Biosorption of Heavy Metals from Landfill Leachate Onto Activated Sludge

This article was downloaded by: [TÜBİTAK EKUAL] On: 29 November 2010 Access details: Access Details: [subscription number 772815469] Publisher Taylor & Francis Informa Ltd Registered in England and Wales Registered Number: 1072954 Registered office: Mortimer House, 3741 Mortimer Street, London W1T 3JH, UK Journal of Environmental Science and Health, Part A Publication details, including instructions for authors and subscription information: http://www.informaworld.com/smpp/title~content=t713597268 BIOSORPTION OF HEAVY METALS FROM LANDFILL LEACHATE ONTO ACTIVATED SLUDGE Ferhan Çeçena; Gül Gürsoya a Boğaziçi University, Institute of Environmental Sciences, Istanbul, Turkey Online publication date: 30 June 2001 To cite this Article Çeçen, Ferhan and Gürsoy, Gül(2001) 'BIOSORPTION OF HEAVY METALS FROM LANDFILL LEACHATE ONTO ACTIVATED SLUDGE', Journal of Environmental Science and Health, Part A, 36: 6, 987 — 998 To link to this Article: DOI: 10.1081/ESE-100104126 URL: http://dx.doi.org/10.1081/ESE-100104126 PLEASE SCROLL DOWN FOR ARTICLE Full terms and conditions of use: http://www.informaworld.com/terms-and-conditions-of-access.pdf This article may be used for research, teaching and private study purposes. 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HEALTH, A36(6), 987–998 (2001) BIOSORPTION OF HEAVY METALS FROM LANDFILL LEACHATE ONTO ACTIVATED SLUDGE Downloaded By: [TÜBTAK EKUAL] At: 14:53 29 November 2010 Ferhan Çeçen* and Gül Gürsoy Boğaziçi University, Institute of Environmental Sciences, 80815, Bebek, Istanbul, Turkey ABSTRACT The removal of various heavy metals was studied when activated sludge was exposed to heavy metals in landfill leachate. Batch uptake tests were conducted for this purpose. Adsorption was the main mechanism of removal when biomass was contacted with heavy metals. Activated sludge had a high biosorption capacity and equilibrium was reached in a short time with respect to copper, iron, manganese, zinc and chromium. Adsorption isotherms were generated for those heavy metals and the Freundlich constants were calculated. Among the metals studied, manganese became very concentrated on activated sludge with time. Key Words: Landfill leachate; Biosorption; Isotherm. Heavy metal; Activated sludge; INTRODUCTION Landfill leachates contain significant amounts of heavy metals due to disposal of metal containing wastes into sanitary landfills. Relatively little knowledge exists about the behaviour and removal of heavy metals in * Corresponding author. E-mail: cecenf@boun.edu.tr 987 Copyright # 2001 by Marcel Dekker, Inc. www.dekker.com Downloaded By: [TÜBTAK EKUAL] At: 14:53 29 November 2010 988 ÇEÇEN AND GÜRSOY real landfill leachates (1,2). The high organics concentration in both the acidogenic and methanogenic phases of landfill stabilisation leads to important metal-organic complexes in leachate (3,4) making treatment by precipitation difficult. Cadmium, zinc and nickel were reported as the heavy metals most susceptible to complexation (4–6). A study conducted with landfill leachates revealed that in the case of physicochemical leachate treatment the residual heavy metal concentrations remained above the theoretical solubilities (7). Especially, Cd and Ni were shown to be highly complexed in precipitation experiments (7). Thus, even after pretreatment, metals are likely to be transferred to biological treatment units. Although the aim of biological treatment is not the removal of heavy metals, a considerable portion of heavy metals and alkaline earth metals could be removed in such systems due to biosorption (8). Biosorption of heavy metals can employ different biomasses (8–11) and different mechanisms such as ion exchange, chelation and adsorption by physical forces (8,12). The concentration range of the metal as well as the existence of other metals (8,13,14) and the speciation of metals (10) are among the important factors. Biosorption of heavy metals has been widely studied using pure cultures (10). However, these studies do not provide direct information if mixed cultures such as activated sludge are of interest. Surprisingly, very little information exists on the uptake of heavy metals onto activated sludge when landfill leachate is treated biologically. The purpose of this study was the investigation of the extent of heavy metal removal by biosorption onto activated sludge when landfill leachate and domestic wastewater were combined. Although the level of heavy metals may not be inhibitory for activated sludge, the accumulation of heavy metals in the sludge phase may still be of concern. MATERIALS AND METHODS Leachate Characterisation Leachate samples taken from the Gaziantep Sanitary Landfill in Turkey in the period of January–September 1997 have been characterised as shown in Table 1. This landfill is a 160 000 m2 solid waste disposal facility, serving a population of 750 000 people. The total useful life was calculated to be 50 years. The site was established in 1994 and received mainly domestic wastes and some industrial wastes. The leachate control system consisted of drainage pipes, a storage lagoon, and a recirculation system. As seen in Table 1, leachates had a very high organic content representing the first years of decomposition. The high concentrations and the relatively high BOD5/COD ratio indicate that the landfill was in the acidogenic phase. In lagoon samples the organic strength (COD and BOD5) and heavy metal concentrations were higher than in samples taken from the drainage BIOSORPTION OF HEAVY METALS Table 1. Sampling Date Sampling Point Sample No. 989 Characterisation of Landfill Leachate Samples 21.01.97 (B) 1 24.02.97 (A) (B) 2 3 09.05.97 (A) (B) 4 5 23.07.97 (A) (B) 6 7 16.09.97 (B) 8 Downloaded By: [TÜBTAK EKUAL] At: 14:53 29 November 2010 Parameters COD (mg/L) BOD5 (mg/L) TKN (mg/L) NH4-N (mg/L) NOx-N (mg/L) pH Cl
(mg/L) Alkalinity (mg CaCO3/L) Hardness (mg CaCO3/L) Cu (mg/L) Pb (mg/L) Fe (mg/L) Mn (mg/L) Zn (mg/L) Ni (mg/L) Cr (mg/L) Cd (mg/L) 18860 10055 1116 7.50 5499 10571 4801 0.27 0.79 11.23 0.83 0.51 2.90 0.40 0.15 9630 12710 3784 12850 2431 3312 2400 7380 1100 6350 500 1628 1144 1543 871 1602 2122 1604 979 1500 734 1379 1828 147 136 52 2256 60.7 200 7.78 7.9 7.70 7.97 7.90 8.00 5705 4762 5489 4688 5725 12084 9540 11752 9418 12897 1675 1675 1140 1746 1634 0.09 0.19 0.01 0.03 0.26 0.11 0.49 0.76 1.00 0.90 0.67 1.20 9.56 8.94 4.30 8.10 2.66 6.60 0.32 0.25 0.47 0.30 0.20 0.36 0.29 0.49 0.43 0.51 0.47 0.16 2.20 2.40 2.30 2.20 1.23 2.01 0.20 0.50 0.35 0.50 0.00 0.29 0.08 0.10 0.22 0.17 0.12 0.08 37024 15625 2730 2430 285 7.30 9702 18150 3556 1.45 1.91 25.2 0.85 2.20 5.80 2.24 0.25 A: Drainage pipe exit. B: Storage lagoon. pipe exit (15). The lagoon could be considered as an equalisation basin, whereas samples from the drainage pipe reflected instantaneous values. The concentration of heavy metals was significant and usually paralleled the organic strength. In the samples collected from January to June 1997, only iron and nickel concentrations exceeded 1 mg/L. Conversely, in the high-strength leachate taken in September (Leachate No. 8) almost all heavy metal concentrations, except cadmium and manganese, exceeded 1 mg/L. Physicochemical pretreatment alternatives such as coagulation/flocculation, precipitation, base addition, aeration, stripping of ammonia were applied in another study (7) using various combinations of lime, alum, ferric chloride, ferrous sulfate and polyelectrolytes. Generally very high coagulant and precipitant doses were required to achieve a considerable reduction in the heavy metals Cu, Pb, Zn, Ni, Cd, Cr, Mn and Fe. Experiments on Sorption of Heavy Metals onto Biomass Biological treatability of the leachate has been reported in detail in another study (16). In those biological treatment studies landfill leachate was mixed with domestic wastewater in order to examine combined treatability. 990 ÇEÇEN AND GÜRSOY In parallel to that study, the biosorption of the heavy metals Cu, Fe, Mn, Zn and Cr onto activated sludge was investigated. These metals are among the major heavy metals in landfill leachates. Biosorption studies were carried out in three steps as follows: Downloaded By: [TÜBTAK EKUAL] At: 14:53 29 November 2010 Determination of Equilibrium Time Biological sludge used as an adsorbent was taken from an activated sludge reactor fed with domestic wastewater (16). Domestic wastewater was prepared synthetically using sodium acetate, glucose, peptone, (NH4)2SO4, KH2PO4, K2HPO4, MgSO47H2O, CaCl22H2O and FeCl36H2O. This sludge was therefore initially not contaminated (‘‘uncontaminated sludge’’) with leachate. In shaker flasks, heavy metals in the leachate were contacted with this biological sludge in order to estimate the equilibrium time. The procedure was as follows: In the main activated sludge reactor (16) the MLSS concentration was determined. An appropriate amount of sludge was then taken and added to 300 mL Erlenmeyer flasks to yield adsorbent concentrations of 200, 500, 1000 mg/L MLSS, respectively. The typical MLVSS/MLSS ratio in the biological sludge was about 0.8. Then 200 mL diluted leachate (Leachate No. 8) was added to each flask. The concentrated leachate was diluted since in a real system it will also be diluted with domestic wastewater. Thus the heavy metal concentrations in the initial wastewater would be lowered. All flasks were put into a shaker and samples were taken from the supernatant at t ¼ 0, 5, 10, 30, 60, 90 and 120 minutes and analysed for copper, iron, manganese, zinc and chromium. Generation of Heavy Metal Isotherms In isotherm studies an excess shaking time of 180 minutes was allowed to ensure adequate uptake of copper, iron, manganese, zinc and chromium. The same procedure as above was applied. These isotherms were first generated using an ‘‘uncontaminated biomass’’ as an adsorbent material. The supernatant of the samples was analysed for heavy metals at the beginning and end of the shaking period. Isotherms were also determined using a ‘‘contaminated’’ sludge. This sludge was taken from an activated sludge reactor treating leachate and domestic wastewater for a long time. Therefore it was acclimated to leachate and had probably adsorbed some of the heavy metals. The hypothesis here was to test the differences in metal adsorptivity of ‘‘contaminated’’ and ‘‘uncontaminated’’ sludges. In all experiments the adsorbent sludges were first washed with water to eliminate the effect of previously sorbed compounds. BIOSORPTION OF HEAVY METALS 991 Determination of Heavy Metal Uptake in an Activated Sludge Reactor In the last step, the removal of heavy metals was examined in a batch activated sludge reactor in parallel to aerobic biological treatability of leachate (16). Pretreatment of the raw Leachate No. 8 was conducted using FeSO4 and polyelectrolyte; this lowered its COD from 37000 to 25000 mg/L (7). After this pretreatment, Cu, Fe, Mn, Zn, and Cr were at concentrations of 1.12, 32, 0.52, 1.2, 0.2 mg/L, respectively. This leachate was then mixed with domestic wastewater and fed to a batch activated sludge reactor. Samples were taken with respect to time and analysed for heavy metals and COD. Downloaded By: [TÜBTAK EKUAL] At: 14:53 29 November 2010 Analytical Methods The leachate samples were stored at 4 C until use. All analyses were made according to standardised methods (17). Sample pH was measured by an Orion SAS20 pH meter. COD analyses were made by the dichromate closed reflux method. Samples were analysed for the heavy metals Cu, Pb, Zn, Ni, Cd, Cr, Mn and F using the SCINO-4 Model (Manufacturer: Baird Atomic (Alfa Line)) Flame Atomic Absorption Spectrometry (AAS) by Direct Aspiration. Soluble metal concentrations were determined after filtration of unacidified samples through 0.45 mm membrane filters. Total concentrations of metals were determined in unfiltrated samples. Sample digestion was carried out using nitric acid. The digested solution was diluted, filtered through white band filter and heavy metal concentrations measured (17). Calibration was made with two standard solutions covering the range of the expected metal concentration. During analyses, the accuracy of readings was constantly checked with those standard solutions. Metal concentrations lower than 0.01 mg/L were recorded as zero. RESULTS AND DISCUSSION Heavy Metal Equilibration Figure 1a and b shows the remaining Zn and Cr concentrations in the supernatant with respect to shaking time when mixed liquor suspended solids (MLSS) were used as adsorbents. As shown in Figure 1a and b, a strong adsorption of heavy metals took place during the first 60 minutes; the equilibrium was established in approximately 90 minutes. The same response was observed in the case of other metals, Fe, Mn, and Cu. As the adsorbent concentration MLSS increased, all metals exhibited a decrease in concentration. This showed that an increase in adsorbent concentration increased the overall metal uptake. Biological sludge had the ability to remove and accumulate metal ions from solution in a rapid initial phase, Downloaded By: [TÜBTAK EKUAL] At: 14:53 29 November 2010 992 ÇEÇEN AND GÜRSOY Figure 1. Residual concentrations of (a) zinc and (b) chromium at various adsorbent concentrations with respect to shaking period. followed by a second and slower phase of uptake as shown in literature (18,19); this removal achieved in the second phase was relatively insignificant (12). It was reported that the uptake of cadmium, copper and zinc by activated sludge bacteria occurred rapidly, reaching equilibrium in 1–2 hours after dosing (19). The results of the present study were in accordance with this and implied that the equilibration of heavy metals will be quite rapid in an activated sludge system. Heavy Metal Isotherms with Uncontaminated and Contaminated Sludges Adsorption isotherms generated with ‘‘uncontaminated’’ and ‘‘contaminated’’ sludges showed the equilibrium distribution of heavy metals between BIOSORPTION OF HEAVY METALS 993 the bulk solution (Ce) and the biomass (X/M). In isotherm studies with ‘‘uncontaminated sludge’’, the initial Cu, Fe, Mn, Zn and Cr concentrations in the wastewater were about 0.13 mg/L, 1.75 mg/L, 0.10 mg/L, 0.17 mg/L, 0.20 mg/L, respectively. In isotherm studies with ‘‘contaminated sludge’’ the initial Cu, Fe, Mn, Zn and Cr concentrations were about 0.09 mg/L, 9.5 mg/L, 0.12 mg/L, 0.15 mg/L, 0.20 mg/L, respectively. The adsorbent sludges were all taken from an activated sludge system operating at a high sludge age and therefore the uptake of metals was favoured. The isotherm data best fitted into the Freundlich model shown below: 1=n X=M ¼ kCe ð1Þ Downloaded By: [TÜBTAK EKUAL] At: 14:53 29 November 2010 The linearized form of the equation is as follows: logðX=MÞ ¼ logk þ ð1=nÞlogCAe ð2Þ where X/M: Adsorbed heavy metal per unit weight of dry activated sludge, mg metals/gMLSS k: Freundlich capacity constant 1/n: Freundlich intensity constant CAe: Equilibrium metal concentration (mg/L) The Freundlich constants k and 1/n were determined by regression analysis of isotherm data. Figure 2a–e illustrate the Freundlich isotherms for various heavy metals. In each case, the equilibrium concentrations of the heavy metals Cu, Mn, Zn, Cr were relatively low and the linearity of isotherms (Figure 2a–e) indicated that adsorption was the dominant mechanism in the removal of these metals as reported in other studies (19). In Table 2 the Freundlich constants k and 1/n for different metals are shown. Although it was very difficult to analyse the results in this complex leachate matrix, the adsorption capacity constant, k, for Mn and Fe uptake was obviously higher compared to other metals. Care should be taken in the case of Fe since some removal might have occurred by precipitation too. Since the adsorption isotherms for Mn, Cu, Zn and Cr were determined at relatively low equilibrium concentrations, precipitation of those metals was disregarded. The high k for Mn indicated that the biomass had a high capacity for manganese as also concluded from the sludge analysis reported in a later section. On the other hand, for Mn the slope 1/n was very high, indicating a lower adsorption intensity. A quantitative comparison of two different isotherms can only be done in the same equilibrium concentration range (8,20). Isotherms generated with ‘‘uncontaminated’’ and ‘‘contaminated’’ sludges (Figure 2a–e) were statistically compared to each other using the paired t-test at 95% confidence level. There were no significant differences for Fe, Mn and Zn in terms of 994 ÇEÇEN AND GÜRSOY Downloaded By: [TÜBTAK EKUAL] At: 14:53 29 November 2010 adsorption onto ‘‘uncontaminated’’ or ‘‘contaminated’’ sludge. On the other hand, for Cr and Cu there were statistically significant differences in this respect. In practice, these isotherms can be used to predict the approximate uptake of each heavy metal in an activated sludge system. For example, if the final residual Cu is about 0.05 mg/L, using Figure 2e and the adsorption constants in Table 2, one may estimate that the uptake onto biomass will be about 0.09 mg Cu/gMLSS and 0.02 mg Cu/g MLSS, for ‘‘uncontaminated’’ and ‘‘contaminated’’ sludges, respectively. Figure 2. Heavy metal isotherms showing a) iron, b) manganese, c) chrominm, d) zinc, e) copper uptake onto biomasses previously uncontacted with leachate (uncontaminated) and contacted with leachate (contaminated). Downloaded By: [TÜBTAK EKUAL] At: 14:53 29 November 2010 BIOSORPTION OF HEAVY METALS 995 Continued Figure 2. Table 2. Comparison of Freundlich Constants in the Case of Adsorption onto ‘‘Uncontaminated’’ and ‘‘Contaminated’’ Activated Sludges Adsorbent: Uncontaminated Activated Sludge Metal Cu Fe Mn Zn Cr Adsorbent: Contaminated Activated Sludge k mg metal/gMLSS 1/n k mg metal/gMLSS 1/n 0.3 1.7 9.1 0.8 0.4 0.4 0.7 1.1 1.2 0.5 4.5 2.4 5.4 0.4 0.9 1.8 0.4 1.0 0.8 1.2 Heavy Metal Accumulation in Activated Sludge In the ‘‘uncontaminated’’ biomass the concentrations of Cu, Fe, Mn, Zn, and Cr were about 0.89, 6.1, 0.0064, 0.944, 0.064 mg/g MLSS, respectively. In the ‘‘contaminated sludge’’ contacted with leachate, these 996 ÇEÇEN AND GÜRSOY metals had accumulated up to 12.01, 72.79, 0.92, 8.62, 1.06 mg/g MLSS, respectively. With respect to its low initial concentration, Mn became excessively concentrated on the sludge as time passed. The adsorption capacity (k) for Mn was high as concluded from the isotherm shown in Figure 2b. Also Fe became concentrated on biological sludge due to its high initial concentration and precipitation. The magnitude of heavy metal accumulation on biological sludge was comparable to literature values (21), although a direct comparison cannot be made since biosorbents and methods differ a lot as stated in the literature (8). Downloaded By: [TÜBTAK EKUAL] At: 14:53 29 November 2010 Heavy Metal Removal in a Batch Activated Sludge Reactor An aerobic batch activated sludge reactor was fed with Leachate No: 8 and synthetic domestic wastewater. The volume ratio of the leachate in the total feed was about 2% and on COD basis approximately 50% of the initial COD originated from leachate. Previous studies showed that combined treatment of landfill leachate and domestic wastewater was a feasible option (16). Data about the uptake of metals and change in total and soluble COD are presented in Table 3. Initial MLSS and MLVSS concentrations in the batch reactor were as 2830 and 2340 mg/L, respectively. After a contact time of 1.5 hours no significant changes occurred in total and soluble heavy metal concentrations. The pH increased from 7.2 to 8.1 as a result of CO2 stripping by aeration. The amount of heavy metal adsorbed and the time to reach equilibrium were in accordance with previous isotherm results. In the presence of oxygen, ferrous iron was oxidised to ferric iron and was precipitated as Fe(OH)3, therefore the soluble Fe was much lower than Table 3. Heavy Metal and COD Uptake in an Activated Sludge Reactor Total Heavy Metal Conc. (mg/L) Time (h) Cu Mn Zn Cr Fe Total COD (mg/L) 0 0.5 1.5 3 24 0.84 0.68 0.32 0.32 0.32 0.25 0.15 0.05 0.05 0.05 0.7 0.38 0.3 0.3 0.3 1.7 1.1 0.7 0.7 0.7 67 61 57 57 57 889 – – 322 104 Soluble Heavy Metal Conc. (mg/L) Time (h) Cu Mn Zn Cr Fe Soluble COD (mg/L) 0 0.5 1.5 3 24 0.47 0.34 0.18 0.12 0.12 0.15 0.12 0.03 0.02 0.02 0.35 0.18 0.16 0.14 0.14 0.7 0.6 0.32 0.3 0.3 9.7 6.9 6 5.4 5.4 830 – – 301 97 BIOSORPTION OF HEAVY METALS 997 Downloaded By: [TÜBTAK EKUAL] At: 14:53 29 November 2010 the total Fe as seen in Table 3. On the other hand, soluble concentrations of Mn, Cu, Cr and Zn did not show sharp decreases. They were probably taken up by the sludge since their initial concentrations were too low to precipitate. As shown in Figure 2b–e, in the concentration range of 0.01–0.05 mg/L of these metals isotherms indicate a removal by adsorption. If a biological system like this is constantly fed with a mixture of leachate and domestic wastewater, it is likely that the sludge will accumulate metals. Biosorption or adsorption of metals on viable organisms may be mechanisms producing toxic effects (22). In the present system there were a number of different heavy metals and these may have exerted synergistic or antagonistic effects. CONCLUSIONS Biological sludge had a high affinity for various heavy metals. Uptake of heavy metals from landfill leachate onto activated sludge took place very rapidly. Therefore, in the hydraulic retention time commonly used in activated sludge systems, metals will certainly reach an equilibrium between the liquid and sludge phases. Isotherms generated for the heavy metals copper, iron, manganese, zinc and chromium depicted the uptake of these metals with respect to their equilibrium concentrations. Activated sludges previously contacted with landfill leachate exhibited usually a lower uptake than those uncontacted with leachate. In combined landfill leachate and domestic wastewater treatment, it is very likely that the biological sludge becomes a sludge laden with heavy metals due to its high sorption capacity. Especially manganese accumulation on activated sludge was very excessive. ACKNOWLEDGMENTS The financial support of this study by the Research Fund of Boǧaziçi University (Project No: 96 HY0029) is gratefully acknowledged. REFERENCES 1. Keenan, D.; Steiner, R.L.; Fungaroli, A.A. Chemical-physical leachate treatment. J. Environ. Eng., 1983, 109, 1371–1384. 2. Sletten, R.S.; Benjamin, M.M.; Horng, J.J.; Ferguson, J.F. Physical-Chemical Treatment of Landfill Leachate for Metals Removal. Water Res., 1995, 29, 2376–2386. 3. Moit, H.V.; Hutz, K.F.; Yonge, D.R. Metal precipitation in two landfill leachate. J. Environ. 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Res., 1996, 68(1), 19–24. Received September 18, 2000 View publication stats