Summary of doctoral thesis in Environmental technology: Study on the production of modified biochar and activated carbon derived from corncob and their application in ammonium removal from domestic water

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Objectives of this dissertation: Develop the optimal preparation procedure of modified biochar and activated carbon derived from an agricultural byproduct, such as corncob wastes; Investigate the physical and chemical properties of modified biochar and activated carbon; apply modified biochar and activated carbon in removal of ammonium from synthesised and real water under batch and column experiments.

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Nội dung Text: Summary of doctoral thesis in Environmental technology: Study on the production of modified biochar and activated carbon derived from corncob and their application in ammonium removal from domestic water

MINISTRY OF EDUCATION VIETNAM ACADEMY OF AND TRAINING SCIENCE AND TECHNOLOGY GRADUATE UNIVERSITY SCIENCE AND TECHNOLOGY ………***………. VU THI MAI STUDY ON THE PRODUCTION OF MODIFIED BIOCHAR AND ACTIVATED CARBON DERIVED FROM CORNCOB AND THEIR APPLICATION IN AMMONIUM REMOVAL FROM DOMESTIC WATER Major: Environmental Engineering Code: 62 52 03 20 SUMARY OF DOCTORAL THESIS IN ENVORONMET TECHNOLOGY Hanoi - 2018 1
The thesis has been completed at: Institute for Environemtal Technology – Graduate university science and technology – Vietnam Academy of Science and Technology Science supervisor: 1.Assoc.Prof.Dr Trinh Van Tuyen 2. Assoc.Prof.Dr Doan Dinh Phuong Reviewer 1: …………………………………………………… …………………………………………………… Reviewer 2: …………………………………………………… …………………………………………………… Reviewer 3: …………………………………………………… …………………………………………………… The thesis was defended at National level Council of Thesis Assessment held at Graduate University of Science and Technology – Vietnam Academy of Science and Technology at….on…… Thesis can be futher referred at: -The Library of Graduate University of Science and Technology -National Library of Vietnam 2
INTRODUCTION 1. Background In recent years, groundwater levels in Vietnam have been declining in quantity and quality due to the impacts of climate change and exploitation for economic. Vietnam has abundant surface and ground water resources (the average total runoff is 848 km3/year); however, approximately 6 million Hanoi inhabitants receive 80% of their drinking water from groundwater. Excessive presence of ammonium could negatively affect the quality of groundwater and surface water. Households might suffer potential health risks from using directly water resources with uncontrolled quality. In some areas in Vietnam, groundwater often contains a higher level of iron, manganese, arsenic, ammonium concentrations than the allowable limitation. According to previous reports, the presence of ammonium concentration in groundwater in some areas exceeded the surface water quality standards in Vietnam. Such typical areas are in the northern (i.e., Vinh Phuc, Bac Ninh, Hai Duong, Hung Yen, Hanoi provinces) and the south (i.e., Ho Chi Minh City) of Vietnam. Numerous techniques have been applied to remove ammonium ions from environmental bodies, such as ion exchange, membrane technology, adsorption, nitrification-denitrification processes, chemical precipitation, and electrochemical separation. Among these methods, adsorption is considered an effective, inexpensive, and simple technique for removing ammonium from water media. Carbonaceous porous materials—activated carbon and biochar—have been acknowledged as promising adsorbents to remove the various kinds of pollutants (i.e., potentially toxic metals and dyes) from 3
environmental water. According to the literature, however, pristine activated carbon (AC) often exhibits its poor maximum adsorption capacity toward ammonium (i.e., 0.5–5.4 mg/g). Therefore, it is necessary to apply further treatment or modification process to the surface of AC in order to enhance its adsorption capacity to ammonium. According to Statistical Yearbook of Vienam 2015, the planted area and maize production in Hanoi were approximately 21,100 ha and 102,300 tons, while the corresponding data for the whole country were 1,179,300 ha and 5,281,000 tons, respectively. Therefore, corncob wastes can be considered an abundant, renewable, and low-cost byproduct to prepare biochar and AC. Therefore, the study on “Study on the production of modified biochar and activated carbon derived from corncob and their application in ammonium removal from domestic water” was conducted. 2. Objectives of this dissertation □ Develop the optimal preparation procedure of modified biochar and activated carbon derived from an agricultural by- product, such as corncob wastes; □ Investigate the physical and chemical properties of modified biochar and activated carbon; □ Apply modified biochar and activated carbon in removal of ammonium from synthesised and real water under batch and column experiments; □ Propose adsorption mechanism. 4. The composition of the thesis 4
The thesis consists of 101 pages with 38 tables, 50 images, 123 references. The thesis was composed of 3 pages, 37 pages of literature review, 15 pages of research subjects and methods, 44 pages of research results and discussion, conclusion of 2 pages. THESIS CONTENT CHAPTER 1: LITERATURE REVIEW Ammonium contamination in ground water, methods of ammonium treatment, overview of methods of biochar production, modification methods in terms of biochar, activated carbon and application of biochar as organic adsorbent, heavy metals and ammonium treatment in water have been summarized. The research results show that: The researches focus on the application of biochar, modified activated carbon for ammonium treatment in water but there have not many researches focusing on the biochar surface modification for the adsorption of ammonium in water. The use of corncob to produce modified biochar for the adsorption of ammonium has not been investigated. Based on the review of the research materials, the thesis will focus on the following issues: - Providing optimum conditions for the production of modified biochar from corncob and modified activated carbon to enhance the ammonium adsorption capacity. - Determining the characteristics of dynamics and thermodynamics of ammonium adsorption in the water of the materials on the scale of batch adsorption and adsorption on the column. 5
CHAPTER 2: MATERIALS AND METHODS 2.1. Research subjects Adsorbent: corncob wastes were collected from Da Bac district, Hoa Binh province, Vietnam. Adsorbate: the ammonium solution was prepared in the laboratory by dissolving the suitable mass of NH4Cl in doubly distilled water to obtain a stock solution (1,000 mg/L). The synthesized water was used in the batch experiments. Meanwhile, the real water was collected from a well in a ammonium-polluted area (Mr. Nguyen Dinh Lam; Address: hamlet 3, Yen So commune, Hoai Duc district, Ha Noi city, Vietnam). The concentrations of NH4+, Fe3+, and Mn2+ ions in groundwater were 10.13 mg/L, 0.4 mg/L, and 0.02 mg/L, respectively. The real groundwater was used in the column experiments. groundwater 2.2. 1. Reagent All chemicals used in this study were of analytical reagent grade (purchased from Merck). 2.2.2. Device Equipment used in materials manufacturing and analysis at the Institute of Environmental Technology, Environmental Laboratory, Hanoi University of Natural Resources and Environment: - UV-VIS colorimeter (Hach, DR5000, USA) for ammonium content analysis - Atomic absorption spectrometer (AAS - Thermo Fisher, Solar- M6) for Mn, Fe analysis. 6
- Analytical balance, US, accuracy 10-5 and 10-2 mg - pH meter (Toledo, China). - Temperature controlled shaking apparatus (GFL 1083, Germany) for conducting static adsorption experiments. - Nabertherm kiln (L3/11/B170, Germany) used for making biochar, modified charcoal 2.3. Experimental 2.3.1. Adsorbent preparation Figure 2.1 represents the preparation procedure of modified biochar and activated carbon derived from corncob wastes. Briefly, biochar (Bio) was prepared at different pyrolysis conditions (i.e., pyrolysis temperatures and times) under an oxygen-limited environment. Subsequently, Bio was oxidized with HNO3 (BioN) to increase the concentration of oxygen-containing functionally groups (i.e., carboxylic group) on its surface. Lastly, BioN was treated with NaOH (BioN-Na) to enhance its capacity cation exchange. Meanwhile, corncob-derived activated carbon (BioP) was prepared through a one-stage chemical activation method using H3PO4. Similar to biochar, BioP was also treated with NaOH (BioP- Na) to enhance its capacity cation exchange. Notably, the pyrolysis process was done in the non-circulated air atmosphere (i.e., within lid-enclosed crucible) at different temperatures and heating times. 7
Figure 2.1. Schematic illustration of the preparation procedure of modified biochar and activated carbon 2.3.2. Adsorption experiment The process of ammonium adsorption onto modified biochar and activated carbon was conducted in batch and column experiments. The batch experiments were run in the synthesized solutions at different operation conditions (i.e., varying solutions pH, initial ammonium concentrations, contact times, solution temperatures, NaCl concentrations). Meanwhile, the column experiments were conducted in the real groundwater to analyse the effects of different flow rates, influent concentrations, and bed heights on the adsorption capacity. Two fixed-bed systems comprised a downflow (using a glass laboratory mini-column) and an upflow (using a column in pilot 8
scale). Furthermore, the adsorption reversibility was determined through desorption experiments. 2.3.3. Adsorbent characterization The textural characteristics of adsorbent (i.e., specific surface area and total pore volume) were determined by the nitrogen adsorption/desorption isotherm at 77 K (ASAP-200, Micromeritics). Morphological property was obtained using an electron microscope S- 4800 (FE-SEM, Hitachi). The thermal stability of corncob was measured by a thermo-gravimetric analysis (TGA; DuPont TA Q50, USA). Qualitative information on functional groups present in the adsorbent surface was analysed by a Fourier Transform Infrared Spectrometer (FTIR, NEXUS 670, Nicolet, USA). The Boehm titration method was applied to determine the quantitative information on the acidic and basic groups on the adsorbent surfaces. The electrical state of adsorbent surfaces in solution was characterized by the point of zero charge (pHPZC) that was determined using the drift method. Proximate analysis was performed by following the international standard procedure (ASTM D2867-09, D2866, and D5832-98). CHAPTER 3: RESULTS AND DISCUSSION 3.2. The optimal preparation condition of modified biochar The results of ammonium adsorption (data not showed) indicated that the optimal preparation conditions of modified biochar were obtained. Briefly, BioN-Na was prepared at the optimal conditions as follows: 400 °C, 60 min, 6 M HNO3 (5/1, v/w) and 0.3 M NaOH (20/1, v/w). Therefore, the modified carbounous adsorbent 9
prepared at the optimal conditions (BioN-Na) were used for further experiments. 3.3. The optimal preparation condition of modified activated carbon. The results of ammonium adsorption (data not showed) indicated that the optimal preparation conditions of modified activated carbon (BioP-Na) were obtained. BioP-Na was prepared at 400 °C, 90 min, 50% H3PO4 (1.5/1, v/w), and 0.3 M NaOH (20/1, v/w). Therefore, the modified carbounous adsorbent prepared at the optimal conditions (BioP-Na) were used for further experiments. 3.4. Adsorbent characterization 3.4.1. Textural and morphology property As expected, the BET surface area (m2/g) and total pore volume (cm3/g) of adsorbent exhibited the following order: BioP-Na (1097 and 0.804) > BioN-Na (10.4 and 0.00664), respectively. The average pore width of BioP-Na (3.95 nm) and BioN-Na (3.71 nm) was greater 2 nm. The results of scanning electron micrographs (Figure 3.14) demonstrated that BioP-Na and BioN-Na had an irregular and heterogeneous surface morphology. The formation of well-developed pores of various sizes and shapes in BioP-Na was attributed to the chemical activation method used in the activated carbon preparation. 10
Figure 3.14. Scanning electron microscope (SEM) image of the (a) NaOH-treated biochar and (b) NaOH-treated activated carbon 3.4.2. Surface chemistry Figure 3.15 represents qualitative information about the functional groups on the adsorbent surfaces. The presence of several important function groups on the surfaces of six target adsorbents was identified at peaks at approximately 3430 cm-1 (the hydroxyl groups, –OH, in the carboxylic groups, phenol groups, or adsorbed water), 1700 cm-1 (C=O in the carboxylic and lactonic groups), 1380 cm-1 (stretching C–O groups), and 1620 cm‒1 (the C=C double bonds in the aromatic rings). The decrease in intensity was attributed to the change of corresponding surface chemistry of the adsorbents, which is consistent with the change of (1) the concentration of oxygen- containing functional groups on the adsorbent’s surfaces, and (2) the point of zero charge (pHPZC) (Table 3.8). The results demonstrated that the treatment process (pyrolysis, chemical activation, oxidation, and NaOH impregnation) significantly affected the surface chemistry of the adsorbents. 11
Figure 3.15. Fourier transform infrared spectroscopy (FTIR) spectra of prepared adsorbents Table 3.8. Concentration of oxygen-containing functional groups on the surface of adsorbent Oxygen-containing groups Total acid groups pHPZC (mmol/g) (mmol/g) Carboxylic Lactonic Phenolic Biosorbent CC 7.0 0.131 0.490 0.873 1.494 Biochar Bio 5.3 0.619 1.479 0.486 2.584 BioN 4.6 1.382 2.745 0.171 4.298 Activated carbon BioP 4.3 0.988 1.601 0.980 3.569 3.4.3. Physical property The results of proximate analysis demonstrated that the modified biochar and activated carbon exhibited a low percentage of moisture and ash content, suggesting a high quality of BioN-Na and BioP-Na. In addition, a low volatile content reflects a high potential 12
for industrial applications or real water treatment in household scales. Notably, a high fixed carbon content demonstrated that modified biochar and activated carbon consist mainly of carbon. Table 3.9. Proximate analysis of modified biochar and activated carbon BioN-Na BioP-Na Yield (%)a 34.9 81.5 Moisture (%) 4.36 5.01 Volatile (%) 18.1 13.0 Total ash (%) 18.0 13.1 Fixed carbon (%) 71.9 79.3 Note: athe yield was calculated from the different mass between before and after pyrolysis for the samples of biochar and activated carbon. 3.5. Adsorption result in batch experiment 3.5.1. Effect of pH The effects of solution pH on the NH4-N adsorption process are provide in Figure 3.16 and 3.1. The result showed that the adsorption process was strongly dependent on the solution pH (pHsolution). At strong acidic condition (pH = 4), the amount of ammonium uptake onto M-CCAC and M-CCB seems negligible. This is because (1) the excess H+ ions in the system strongly competed with the NH4+ ions for the active adsorption sites, and (2) repulsion occurred between the positively charged surface of adsorbent (M-CCAC of M-CCB) and the NH4+ ions. Furthermore, the adsorption efficiency decreased when pHsolution >9.0. The decrease in adsorption capacity resulted from the transformation of ammonium (NH4+) ion into gaseous ammonia 13
(NH3), which makes the electrostatic attraction mechanism no longer effective. In general, optimal pHsolution was obtained at 7.0–8.0. Figure 3.16. Effects of initial solution pH onFigure 3.17. Effects of initial solution pH the capacity of ammonium adsorption onto on the capacity of ammonium adsorption BioN-Na onto (a) BioP-Na 3.5.3. Adsorption isotherms The adsorption isotherms of corncob-derived adsorbents (Figure 3.22) were classified according to their shapes as L-type (Langmuir) isotherms, which are characterized by an initial concave region relative to the concentration axis (concave downward curve). Typically, the Langmuir model better fits the experimental data on the adsorption of ammonium onto BioP-Na, BioN-Na, BioN, Bio, and CC than dose the Freundlich model. The maximum Langmuir adsorption capacity (qm; mg/g) at 30 °C decreased the following order: BioN-Na (qm = 22.6 mg/g) > BioP-Na (15.4 mg/g) > BioN (8.60 mg/g) > Bio (3.93 mg/g) > CC (2.05 mg/g), suggesting that the treatment processes efficiently enhanced the NH4+ adsorption capacity onto biochar and activated carbon. 14
Figure 3.22. Adsorption isotherms of ammonium onto corncob derived-biosorbent (CC), biochar (Bio), oxidized biochar (BioN), modified biochar (BioN-Na), pristine activated carbon (BioP), and modified activated carbon (BioP-Na) 3.5.4. Adsorption kinetics The effects of contact time on the adsorption process were examined at different initial ammonium concentrations (10 mg/L, 20 mg/L, and 40 mg/L) and operation temperatures (20 °C, 30 °C, and 40 °C). As expected, the adsorption process reached a fast equilibrium at approximately 60 min (Figure 3.17 and 3.18). The experimental data of adsorption kinetics were adequately described by the pseudo- second-order equation. The adsorption rate (k2; g/mg × min) was calculated from this model. The results demonstrated that the adsorption rate of ammonium onto BioP-Na and BioN-Na at an initial NH4+ concentration of 10 mg/L increased when the temperature increased. The k2 values exhibited the following order: 20 °C (k2 = 0.04 15
g/mg × min) < 30 °C (0.09) < 40 °C (0.14) for BioP-Na, and 20 °C (0.06) < 30 °C (0.15) < 40 °C (0.21) for BioN-Na. Moreover, in the same operation conditions, BioN-Na exhibited higher k2 values than BioP-Na, suggesting that the ammonium adsorption process onto BioN-Na occurred faster than that onto BioP- Na. Notably, the activated energy (calculated from the Arrhenius equation) of the process of ammonium adsorption onto BioP-Na (Ea = 47.89 kJ/mol) and BioN-Na (52.46 kJ/mol) demonstrated that ion exchange played an important role in the adsorption mechanism. Figure 3.18. Effects of contact time on Figure 3.19. Effects of contact the capacity of ammonium adsorption time on the capacity of onto BioN-Na ammonium adsorption onto BioP-Na 3.5.5. Adsorption thermodynamics As showed in Figure 3.25, the adsorption process was strongly dependent on the operation temperature. The amount of ammonium adsorption onto modified biochar and activated carbon decreased when the temperature increased, which implies that the ammonium adsorption was an exothermic process. The qm values at 20 °C, 35 °C, and 50 °C were as follows: 24.52 mg/g > 22.58 mg/g > 10.40 mg/g for 16
BioN-Na, and 17.03 mg/g > 15.40 mg/g > 11.99 mg/g for BioP-Na, respectively. Essentially, when the adsorption process reached a true equilibrium, the equilibrium constant (KC; dimensionless) can be obtained (Figure 3.25). In this case, the adsorption thermodynamic parameters (∆G°, ∆H°, and ∆S°) can be directly calculated from the well-known van’t Hoff equation. Table 3.20 shows that the negative value of Gibbs energy change (∆G°) all investigated temperatures indicate that the NH4+-N adsorption process onto modified biochar and activated carbon occurred spontaneously. Meanwhile, the positive values of the change in entropy (∆S°) suggest that the organization of NH4+ ions at the solid/liquid interface becomes more random during the adsorption process. Furthermore, the negative values of the change in enthalpy (∆H°) reflect the exothermic nature of the adsorption process, which was demonstrated by a decrease in the adsorption capacity (qe; Figure 3.25) and equilibrium constant (KC; Table 3.20) at a higher temperature. Figure 3.25. Effects of temperature on the adsorption process of (a) BioN-Na and (b) BioP-Na 17
Table 3.20. Thermodynamic parameters of ammonium adsorption onto modified biochar and activated carbon ΔS° T Van’t Hoff ΔG° ΔH° KC (kJ/mol × (K) equation (kJ/mol) (kJ/mol) K) Modified biochar (BioN-Na) 293 y = 140x + 32.92 –8.512 –1.164 0.0251 308 3.02 32.53 –8.917 323 R² = 0.9185 31.48 –9.263 Modified activated carbon (BioP-Na) 293 y = 39x + 27.35 –8.060 –0.320 0.0264 308 3.18 27.13 –8.452 323 R² = 0.982 27.02 –8.852 3.5.6. Co-existent effects of other cations The Fe3+, Ca2+, and Mn2+ cations are commonly present in groundwater in Hanoi. Therefore, they were selected as the foreign cations in this study. The results showed that the amount of NH4+-N adsorbed onto the adsorbents (BioN-Na and BioP-Na) remarkably decreased with an increase in the concentrations of Fe3+, Ca2+, and Mn2+ ions (Figure 3.26). This is presumably because: (1) a screening effect (known as the electrostatic screening) occurred between the positively charged adsorbent surfaces and the NH4+ ions, and (2) there is a competition between the NH4+ ions and the Fe3+, Ca2+, and Mn2+ ions for the adsorbing or exchanging sites on the adsorbent’s surfaces (i.e., —COO– or —COONa+). 18
Figure 3.26. Effects of the presence of other cations on the adsorption capacity of modified biochar and activated carbon 3.5.7. Desorption study and adsorption mechanism The adsorption efficiency of ammonium ions using various desorbing agents is provided in Figure 3.27. The order of ammonium desorption from BioN-Na and BioP-Na was as follows: (43% and 41%) > NaCl (34% and 29%) > NaCl + NaOH (28% and 23%) > NaOH (22% and 17%) respectively. The percentage of ammonium desorbed by HCl was assumed to correspond to both electrostatic attraction and ion exchange mechanisms, and thus it can be concluded that approximately 41% of ammonium ions was removed from the solution (adsorbed onto BioN-Na and BioP-Na) through electrostatic attraction and ion exchange mechanisms. 19
50 BioP-Na BIoN-Na 40 % Desorption 30 20 10 0 HCl 0,1M HCl 1M NaCl 0,5M NaOH 0,5M + NaOH 0,5M NaCl 0,5M Figure 3.27. Percentage of NH4+-N desorbed using various desorbing agents 3.6. Adsorption result in column experiment 3.6.1. Adsorption performance in laboratory mini-column (downflow) 3.6.1.1. Effect of solution flow rate Figure 3.28. Breakthrough curves for Figure 3.29. Breakthrough curves for different flow rates BioN-Na different flow rates BioP-Na 20