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Heavy metal removal in groundwater originating from acid mine drainage using dead Bacillus drentensis sp. immobilized in polysulfone polymer
Journal of Environmental Management 146 (2014) 568e574
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Journal of Environmental Management journal homepage: www.elsevier.com/locate/jenvman
Heavy metal removal in groundwater originating from acid mine drainage using dead Bacillus drentensis sp. immobilized in polysulfone polymer Insu Kim a, Minhee Lee b, *, Sookyun Wang c a b c
Korea Basic Science Institute, Division of Earth and Environmental Science, 804-1 Yangcheongri, Ochangeup, Cheongwongun, Chungbuk, Republic of Korea Department of Earth Environmental Sciences, Pukyong National University, 599-1 Daeyondong, Namgu, Busan 608-737, Republic of Korea Department of Energy and Resource Engineering, Pukyong National University, 599-1 Daeyondong, Namgu, Busan 608-737, Republic of Korea
a r t i c l e i n f o
a b s t r a c t
Article history: Received 15 February 2014 Received in revised form 28 May 2014 Accepted 30 May 2014 Available online 8 September 2014
Batch, column, and pilot scale feasibility experiments for a bio-sorption process using a bio-carrier (beads) with dead Bacillus drentensis sp. in polysulfone polymer were performed to remove heavy metals in groundwater originating from an acid mine drainage (AMD). For batch experiments, various amounts of bio-carrier each containing a different amount of dead biomass were added in artificial solution, of which the initial heavy metal concentration and pH were about 10 mg/L and 3, respectively. The heavy metal removal efficiencies of the bio-carrier under various conditions were calculated and more than 92% of initial Pb and Cu were found to have been removed from the solution when using 2 g of bio-carriers containing 5% biomass. For a continuous experiment with a column packed with bio-carriers (1 m in length and 0.02 m in diameter), more than 98% of Pb removal efficiency was maintained for 36 pore volumes and 1.553 g of Pb per g of bio-carrier was removed. For the pilot scale feasibility test, a total of 80 tons of groundwater (lower than pH of 4) were successfully treated for 40 working days and the removal efficiencies of Cu, Cd, Zn, and Fe were maintained above 93%, demonstrating that one kg of biocarrier can clean up at least 1098 L of groundwater in the field. © 2014 Elsevier Ltd. All rights reserved.
Keywords: AMD Bio-carrier Bacillus sp. Polysulfone Groundwater remediation Heavy metals
1. Introduction There exist about 2500 mines, including 900 metal mines, in South Korea; more than 200 abandoned metal mines have continued to discharge acid mine drainage (AMD), which leaches out large amounts of heavy metals (KMOE, 2007). AMD drastically alters the acidity and chemistry of groundwater and streams, and may endanger not only plant and animal populations but also human health (Gray, 1997; McCullough and Lund, 2006). The development of remediation processes to remove heavy metals in groundwater originating from AMD is thus necessary. To date, various physicochemical remediation processes such as coprecipitation, ion exchange, adsorption, and solvent extraction have been widely applied to heavy metal contaminated groundwater (Cheng et al., 2011; Flores et al., 2012; Hashim et al., 2011; Macias et al., 2012). However, most of these processes are not effective or are impractical for acidic groundwater originating from
* Corresponding author. Tel.: þ82 51 629 6630; fax: þ82 51 629 6623. E-mail address: [email protected] (M. Lee). http://dx.doi.org/10.1016/j.jenvman.2014.05.042 0301-4797/© 2014 Elsevier Ltd. All rights reserved.
AMD due to low pH of AMD and/or high operating cost (Hlabel et al., 2007; Luptakova and Kusnierova, 2005; Silveira et al., 2009). It has recently been recognized that bio-treatment, one of the alternative processes to remove heavy metals in water, has distinct advantages such as low operating cost, minimization of the volume of sludge, and high efficiency in detoxifying dilute effluents (Gadd, 2000; Malik, 2004; Radhika et al., 2006; Sprocati et al., 2006). Bio-treatment for heavy metals generally includes bioaccumulation by dead or living biomass and the application of living biomass such as bacterial, algae, fungi, and seaweed as a biosorbent; this type of bio-treatment has emerged as a more cost effective process than other chemical processes and also as an ecofriendly process, which minimize byproducts (Kratochvil and Volesky, 1998; Puranik and Panikar, 1999; Song et al., 2012; Wang and Zhao, 2009). Despite these advantages of the use of living biomass, this process requires the continuous supply of nutrients; further, it is difficult to maintain healthy microorganisms because they are very sensitive to the water quality, oxidation-reduction status, and pH (Aksu, 2002; Bai et al., 2013; Hashim et al., 2011; Lovely and Coates, 1997; Martins et al., 2009; Park et al., 2013). It was suggested that the use of dead biomass as bio-sorbent could
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overcome these problems, but there exist other application problems such as the difficulty of separation of biomass from water after the treatment and the low mechanical strength during long term usage and recycling (Bayramoglu, 2003; Simeonova et al., 2008). However, when dead biomass is immobilized in a polymeric matrix as a bio-carrier, its presence confers high resistance to chemical environments and also provides additional advantages such as efficient regeneration and easy separation from solution (Çabuk et al., 2006; El-Naas et al., 2009; Volesky, 2001). The selection of an optimal immobilization matrix in a biocarrier is vital to the environmental application of immobilized dead biomass as bio-sorbent because the polymeric matrix determines the mechanical strength, rigidity and porosity characteristics of the bio-carrier. Various polymeric materials such as polysulfone, alginate, polyacrylamide, and polyvinyl alcohol have been used as immobilized matrixes for bio-sorption (Al-Hakawati and Banks, 2000; Arica et al., 2003; Hu and Reeves, 1997). Several previous studies have reported that polysulfone has the advantage of being cheaper and easier to handle than other polymer matrices, but the study for polysulfone has remained at a fundamental level on a laboratory scale (Beolchini et al., 2003; Jeffers et al., 1991; Lee et al., 2010; Vijayaraghavan et al., 2007). The use of dead biomass in polysulfone for a heavy metal remediation process to groundwater originating from AMD (lower than pH of 4) has never been investigated, even in the laboratory. This study aims to demonstrate the removal of heavy metals in groundwater affected from AMD by using a bio-carrier (bead shape), which is composed of dead biomass in a polysulfone matrix. This is novel feasibility study on a pilot scale using immobilized biomass with polysulfone for AMD originated groundwater in the field. The dead biomass used in this study was Bacillus drentensis sp. strain isolated from heavy metal contaminated soils near an AMD outlet of the Ilkwang abandoned mine in Korea. The results of this study will provide meaningful information for the future application of the bio-carriers to remove heavy metals in groundwater having low pH. 2. Experimental method 2.1. Preparation of bio-carrier Indigenous microorganisms were isolated from soil samples near the Ilkwang abandoned mine, Korea. The Ilkwang abandoned mine was active from 1931 to 1978, producing approximately 40,000 tons of copper ores and about 15,000 tons of waste rocks and mine tailings, which were put back inside the mine shaft (KMOE, 2007). However, the abandoned mine continues to discharge AMD that is rich in iron and highly acidic; this flow contaminates the soil and groundwater in the vicinity of the mine. For the isolation of a bacterial strain from soil samples, 1 g of randomly selected soil from the soil samples and 9 ml of sterile distilled water were shaken vigorously using a vortex for at least 1 min. The mixed solution of 0.1 ml was blended with 0.9 ml of sterile distilled water. This process was aseptically repeated several times and each time the transferred sample was thoroughly mixed with the dilution fluid before being transferred to the next tube. Using the streak-plate method, a dilution solution of 0.1 ml was injected into and smeared on a nutrient agar (NA) medium in a petri-dish. After spreading, the sample was aerobically incubated for 48 h at 35 C. Colonies representative of all different morphologies from the NA medium were chosen at random. Representative colonies of all different morphologies in the nutrient agar plate were identified through sequencing by using the 16S rRNA gene (Petti et al., 2005; Schmalenberger et al., 2001).
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Among the isolated microorganisms, Bacillus drentensis LMG 21831T was selected for this study; more information on Bacillus drentensis LMG 21831T can be found in a previous study (Lee et al., 2010; Moyer et al., 1994). Bacillus drentensis LMG 21831T was stored by freeze-drying with 10% glycerol before use and all culture works were conducted aseptically in a clean-bench. After the massive cultivation of Bacillus drentensis LMG 21831T, the biomass was collected by centrifugation at 15,000 rpm (TOMOE Engineering Tomoe ASM 260PL) and the supernatant was freeze-dried. The dried biomass was deactivated by autoclaving at 121 C and 1 atm for 20 min. The dead biomass was powdered using a pestle and mortar and was sieved through a 100-mesh sieve. Then, it was stored in a refrigerator for the preparation of the bio-carrier. To immobilize the dead biomass in a polysulfone matrix for biocarriers (beads), 10 g of polysulfone was shaken in 90 g of N,Ndimethyl formamide (DMF) solvent for 16 h on a rotary shaker at 125 rpm to dissolve polysulfone completely. The amount of dead biomass in the bio-carrier may control the removal efficiency of heavy metals. Bio-carriers containing different amounts of biomass in the polysulfone matrix (from 0% to 5%) were produced and the bio-carriers' removal efficiency for heavy metals such as Pb and Cu was investigated using batch experiments. Powdered biomass was homogeneously blended into a 10% solution of polysulfone on a stirrer. The resulting slurry was dropped into 80% methanol solution through a peristaltic pump with an 18-gauge needle; spherical beads as the bio-carrier were formed by phase inversion (Jeffers and Corwin, 1993; Lee et al., 2010). Beads were washed in distilled water for 1 h on a rotary shaker to diffuse out DMF; beads were then dried for 48 h at room temperature (22 ± 1 C). After drying, beads that had taken an irregular shape were discarded. A scanning electron micrograph (SEM; S-2700, Hitachi), an energy dispersive spectroscopy (EDS; EX-250, Horiba Scientific), and a transmission electron micrograph (TEM; JEM-1210EX II, JEOL) were used to visualize the structure of bio-carrier and the compositional characteristics. 2.2. Batch experiments Batch experiments were performed to investigate the heavy metal removal efficiency of the immobilized bio-carriers (beads) from groundwater under low pH conditions. Artificially contaminated solutions were used as groundwater and distilled water was titrated with each standard solution of Pb and Cu purchased from AnApex Ltd. (1000 mg/L) to make certain of the initial concentrations for the experiments (about 10 mg/L). The pH condition of the solution was also artificially adjusted to pH 3 by addition of 0.1 M HNO3 to simulate groundwater originating from AMD. To determine the optimal amount of beads for heavy metal removal, various numbers of beads in solution were applied to the experiment. Batch experiments with beads having different amounts of dead biomass in the polysulfone matrix were also duplicated. Each different number of beads (0.1, 0.2, 0.5, 1, 2 and 5 g) was added to the contaminated solution of 50 ml. The mixed solution was shaken on a rotary shaker at 120 rpm for 48 h (at 20 C) and the supernatant was filtered with filter paper (Whatman No. 40). Heavy metal concentration in solution was analyzed using inductively coupled plasma-optical emission spectrometry (ICP/OES; Optima 7000DV, PerkinElmer) to calculate the removal efficiency. The amounts of heavy metal removed at equilibrium and the removal efficiency (%) when using the immobilized bio-carriers were calculated by applying Eq. (1) and Eq. (2), respectively:
q¼
V Co Cf M
(1)
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2.3. Column experiments The glass column was designed with an internal diameter of 2.5 cm (100 cm in height); using a gravitational packing process, the column was filled with immobilized bio-carriers (61.8 g) including 5% of dead biomass. The photograph of the column used in the experiment is shown in Fig. 1. The column was slowly flooded with distilled water (263.4 ml of one pore volume; porosity of 0.537) from the bottom at a flow rate of 2.2 ml/min. Pb-contaminated solution (10.3 mg/L of initial concentration and pH of 3) was pumped through a peristaltic pump connected to the bottom of the column at 2.2 ml/ min. Flushed water samples were collected from 4 points (A, B, C, and D) of the column (25 cm distance between points) at different time intervals (0, 0.2, 1, 2, 3, 5, 8, 12, 15, 18, 24, 30, 36, 44, 54, and 66 pore volume). Water samples were analyzed on an ICP/OES for Pb concentration in the effluent; Pb removal efficiency (and the amount of heavy metal uptake (q) in Eq. (1)) of the bio-carrier for the column experiment was calculated. 2.4. Pilot scale feasibility test for groundwater originating from AMD
Fig. 1. Photograph and schematic systems of column experiments (A, B, C, and D: sampling point).
removal efficiencyð%Þ ¼
Co Cf Co
100
(2)
where q is the amount of specific heavy metal uptake (mg of removed heavy metal/g of bio-carriers), V is the volume of contaminated solution (ml), Co is the initial concentration of heavy metal in solution (mg/L), Cf is the final concentration of heavy metal in solution (mg/L), and M is the dry weight of the bio-carriers (g). All batch experiments were repeated three times and their arithmetic average was used as the final result. The pH is an important parameter that affects the bio-chemical behaviors of metal ions in an aqueous system since it directly influences the metal speciation in solution, which can change the biosorption capability (Fourest and Roux, 1992; Lovely and Coates, 1997; Yan and Viraraghavan, 2003). The oxidation of sulfide minerals in rock waste or tailings from mine activity contributes to AMD that has very low pH; the sorption capability of bio-carriers for heavy metals directly depends on the pH of the solution (Arica et al., 2003; Bai et al., 2013). Batch experiments were repeated at various levels of pH (1e12) of Cu and Pb-contaminated solution to investigate the maintenance of high Cu and Pb removal efficiencies of the bio-carrier under low pH conditions. Distilled water was titrated with the standard solution of Cu and Pb to about 10 mg/L; the pH condition of the solution was artificially adjusted by the addition of 0.1 M HNO3 or NaOH solution. A control test without the bio-carrier was also performed in the pH experiments to distinguish between the effects the bio-carrier and the precipitation on heavy metal removal. The process of the batch experiment for pH change in solution was the same as that employed in the previous batch experiment; Cu and Pb removal efficiencies of the bio-carrier at different levels of pH of solution were calculated.
On the basis of the column experiment results, a pilot scale feasibility test was performed using genuine groundwater. The reaction tank was made of an HDPE (high density polyethylene) cylinder (1.0 m in length and 1.0 m in diameter; 0.785 m3 in capacity); the top of the tank had a spray system with a flow regulator for groundwater injection. The bottom of the tank had a valve gear and a flow regulator controlling the flux of treated groundwater. The heavy metal contaminated groundwater was transported to the reaction tank by the autotimer and the constant-flow regulator from the extraction well (1.2 m of groundwater table in depth) around the ditch built to collect AMD from the pit mouth at the Ilkwang abandoned mine. The extraction well was composed of HIVP (high-impact PVC pipe; 0.08 m in diameter) from the surface to 3 m in depth; the well was screened from 2 m to 3 m in length. To prevent the inflow of suspended solids or impurities from groundwater to the reaction tank, all pumped groundwater was gathered in the storage chamber (2 m3 in capacity) and the overflowing groundwater from the chamber was injected into the reaction tank through a flow regulator by gravity. Before the bio-carriers (beads) were packed in the middle of the tank (80 cm in thickness), the pebbles (8e10 mm in diameter) were packed at 10 cm in thickness on the bottom and the top of packed bead layers in order to minimize the irregular flow in the tank. A stainless steel frame made of crisscross lattice beams (net size: 5 mm in diameter) was located at the boundary between the bead layer and the pebble layer to sustain the weight of each layer. The concentration of heavy metals in groundwater and AMD at the Ilkwang abandoned mine is shown in Table 1; concentrations of Cu, Cd, Zn, and Fe in groundwater exceeded the Korea Groundwater Tolerance Limit (KGTL), indicating that the groundwater was seriously affected from AMD and was contaminated by heavy metals. Contaminated groundwater was pumped from the extraction well and sprayed from the top of the reaction tank at velocity in the range of 3e5 L/min for 8 h during the daytime (8 h per day only on weekdays) for about two months (from May 30th, 2012 to July 30th, 2012). About 1.5e2 tons of groundwater was treated in the tank per day and the total volume of treated groundwater was 80 tons for 40 working days. Fifty milliliters of untreated and treated groundwater were sampled from the top and the bottom of the reaction tank every working day and were analyzed on ICP/OES for heavy metal concentration in order to calculate the removal efficiencies. The pebbles in the upper layer of the tank were replaced with new
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571
Table 1 Heavy metal concentrations and pH of AMD and groundwater for the feasibility test (all values are means of triplicates ± SDs). Sampling type
Sampling time
pH
Concentration (mg/L) Cu
AMD Groundwater
12-04-15 12-05-15 12-03-15 12-04-15 12-05-15
Korea groundwater tolerance limit
2.1 2.2 3.3 3.5 3.3
± ± ± ± ±
0.5 0.3 0.3 0.5 0.1
5.8e8.6
31.0 27.7 15.6 27.0 21.6
Cd ± ± ± ± ±
1.5 1.2 1.2 1.3 0.6
3.0
ones every 20 working day (2 times for 40 days) to prevent clogging in the bio-carrier packed layer of the reaction tank. Because all treated groundwater satisfied the Korean Groundwater Tolerance Limit, the treated groundwater was gathered in a storage tank (2.0 m3 of capacity), and was finally discharged into a nearby stream. Fig. 2 provides a schematic of the pilot scale feasibility test. 3. Results and discussion 3.1. Characteristics of bio-carrier The bio-carrier created with dead biomass in polysulfone was yellowish in color, spherical in shape, and with a diameter of about 2e3 mm (bead type). The average dry density of beads was 0.288 g/ cm3 and the average specific surface area, measured by BrunauerEmmer-Teller (BET) analysis, was 2.65 m2/g, which is 250 times larger than the external surface area of the bead. The crosssectional image of one bead by SEM analysis shows a thin outer layer to coat the irregularly shaped pore structure; the inner layers were mostly composed of large pore spaces and walls, which are useful for the adsorption of heavy metal ions (Fig. 3(a) and (b)). In order to distinctively visualize the bio-mass and polysulfone matrix in the bead, TEM analysis was also performed and showed that the dead biomass of Bacillus drentensis sp. was tightly conjoined with the polysulfone matrix, suggesting that the bead is insoluble and mechanically stable during the recycling or desorption process (Fig. 3(c)). TEM imaging and EDS analysis of the bead structure after the Pb-removal experiment show many clods of Pb (red color circles in Fig. 3(d)) adsorbed on the biomass in the bead, demonstrating that Pb in groundwater is successfully removed in the form
0.4 0.5 0.3 0.4 0.4
As ± ± ± ± ±
0.1 0.1 0.0 0.0 0.0
0.1
0.5 0.4 0.3 0.3 0.5 0.5
± ± ± ± ±
0.0 0.1 0.0 0.0 0.0
Zn
Fe
8.7 ± 0.1 10.0 ± 0.2 2.5 ± 0.3 15.6 ± 0.2 7.2 ± 0.3
251.9 222.4 146.0 189.2 162.3
5.0
10.0
± ± ± ± ±
6.2 8.3 9.0 12.3 8.8
of a solid phase sorbed on the immobilized biomass (Seo et al., 2013). 3.2. Batch experiments Results for the removal efficiencies of Pb and Cu in artificial groundwater according to ① biomass concentrations inside beads and ② the amount of polysulfone beads in groundwater are shown in Fig. 4. Pb and Cu removal efficiencies generally increased with the increase of both the biomass amount in the beads and the beads added to groundwater. For 0% and 1% of biomass in beads, Pb and Cu removal efficiency from solution was less than 4%, regardless of the number of beads in groundwater. Pb and Cu removal efficiencies of 2% biomass in the beads dramatically increased up to 86% and 81%, respectively with an addition of 5 g of beads in 50 ml of groundwater. With more than 5% of the biomass concentration in the beads, Pb and Cu removal efficiencies ranged from 92% to 99% when beads were added at a mass of more than 2 g to groundwater. These results indicate that heavy metals were rarely sorbed on only the polysulfone matrix; rather, they were mostly attached in the biomass and/or at the boundary in the beads. For the experiments, the optimum ratio of biomass in the bead and the number of beads in groundwater for the removal of heavy metals were determined at 5% of the biomass in the beads and 2 g of beads in 50 ml of groundwater. The changes of Cu and Pb removal efficiency for the bio-carrier, caused by different pH conditions in solution, are shown in Fig. 5. Initial Cu concentration in solutions was maintained at about 10 mg/L in the entire pH range. Without the bio-carrier, Cu and Pb concentrations in solution were similar to their initial
Fig. 2. Schematic of the pilot scale feasibility test.
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Fig. 3. SEM images ((a) and (b)) and TEM images ((c) and (d)) of the cross sectional bio-carrier structure (O: Pb clods sorbed on the biomass in the bio-carrier).
concentrations at the range of pH 1e6, but Cu concentration in solution abruptly decreased as pH increased to 8 (>pH 8 for Cu; >pH 7 for Pb). Some precipitates were created on the bottom of the flask in high pH conditions (>pH 10), suggesting that the behavior
and speciation of Cu and Pb are strongly affected by pH condition. It was speculated that observed precipitates were hydroxide complexes under alkaline conditions (pH > 10) and, thus, that Cu and Pb concentration in solution decreased without the addition of biocarriers (Cuppett et al., 2006; Lee et al., 2010). For the experiments with bio-carriers, Cu and Pb concentrations in solution were high at pH 1, but they considerably decreased at pH 2, suggesting the bio-carrier become active to remove heavy metals at a pH of higher than 2 (Fig. 5). At below pH 7, Cu and Pb removal from the solution mostly resulted from the sorption ability of immobilized biomass in bio-carrier rather than from precipitation. In batch experiments, Pb and Cu removal efficiencies, even at pH 2e4 in solution, remained at more than 87%, suggesting that when considering the pH condition of AMD as below pH 4 in the field, the
Fig. 4. Pb and Cu removal efficiencies of the bio-carrier according to the mass ratio (%) of biomass in the bead and its concentration in groundwater (g/50 ml).
Fig. 5. Cu and Pb removal efficiencies of the bio-carrier and the precipitation according to pH of solution.
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573
Table 2 Results of Pb removal efficiency for the column experiment (all values are means of triplicates ± SDs). Sampling Point of the column
Removal efficiency (%) at each pore volume
A B C D
99.0 98.8 99.0 99.0
1
3 ± ± ± ±
0.6 0.8 1.7 0.2
5
98.9 98.7 99.0 98.9
± ± ± ±
0.6 1.3 0.6 1.2
98.7 98.5 98.4 97.3
8 ± ± ± ±
1.6 0.6 0.8 1.2
98.4 98.4 98.2 74.1
12 ± ± ± ±
1.3 2.2 0.6 3.6
98.1 98.3 98.3 3.5
15 ± ± ± ±
1.2 0.3 1.0 0.2
heavy metal can be removed effectively by bio-carriers even under acidic conditions. 3.3. Column experiments Pb removal efficiency values at different points (A, B, C, and D) of the column (See Fig. 1) were calculated; the results are shown in Table 2. In the column experiment using bio-carriers, Pb removal efficiency at the lowest sampling point ‘D’ of the column maintained more than 97% for 5 pore volume, decreasing to 74% at 8 pore volume; this figure finally went down 3% after 15 pore volume of groundwater treated. However, Pb removal efficiency at the highest sampling point ‘A’ of the column remained at more than 98%, while 36 pore volumes (9.48 L) of solution were injected into the column (Table 2). The Pb removal capability of the bio-carrier (the specific heavy metal uptake (q) from Eq. (1)) in the column experiment was 1.553 g/g, suggesting that a small quantity of a biocarrier can remove a lot of heavy metals in from groundwater (more than 1.5 times of bio-carrier mass). From batch and column experiments, it was determined that the bio-carrier manufactured by Bacillus drentensis sp. and polysulfone has a great possibility to clean up heavy metal contaminated groundwater even under low pH conditions in the field. 3.4. Pilot scale feasibility test for groundwater originating from AMD The pH of the initial groundwater from the extraction well ranged from 3 to 4; the pH of the effluent from the reaction tank
98.0 98.2 97.1 2.8
18 ± ± ± ±
1.5 1.8 0.2 0.2
97.7 98.1 91.5 2.1
24 ± ± ± ±
1.0 1.1 6.4 0.1
98.0 98.0 6.4 1.7
30 ± ± ± ±
1.3 0.9 0.1 0.1
97.9 7.2 2.0 1.4
36 ± ± ± ±
1.0 0.2 0.1 0.1
97.9 1.3 1.0 0.9
44 ± ± ± ±
0.8 0.1 0.1 0.1
1.3 1.2 1.0 1.1
66 ± ± ± ±
0.1 0.2 0.1 0.1
0.1 0.2 0.2 0.2
± ± ± ±
0.0 0.0 0.0 0.0
increased up to 6.5 according to the buffering of bio-carriers and pebbles in the tank. Results of the pilot scale feasibility test are shown in Fig. 6. For 40 reaction days, the average removal efficiencies of Cu, Cd, Zn, and Fe were 92.8%, 93.3%, 93.2%, and 96.7%, respectively. The heavy metal concentrations of the treated groundwater remained lower than the Korea Groundwater Tolerance Limit (KGTL) during the feasibility test, demonstrating that the usage of a reaction tank packed with bio-carriers is an effective onsite process to remove heavy metals from AMD originated groundwater. For 40 reaction days, 80 tons of groundwater were treated in the reaction tank and, considering that the bulk density of the bio-carriers is 0.116 g/cm3, at least 1.098 tons of groundwater were successfully treated using only 1 kg of bio-carrier in the feasibility test. 4. Conclusions Conclusions derived from this research are shown below. (1) From SEM and TEM analyses of the bio-carrier after Pb removal, it was determined that the bio-carrier has a complicated porous structure and that Pb was sorbed as the form of solid phase in the boundary between the biomass and the polysulfone matrix and/or the interior of the biomass in the bio-carrier. (2) From batch experiments, Pb and Cu removal efficiencies of the bio-carriers even at pH 3 of solution were more than 87% and the average removal efficiencies for heavy metals in the field test also remained at more than 92%, suggesting that the
Fig. 6. .Results of the pilot scale feasibility test (——: Korea Groundwater Tolerance Limit (KGTL)).
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bio-carrier is available to remove heavy metals from AMD or groundwater even under low pH conditions (pH of 2e4). (3) The amount of Pb uptake per 1 g of bio-carrier was 1.553 g in the column experiment, showing the high sorption capacity of the bio-carrier for heavy metals, which is the main mechanism for heavy metal removal from solution. (4) A total of 80 tons of groundwater contaminated with various heavy metals were successfully treated in the pilot scale feasibility test for 40 days; the removal capacity of the biocarrier was at least 1.098 tons per 1 kg of bio-carrier (more than 1000 times the removal rate of groundwater), suggesting that the bio-carrier manufactured with Bacillus drentensis sp. and polysulfone is an excellent and practical bio-sorbent for heavy metal removal from groundwater originating from AMD. Acknowledgments This work was supported by the Korea CCS R&D Center (KCRC) grant funded by the Korea government (Ministry of Science, ICT & Future Planning) (NRF-2013-M1A8A1035830). References Aksu, Z., Gӧnen, F., Demircan, Z., 2002. Biosorption of chromium (VI) ions by Mowital®B30H resin immobilized activated sludge in a packed bed: comparison with granular activated carbon. Process Biochem. 38, 175e186. Al-Hakawati, M.S., Banks, C.J., 2000. Copper removal by polymer immobilized Rhizopus oryzae. Water Sci. Technol. 42, 345e352. lu, G., Genç, O., 2003. Ca-alginate as a Arica, M.Y., Arpa, Ç., Ergene, A., Bayramog support for Pb(II) and Zn(II) biosorption with immobilized Phanerochaete chrysosporium. Carbohyd. Polym. 52, 167e174. Bai, H., Kang, Y., Quan, H., Han, Y., Sun, J., Feng, Y., 2013. Bioremediation of coppercontaining wastewater by sulfate reducing bacteria coupled with iron. J. Environ. Manag. 129, 350e356. Bayramoglu, G., Bektas¸, S., Arica, M.Y., 2003. Biosorption of heavy metal ions on immobilized white-rot fungus Trametes versicolor. J. Hazard. Mater. 101, 285e300. , F., 2003. Biosorption of copper by Beolchini, F., Pagnanelli, F., Toro, L., Veglio Sphaerotilus natans immobilized in polysulfone matrix: equilibrium and kinetic analysis. Hydromet 70, 101e112. € 2006. Biosorption characteristics of Bacillus Çabuk, A., Akar, T., Tunali, S., Tabak, O., sp. ATS-2 immobilized in silica gel for removal of Pb(Ⅱ). J. Hazard. Mater. 136, 317e323. Cheng, S., Jang, J., Dempsey, B.A., Logan, B.E., 2011. Efficient recovery of nano-sized iron oxide particles from synthetic acid-mine drainage (AMD) water using fuel cell technologies. Water Res. 45, 303e307. Cuppett, J.D., Duncan, S.E., Dietrich, A.M., 2006. Evaluation of copper speciation and water quality factors that affect aqueous copper tasting response. Chem. Senses 31, 689e697. El-Naas, M.H., Al-Muhtaseb, S.A., Makhlouf, S., 2009. Biodegradation of phenol by Pseudomonas putida immobilized in polyvinyl alcohol (PVA) gel. J. Hazard. Mater. 164, 720e725. , H.J., Moreira, R.F.P.M., 2012. Recovery Flores, R.G., Andersen, S.L.F., Maia, L.K.K., Jose of iron oxides from acid mine drainage and their application as adsorbent or catalyst. J. Environ. Manag. 111, 53e60. Fourest, E., Roux, J.C., 1992. Heavy metal biosorption by fungal mycelial byproducts: mechanism and influence of pH. Appl. Microbiol. Biotechnol. 37, 399e403. Gadd, G.M., 2000. Bioremedial potential of microbial mechanisms of metal mobilization and immobilization. Curr. Opin. Biotechnol. 11, 271e279. Gray, N.F., 1997. Environmental impact and remediation of acid mine drainage: a management problem. Environ. Geol. 30, 62e71. Hashim, M.A., Mukhopadhyay, S., Sahu, J.N., Sengupta, B., 2011. Remediation technologies for heavy metal contaminated groundwater. J. Environ. Manag. 92, 2355e2388. Hlabel, P., Maree, J., Bruinsma, D., 2007. Barium carbonate process for sulphate and metal removal from mine water. Mine Water Environ. 26, 14e22.
Hu, M.Z.C., Reeves, M., 1997. Biosorption of uranium by Pseudomonas aeruginosa strain CSU immobilized in a novel matrix. Biotechnol. Prog. 13, 60e70. Jeffers, T.H., Corwin, R.R., 1993. Wastewater remediation using immobilized biological extractants. In: Torma, A.E., Apel, M.L., Brierley, C.L. (Eds.), Biohydrometallurgical Technologies. The Minerals, Metals & Materials Society, Warrendale, pp. 1e13. Jeffers, T.H., Ferguson, C.R., Bennet, P.G., 1991. Biosorption of metal contaminants from acidic mine waters. In: Smith, R.W., Misra, M. (Eds.), Mineral Bioprocessing. The Minerals, Metals & Materials Society, Warrendale, pp. 289e298. KMOE(Korea Ministry of Environment), 2007. Precise Investigation of Soil Contamination Around Abandoned Metal Mines, Korea, p. 106. Final Report. Kratochvil, D., Volesky, B., 1998. Advances in the biosorption of heavy metals. Trends Biotechnol. 16, 291e300. Lee, M., Lee, J., Wang, S., 2010. Remediation of heavy metal contaminated groundwater by using the bio-carrier with dead Bacillus sp. B1 and polysulfone. Econ. Environ. Geol. 43, 555e564. Lovely, D.R., Coates, J.D., 1997. Bioremediation of metal contamination. Curr. Opin. Biotechnol. 8, 285e289. Luptakova, A., Kusnierova, M., 2005. Bioremediation of acid mine drainage contaminated by SRB. Hydromet 77, 97e102. €tting, T.S., Ayora, C., 2012. Natural preMacias, F., Caraballo, M.A., Nieto, J.M., Ro treatment and passive remediation of highly polluted acid mine drainage. J. Environ. Manag. 104, 93e100. Malik, A., 2004. Metal bioremediation through growing cells. Environ. Int. 30, 261e278. Martins, M., Faleiro, M.L., Barros, R.J., Veríssimo, A.R., Barreiros, M.A., Costa, M.C., 2009. Characterization and activity studies of highly heavy metal resistant sulphate-reducing bacteria to be used in acid mine drainage decontamination. J. Hazard. Mater. 166, 706e713. McCullough, C.D., Lund, M.A., 2006. Opportunities for sustainable mining pit lakes in Australia. Mine Water Environ. 25, 220e226. Moyer, C.L., Dobbs, F.C., Karl, D.M., 1994. Estimation of diversity and community structure through RFLP distribution analysis of bacterial 16S rRNA genes from a microbial mat at an active, hydrothermal vent, Loihi Seamount, Hawaii. Appl. Environ. Microb. 60, 871e879. Park, Y., Lee, H., Yun, H., Song, K., Yeon, S., Choi, J., 2013. Removal of metal from acid mine drainage using a hybrid system including a pipes inserted microalgae reactor. Bioresour. Technol. 150, 242e248. Petti, C.A., Polage, C.R., Schreckenberger, P., 2005. The role of 16S rRNA gene sequencing in identification of microorganisms misidentified by conventional methods. J. Clin. Microbiol. 43, 6123e6125. Puranik, P.R., Panikar, K.M., 1999. Biosorption of lead, cadmium, and zinc by Citrobacter strain MCM B-181: characterization studies. Biotechnol. Prog. 15, 228e237. Radhika, V., Subramanian, S., Natarajan, K.A., 2006. Bioremediation of zinc using Desulfotomaculum nigrificans: bioprecipitation and characterization studies. Water Res. 40, 3628e3636. Schmalenberger, A., Schwieger, F., Tebbe, C.C., 2001. Effect of primers hybridizing to different evolutionarily conserved regions of the small-subunit rRNA gene in PCR-based microbial community analyses and genetic profiling. Appl. Environ. Microb. 67, 3557e3563. Seo, H., Lee, M., Wang, S., 2013. Equilibrium and kinetic studies of the biosorption of dissolved metals on Bacillus drentensis immobilized in biocarrier beads. Environ. Eng. Res. 18, 45e53. Silveira, A.N., Silva, R., Rubio, J., 2009. Treatment of acid mine drainage (AMD) in south Brazil comparative active processes and water reuse. Int. J. Miner. Process 93, 103e109. Simeonova, A., Godjevargova, T., Ivanova, D., 2008. Biosorption of heavy metals by dead Streptomyces fradiae. Environ. Eng. Sci. 25, 627e633. Song, H., Yim, G., Ji, S., Nuculita, C.M., Hwang, T., 2012. Pilot-scale passive bioreactors for the treatment of acid mine drainage: efficiency of mushroom compost vs. mixed substrates for metal removal. J. Environ. Manag. 111, 150e158. Sprocati, A.R., Alisi, C., Segre, L., Tasso, F., Galletti, M., Cremisini, C., 2006. Investigating heavy metal resistance, bioaccumulation and metabolic profile of a metallophile microbial consortium native to an abandoned mine. Sci. Total Environ. 366, 649e658. Vijayaraghavan, K., Han, M.H., Choi, S.B., Yun, Y., 2007. Biosorption of reactive black 5 by Corynebacterium glutamicum biomass immobilized in alginate and polysulfone matrices. Chemosphere 68, 1838e1845. Volesky, B., 2001. Detoxification of metal-bearing effluents: biosorption for the next century. Hydromet 59, 203e216. Wang, S., Zhao, X., 2009. On the potential of biological treatment for arsenic contaminated soils and groundwater. J. Environ. Manag. 90, 2367e2376. Yan, G., Viraraghavan, T., 2003. Heavy-metal removal from aqueous solution by fungus Mucor rouxii. Water Res. 37, 4486e4496.
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Journal of Environmental Management journal homepage: www.elsevier.com/locate/jenvman
Heavy metal removal in groundwater originating from acid mine drainage using dead Bacillus drentensis sp. immobilized in polysulfone polymer Insu Kim a, Minhee Lee b, *, Sookyun Wang c a b c
Korea Basic Science Institute, Division of Earth and Environmental Science, 804-1 Yangcheongri, Ochangeup, Cheongwongun, Chungbuk, Republic of Korea Department of Earth Environmental Sciences, Pukyong National University, 599-1 Daeyondong, Namgu, Busan 608-737, Republic of Korea Department of Energy and Resource Engineering, Pukyong National University, 599-1 Daeyondong, Namgu, Busan 608-737, Republic of Korea
a r t i c l e i n f o
a b s t r a c t
Article history: Received 15 February 2014 Received in revised form 28 May 2014 Accepted 30 May 2014 Available online 8 September 2014
Batch, column, and pilot scale feasibility experiments for a bio-sorption process using a bio-carrier (beads) with dead Bacillus drentensis sp. in polysulfone polymer were performed to remove heavy metals in groundwater originating from an acid mine drainage (AMD). For batch experiments, various amounts of bio-carrier each containing a different amount of dead biomass were added in artificial solution, of which the initial heavy metal concentration and pH were about 10 mg/L and 3, respectively. The heavy metal removal efficiencies of the bio-carrier under various conditions were calculated and more than 92% of initial Pb and Cu were found to have been removed from the solution when using 2 g of bio-carriers containing 5% biomass. For a continuous experiment with a column packed with bio-carriers (1 m in length and 0.02 m in diameter), more than 98% of Pb removal efficiency was maintained for 36 pore volumes and 1.553 g of Pb per g of bio-carrier was removed. For the pilot scale feasibility test, a total of 80 tons of groundwater (lower than pH of 4) were successfully treated for 40 working days and the removal efficiencies of Cu, Cd, Zn, and Fe were maintained above 93%, demonstrating that one kg of biocarrier can clean up at least 1098 L of groundwater in the field. © 2014 Elsevier Ltd. All rights reserved.
Keywords: AMD Bio-carrier Bacillus sp. Polysulfone Groundwater remediation Heavy metals
1. Introduction There exist about 2500 mines, including 900 metal mines, in South Korea; more than 200 abandoned metal mines have continued to discharge acid mine drainage (AMD), which leaches out large amounts of heavy metals (KMOE, 2007). AMD drastically alters the acidity and chemistry of groundwater and streams, and may endanger not only plant and animal populations but also human health (Gray, 1997; McCullough and Lund, 2006). The development of remediation processes to remove heavy metals in groundwater originating from AMD is thus necessary. To date, various physicochemical remediation processes such as coprecipitation, ion exchange, adsorption, and solvent extraction have been widely applied to heavy metal contaminated groundwater (Cheng et al., 2011; Flores et al., 2012; Hashim et al., 2011; Macias et al., 2012). However, most of these processes are not effective or are impractical for acidic groundwater originating from
* Corresponding author. Tel.: þ82 51 629 6630; fax: þ82 51 629 6623. E-mail address: [email protected] (M. Lee). http://dx.doi.org/10.1016/j.jenvman.2014.05.042 0301-4797/© 2014 Elsevier Ltd. All rights reserved.
AMD due to low pH of AMD and/or high operating cost (Hlabel et al., 2007; Luptakova and Kusnierova, 2005; Silveira et al., 2009). It has recently been recognized that bio-treatment, one of the alternative processes to remove heavy metals in water, has distinct advantages such as low operating cost, minimization of the volume of sludge, and high efficiency in detoxifying dilute effluents (Gadd, 2000; Malik, 2004; Radhika et al., 2006; Sprocati et al., 2006). Bio-treatment for heavy metals generally includes bioaccumulation by dead or living biomass and the application of living biomass such as bacterial, algae, fungi, and seaweed as a biosorbent; this type of bio-treatment has emerged as a more cost effective process than other chemical processes and also as an ecofriendly process, which minimize byproducts (Kratochvil and Volesky, 1998; Puranik and Panikar, 1999; Song et al., 2012; Wang and Zhao, 2009). Despite these advantages of the use of living biomass, this process requires the continuous supply of nutrients; further, it is difficult to maintain healthy microorganisms because they are very sensitive to the water quality, oxidation-reduction status, and pH (Aksu, 2002; Bai et al., 2013; Hashim et al., 2011; Lovely and Coates, 1997; Martins et al., 2009; Park et al., 2013). It was suggested that the use of dead biomass as bio-sorbent could
I. Kim et al. / Journal of Environmental Management 146 (2014) 568e574
overcome these problems, but there exist other application problems such as the difficulty of separation of biomass from water after the treatment and the low mechanical strength during long term usage and recycling (Bayramoglu, 2003; Simeonova et al., 2008). However, when dead biomass is immobilized in a polymeric matrix as a bio-carrier, its presence confers high resistance to chemical environments and also provides additional advantages such as efficient regeneration and easy separation from solution (Çabuk et al., 2006; El-Naas et al., 2009; Volesky, 2001). The selection of an optimal immobilization matrix in a biocarrier is vital to the environmental application of immobilized dead biomass as bio-sorbent because the polymeric matrix determines the mechanical strength, rigidity and porosity characteristics of the bio-carrier. Various polymeric materials such as polysulfone, alginate, polyacrylamide, and polyvinyl alcohol have been used as immobilized matrixes for bio-sorption (Al-Hakawati and Banks, 2000; Arica et al., 2003; Hu and Reeves, 1997). Several previous studies have reported that polysulfone has the advantage of being cheaper and easier to handle than other polymer matrices, but the study for polysulfone has remained at a fundamental level on a laboratory scale (Beolchini et al., 2003; Jeffers et al., 1991; Lee et al., 2010; Vijayaraghavan et al., 2007). The use of dead biomass in polysulfone for a heavy metal remediation process to groundwater originating from AMD (lower than pH of 4) has never been investigated, even in the laboratory. This study aims to demonstrate the removal of heavy metals in groundwater affected from AMD by using a bio-carrier (bead shape), which is composed of dead biomass in a polysulfone matrix. This is novel feasibility study on a pilot scale using immobilized biomass with polysulfone for AMD originated groundwater in the field. The dead biomass used in this study was Bacillus drentensis sp. strain isolated from heavy metal contaminated soils near an AMD outlet of the Ilkwang abandoned mine in Korea. The results of this study will provide meaningful information for the future application of the bio-carriers to remove heavy metals in groundwater having low pH. 2. Experimental method 2.1. Preparation of bio-carrier Indigenous microorganisms were isolated from soil samples near the Ilkwang abandoned mine, Korea. The Ilkwang abandoned mine was active from 1931 to 1978, producing approximately 40,000 tons of copper ores and about 15,000 tons of waste rocks and mine tailings, which were put back inside the mine shaft (KMOE, 2007). However, the abandoned mine continues to discharge AMD that is rich in iron and highly acidic; this flow contaminates the soil and groundwater in the vicinity of the mine. For the isolation of a bacterial strain from soil samples, 1 g of randomly selected soil from the soil samples and 9 ml of sterile distilled water were shaken vigorously using a vortex for at least 1 min. The mixed solution of 0.1 ml was blended with 0.9 ml of sterile distilled water. This process was aseptically repeated several times and each time the transferred sample was thoroughly mixed with the dilution fluid before being transferred to the next tube. Using the streak-plate method, a dilution solution of 0.1 ml was injected into and smeared on a nutrient agar (NA) medium in a petri-dish. After spreading, the sample was aerobically incubated for 48 h at 35 C. Colonies representative of all different morphologies from the NA medium were chosen at random. Representative colonies of all different morphologies in the nutrient agar plate were identified through sequencing by using the 16S rRNA gene (Petti et al., 2005; Schmalenberger et al., 2001).
569
Among the isolated microorganisms, Bacillus drentensis LMG 21831T was selected for this study; more information on Bacillus drentensis LMG 21831T can be found in a previous study (Lee et al., 2010; Moyer et al., 1994). Bacillus drentensis LMG 21831T was stored by freeze-drying with 10% glycerol before use and all culture works were conducted aseptically in a clean-bench. After the massive cultivation of Bacillus drentensis LMG 21831T, the biomass was collected by centrifugation at 15,000 rpm (TOMOE Engineering Tomoe ASM 260PL) and the supernatant was freeze-dried. The dried biomass was deactivated by autoclaving at 121 C and 1 atm for 20 min. The dead biomass was powdered using a pestle and mortar and was sieved through a 100-mesh sieve. Then, it was stored in a refrigerator for the preparation of the bio-carrier. To immobilize the dead biomass in a polysulfone matrix for biocarriers (beads), 10 g of polysulfone was shaken in 90 g of N,Ndimethyl formamide (DMF) solvent for 16 h on a rotary shaker at 125 rpm to dissolve polysulfone completely. The amount of dead biomass in the bio-carrier may control the removal efficiency of heavy metals. Bio-carriers containing different amounts of biomass in the polysulfone matrix (from 0% to 5%) were produced and the bio-carriers' removal efficiency for heavy metals such as Pb and Cu was investigated using batch experiments. Powdered biomass was homogeneously blended into a 10% solution of polysulfone on a stirrer. The resulting slurry was dropped into 80% methanol solution through a peristaltic pump with an 18-gauge needle; spherical beads as the bio-carrier were formed by phase inversion (Jeffers and Corwin, 1993; Lee et al., 2010). Beads were washed in distilled water for 1 h on a rotary shaker to diffuse out DMF; beads were then dried for 48 h at room temperature (22 ± 1 C). After drying, beads that had taken an irregular shape were discarded. A scanning electron micrograph (SEM; S-2700, Hitachi), an energy dispersive spectroscopy (EDS; EX-250, Horiba Scientific), and a transmission electron micrograph (TEM; JEM-1210EX II, JEOL) were used to visualize the structure of bio-carrier and the compositional characteristics. 2.2. Batch experiments Batch experiments were performed to investigate the heavy metal removal efficiency of the immobilized bio-carriers (beads) from groundwater under low pH conditions. Artificially contaminated solutions were used as groundwater and distilled water was titrated with each standard solution of Pb and Cu purchased from AnApex Ltd. (1000 mg/L) to make certain of the initial concentrations for the experiments (about 10 mg/L). The pH condition of the solution was also artificially adjusted to pH 3 by addition of 0.1 M HNO3 to simulate groundwater originating from AMD. To determine the optimal amount of beads for heavy metal removal, various numbers of beads in solution were applied to the experiment. Batch experiments with beads having different amounts of dead biomass in the polysulfone matrix were also duplicated. Each different number of beads (0.1, 0.2, 0.5, 1, 2 and 5 g) was added to the contaminated solution of 50 ml. The mixed solution was shaken on a rotary shaker at 120 rpm for 48 h (at 20 C) and the supernatant was filtered with filter paper (Whatman No. 40). Heavy metal concentration in solution was analyzed using inductively coupled plasma-optical emission spectrometry (ICP/OES; Optima 7000DV, PerkinElmer) to calculate the removal efficiency. The amounts of heavy metal removed at equilibrium and the removal efficiency (%) when using the immobilized bio-carriers were calculated by applying Eq. (1) and Eq. (2), respectively:
q¼
V Co Cf M
(1)
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2.3. Column experiments The glass column was designed with an internal diameter of 2.5 cm (100 cm in height); using a gravitational packing process, the column was filled with immobilized bio-carriers (61.8 g) including 5% of dead biomass. The photograph of the column used in the experiment is shown in Fig. 1. The column was slowly flooded with distilled water (263.4 ml of one pore volume; porosity of 0.537) from the bottom at a flow rate of 2.2 ml/min. Pb-contaminated solution (10.3 mg/L of initial concentration and pH of 3) was pumped through a peristaltic pump connected to the bottom of the column at 2.2 ml/ min. Flushed water samples were collected from 4 points (A, B, C, and D) of the column (25 cm distance between points) at different time intervals (0, 0.2, 1, 2, 3, 5, 8, 12, 15, 18, 24, 30, 36, 44, 54, and 66 pore volume). Water samples were analyzed on an ICP/OES for Pb concentration in the effluent; Pb removal efficiency (and the amount of heavy metal uptake (q) in Eq. (1)) of the bio-carrier for the column experiment was calculated. 2.4. Pilot scale feasibility test for groundwater originating from AMD
Fig. 1. Photograph and schematic systems of column experiments (A, B, C, and D: sampling point).
removal efficiencyð%Þ ¼
Co Cf Co
100
(2)
where q is the amount of specific heavy metal uptake (mg of removed heavy metal/g of bio-carriers), V is the volume of contaminated solution (ml), Co is the initial concentration of heavy metal in solution (mg/L), Cf is the final concentration of heavy metal in solution (mg/L), and M is the dry weight of the bio-carriers (g). All batch experiments were repeated three times and their arithmetic average was used as the final result. The pH is an important parameter that affects the bio-chemical behaviors of metal ions in an aqueous system since it directly influences the metal speciation in solution, which can change the biosorption capability (Fourest and Roux, 1992; Lovely and Coates, 1997; Yan and Viraraghavan, 2003). The oxidation of sulfide minerals in rock waste or tailings from mine activity contributes to AMD that has very low pH; the sorption capability of bio-carriers for heavy metals directly depends on the pH of the solution (Arica et al., 2003; Bai et al., 2013). Batch experiments were repeated at various levels of pH (1e12) of Cu and Pb-contaminated solution to investigate the maintenance of high Cu and Pb removal efficiencies of the bio-carrier under low pH conditions. Distilled water was titrated with the standard solution of Cu and Pb to about 10 mg/L; the pH condition of the solution was artificially adjusted by the addition of 0.1 M HNO3 or NaOH solution. A control test without the bio-carrier was also performed in the pH experiments to distinguish between the effects the bio-carrier and the precipitation on heavy metal removal. The process of the batch experiment for pH change in solution was the same as that employed in the previous batch experiment; Cu and Pb removal efficiencies of the bio-carrier at different levels of pH of solution were calculated.
On the basis of the column experiment results, a pilot scale feasibility test was performed using genuine groundwater. The reaction tank was made of an HDPE (high density polyethylene) cylinder (1.0 m in length and 1.0 m in diameter; 0.785 m3 in capacity); the top of the tank had a spray system with a flow regulator for groundwater injection. The bottom of the tank had a valve gear and a flow regulator controlling the flux of treated groundwater. The heavy metal contaminated groundwater was transported to the reaction tank by the autotimer and the constant-flow regulator from the extraction well (1.2 m of groundwater table in depth) around the ditch built to collect AMD from the pit mouth at the Ilkwang abandoned mine. The extraction well was composed of HIVP (high-impact PVC pipe; 0.08 m in diameter) from the surface to 3 m in depth; the well was screened from 2 m to 3 m in length. To prevent the inflow of suspended solids or impurities from groundwater to the reaction tank, all pumped groundwater was gathered in the storage chamber (2 m3 in capacity) and the overflowing groundwater from the chamber was injected into the reaction tank through a flow regulator by gravity. Before the bio-carriers (beads) were packed in the middle of the tank (80 cm in thickness), the pebbles (8e10 mm in diameter) were packed at 10 cm in thickness on the bottom and the top of packed bead layers in order to minimize the irregular flow in the tank. A stainless steel frame made of crisscross lattice beams (net size: 5 mm in diameter) was located at the boundary between the bead layer and the pebble layer to sustain the weight of each layer. The concentration of heavy metals in groundwater and AMD at the Ilkwang abandoned mine is shown in Table 1; concentrations of Cu, Cd, Zn, and Fe in groundwater exceeded the Korea Groundwater Tolerance Limit (KGTL), indicating that the groundwater was seriously affected from AMD and was contaminated by heavy metals. Contaminated groundwater was pumped from the extraction well and sprayed from the top of the reaction tank at velocity in the range of 3e5 L/min for 8 h during the daytime (8 h per day only on weekdays) for about two months (from May 30th, 2012 to July 30th, 2012). About 1.5e2 tons of groundwater was treated in the tank per day and the total volume of treated groundwater was 80 tons for 40 working days. Fifty milliliters of untreated and treated groundwater were sampled from the top and the bottom of the reaction tank every working day and were analyzed on ICP/OES for heavy metal concentration in order to calculate the removal efficiencies. The pebbles in the upper layer of the tank were replaced with new
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571
Table 1 Heavy metal concentrations and pH of AMD and groundwater for the feasibility test (all values are means of triplicates ± SDs). Sampling type
Sampling time
pH
Concentration (mg/L) Cu
AMD Groundwater
12-04-15 12-05-15 12-03-15 12-04-15 12-05-15
Korea groundwater tolerance limit
2.1 2.2 3.3 3.5 3.3
± ± ± ± ±
0.5 0.3 0.3 0.5 0.1
5.8e8.6
31.0 27.7 15.6 27.0 21.6
Cd ± ± ± ± ±
1.5 1.2 1.2 1.3 0.6
3.0
ones every 20 working day (2 times for 40 days) to prevent clogging in the bio-carrier packed layer of the reaction tank. Because all treated groundwater satisfied the Korean Groundwater Tolerance Limit, the treated groundwater was gathered in a storage tank (2.0 m3 of capacity), and was finally discharged into a nearby stream. Fig. 2 provides a schematic of the pilot scale feasibility test. 3. Results and discussion 3.1. Characteristics of bio-carrier The bio-carrier created with dead biomass in polysulfone was yellowish in color, spherical in shape, and with a diameter of about 2e3 mm (bead type). The average dry density of beads was 0.288 g/ cm3 and the average specific surface area, measured by BrunauerEmmer-Teller (BET) analysis, was 2.65 m2/g, which is 250 times larger than the external surface area of the bead. The crosssectional image of one bead by SEM analysis shows a thin outer layer to coat the irregularly shaped pore structure; the inner layers were mostly composed of large pore spaces and walls, which are useful for the adsorption of heavy metal ions (Fig. 3(a) and (b)). In order to distinctively visualize the bio-mass and polysulfone matrix in the bead, TEM analysis was also performed and showed that the dead biomass of Bacillus drentensis sp. was tightly conjoined with the polysulfone matrix, suggesting that the bead is insoluble and mechanically stable during the recycling or desorption process (Fig. 3(c)). TEM imaging and EDS analysis of the bead structure after the Pb-removal experiment show many clods of Pb (red color circles in Fig. 3(d)) adsorbed on the biomass in the bead, demonstrating that Pb in groundwater is successfully removed in the form
0.4 0.5 0.3 0.4 0.4
As ± ± ± ± ±
0.1 0.1 0.0 0.0 0.0
0.1
0.5 0.4 0.3 0.3 0.5 0.5
± ± ± ± ±
0.0 0.1 0.0 0.0 0.0
Zn
Fe
8.7 ± 0.1 10.0 ± 0.2 2.5 ± 0.3 15.6 ± 0.2 7.2 ± 0.3
251.9 222.4 146.0 189.2 162.3
5.0
10.0
± ± ± ± ±
6.2 8.3 9.0 12.3 8.8
of a solid phase sorbed on the immobilized biomass (Seo et al., 2013). 3.2. Batch experiments Results for the removal efficiencies of Pb and Cu in artificial groundwater according to ① biomass concentrations inside beads and ② the amount of polysulfone beads in groundwater are shown in Fig. 4. Pb and Cu removal efficiencies generally increased with the increase of both the biomass amount in the beads and the beads added to groundwater. For 0% and 1% of biomass in beads, Pb and Cu removal efficiency from solution was less than 4%, regardless of the number of beads in groundwater. Pb and Cu removal efficiencies of 2% biomass in the beads dramatically increased up to 86% and 81%, respectively with an addition of 5 g of beads in 50 ml of groundwater. With more than 5% of the biomass concentration in the beads, Pb and Cu removal efficiencies ranged from 92% to 99% when beads were added at a mass of more than 2 g to groundwater. These results indicate that heavy metals were rarely sorbed on only the polysulfone matrix; rather, they were mostly attached in the biomass and/or at the boundary in the beads. For the experiments, the optimum ratio of biomass in the bead and the number of beads in groundwater for the removal of heavy metals were determined at 5% of the biomass in the beads and 2 g of beads in 50 ml of groundwater. The changes of Cu and Pb removal efficiency for the bio-carrier, caused by different pH conditions in solution, are shown in Fig. 5. Initial Cu concentration in solutions was maintained at about 10 mg/L in the entire pH range. Without the bio-carrier, Cu and Pb concentrations in solution were similar to their initial
Fig. 2. Schematic of the pilot scale feasibility test.
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Fig. 3. SEM images ((a) and (b)) and TEM images ((c) and (d)) of the cross sectional bio-carrier structure (O: Pb clods sorbed on the biomass in the bio-carrier).
concentrations at the range of pH 1e6, but Cu concentration in solution abruptly decreased as pH increased to 8 (>pH 8 for Cu; >pH 7 for Pb). Some precipitates were created on the bottom of the flask in high pH conditions (>pH 10), suggesting that the behavior
and speciation of Cu and Pb are strongly affected by pH condition. It was speculated that observed precipitates were hydroxide complexes under alkaline conditions (pH > 10) and, thus, that Cu and Pb concentration in solution decreased without the addition of biocarriers (Cuppett et al., 2006; Lee et al., 2010). For the experiments with bio-carriers, Cu and Pb concentrations in solution were high at pH 1, but they considerably decreased at pH 2, suggesting the bio-carrier become active to remove heavy metals at a pH of higher than 2 (Fig. 5). At below pH 7, Cu and Pb removal from the solution mostly resulted from the sorption ability of immobilized biomass in bio-carrier rather than from precipitation. In batch experiments, Pb and Cu removal efficiencies, even at pH 2e4 in solution, remained at more than 87%, suggesting that when considering the pH condition of AMD as below pH 4 in the field, the
Fig. 4. Pb and Cu removal efficiencies of the bio-carrier according to the mass ratio (%) of biomass in the bead and its concentration in groundwater (g/50 ml).
Fig. 5. Cu and Pb removal efficiencies of the bio-carrier and the precipitation according to pH of solution.
I. Kim et al. / Journal of Environmental Management 146 (2014) 568e574
573
Table 2 Results of Pb removal efficiency for the column experiment (all values are means of triplicates ± SDs). Sampling Point of the column
Removal efficiency (%) at each pore volume
A B C D
99.0 98.8 99.0 99.0
1
3 ± ± ± ±
0.6 0.8 1.7 0.2
5
98.9 98.7 99.0 98.9
± ± ± ±
0.6 1.3 0.6 1.2
98.7 98.5 98.4 97.3
8 ± ± ± ±
1.6 0.6 0.8 1.2
98.4 98.4 98.2 74.1
12 ± ± ± ±
1.3 2.2 0.6 3.6
98.1 98.3 98.3 3.5
15 ± ± ± ±
1.2 0.3 1.0 0.2
heavy metal can be removed effectively by bio-carriers even under acidic conditions. 3.3. Column experiments Pb removal efficiency values at different points (A, B, C, and D) of the column (See Fig. 1) were calculated; the results are shown in Table 2. In the column experiment using bio-carriers, Pb removal efficiency at the lowest sampling point ‘D’ of the column maintained more than 97% for 5 pore volume, decreasing to 74% at 8 pore volume; this figure finally went down 3% after 15 pore volume of groundwater treated. However, Pb removal efficiency at the highest sampling point ‘A’ of the column remained at more than 98%, while 36 pore volumes (9.48 L) of solution were injected into the column (Table 2). The Pb removal capability of the bio-carrier (the specific heavy metal uptake (q) from Eq. (1)) in the column experiment was 1.553 g/g, suggesting that a small quantity of a biocarrier can remove a lot of heavy metals in from groundwater (more than 1.5 times of bio-carrier mass). From batch and column experiments, it was determined that the bio-carrier manufactured by Bacillus drentensis sp. and polysulfone has a great possibility to clean up heavy metal contaminated groundwater even under low pH conditions in the field. 3.4. Pilot scale feasibility test for groundwater originating from AMD The pH of the initial groundwater from the extraction well ranged from 3 to 4; the pH of the effluent from the reaction tank
98.0 98.2 97.1 2.8
18 ± ± ± ±
1.5 1.8 0.2 0.2
97.7 98.1 91.5 2.1
24 ± ± ± ±
1.0 1.1 6.4 0.1
98.0 98.0 6.4 1.7
30 ± ± ± ±
1.3 0.9 0.1 0.1
97.9 7.2 2.0 1.4
36 ± ± ± ±
1.0 0.2 0.1 0.1
97.9 1.3 1.0 0.9
44 ± ± ± ±
0.8 0.1 0.1 0.1
1.3 1.2 1.0 1.1
66 ± ± ± ±
0.1 0.2 0.1 0.1
0.1 0.2 0.2 0.2
± ± ± ±
0.0 0.0 0.0 0.0
increased up to 6.5 according to the buffering of bio-carriers and pebbles in the tank. Results of the pilot scale feasibility test are shown in Fig. 6. For 40 reaction days, the average removal efficiencies of Cu, Cd, Zn, and Fe were 92.8%, 93.3%, 93.2%, and 96.7%, respectively. The heavy metal concentrations of the treated groundwater remained lower than the Korea Groundwater Tolerance Limit (KGTL) during the feasibility test, demonstrating that the usage of a reaction tank packed with bio-carriers is an effective onsite process to remove heavy metals from AMD originated groundwater. For 40 reaction days, 80 tons of groundwater were treated in the reaction tank and, considering that the bulk density of the bio-carriers is 0.116 g/cm3, at least 1.098 tons of groundwater were successfully treated using only 1 kg of bio-carrier in the feasibility test. 4. Conclusions Conclusions derived from this research are shown below. (1) From SEM and TEM analyses of the bio-carrier after Pb removal, it was determined that the bio-carrier has a complicated porous structure and that Pb was sorbed as the form of solid phase in the boundary between the biomass and the polysulfone matrix and/or the interior of the biomass in the bio-carrier. (2) From batch experiments, Pb and Cu removal efficiencies of the bio-carriers even at pH 3 of solution were more than 87% and the average removal efficiencies for heavy metals in the field test also remained at more than 92%, suggesting that the
Fig. 6. .Results of the pilot scale feasibility test (——: Korea Groundwater Tolerance Limit (KGTL)).
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bio-carrier is available to remove heavy metals from AMD or groundwater even under low pH conditions (pH of 2e4). (3) The amount of Pb uptake per 1 g of bio-carrier was 1.553 g in the column experiment, showing the high sorption capacity of the bio-carrier for heavy metals, which is the main mechanism for heavy metal removal from solution. (4) A total of 80 tons of groundwater contaminated with various heavy metals were successfully treated in the pilot scale feasibility test for 40 days; the removal capacity of the biocarrier was at least 1.098 tons per 1 kg of bio-carrier (more than 1000 times the removal rate of groundwater), suggesting that the bio-carrier manufactured with Bacillus drentensis sp. and polysulfone is an excellent and practical bio-sorbent for heavy metal removal from groundwater originating from AMD. Acknowledgments This work was supported by the Korea CCS R&D Center (KCRC) grant funded by the Korea government (Ministry of Science, ICT & Future Planning) (NRF-2013-M1A8A1035830). References Aksu, Z., Gӧnen, F., Demircan, Z., 2002. Biosorption of chromium (VI) ions by Mowital®B30H resin immobilized activated sludge in a packed bed: comparison with granular activated carbon. Process Biochem. 38, 175e186. Al-Hakawati, M.S., Banks, C.J., 2000. Copper removal by polymer immobilized Rhizopus oryzae. Water Sci. Technol. 42, 345e352. lu, G., Genç, O., 2003. Ca-alginate as a Arica, M.Y., Arpa, Ç., Ergene, A., Bayramog support for Pb(II) and Zn(II) biosorption with immobilized Phanerochaete chrysosporium. Carbohyd. Polym. 52, 167e174. Bai, H., Kang, Y., Quan, H., Han, Y., Sun, J., Feng, Y., 2013. Bioremediation of coppercontaining wastewater by sulfate reducing bacteria coupled with iron. J. Environ. Manag. 129, 350e356. Bayramoglu, G., Bektas¸, S., Arica, M.Y., 2003. Biosorption of heavy metal ions on immobilized white-rot fungus Trametes versicolor. J. Hazard. Mater. 101, 285e300. , F., 2003. Biosorption of copper by Beolchini, F., Pagnanelli, F., Toro, L., Veglio Sphaerotilus natans immobilized in polysulfone matrix: equilibrium and kinetic analysis. Hydromet 70, 101e112. € 2006. Biosorption characteristics of Bacillus Çabuk, A., Akar, T., Tunali, S., Tabak, O., sp. ATS-2 immobilized in silica gel for removal of Pb(Ⅱ). J. Hazard. Mater. 136, 317e323. Cheng, S., Jang, J., Dempsey, B.A., Logan, B.E., 2011. Efficient recovery of nano-sized iron oxide particles from synthetic acid-mine drainage (AMD) water using fuel cell technologies. Water Res. 45, 303e307. Cuppett, J.D., Duncan, S.E., Dietrich, A.M., 2006. Evaluation of copper speciation and water quality factors that affect aqueous copper tasting response. Chem. Senses 31, 689e697. El-Naas, M.H., Al-Muhtaseb, S.A., Makhlouf, S., 2009. Biodegradation of phenol by Pseudomonas putida immobilized in polyvinyl alcohol (PVA) gel. J. Hazard. Mater. 164, 720e725. , H.J., Moreira, R.F.P.M., 2012. Recovery Flores, R.G., Andersen, S.L.F., Maia, L.K.K., Jose of iron oxides from acid mine drainage and their application as adsorbent or catalyst. J. Environ. Manag. 111, 53e60. Fourest, E., Roux, J.C., 1992. Heavy metal biosorption by fungal mycelial byproducts: mechanism and influence of pH. Appl. Microbiol. Biotechnol. 37, 399e403. Gadd, G.M., 2000. Bioremedial potential of microbial mechanisms of metal mobilization and immobilization. Curr. Opin. Biotechnol. 11, 271e279. Gray, N.F., 1997. Environmental impact and remediation of acid mine drainage: a management problem. Environ. Geol. 30, 62e71. Hashim, M.A., Mukhopadhyay, S., Sahu, J.N., Sengupta, B., 2011. Remediation technologies for heavy metal contaminated groundwater. J. Environ. Manag. 92, 2355e2388. Hlabel, P., Maree, J., Bruinsma, D., 2007. Barium carbonate process for sulphate and metal removal from mine water. Mine Water Environ. 26, 14e22.
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