Simultaneous removal of phenol, Cu and Cd from water with corn cob silica-alginate beads

Journal of Hazardous Materials 272 (2014) 129–136

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Simultaneous removal of phenol, Cu and Cd from water with corn cob silica-alginate beads Jaehong Shim a,b , Jeong-Muk Lim a , Patrick J. Shea b , Byung-Taek Oh a,∗ a Division of Biotechnology, Advanced Institute of Environment and Bioscience, College of Environmental and Bioresource Sciences, Chonbuk National University, Iksan, Jeonbuk 570-752, South Korea b School of Natural Resources, University of Nebraska-Lincoln, Lincoln, NE 68583-0817, USA

h i g h l i g h t s • • • •

Bacteria were immobilized on reusable beads made from alginate and corn cob silica. Growth on bead surfaces reduced toxicity to the bacteria in highly contaminated water. The beads effectively removed phenol, Cu and Cd from contaminated water. Beads with corn cob silica were superior to zeolite beads for metal removal.

a r t i c l e

i n f o

Article history: Received 12 October 2013 Received in revised form 7 February 2014 Accepted 5 March 2014 Available online 18 March 2014 Keywords: Immobilized bacteria Phenol Heavy metals Degradation Corn cob silica Pseudomonas putida

a b s t r a c t Phenol and heavy metals in petroleum waste are environmental and human health concerns, but physicochemical removal is often cost-prohibitive and can produce toxic secondary products and treatment residues. An environmentally benign alternative combines corn cob silica with alginate and immobilized bacteria into beads for treating contaminated water. The concentration of phenol was decreased >92% by Pseudomonas putida YNS1 on aliginate-silica beads (2%, w/v) after equilibrating for 96 h with water containing 214 mg phenol/L. GC–MS analysis indicated formation of benzoquinone and other polar products. Beads containing corn cob silica decreased Cu concentrations by 84–88% and Cd by 83–87% within 24 h. In a mixture of 114 mg phenol, 43 mg Cu and 51 mg Cd/L, phenol removal (93% within 96 h) only occurred with beads containing the silica and bacterial strain. Beads containing corn cob silica removed >97% of the Cu and >99% of the Cd, critical for reducing toxicity to the bacteria. Beads with the immobilized strain removed phenol when zeolite was used instead of corn cob silica, but beads with silica were more effective for Cu and Cd removal. Results show the potential of corn cob silica combined with alginate and immobilized bacteria for removing phenol and heavy metals from contaminated water. © 2014 Elsevier B.V. All rights reserved.

1. Introduction Petroleum waste is a problem for modern industry. Phenol, polycyclic aromatic hydrocarbons (PAHs), and heavy metals are the main toxic components of petroleum waste [1]. Environmental pollution due to inevitable spills during exploration, production, refining, and storage of petroleum products remains a critical issue. The toxicity and high solubility of phenol in water makes it a significant threat to the environment [2]. In addition, microbial growth induced by phenol impedes the operation of waste water treatment plants [3].

∗ Corresponding author. Tel.: +82 63 850 0838; fax: +82 63 850 0834. E-mail address: [email protected] (B.-T. Oh). http://dx.doi.org/10.1016/j.jhazmat.2014.03.010 0304-3894/© 2014 Elsevier B.V. All rights reserved.

Physical and chemical methods of removing petroleum waste, such as charcoal and membrane filtration, ozonation, H2 O2 /UV treatment, and solvent extraction are often cost-prohibitive and can produce toxic secondary products and treatment residues [4]. Alternative treatment systems, employing immobilized microorganisms, are receiving increased interest [5,6]. Biodegradation can result in complete mineralization at low cost and immobilization increases capacity and efficiency. However, appropriate environmental conditions are critical for effective use of microorganisms [7]. Synthetic polyacrylate, polyurethane and polyether polymers are typically used for the immobilization [8]. However, natural biopolymers such as alginate, chitosan and guar gum are becoming increasingly popular because they are effective, inexpensive, nontoxic, biodegradable, and environmentally benign [9–11].

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Alginate, a natural polysaccharide produced by brown algae, has been evaluated for microbial immobilization [12,13]. Alginate consists of (1-4)-␤-d-mannuronic acid (M) and (1-4)-␣-l-guluronic acid (G) through homopolymeric (MM or GG blocks) and heteropolymeric (MG or GM blocks) sequences [14–16]. It is water soluble but becomes insoluble when it reacts with divalent or multivalent metal ions. A gel forms when two alginate carboxyl groups cross-bridge with divalent metal ions [17,18]. Alginate beads can be used over a wide pH range and have reuse potential [19]. Silica is effective in removing heavy metals [20,21]. Silica extracted from corn cob is less toxic than synthetic silica and valued because it is a reuse of an agricultural byproduct. Previous research has shown that Pseudomonas putida can efficiently eliminate phenol [22] and is effective when immobilized on alginate beads [23]. In this study, we combined alginate with corn cob silica and a P. putida strain into beads for purification of water contaminated with phenol and heavy metals.

2. Materials and methods 2.1. Bacteria growth, phenol degradation and heavy metal tolerance A phenol-degrading bacterial strain (YNSI) was obtained from oil-polluted soil and identified as Pseudomonas putida sp. based on 16s rRNA base sequence analysis [24]. The strain was grown at 30 ◦ C for 24 h on minimal salt medium (MSM) containing 4.0 g NaNO3 , 4.0 g Na2 HPO4 , 3.61 g KH2 PO4 , 1.75 g MgSO4 ·7H2 O, 0.2 g CaCl2 ·2H2 O, 0.05 g FeSO4 ·5H2 O, 1.0 mg CuSO4 ·5H2 O, 50 ␮g Na2 MoO3 , 10 ␮g MnSO4 and 3 g yeast extract/L. Deionized, distilled water was used for all experiments, which were conducted under ambient aerobic conditions. The capacity of the strain to eliminate phenol was evaluated in phenol-supplemented Luria-Bertani (LB) broth and by injecting LB broth containing the strain into MSM with 100, 300, 500, 700 mg phenol/L and incubating for 120 h at 30 ◦ C. Phenol concentrations were determined by UV–vis spectrophotometry (8453 UV-Vis, Agilent, Santa Clara, CA, USA) at 270 nm [25]. The mechanism of phenol removal was confirmed using live and dead microbial biomass. LB broth containing 10 mg phenol/L was inoculated with medium containing the strains and incubated for 24 h at 30 ◦ C. Biomass was harvested by centrifuging at 13,000 rpm and 4 ◦ C and washed several times with distilled water. Suspensions of live cells were prepared by re-suspending the cell pellet in distilled water. Dead cell suspensions were prepared by drying the cell pellet at 80 ◦ C for 12 h. Phenol removal was determined by adding 0.05 g live or dead biomass to 50 mL of solution containing 100 mg phenol/L and incubating at 30 ◦ C with agitation at 180 rpm. The product of phenol degradation was determined by GC–MS (7890A-5975C, Agilent Technologies, Shanghai, China). Samples were prepared by centrifuging the LB broth at 6000 rpm for 20 min. The supernatant was then extracted with ethyl acetate, dried under nitrogen gas for 1–5 min, dissolved into acetonitrile and filtered using solvent-resistant syringe filters (0.5 ␮m pore size) [26]. The minimum inhibitory concentration (MIC) of phenol was determined by incubating P. Putida YNSI on MSM agar plates containing 50–1500 mg phenol/L. MICs for Cu and Cd were determined on diluted (1/10) LB plates containing 10-1500 mg Cu or Cd/L. Metal salts used in this study were CuCl2 ·2H2 O and Cd(NO3 )2 ·4H2 O. Growth of the strain was checked after incubating the plates for 7 d at 30 ◦ C. The MIC was the concentration of phenol, Cu or Cd that completely inhibited growth.

2.2. Preparation of alginate-silica beads and immobilization of bacteria One hundred microliters of MSM previously incubated with P. putida YNS1 and 50 mg phenol/L was added to 1 L of LB broth containing the strain and incubated for 24 h at 30 ◦ C. Bacterial biomass was separated from the medium by centrifugation and washed three times with phosphate buffer (pH 7). Cells were collected by centrifuging at 13,000 rpm and stored at 4 ◦ C. Corn cobs were obtained from a local agricultural field in South Korea during the process of removing kernels. The cobs were dehydrated under sunlight and ashed at 350–400 ◦ C. Silica was extracted from the ash [27] and passed through a 200 mesh sieve. The extracted corn cob silica (1.3 g) was added to 100 mL of sterilized, 2% (w/w) sodium alginate (Daejung Chemicals & Metals Co., Ltd., Incheon, Korea) solution and homogenized by ultrasonication at 60% amplitude for 50 s and pulsing four times (750-W ultrasonic processor, Sonics & Materials, Inc, Newtown, CT, USA). The bacterial biomass (3.46 g) was added to the solution and mixed by agitation. Beads were formed by adding droplets of the alginate-silica-P. putida YNS1 mixture to 0.1 M CaCl2 solution. The beads were hardened at 4 ◦ C for 12 h, washed with distilled water, filtered, air-dried and stored at 4 ◦ C. Beads were similarly prepared with silica alone or silica + the strain. Beads containing zeolite (Alfa Aesar, A Johnson Matthey Co., Seoul, South Korea) were also made following the same procedure. The zeolite was composed of Al2 (SiO3 )3 , Na, Ca, K, and H2 O and had a Mohs hardness of 3.5–5.5. Zeta potential measurements [28] were made to determine surface charge; the zeta potential of the zeolite (−32 mV) was similar to that of the corn cob silica (−35 mV). The zeolite had a lower cation exchange capacity than the corn cob silica (105.4 compared to 132.0 cmol+/kg), as determined using the ammonium acetate method [29]. 2.3. Characterization of prepared beads The prepared composite beads were dehydrated by freezedrying at −80 ◦ C. Surface area was determined by BET analysis (Micromeritics Accelerated Surface Area and Porosimetry 2020 analyzer BELSORP-MINI, BEL Japan, Inc., Osaka, Japan). Functional groups were characterized by Fourier transform infrared (FTIR) spectrophotometry (Irvine, CA, USA). The morphology of bead surfaces was characterized by field emission scanning electron microscopy (FE-SEM; Hitachi S-4700. Tokyo, Japan) and surface elements determined by energy-dispersive X-ray spectra (EDS) analysis. 2.4. Contaminant removal by the beads Adsorption of Cd and Cu by the beads was described using kinetic and isotherm models. Beads (2 g) were added to 100 mL of aqueous solution containing Cd or Cu and mixed on an orbital shaker at room temperature. Samples (2 mL) were removed after 0, 5, 10, 15, 30, 60, 180, 360, 720 and 1440 min. The adsorption process was characterized by fitting first- and second-order expressions to the data. The pseudo-first order rate equation is represented as: dqt = k1 (qe − qt ) dt

(1)

where qt , qe and k1 are the amount of metal adsorbed at time t (mg/g), the amount adsorbed at equilibrium (mg/g), and the pseudo first-order rate constant (1/min), respectively. The pseudo-second order rate equation is expressed as: dqt = k2 (qe − qt )2 dt where k2 is the pseudo second-order rate constant (g/mg min).

(2)

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Fig. 1. (A) Ca-alginate beads alone and (B) Ca-alginate beads containing corn cob silica + immobilized Pseudomonas putida YNSI.

Adsorption isotherms were used to describe the relationship between the mass of metal adsorbed per unit mass of adsorbent and the aqueous phase metal concentration at equilibrium and constant temperature. The composite beads (1 g) were added to aqueous solution (100 mL) containing 10, 30, 50, 100, 150 and 200 mg Cd or Cu/L and equilibrated by shaking for 12 h at 180 rpm on a rotary shaker (JSSI-100C, JS Research Inc., Gongju, South Korea). The Langmuir model, which is frequently used to describe the adsorption of cations, is: qe =

qmax KL Ce (1 + KL Ce )

(3)

where qmax , Ce and KL are the maximum adsorption capacity (mg/g), concentration of the metal in solution at equilibrium (mg/L), and the Langmuir adsorption constant (L/mg), respectively. The Freundlich isotherm, often used to describe the adsorption of a broad range of adsorbates, is expressed as: 1/n

qe = KF Ce

(4)

where KF is the Freundlich adsorption constant (L/mg) and 1/n is the adsorption intensity. Adsorption capacity at equilibrium is calculated as: qe =

C − C  e 0 m

V

Q (%) =

C0

2.5. Reuse of the composite beads The potential to reuse the composite beads was determined using multiple adsorption–desorption cycles. Aqueous solutions (100 mL) containing 50 mg Cd, 50 mg Cu and 100 mg phenol/L were first equilibrated with 2 g of beads (adsorption). The beads were then separated from the solution by filtration and washed with distilled water until the pH of wash solution was neutral. The Cdand Cu-loaded beads were then added to 50 mL of distilled water or 0.05 M HCl and mixed by shaking at 25 ◦ C for more than 2 h (desorption). The regenerated beads were reused in a subsequent adsorption experiment and the process was repeated.

(5) 3. Results and discussion

where C0 (mg/L) and Ce (mg/L) are the initial and equilibrium concentrations of Cu and Cd, respectively, m (g) is the mass of adsorbent, and V (L) is solution volume. Percent removal, Q (%), at time t is calculated as:

C − C  t 0

diluted with 2.5% (v/v) HNO3 solution, and analyzed by inductively coupled plasma–atomic emission spectrophotometry (ICP-AES; Leeman Labs, Inc., Hudson, NH, USA). For phenol analysis, 500 ␮L of the sample was diluted ten-fold with distilled water and concentration determined by UV–vis spectrophotometry as previously described. At the end of the experiment the beads were examined for morphological changes using a light microscope.

× 100

(6)

Batch tests were used to determine the effect of pH (3, 4, 5, 6, 7 and 8) on Cd and Cu removal by the composite beads in the presence of phenol. Alginate beads (2%, w/v) with corn cob silica and the strain were added to aqueous solution containing 100 mg phenol, 50 mg Cd and 50 mg Cu/L in 250-mL Erlenmeyer flasks. The flasks were agitated for 12 h at 180 rpm and 30 ◦ C. Metal analysis was as described below. The capacity of the composite beads to degrade phenol and remove Cu and Cd was determined by adding beads (2%, w/v) to flasks containing 200 mg phenol, 100 mg Cu, or 100 mg Cd/L of water at an initial pH of 6.65 ± 0.12. Removal of phenol, Cu and Cd from a mixed contaminant solution was also determined. Contaminant concentration was monitored by periodically removing 2 mL of solution from the flasks during incubation at 30 ◦ C with agitation at 180 rpm. Sampling consisted of collecting 2 mL supernatant within 1–2 s after stopping agitation. Before analysis, the samples were centrifuged at 13,000 rpm to ensure removal of all suspended material, 1-mL aliquots were

3.1. Characteristics of prepared beads The prepared beads were 2–3 mm in diameter and almost globular (Fig. 1). The surface of alginate beads was smooth and soft, in contrast to the rough surface of beads containing silica and microorganisms (Fig. 2). The BET surface area of pure alginate beads was 21 m2 /g but increased to 450 m2 /g when the corn cob silica was added. While swelling in water will increase the effective surface area in all beads containing alginate, BET measurements showed that amorphous corn cob silica adds surface area to the composite beads [30]. A large surface area provides more sites for contaminant adsorption and reaction. FTIR analysis (Fig. 3) indicated –OH stretching near 3445 cm−1 . Asymmetric and symmetric stretching vibrations of alginate –COO− were observed at 1424 and 1601 cm−1 , respectively. Peaks at 1072 and 1025 cm−1 can be attributed to O-glycosidic bonding between (1-4)-␤-d-mannuronic acid and (1-4)-␣-l-guluronic acid, indicating stability of the linear chain in the alginate beads [31]. Characteristic Si–O–Si stretching was observed near 1100 cm−1 in beads containing silica [32]. Because stretching of the silanol (Si–OH) functional group occurs near –OH, the 3000–3700 cm−1 band is largest in beads containing both silica and the strain. The intensity of these bands decreased after reaction with the contaminants.

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Fig. 2. SEM micrographs of beads containing: (A) alginate alone, or alginate + corn cob silica + immobilized Pseudomonas putida YNSI (B) before and (C) after equilibrating with aqueous solution containing phenol, Cu and Cd.

Fig. 3. FTIR spectra of alginate beads (alone and containing corn cob silica + immobilized Pseudomonas putida YNSI) before and after equilibrating with aqueous solution containing phenol, Cu and Cd.

3.2. Phenol degradation and heavy metal tolerance by the strain Previous research has shown the potential of immobilized bacteria to degrade phenol [33]. In the present study, the concentration of phenol in the medium decreased to <0.1 mg/L (limit of quantification) after incubating a 100 mg/L solution with P. putida YNS1 for 24 h. A test of phenol removal comparing live and dead cells supported phenol degradation by the YNS1 strain. Live cells removed essentially all of the phenol from a 100 mg/L solution within 24 h (Fig. 4), while no removal was observed with dead cells (data not shown). For solutions containing 300, 500 and 700 mg phenol/L, 72, 96 and 120 h were required, respectively, to achieve the same reduction in concentration. GC–MS analysis indicated formation of benzoquinone and other polar degradation products of phenol. At 700 mg/L, degradation of phenol increased significantly

Fig. 4. Microbial biomass (measured by optical density) and degradation of phenol [(䊉) 100, () 300, () 500, and () 700 mg/L] by Pseudomonas putida YNS1.

after 48 h (Fig. 4), which may be due to slowed growth of the bacteria. No phenol was degraded when yeast extract was excluded from MSM culture medium, indicating the importance of a readily available carbon source. Respective MICs for phenol, Cu, and Cd were 700, 200, 200 mg/L; no growth was observed at higher concentrations. The color of the liquid changed from clear to brown as phenol was degraded and Oquinone formed [34]. Decomposition of phenol by P. putida YNS1 can be attributed to tyrosinase, which is secreted by microorganisms [35]. In addition to its capacity to degrade phenol, P. putida YNS1 exhibited moderate tolerance to Cu and Cd; the MIC for both metals was 200 mg/L. The concentration of phenol was decreased about 90% by P. putida YNS1 immobilized on alginate beads or on silica-alginate beads after equilibrating for 144 h with a solution containing 214 mg phenol/L (Fig. 5). Little change in phenol concentration was observed in the absence of the strain or in inoculated media without immobilization. The immobilized bacteria colonize the alginate matrix where direct contact with the surface of the material reduces exposure to contaminants, allowing growth at higher concentrations of toxins [36]. Immobilization allows the microorganisms to effectively degrade contaminants in an otherwise unsuitable environment [34]. 3.3. Cu and Cd removal Heavy metal removal by the composite beads increased with increasing pH, up to 99.3% for Cu and 83.5% for Cd (Fig. 6). Cu2+ will dominate in aqueous solution at low pH, with increasing concentrations of Cu(OH)+ and Cu(OH)2 as pH increases within the test

Fig. 5. Removal of phenol by (䊉) Pseudomonas putida YNS1 alone (100 ␮l/100 mL) and by alginate beads () alone, () containing the immobilized strain, () with corn cob silica added, and () with silica + the strain. Error bars indicate standard deviations; where.

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Alginate beads containing silica were most effective, resulting in 84% (4.73 mg/g) removal of Cu and 83% (4.60 mg/g) removal of Cd within 3 h of equilibration. EDS analysis confirmed the presence of Cu and Cd on the surface of the beads (data not shown). Beads containing alginate without silica were somewhat less effective, removing approximately 75% (4.21 mg/g) of the Cu and 80% (3.93 mg/g) of the Cd within 3 h. Removal of Cd and Cu is by electrostatic adsorption to alginate carboxylate groups and to the silanol groups of silica, which ionize at pH > 3.0 [36]. The pH of the solution after agitating for 24 h with the strain alone was 7.47 ± 0.12. The final pH was 6.68 ± 0.37, 7.11 ± 0.08, 7.58 ± 0.04, and 7.68 ± 0.11 for solutions containing beads composed of alginate only, alginate + strain, alginate + silica, and alginate + silica + strain, respectively. 3.4. Phenol and metal removal from a contaminant mixture Fig. 6. Effect of pH on cadmium (䊉) and copper () removal by composite beads containing corn cob silica + Pseudomonas putida YNS1. Error bars indicate standard deviations; where absent bars fall within symbols.

range [37]. Precipitation starts becoming significant as pH becomes increasingly alkaline. Because CuCl2 was used for the experiment, some CuCl+ may be present. The Cd is likely present mainly as Cd2+ at the pH values tested because hydrolysis is minimal below pH 8 [37]. Some Cd(NO3 )+ is possible because Cd was added as Cd(NO3 )2 . Bicarbonate and carbonate forms of the metals may also be present. Little change in metal concentration was observed in water containing 108 mg Cu or 106 mg Cd/L and the strain alone (Fig. 7).

In a mixture containing 114 mg phenol, 43 mg Cu and 51 mg Cd/L, phenol degradation was only observed with beads containing both silica and the strain (Fig. 8). In that treatment about 93% of the phenol was degraded within 96 h. Differences in the efficiency of phenol removal compared to solutions containing the strain alone or immobilized on pure alginate beads can be attributed to the lower concentrations of the metals remaining in solution in the presence of the alginate-silica beads. Beads containing silica removed up to 98% of the Cu and 99% of the Cd, which was critical for reducing their toxicity to the strain. Alginate beads without silica were less effective in removing the metals, as observed in the single contaminant experiments. Available alginate carboxylate groups would also be more limiting in the multiple contaminant mixture and some competition between Cd and Cu for adsorption sites was apparent. The kinetics study indicated a better fit of the pseudo secondorder rate model than the first-order rate model to the data (Table 1). A higher K2 value indicated that Cd will likely be more rapidly adsorbed by the composite beads than Cu. Equilibrium was reached within 3–6 h. The Langmuir isotherm gave a better fit to the Cd and Cu adsorption data than the Freundlich model. Langmuir adsorption constants (KL ) indicated similar affinities of Cd and Cu for the beads; maximum adsorption capacities (qmax ) were 4.07 mg Cd and 4.24 mg Cu/g. 3.5. Comparison with zeolite beads After 72 h, phenol removal from solution containing Cu and Cd by alginate-silica beads with the immobilized strain was similar to that observed for beads containing zeolite and the strain, but the initial rate of degradation was higher for beads containing the corn cob silica (Fig. 9). However, after 96 h only 48% (1.09 mg/g) of the Cd in solution was removed by zeolite beads, in contrast to silica beads, which removed 97% (2.16 mg/g) of the Cd within 24 h. Although the difference was smaller for Cu, zeolite beads removed about 73% (1.75 mg/g) of the Cu after 72 h while >98% (2.47 mg/g) was removed by silica beads. After a 60-min equilibration with solution containing 50 mg Cu2+ or Cd2+ /L, corn cob silica removed >99% of the metals compared to 12% (Cu2+ ) and 19% (Cd2+ ) removal by zeolite (data not shown). Greater heavy metal removal by the corn cob silica can be attributed to its amorphous structure and higher CEC compared to the crystalline zeolite [38,39]. 3.6. Reuse of the beads

Fig. 7. Removal of cadmium and copper by (䊉) Pseudomonas putida YNS1 alone (100 ␮L/100 mL) and by alginate beads () alone; () containing the immobilized strain, () with corn cob silica added, or () with silica + the strain.

Results of the bead regeneration experiments are shown in Table 2. Dilute HCl was more effective than distilled water for desorbing metals from the beads. The regenerated beads removed 64%

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Table 1 Parameters for pseudo first- and second-order kinetic models and parameters for Langmuir and Freundlich isotherms for the adsorption of cadmium and copper by composite beads during agitation at 180 rpm and 30 ◦ C. Model and parameter

Cu2+

Cd2+

Pseudo-first order

q1 (mg/g) 4.28

k1 (1/min) 2.15

R 0.91

q1 (mg/g) 4.01

k1 (1/min) 2.82

R2 0.94

Pseudo-second order

q2 (mg/g) 4.57

k2 (g/mg min) 0.66

R2 0.97

q2 (mg/g) 4.27

k2 (g/mg min) 0.93

R2 0.98

Langmuir

qmax (mg/g) 4.24

kL (L/mg) 0.17

R2 0.95

qmax (mg/g) 4.07

kL (L/mg) 0.07

R2 0.98

Freundlich

KF 1.33

n 4.17

R2 0.94

KF 0.96

n 3.12

R2 0.96

Fig. 8. Concentrations of phenol, copper and cadmium in solution during agitation with (䊉) Pseudomonas putida YNS1 alone (100 ␮l/100 mL), () alginate beads alone, () beads + the immobilized strain, () beads + corn cob silica, or () beads + silica + the strain. Error bars indicate standard deviations; where absent bars fall within symbols.

2

Fig. 9. Removal of phenol (Q) and adsorption (qt ) of copper and cadmium by alginate beads containing (䊉) zeolite, () corn cob silica, () zeolite + immobilized Pseudomonas putida YNS1, () silica + the strain, or () alginate alone.

J. Shim et al. / Journal of Hazardous Materials 272 (2014) 129–136 Table 2 Adsorption capacity of composite beads containing corn cob silica + Pseudomonas putida YNS1 after multiple regeneration cycles by desorption. Conditions: 1 g adsorbent; 20 mL solution; 100 mg phenol/L; 50 mg Cd/L, 50 mg Cu/L; 30 ◦ C; 48 h contact time [Q (%) = (C0 − Ct )/(C0 ) × 100]. Desorbent

Adsorption capacity (Q, %)

Contaminants

0.05 M HCl

Cycle 1 Cycle 2 Cycle 3

[6] [7]

[8]

Distilled water

Cd2+

Cu2+

Phenol

Cd2+

Cu2+

Phenol

97.9 69.8 64.0

95.7 59.8 55.9

92.8 34.5 13.3

98.0 13.8 11.7

95.2 45.3 22.6

92.2 75.2 68.9

of the Cd and 56% of the Cu from solution in the second reuse cycle. In contrast, distilled water was more effective than dilute HCl in regenerating the composite beads for phenol removal, with those beads removing 69% of the phenol after two reuse cycles. Exposure to HCl and the associated acidity may have significantly reduced bacterial cell numbers. While these tests indicate that the beads have some potential for reuse, further testing will be required to optimize regeneration and determine what will be acceptable.

[9]

[10]

[11]

[12]

[13]

[14]

4. Conclusions

[15]

Beads formed by combining the natural polysaccharide alginate with silica extracted from corn cob and P. putida YNS1 were used to remove phenol, Cu and Cd from water. These beads (2%, w/v) degraded >90% of the phenol from water containing 214 mg phenol/L within 96 h and within 24 h removed >82% of the Cu and Cd initially present at respective concentrations of 108 and 106 mg/L. In aqueous solution containing a mixture of 114 mg phenol, 43 mg Cu, and 51 mg Cd, respective removal efficiencies were 93, 98 and 99% within 96 h. Beads containing corn cob silica were more effective than zeolite beads in removing Cu and Cd. Results show the high potential of corn cob silica in combination with alginate and immobilized bacteria for simultaneous removal of phenol, Cu and Cd from contaminated water. Further research will be needed to test the effectiveness of the composite beads for removing mixed contaminants from wastewater and to more fully evaluate regeneration and reuse of the beads.

[16]

[17]

[18]

[19]

[20]

[21]

[22]

[23]

Acknowledgments [24]

This research was supported by the National Research Foundation of Korea (NRF) grant funded by the government (MEST) (No. 2011-0020202), with assistance from the University of NebraskaLincoln in manuscript preparation in association with USDA multistate project W2082. This paper was partially supported by the international collaborative research funds of Chonbuk National University, 2011.

[25]

[26]

[27]

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