Study of biochar from gro-waste for dye adsorption: Capacity and kinetics

Kỷ yếu Hội nghị: Nghiên cứu cơ bản trong “Khoa học Trái đất và Môi trường” DOI: 10.15625/vap.2019.000215 602 STUDY OF BIOCHAR FROM GRO-WASTE FOR DYE ADSORPTION: CAPACITY AND KINETICS Nguyen Xuan Cuong 1* , Tran Thi Cuc Phuong 2 , Vo Thi Yen Binh 2 1 Center for Advanced Chemistry, Institute of Research and Development, Duy Tan University 2 Faculty of Environmental Engineering Technology, Hue University, Quang Tri Campus, Viet Nam Email: nguyencuongqt2008@gmail.com ABSTRACT Two biochars derived from wattle bark (BA) and coffee husks (BC) used to remove methylene blue (MB) which achieved the yield values of 33.3 % to 35.08% at 500 o C of pyrolysis. Adsorption increased with the rising of the dose until 2 g/L for BC, and 5 g/L for BA, respectively. When rising pH, the increasing trend was observed for BA, and BC, from 67 % at pH of 2 to 93% at pH of 12. The equilibrium time depended on the initial MB concentration and the MB removal accounted for over 83% at the first 30 minutes. The experiment data fits better with Avrami, and Elovich than Pseudo-first-order equation (PSO), and Pseudo-second-order model (PFO). Adsorption process comprised more than one reaction pathway including integer-kinetic order, and multiple kinetic orders or fractionary kinetic order. 1. INTRODUCTION Dyes cause primarily to colored compounds in water (Hao et al., 2000; Santos & Boaventura, 2015), in which azo dyes like MB is being used extensively (Hao et al., 2000; Tan et al., 2016). To treat these dyes, many methods have been introducing such as coagulation, advanced oxygen process, membrane, and adsorption (Hao et al., 2000; Park et al., 2019). However, many of them are expensive, high energy consumption and toxic secondary generation. Biochar - a low cost carbonaceous material to eliminate contaminants, has attracted much attention. In general, the studies of biochar for dye removal and decolorization have achieved significant results. Moreover, biochars produced from agro-waste bring other benefits in terms of waste minimization, recovery and reuse, and environmental conservation. The focus of this work is to compare the adsorption capacity of biochars derived from wattle bark, and coffee husks for MB removal and to clarify the adsorption kinetics. These materials using to produce biochars in this study are not yet investigated for dye removal. 2. MATERIALS AND METHODS 2.1. Raw materials The wattle bark and the coffee husks collected from local processing factories. MB is an organic cation dye which chosen to test adsorption potential of biochars. 2.2. Biochar production Fig.1. Raw materials, biochars and SEM images at 10 µm. Hồ Chí Minh, tháng 11 năm 2019 603 The prepared materials heated in the furnace which programmed with the heating rate of 10 o C/min until 500 o C and kept there for 2 hours of retention time. Then, biochars crushed and passed through the sieve with a size of 0.25 mm (60-mesh). 2.3. Characteristics of biochar The chemical properties of biochars were tested by, pH, moisture, volatile fraction, ash, and elemental analysis. Moisture, volatile fraction and ash determined by ASTM D-1762-84 standard. pH value was measured by Multi-parameter Water Quality Meter (HQ40d, Hach, USA). The pH of point of zero charge (pHpzc) of biochars also was determined according to pH drift method. Surface of biochars were studied using a scanning electron microscope (SEM). 2.4. Batch adsorption studies Batch experiments were implemented to determine the influence of operational factors such as dose, time, temperature, pH, etc. on the adsorption process. The adsorption experiments used 50 mL of MB solution. After adsorption finished, suspensions were centrifuged at 4.000 rpm for 10 minutes. The solution was then measured by UV-spectrophotometer at 665 nm. 2.5. Adsorption kinetics The kinetic models consist of PFO, PSO, Avrami fractional-order equation, and Elovich model (chemisorption). 3. RESULTS AND DISCUSSION 3.1. Biochar characterization pHpzc of BC and BA were found to be 8.82, and 5.48, respectively. BC moisture obtains only 0.2% and BA was 2.04. The values of ash were 7.16, and 7.48 % for BA, and BC, respectively. 3.2. Adsorption capacity and influent factors 3.2.1. Effect of doge and pH pH changed did not affect significantly on MB mass removal by BA while this rate rose gradually for BC (Fig. 2a). With pH > 5.48 (pHpzc) for BA and > 8.82 (pHpzc) for BC, meaning that the biochar surface becomes negative charge which absorbed positive MB molecule, and consequently enhanced the adsorption capacity. The adsorption of BA increased with the rising of dose while that trend is the case of BC until 2 g/L. When the dose was bigger than 2 g/L, the adsorption of BC leveled off and then dropped at 81.07% at 10 mg/L. This might be due to the high lignin content (21 - 28%) in coffee husks which cannot be converted to biogas (Oosterkamp, 2014). 3.2.2. Effect of contact time and reaction temperature For the initial MB strengths of 10 to 20 mg/L, the equilibrium time just was about 30 minute or lower. Generally, at the first 30 minutes, the MB removal ability of three biochars accounted for over 83%, except for BC with initial MB of 60 mg/L (Fig. 3). Fig.2. Effect on MB adsorption of: a) dose; and b) pH. Kỷ yếu Hội nghị: Nghiên cứu cơ bản trong “Khoa học Trái đất và Môi trường” 604 Fig. 3. Effect of time on MB adsorption of: a) BM; b) BC; and c) BM. 3.3. Adsorption kinetics RSS (residual sum of squares) values are lowest in the following order: Avrami, Elovich, PSO, and PFO. This indicates that data fit better with Avrami and Elovich than remaining models (Fig. 4). The better fitting of PSO, and Elovich compared to PFO indicating that besides physical adsorption mechanism the test also is controlled by chemisorption as the assumption of PSO (Shawabkeh & Tutunji, 2003; Sun et al., 2013) and Elovich (Vaghetti et al., 2009). Fig. 4. Non-linear kinetic model for MB adsorption: a) BA; b) BC. 4. CONCLUSIONS Adsorption efficiency increased with the rising of the dose until 2 g/L for BC, and 5 g/L for BA, and BC, respectively and those values are also the optimal points of dose. The range of pH is appropriate for using biochars without any pH adjustment. The increasing of temperature enhanced the MB removal ability, but this trend is uneven at different concentrations. The experiment data fits better with Avrami, and Elovich than PSO, and PFO. Acknowledgment This research is funded by Vietnam National Foundation for Science and Technology Development (NAFOSTED) under grant number 105.99-2019.25. REFERENCES [1]. Hao, O.J., Kim, H., Chiang, P.-C. (2000). Decolorization of Wastewater. Critical Reviews in Environmental Science and Technology, 30(4), 449-505. [2]. Oosterkamp, W.J. (2014). Chapter 13 - Use of Volatile Solids from Biomass for Energy Production. in: Bioenergy Research: Advances and Applications, (Eds.) V.K. Gupta, M.G. Tuohy, C.P. Kubicek, J. Saddler, F. Xu, Elsevier. Amsterdam, pp. 203-217. [3]. Park, J.-H., Wang, J.J., Meng, Y., Wei, Z., DeLaune, R.D., Seo, D.-C. (2019). Adsorption/desorption behavior of cationic and anionic dyes by biochars prepared at normal and high pyrolysis temperatures. Colloids and Surfaces A: Physicochemical and Engineering Aspects, 572, 274-282. Hồ Chí Minh, tháng 11 năm 2019 605 [4]. Santos, S.C., Boaventura, R.A. (2015). Treatment of a simulated textile wastewater in a sequencing batch reactor (SBR) with addition of a low-cost adsorbent. J Hazard Mater, 291, 74-82. [5]. Shawabkeh, R.A., Tutunji, M.F. (2003). Experimental study and modeling of basic dye sorption by diatomaceous clay. Applied Clay Science, 24(1), 111-120. [6]. Sun, L., Wan, S., Luo, W. (2013). Biochars prepared from anaerobic digestion residue, palm bark, and eucalyptus for adsorption of cationic methylene blue dye: Characterization, equilibrium, and kinetic studies. Bioresource Technology, 140, 406-413. [7]. Tan, K.A., Morad, N., Qi Ooi, J. (2016). Phytoremediation of Methylene Blue and Methyl Orange Using Eichhornia crassipes. [8]. Vaghetti, J.C.P., Lima, E.C., Royer, B., da Cunha, B.M., Cardoso, N.F., Brasil, J.L., Dias, S.L.P. (2009). Pecan nutshell as biosorbent to remove Cu(II), Mn(II) and Pb(II) from aqueous solutions. Journal of Hazardous Materials, 162(1), 270-280.