 10 mL/min flow rate for 120 min. Finally, the regeneration of the adsorbent was achieved using desorption studies conducted under the proposed experimental conditions resulted in 90–93% removal of AV even after five cycles of regeneration.
Highlights
The demand for water in the industrial sector is expected to increase ∼300% during the first half of the 21st century.[1]
This study focused on developing a process for removing synthetic and real acid dyes from aqueous solutions and designing a treatment process
This study’s biochar bulk density is ∼0.1 g/cm[3], and the porosity is ∼74%, which is similar to the literature.[26]
Summary
The demand for water in the industrial sector is expected to increase ∼300% during the first half of the 21st century.[1] The textile industry is one of the largest water consumers in many developing countries, especially in Asia, second to agriculture.[2]. This industry requires a large amount of water for the production process and is one of the major producers of toxic and polluted wastewater.[3] Over 7 × 107 tons of synthetic dyes are produced yearly, and 10−15% are not integrated into the final product.[4]. Adsorption by porous materials is one of the most promising and affordable techniques for removing dissolved pollutants, serving as an alternative to energy-intensive technologies.[8]
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