Malaysian Journal of Science 24(2): 1-8 (2005)
A preliminary study on the application of locally produced charcoal as the activated carbon for the adsorption of organic and non organic water pollutants Ghufran Redzwan*, S.Rofeah Ali, Yushamida Yusof and N.Marini Mohamed *
Corresponding author Programme of Science and Environmental Management, ISB-Faculty of Science, University of Malaya, 50603 Kuala Lumpur, Malaysia. Telephone: (+6) 03 7967 6797
Fax: (+6) 03 7967 4178
Email:
[email protected]
ABSTRACT Local charcoal (LC), which is derived from mangrove wood, has been tested as the activated carbon (AC) for its adsorption capacity in wastewater treatment process. Synthetic wastewaters were prepared from solution of sapharine dye and chromium ions to simulate the organics and metals ion pollutant. The performance of LC was measured based on colour removal given by the spectrophotometer reading. The performance of LC was further compared with the other two analytical grades of activated carbon materials, namely BDH and Sigma. This study showed that local charcoal is more effective in removing Cr(III) solution, in which more than 90% could be removed. Meanwhile the performance of LC for the removal of dye solution was found to be inefficient. The removal efficiency was less than 10%. Therefore this study indicates that LC is more suitable to be used for the removal of metallic compound instead of organic substances. Further investigation with the use of phenol and glucose to simulate the aromatic and aliphatic organic substances, respectively, had showed that LC is not as efficient as its ability to remove Cr(III) compared to removal of organic compounds.
ABSTRAK Arang tempatan (LC) yang diperbuat dari kayu bakau telah diuji dari segi keupayaan menjerap sebagai karbon teraktif (AC) untuk digunakan dalam proses rawatan air sisa. Penyediaan air sisa telah dilakukan secara sintetik dengan menggunakan larutan pewarna safranin dan ion kromium sebagai bahan pencemar organik dan logam berat. Prestasi LC juga dibandingkan dengan dua jenis AC yang berkualiti tinggi iaitu BDH dan Sigma. Kajian awal menunjukkan LC adalah berkesan untuk menyingkirkan lebih dari 90% ion kromium (III) dari larutan asal. Manakala untuk penyingkiran larutan pewarna, ia hanya berupaya menyingkirkan kurang dari 10% dari kepekatan asal. Kajian ini menunjukkan LC adalah sesuai untuk digunakan bagi penyingkiran bahan berlogam berbanding dengan bahan organik. Kajian lanjutan dengan menggunakan larutan fenol dan glukosa untuk simulasi sebagai bahan organik aromatik dan alifatik, telah menunjukkan keberkesanan LC bila dibandingkan dengan penyingkiran sebatian bahan organik adalah tidak setinggi kemampuannya untuk menyingkirkan Cr (III). (wastewater, mangrove charcoal, activated carbon, dye, chromium)
1
Malaysian Journal of Science 24(2): 1-8 (2005) INTRODUCTION Heavy metals and dyes have been classified as hazardous waste under the Malaysian Laws and Regulations [1]. These are the two substances, which can commonly be found in the industrial effluent discharge. Finding methods to remove such substances from the wastewater would save the operating cost, which normally incurred to transfer the waste to a scheduled waste disposal site. The waste disposal site operator normally charges the management fees based on the amount of mass delivered. Unnecessary cost will be added if such substances are delivered in liquid form, but on the other hand, setting up a dryer to minimise the bulk of waste is not considered an economical options for small and medium industries (SMIs). Treatment of metallic compounds in industrial discharges is normally done by chemical processes; while biodegradable dyes would go through the normal aerobic processes. Non biodegradable dyes discharge is often being treated by “dilution” instead of being actually removed from the water. Activated carbon (AC) is one of the options, which has been used to remove such substances in the wastewater. It is has been recognised as a “best available technology”. Referring to the report by local newspapers [2], almost all of the local charcoal (LC) is produced from mangrove wood. Some of the high quality LC also has been reported being exported to Japan in which the further application was not published. It can be assumed that Malaysian charcoal could be used as AC for adsorption process as the total amount of the material exported is not at the significant amount to be used as energy source. Considering the source for mangrove charcoal as the renewable resource, the interest of sustainable development for mangrove plantation could be established if the economic value of this material is identified. Based on the life span of the mangrove, it takes between four to five years for the plant to mature for harvesting. A systematic forestation for the mangrove will provide more systematic ways of sustaining the wetland. Therefore, the full potential of local carbon (LC) as the activated carbon should be determined since not all activated carbon will give the same performance [3, 4]. In this study, a preliminary assessment for the performance of LC was done on the removal of chromium ions to represent non-organic substances and followed by dye to represent the organic substances. Different bases of activated carbon, i.e. bituminous, coal and lignite will give different performances [4]. Thus this study will assess the performance of LC to be applied as activated carbon. The introduction of more stringent environmental legislation worldwide envisages a potential future growth in demand for activated carbon. This will provide better economic values for LC to perform as the activated carbon if it can be used in the wastewater treatment industry instead of the use of it in the recreational culinary activities. MATERIALS AND METHODS The preliminary performance of LC as AC in this study was carried out based on the batch operation. LC was evaluated based on the percentage of pollutant removal. Although there are other kinds of test, which are used to rank the AC [3], but the performance of LC in reference to the removal efficiency would simplify this preliminary work as for the screening of the ability of LC to be applied as AC. However, this experiment was done with the assumption that adequate surface area has been provided for optimal adsorption process to take place. Experimental Set-up All the apparatus used in the study were washed with deionised water before any test was conducted to remove impurities. The presence of impurities can cause some adsorbate in the liquid phase to adsorb onto the impurities surface instead. Thus the presence of impurities may effect the accuracy of the experimental results. All experiments were done in triplicates.
2
Malaysian Journal of Science 24(2): 1-8 (2005) Removal efficiency is calculated based on the standard formulation as listed in Equation 1. R.E.
Co Ce 100% Co
(Equation 1)
R.E. : removal efficiency Co : influent Ce : effluent Local charcoal (LC) Local carbon (LC) that is produced locally was further processed to granulated activated carbon (GAC) by grinding the commercially available charcoal. The grounded charcoal was further sieved with a mechanical siever using U.S.A Standard Testing Sieve (ASTME-11 specification) (size 20 and 18) to separate coarse GAC and powdered activated carbon (PAC). The selective GAC (diameter + 1mm) was further washed with deionised water to remove the residuals of PAC attached to the GAC and dried in the 100 oC oven. Other types of GAC for comparison study were obtained from analytical grades of GAC, Sigma Chemical Co. and BDH Laboratory. Synthetic wastewater Solution of chromium chloride (CrCl3) to simulate the Cr (III) wastewater was obtained from Fluka (Switzerland). This solution was to represent the non-organic substance or metallic compound in wastewater sample; meanwhile saphranine (C20H19ClN4) supplied by BDH Laboratory was used to represent organic substances. Each wastewater sample was prepared at the concentration of 1000 mg.l -1 from concentrated stocks. Removal of the sample during the batch operation was analysed based on the colour removal which was measured by Metertek SP850 spectrophotometer. Both solutions gave specific colour, which could be measured by the Beer and Lambert approach. Removal of Cr(III) was measured at the wavelength of 650 nm meanwhile for saphranine at the wavelength of 720 nm. Other synthetic wastewaters were also being prepared in this study, namely phenol and glucose. Phenol was used to represent the aromatic molecular organic substances and glucose, to represent the aliphatic molecular organic. The removal of these two substances was measured with COD analysis, which was conducted according to APHA [5]. Batch operation The experiments were carried in batch mode (discontinuous adsorption test) in conical flasks (125mL), which were filled with 50 ml of sample and 5 g of granulated LC to make up the solid phase mass ratio of 1:100 for adsorbate and adsorbent. This was to warrant optimum surface area for adsorption process to take place. Series of batch operation were carried out on a rack mounted on a horizontal platform shaker. The rotation speed was maintained at 150 rpm and shaken for 24 hours. The flasks were capped with rubber stopper to avoid evaporation and spillage of liquid. RESULT AND DISCUSSION Table 1. Comparison of removal efficiency for various substances by three types of GAC Substance
LC
BDH
Sigma
Chromium chloride
91+ 11%
87 + 6%
77 + 8%
Dye
7 + 3%
90 + 7 %
95 + 5%
Phenol
10 + 4%
63 + 5%
54 + 7%
Glucose
37+ 7%
45 + 4%
40 + 2%
3
Malaysian Journal of Science 24(2): 1-8 (2005) Table 1 shows the performance of LC as an activated carbon for the removal of both organic and nonorganic solutions. Comparison with the other two GAC namely as BDH and Sigma are also shown in the tables. The mass ratio of adsorbent and adsorbate for both solutions were at 1:100. Preliminary assessment of LC in these experiments with several substances indicated that LC has adsorbed Cr(III) at higher capacity compared to other three organic substances. It shows that LC has a good potential to be used in removing heavy metal in liquid-phase adsorption, when more 90% of Cr(III) was able to be adsorbed. The use of dye in this experiment is another attempt to search of cheaper material that could treat wastewater with similar pollutant content. Nevertheless, the removal performance by LC to remove such dye was not a big success when compared to the good grade of GAC. LC only removed 7% of the dye concentration based on the spectrometer analysis. Other GACs in Table 1 had shown much higher removal efficiency of dye, which were more than 90%. Most of the dyes contained phenolic compound [6]. Thus, the extended experiments with the adsorption of phenol and glucose were carried out to investigate the adsorbance capacity by LC on dyes. By comparing with glucose adsorption, it indicates that the aromatic compound in dyes play the roles for the low performance of LC to remove dyes. The adsorption of glucose by two other GACs were similar to each other as well as LC. It can be assumed that molecules structure has the effect on LC performance. It has been found that molecular structure and functional group of the substance could affect the adsorbability [7]. Finding an efficient and less expensive method of removing phenol would offer a more economical means of wastewater treatment process as phenol has been known as the recalcitrant organic substance [8]. Another study showed that a combination of physical destructive methods (hydrogen peroxide and ultra violet beam) and the use of activated carbon had been able to remove 88% of phenol compound in wastewater [9]. This method of treatment could be included as the supplement for application of LC to remove phenol. Molecules with low polarity are more sorbable which may explain why Cr(III) has higher adsorption onto the LC. AC in nature is highly porous which provides a large surface area for contaminants (adsorbates) to be attached. In simple terms, physical adsorption occurs because all molecules exert attractive forces, especially molecules at the surface of a solid (pore walls of carbon), and these surface molecules seek other molecules to adhere to. The large internal surface area of carbon has many attractive forces, which work to attract other molecules. Thus contaminants in water are adsorbed (or held) to the surface of carbon by surface attractive forces similar to gravitational forces. Adsorption from solution occurs as a result of differences in adsorbate concentration in the solution and in the carbon pores. The adsorbate migrates from the solution through the pore channels to reach the area where the strongest attractive forces are. There are a few surface forces that can attract contaminants in water and make them as the adsorbates, which are later removed from the liquid phase [10]. The general theory behind removal of adsorbate is that those compounds which are more adsorbable onto activated carbon generally have a lower water solubility, are organic (made up of carbon atoms), have a higher molecular weight, and a neutral or non-polar chemical nature. Nevertheless, the ability for LC to adsorb Cr(III) still could not be fully understood. It can be pointed out that Cr(III) has these characteristics when compared to organic solution when in contact with LC. In addition to that, adsorbates also could become physically adsorbed onto activated carbon, they must be both dissolved in water and smaller than the size of the carbon pore openings so that they can pass into the carbon pores and accumulate. Physical adsorption is the primary means by which activated carbon works to remove contaminants from water. The differences of performance among these GACs are because ACs can be made from different carbonaceous raw material, in which differences will exist in the finished product. These include, in order of decreasing quality, metallurgical-grade bituminous coal, a lower ranked sub-bituminous coal and lignite [10]. The base raw material and pre-treatment steps prior to activation also can affect many of the physical and activity characteristics of activated carbon. The primary raw material used for activated carbon is any organic material with a high carbon content (coal, wood, peat, coconut shells). These different properties in the raw material make some carbons better suited than others for specific applications. In this study, LC as the lignite based AC seems to be efficient in removal of Cr(III), indicating the possibility of being used for
4
Malaysian Journal of Science 24(2): 1-8 (2005) heavy metal removal in wastewater. High atomic weight makes Cr(III) more attractive to surface area for LC. Deithorn and Mazzoni [10] listed down that carbon made from lignite tend to have a large pore diameter (higher molasses number ) which makes them better suited for the removal of large color body molecules from liquids. Not many detailed studies on the specificity for the removal of Cr(III) by other AC have been cited. Meanwhile AC made from bituminous coal has a broad range of pore diameters. Since these carbons have both a fine and wide pore diameter, they are well-suited for the removal of a wider variety of organic chemical contaminants from water, including the larger color bodies which is the saphranine dye with the molecular structure of C20H19ClN4, and followed by phenol, and glucose (C6H12O6) which also take the form of aliphatic chain in a liquid phase. Dissolution of organics substances also turned it as a polarized substance which could be another aspect on the different performance of AC for the adsorbance of organic compound. The other study on acid dye-methyl orange which is also the organic adsorbate by the same BDH adsorbent has shown lower colour removal rate (56%), indicating that molecular weight or pH of the substance has affected the removal performance [11]. The technology of removing the dye in the effluent discharge still is an issue which need to be resolved. Ozonation process is another potential technology that can used to treat such effluent. Ramasamy et. al has used ozonation process with pH adjustment and able to reduce 79.6% of the colour for reactive Blue 38 dye (pthalocyanine structure) [12]. Nevertheless, searching for AC as efficient as the analytical grade GACs which are shown in this study will give more economical and soundly safer solution with higher colour removal. Density factor can also be a major consideration for specific applications. The densities of activated carbons also vary with the raw material. Fewer mass of carbon with a low density will fit into a given container as compared to a carbon with a high density. This is significant because, while a container may require less carbon weight of a low density carbon to make a volume fill, its contaminant removal performance may be severely reduced as compared to a higher density carbon. The concept of volume activity then becomes important when evaluating carbons. In future study for LC assessment should include the density data especially when it is being pursued in a continuous operation. The other important parameter which is related to the density of LC, a simple calculation for determining the volume activity of carbons is to multiply the bulk density by the Iodine number. Thus, two containers having the same volume with carbons having the same Iodine activity (measured in milligrams Iodine per gram carbon) but different densities will have significantly different total surface areas (volume activity) available for adsorption. Deithorn and Mazzoni had studied on volume activity data for carbons made from three different raw materials [10]. These volume activities have been calculated for a standard volume. Differences in volume activity are evident when Iodine activities are the same but bulk densities are different (bituminous vs. subbituminous), and even more dramatic when both Iodine activities and bulk densities are different (bituminous versus lignite). Thus, assessment of LC should include the volume activity with the standard parameter testing. Locally produced charcoal shows a big potential as GAC to remove heavy metals in wastewater. Another study conducted which used local GAC obtained from the palm shells was applied to study the adsorption of copper ions [13]. Adsorption isotherms of Cu(II) were determined at pH 3 and pH 5. The effects of the presence of complexing agents such as boric acid and malonic acid on Cu(II) ultimate uptake were also investigated. The results showed that Cu(II) can be successfully removed by palm shell activated carbon. The presence of complexing agents was found to have a substantial effect on Cu(II) adsorption. In order to compare the performance of LC with palm shell GAC, this study should be further continued by incorporating the actual concentration of metallic compounds, rather than based on qualitative colour removal investigation. The other parameters which should be included are equilibrium carbon column performance, adsorption isotherm capacity and adsorption kinetics [3]. The performance of GAC is typically evaluated with a breakthrough profile that characterizes its removal of target compounds. Removal of the contaminant is normalized on the ordinate with an effluent-to-influent ratio of concentration (Ce/Co). This results in the breakthrough curve commencing at a Ce/Co ratio that is greater than zero. Following a transition period, the breakthrough profile remains nearly constant with increasing bed volumes passed. The term plateau in such
5
Malaysian Journal of Science 24(2): 1-8 (2005) study refers to the horizontal part of the breakthrough curve. At plateau, the removal does not show a trend; rather, it varies about a mean. At plateau, adsorption is assumed to be complete. The amount of water treated to reach the plateau state is often thought to be representative of the adsorptive capacity of GAC. This type of study will be included on this study, in order to exploit LC as the AC. For the study of adsorption equilibrium, Zhou et. al have suggested that this type of study on adsorption equilibrium will allow the estimation of the material to adsorb various molecules [14]. It can be done by constructing adsorption isotherms at equilibrium, which can be done using Freundlich equation. Experimentation with single adsorption and advanced oxidation processes to compare their effectiveness in removal of such substances. Investigation of optimum regenerating conditions for the spent activated carbon and estimation of the operating cost of the system on the basis of optimal phenol removal should also need to be studied. CONCLUSION This preliminary study on the performance of LC to be used in wastewater industry has showed a big potential. It has shown to have high removal efficiency on the Cr(III) based on the colour removal for the solution of chromium chloride. This potential should be further studied. Nevertheless, a more quantitative approach should be conducted before any conclusion could be brought forward for the commercialisation of the carbonization of wood from mangrove plantation on the bigger scale. The quantitative study should include the actual adsorbate mass removal, carrying capacity and breakthrough capacity. This can be achieved with a higher accuracy of metal analysis and adsorption isotherm equilibrium. Removal of the other metallic compounds with LC should also be conducted. Beside the study for other heavy metal removal, another series of study should also be done on the improvement of adsorption process by LC at the tertiary treatment of water and wastewater in Malaysia. Acknowledgments Authors acknowledge the support of this work through Institute of Research Management, University of Malaya for the funding of this project (Vote F 0355/2002D). REFERENCES 1.
Legal Research Board, 2003, Environmental Laws of Malaysia, International Law Book Services, Kuala Lumpur.
2. Star Newspaper, 2002, 10 August, Swampy wonderland, Star Publication Bhd. Petaling Jaya: p. 35-38 3. Greenbank, M. and Spotts, S., 1993, Effects of Starting Material on Activated Carbon Characteristics and Performance, paper presented at WaterTech Expo '93, Nov. 10-12, Houston, Texas. 4. Carlson, M.A., Heffernan, K. M. Ziesemer, C. C. and Snyder, E. G. 1994, Comparing two GAC's for Adsorption and Biostabilization, Journal American Water Works Association, Vol. 88 (3), p. 23-28. 5. APHA (American Public Health Association), 1998, Standard Methods for the Examination of Water and Wastewater.19th ed., Water Environment Federation, Washington DC, USA 6. Rattee, D. and Breuer, M. M. 1974, The physical chemistry of dye adsorption, Academic Press, London. 7. Eckenfelder, W.W., 2000, Industrial Water Pollution Control, McGraw-Hill College, New York 8. Metcalf and Eddy, Inc. 1991, Wastewater Engineering, Treatment, Disposal and Reuse, 3rd Edition, McGraw-Hill, Inc. Singapore. 9. Ince, M. and Apikyan, 2000 Combination of activated carbon adsorption with light enhanced chemical oxidation via hydrogen peroxide, Wat. Res. Vol. 34 (17), pp. 4169-4176
6
Malaysian Journal of Science 24(2): 1-8 (2005) 10. Deithorn, R.T. and Mazzoni, A.F., 1993, Activated Carbon What it Is, How it Works, Calgon Carbon Corp., Pittsburgh, PA 11. Arsyad, J., Beh, K.F., Leong, K.T., Choong, T. S.Y., Idris, A. and Chuah, T.G, 2003, Adsorption Of Acid Dyes Using Activated Carbon in Proceedings of the International Conference Environmental Management & Technology ‘A Clean Environment Towards Sustainable Development’, 4 - 6 August 2003, Putrajaya, Malaysiam, pp. 161 - 164 12. Ramasamy, K.R., Abd-Rahman, N. and Wong, C.S., 2003, The effect of pH on the reduction of colour, COD and TOC upon Ozonation of textile dye, Malaysian Journal of Science 22: 127-131. 13. Issabayeva1, G., Aroua, M. K. and Sulaiman, N.M., 2003, Study on The Adsorption of Copper (II) on Palm Shell Activated Carbon in Proceedings of the International Conference Environmental Management & Technology ‘A Clean Environment Towards Sustainable Development’, 4 - 6 August 2003, Putrajaya, Malaysia, pp. 153 - 155 14. Zhou, M.L., Martin, G., Taha, S. and Santana, F., 1998, Adsorption isotherm comparison and modeling in liquid phase onto activated carbon, Water Research, Vol. 32(4), pp. 1109 –1118
7
