Physical Properties of K-Activated Carbon and its Removal Efficiencies for Chemical Factors

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1 Physical Properties of K-Activated Carbon and its Removal Efficiencies for Chemical Factors Won-Chun Oh and Weon-Bae Ko Department of Advance Materials Science & Engineering, Hanseo University, Chungnam , Korea Department of Chemistry, Sahmyook University, Seoul , Korea Received October 27, 2005; Accepted February 27, 2006 Abstract: A study of the physical properties and the applications of K-activated carbon system after carbon bed filtration was performed on the bench scale. Various types of K-activated carbon bed were used in this study to investigate the removal efficiency of pollutants from wastewater. From the surface properties obtained for carbon samples treated with aqueous solutions containing metallic K ions, our main investigations involved determining the isotherm shape, pore size distribution, SEM, EDX and surface functional groups. K-Activated carbons were filtrated to wastewater to investigate the removal efficiency for the COD, T-N, and T-P. From the removal results of piggery waste using the K-activated carbon bed, a satisfactory removal performance was achieved. The excellent effects of the K-activated carbon bed were proved by the above-mentioned properties of the material, by the adsorption and trapping of organics, and by its catalytic effects. Keywords: adsorption, K-activated carbon, isotherm, SEM, EDX Introduction 1) The application of activated carbon (AC) as a catalyst support material has been fueled by its unique properties, such as its stability in both acidic and basic media, easy recovery of precious metals when supported on AC, very high thermal resistance, and the possibility of changes in its textural and surface chemical properties. In general, granular activated carbon processes have attracted interest for wastewater treatment, with most of the academic research into this field concentrating on the removal of small concentrations of low molecular weight contaminants [1]. Several researchers have since studied industrial wastewater treatment using granular activated carbon. Rozzi and coworkers, after comparing several methods of industrial applications, concluded that granular activated carbon adsorption was the best method for color removal [2]. One of the main problems related to environmental protection is the adequate management and treatment of piggery waste. Because of the high organic matter concentration of piggery wastes, special designs have been recommended by many authors as a To whom all correspondence should be addressed. ( wc_oh@hanseo.ac.kr) primary step of treatment [3-5]. The application of activated carbons treated with metals as catalytic materials has emerged as a very interesting alternative [6-8] for the treatment of these contaminants. Multilayered metal- treated activated carbon bed systems have been studied successfully for the treatment of agricultural and industrial wastewaters [5,9]. In those previous studies, the authors presented the advantage of multilayered metal-treated activated carbon bed system for treatment of piggery wastewater in overall processes. The experimental results have demonstrated the advantages of using the system through the micro-organism and high organic matter removal efficiencies. In this research, which is the first part of a study into the K-activated carbon system, our aim was to investigate the effects that the physical and textural changes of the activated carbon, the chemical treatment sequence, and the catalytic activities have on the removal of chemical pollutants from piggery urine effluent. Full characterization of the K-activated carbon and its removal of pollutants with this system were determined by the nitrogen adsorption properties, SEM-EDX, and the properties of the surface functional groups, as measured using Boehm titration and chemical factors.

2 374 Won-Chun Oh and Weon-Bae Ko Experimental Preparation Procedures The granular-type activated carbon used in this study was prepared from coconut shells, which were carbonized first at 773 K and then activated by steam diluted with nitrogen in a cylinder quartz tube at a temperature in the range K for 30 min. These activated carbons (surface area: 1859 m 2 /g; micropore volume: 0.65 cm 3 /g; average pore diameter: ) were washed with deionized water and dried overnight at ambient temperature. 0.1 M Nitric acid under reflux was used to increase the oxygen surface functional groups without damaging the carbon surface. The oxidized activated carbons were washed and dried at 323 K for 24 h. For potassium treatment, all of the potassium salts were obtained from Duksan Chemical Co. (99+ %, ACS reagent) and used as received. To be free from impurities, doubly distilled water was used. For potassium treatment, 500 g of the activated carbon was dipped into 1 liter of a 0.01 M aqueous potassium salt solution and stirred for 12 h at room temperature. Then, after removal of the liquid, the samples treated with potassium were dried completely in an oven at 378 K. The trial examples of K-activated carbons and the nomenclature used are listed in Table 1. For the effluent characterization, the work involved the treatment of aqueous piggery urine effluent with chemical oxygen demand (COD) and biological oxygen demand (BOD) levels approaching 5000 mg/l from the piggery farm. The analytical results of the as-received piggery waste are listed in Table 2. Those levels were reduced to mg/l by coagulation. The samples of under 1500 mg/l leveled were used for characterization for the activities of the K-activated Measurement Nitrogen adsorption isotherms were obtained by using a BET surface area apparatus (ASAP 2010, Micrometrics) at 77 K. Before the experiment the samples were heated at 473 K and then outgassed at this temperature under a vacuum of Pa to constant pressure. The isotherms were used to calculate the specific surface area and pore volume. The pore size distribution curves of the micropores were obtained by using the H-J method. Scanning electron microscopy (SEM, JSM-5200 JOEL, Japan) was used to observe the pore structure of the potassium-treated activated carbon and the state of the treated potassium salt on the carbon surface. For the elemental analysis of the metal contents in activated carbon, EDX was also used. As one approach toward determining the T-N removal values, a UV/VIS spectrophotometer (Genspec III (Hitachi), Japan) was used to characterize the catalytic efficiency of the K-activated Table 1. Nomenclature of Activated Carbons Treated with Potassium Salts Sample Nomenclature 0.01 M KCl + Activated Carbon 0.01 M KNO 3 + Activated Carbon 0.01 M KMnO 4 + Activated Carbon 0.01 M K 2S 2O 8 + Activated Carbon 0.01 M K 2CO 3 + Activated Carbon 0.01 M KOH + Activated Carbon Boehm Titration We used the Boehm titration method [10] for the identification of the oxygenated surface groups on the carbon surfaces. One gram of carbon sample was placed in 50 ml of the following 0.05 M solutions: sodium hydroxide, sodium carbonate, sodium bicarbonate, and hydrochloric acid. The Erlenmeyer flasks were sealed and shaken for 24 h; 5 ml of each filtrate was then pipetted and the excess of base or acid was titrated with HCl or NaOH, respectively. The number of acidic sites of various types were calculated under the assumption that NaOH neutralizes carboxylic, phenolic, and lactonic groups; Na 2 CO 3, carboxylic and lactonic groups; and NaHCO 3, only carboylic groups. The number of surface basic sites was calculated from the amount of hydrochloric acid, that reacted with the carbon. Bench-Scale Experimental Methods The equipment used during these fixed bed column studies has been described previously [9]. It consisted of a PE (Polyethylene) make-up tank in which the process effluent was added at a concentration of the secondary leveled effluent (Table 2). The solution was then gravity fed into a feed tank, having a volume of 200 liters, from which the effluent was pumped using a peristaltic pump at a constant flow rate of 10 ml min -1. The effluent solution was fed through a bed of K-activated carbons in up-flow mode. The carbon beds were contained in PVC columns (diameter: 50 mm) to which an end plate with both inlet and outlet nozzles was attached. The K- activated carbon bed was supported in the column. The trial examples of K-activated carbon and the nomenclature used are listed in Table 1. The columns gave a standard bed height of 500 mm, which resulted in beds having a K-activated carbon mass of ca. 300 g of 2-mm particle size. The effluents obtained from the bench-scale method were used to measure the chemical factors. The procedures for the measurements from piggery waste are listed in Figure 1. COD,BOD,T-N,andT-PAnalyses The chemical oxygen demand (COD) is an indication of the overall oxygen load that a wastewater will impose on

3 Physical Properties of K-Activated Carbon and its Removal Efficiencies for Chemical Factors 375 Figure 1. Procedure for characterization of piggery waste. Table 2. Analytical Results for the Primitive Piggery Waste Step CDO BOD T-N T-P Original Waste Over 50,000 Over 50,000 Over 500 Over 150 After primary treatment (Flucculation) 1,000 1, an effluent stream. COD is equal to the amount of dissolved oxygen that a sample will absorb from a hot acidic solution containing potassium permanganate. The samples were then analyzed using a standard COD analysis method (potassium permanganate titration method). Biological oxygen demand (BOD) was determined using a general method. BOD removal values were measured by using a 300-mL BOD bottle occupied with effluent after incubation in a dark incubator at 293 K for 5 days [12]. In considering the total nitrogen (T-N) balance in the treatment process, the nitrogen removal was measured using a UV absorbance spectrometric method [12]. The effluents purified by multilayered metal/carbon filter could be prepared to provide samples for the T-N measurement by chemical treatment. T-N removal values were measured using a UV spectrophotometer by monitoring at a wavelength of 220 nm. The measurement of the total phosphorous (T-P) contents of these samples was performed using a Vis spectrophotometer monitored at 880 nm using the ascorbic acid reduction method [12]. These analyses were performed according to standard methods for the examination of water and wastewater [13]. Results and Discussion Adsorption Properties Figure 2 shows the adsorption isotherms of N 2 at 77 K Figure 2. Nitrogen adsorption isotherms obtained from activated carbons treated with potassium salts. Table 3. Comparison of Physical Parameters of Activated Carbons Treated with Potassium Parameter Sample S BET (m 2 /g) Micropore Volume (cm 3 /g) External Surface Area (m 2 /g) Average Pore Diameter ( ) for the potassium-supported activated carbon samples. The values of S BET and the porous structure of the K-activated carbons are summarized in Table 3. All of the isotherms are Type I, with a small amount of capillary condensation hysteresis. Both the external surface area and the total pore volume decreased as the distribution of potassium salts on the activated carbon surfaces. The development of micropores and mesopores was clear from the shape of the isotherms. According to the Kelvin equation, ink-bottle-type pores have a large pore size, given that for these samples hysteresis occurs at a high relative pressure (P/P 0 > 0.5). The smaller amounts of adsorption and narrower hysteresis loops for the potassium-supported activated carbon samples indicate the existence of larger amounts of porous spaces and ink-bottle pores. Differences in the shapes of these isotherms are not very significant, suggesting general similarities in the pore structures of the potassium salt-treated activated carbon samples. The areas of these samples were in the range m 2 /g. The surface areas were higher for the,, and samples than for,, and. The average pore diameters were distributed in the range The average pore diameter was almost constant for the samples

4 376 Won-Chun Oh and Weon-Bae Ko Figure 3. Pore size distributions evaluated from adsorption isotherms. treated with potassium salts. No large differences exist among these samples. The pore size distributions evaluated from the H-J method are shown in Figure 3. The peak distribution for the activated carbons treated with potassium salts is observed at a pore size of 9 with a standard deviation of ca. 1. This result demonstrates that the carbon sample prepared by treatment with aqueous solutions containing potassium ions has a more heterogeneous micropore structure and is characterized by narrow micropores. Micropore size distributions due to the small molecular diameter of the molecule can provide information only about the narrow intervals of pore sizes covering the region of small micropores; they do not provide information about larger micropores. Based on a comparison of the micropore volumes and micropore surface areas from N 2 adsorption isotherms, we conclude that in these samples there are no significant contributions of wider micropores. These pore size distributions also confirm our hypothesis regarding the source of the microporosity being the potassium salts on the activated carbon surfaces. Figure 4 shows the t-plots of the potassium-treated activated carbon samples. These t-plots exhibit c-swing, indicating the presence of both ultra- and supermicropores. Surface and Elemental Analysis The activated carbons treated with potassium salts were also characterized by SEM and SEM-EDX. Figure 5 shows SEM images of some typical activated carbons after their treatment with potassium salts. These Figures indicate the porous texture and localization of the potassium salts on the surfaces for all of the materials used. It is shown that, when potassium is dispersed into activated carbons, the porosity is modified in some cases; this effect was developed in the microporosity in materials having a narrow starting porosity. The SEM images Figure 4. t-plots of the activated carbons treated with potassium. of these K-activated carbon particles provide information about the distribution of the metals. In addition, homogeneous distribution of potassium ions on the large surface area can promote the catalytic efficiencies for the removal of environmental pollutants. This aspect must be taken into account for further analysis of the removal of pollutants, because the porosity strongly influences both the adsorption capacity of pollutants and the catalytic activity toward pollutants. In addition, if the pore size becomes too narrow with decreasing surface area after potassium ion treatment, catalytic activity for the removal will definitely appear during the liquid/k-carbon activity reaction. For elemental microanalysis of the K-activated carbons, these samples were analyzed by EDX; the spectra of the K-activated carbons are shown in Figure 6. These spectra display the presence of C and Au atoms in addition to the major K signals we blieve that the Au metal was introduced during the process of pretreating the samples prior to analysis. Most of the samples are richer in carbon and the major metals treated than in any other element. The results of EDX elemental microanalysis of K-ACs are listed in Table 4. Surface Functional Groups It is well known that oxygen-bearing surface groups act as nucleation centers for introduced potassium and precursors. The changes in the properties of activated carbon are due to an alternation of the carbon surface via introduction of oxygen groups, by using dilute nitric acid, and the removal of some carbon atoms from the matrix. The type and quality of oxygen groups were determined using the Boehm titration method [10]. The results obtained from this method are collected in Table 5. The total acidity and the distributions of groups of various strengths have very similar values. The effect of the surface acidity and basity was also evaluated from correlations as a function of the NaOH, NaHCO 3,and

5 Physical Properties of K-Activated Carbon and its Removal Efficiencies for Chemical Factors 377 (a) (b) (c) (d) (e) (f) Figure 5. SEM micrographs of the potassium-treated activated carbons (a), (b), (c), (d), (e), and (f). Table 4. EDX Elemental Micro-Analysis of K-ACs Spectrum Label (Samples) Matching Elements C, K, Au Different Elements Si, Mn, Cu Na, Si Na 2 CO 3 uptake. The positive influence of the acidic groups on the carbon surface after nitric acid treatment was also demonstrated by an increase in the potassium content upon increasing the number of acidic groups calculated from Boehm titration. It is believed that the affinity of an activated carbon toward potassium depends on the number of surface functional groups. When the distribution of acidic groups is properly introduced, anchoring sites on the carbon surface should be play important role in the deposition of K ions. Removal Efficiencies of K-Activated Carbons The average value of the initial COD and BOD of raw waste was over 50,000 mg/l. The analytical results for the primitive piggery waste are listed in Table 2. The average COD values of the waste after filtration through a K-activated carbon bed filter were distributed between 250 and 280 mg/l, these values dropped to under 160 mg/l after air blowing for 72 h. The results of the cata- Table 5. Number of Surface Species (meq/g) Obtained from Boehm Titration Functional Group (meg/g) Sample Carboxylic Lactonic Phenolic Acidic Basic lytic effect using activated carbons treated with potassium are shown in Figure 7. Almost all of the samples exhibited significant COD removal efficiencies, ranging from 60 to 160 mg/l, after air blowing for 72 h. The results obtained from sample, especially, show that the high removal efficiency contributed to reduce the COD. The BOD removal efficiencies of the K-activated carbon bed filter are shown in Figure 8. The BOD removed by the K-activated carbons also suggested very excellent removal effects in all cases. The results for T-P removal when using the K-activated carbon beds are shown in Figure 9. Again, the K-activated carbons display very excellent removal effects in all cases. The average concentration of T-P in the raw waste was over 150 mg/l (Table 2), whereas the final water purified with the K-activated carbon filters had T-P contents ranging from 3 to 11 mg/l before air blowing. These values for T-P dropped into the range from 1.5 to 7.5 mg/l after air

6 378 Won-Chun Oh and Weon-Bae Ko (a) (b) (c) (d) (e) Figure 6. EDX elemental microanalyses of the potassium-treated activated carbons (a), (b), (c), (d), (e), and (f). (f) Figure 7. Piggery waste COD removal efficiencies of K-activated blowing for 72 h. The average concentration of T-N in the raw waste was over 500 mg/l (Table 2); the T-N values of the final purified water after filtration with the K-activated carbon bed ranged from 18 to 32 mg/l before air blowing. These values for T-N dropped significantly into the range from 3.2 to 9.5 mg/l after air blowing for 72 h. The results of the T-N removal effect by K-activated carbon for the piggery waste are shown in Figure 10. These values are acceptable for the final disposal of the treated effluent. From these results, a possible catalytic mechanism for the removal of N- containing compounds is the formation of potassium salts on the carbon surface, i.e., NO x -N, NH 4 + -N, and NH 2 O-N react with potassium on the activated carbon surface.

7 Physical Properties of K-Activated Carbon and its Removal Efficiencies for Chemical Factors 379 Figure 8. Piggery waste BOD removal efficiencies of K-activated Figure 10. Piggery waste T-N removal effects of K-activated carbon. References Figure 9. Piggery waste T-P removal efficiencies of K-activated Conclusion Various types of K-activated carbon beds were used in this study to investigate the removal of COD, BOD, T-N, and T-P from piggery wastewater. The samples treated with aqueous solutions containing potassium ions were investigated with respect to their isotherm shapes, pore size distributions with micro and mesopore, surface states by SEM, and elemental micreoanalyses by EDX. The positive influence of the acidic groups on the carbon surface after nitric acid treatment was demonstrated by the increase in the content of potassium upon increasing the number of acidic groups, calculated from Boehm titration. The results obtained from the K-activated carbon samples show that the high removal efficiencies are acceptable for the final disposal of the treated effluent for COD, T-N, and T-P before and after air blowing for 72 h. 1. G. Mckey and M. J. Bino, Water, Air Soil Pollut., 51, 33 (1990). 2. G. Rozzi, L. Malpei, and L. Bonomo, Water Sci. Technol., 34, 9 (1996). 3. E. P. Taiganides, Animal Wastes, p. 154 London, UK, Elsevior (1977). 4. P. Y. Yang and C. Gan, Bioresour. Technol., 65, 21 (1998). 5. W. C. Oh and J. S. Bae, J. Korean Ind. Eng. Chem., 14, 29 (2003). 6. A. E. Akysolu, M. Madalena, A. Freitas, and J. L. Figueiredo, Appl. Catal. A : General, 192, 29 (2000). 7. H. Marsh, E. Hientz, and F. Rodriguez-Reinoso, Introduction to Carbon Technologies, p. 45 University of Alicante, Alicante in Spain, (1997). 8. W. C. Oh, Bull. Korean Chem. Soc., 25, 639 (2004). 9. W. C. Oh, H. J. Lee, and J. S. Bae, J. Korean Ind. Eng. Chem., 15, 434 (2004). 10. H. P. Boehm, Advances in Catalysis. Academic Press, New York, 16, 172 (1966). 11. G. M. Walker and L. R. Weatherley, Chem.Eng.J., 84, 125 (2001). 12. K. C. Choi, O. A. Gyoun, Y. D. Kim, Y. H. Kim, U. S. Lee, Z. Y. Lee, S. J. Chon, and S. K. Chung, Anotation for Standard Methods of Water Quality, p.187, Donghwa Technology Publishing Co., (2002). 13. APHA, Standard methods for the examination of water and wastewater, 16th Edn., APHA, Washington DC (1982).