Accepted Manuscript Title: Entrapped elemental selenium nanoparticles affect physicochemical properties of selenium fed activated sludge Author: Rohan Jain Marina Seder-Colomina Norbert Jordan Paolo Dessi Julie Cosmidis Eric D.van Hullebusch Stephan Weiss Franc¸ois Farges Piet N.L. Lens PII: DOI: Reference:
S0304-3894(15)00248-4 http://dx.doi.org/doi:10.1016/j.jhazmat.2015.03.043 HAZMAT 16691
To appear in:
Journal of Hazardous Materials
Received date: Revised date: Accepted date:
30-11-2014 5-3-2015 21-3-2015
Please cite this article as: Rohan Jain, Marina Seder-Colomina, Norbert Jordan, Paolo Dessi, Julie Cosmidis, Eric D.van Hullebusch, Stephan Weiss, Franc¸ois Farges, Piet N.L.Lens, Entrapped elemental selenium nanoparticles affect physicochemical properties of selenium fed activated sludge, Journal of Hazardous Materials http://dx.doi.org/10.1016/j.jhazmat.2015.03.043 This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
Entrapped elemental selenium nanoparticles affect physicochemical properties of selenium fed activated sludge Rohan Jaina,b*, Marina Seder-Colominab,d, Norbert Jordanc, Paolo Dessia, Julie Cosmidisd#, Eric D. van Hullebuschb, Stephan Weissc, François Fargesd, Piet N.L. Lensa a
UNESCO-IHE, Institute for Water Education, Westvest 7, 2611AX Delft, The Netherlands
b
Université Paris-Est, Laboratoire Géomatériaux et Environnement (EA 4508), UPEM, 77454 Marne la Vallée, France c
Institute of Resource Ecology, Helmholtz-Zentrum Dresden-Rossendorf e.V., Bautzner Landstr. 400, D-01328 Dresden, Germany
d
Institut de Minéralogie, de Physique des Matériaux, et de Cosmochimie (IMPMC).
Sorbonne Universités - UPMC Univ Paris 06, UMR CNRS 7590, Muséum National d’Histoire Naturelle, IRD UMR 206, Paris, France. #
Present address: Department of Geological Sciences, University of Colorado. UBC 399, 2200 Colorado Avenue. Boulder, CO 80309-0399.
*Corresponding author: Phone: +31 152151715, fax: +31 152122921, e-mail:
[email protected], mailto: UNESCO-IHE, Institute for Water Education, Westvest 7, 2611AX Delft, The Netherlands
Highlights
•
93% of trapped Se in the Se fed activated sludge is in the elemental form of Se
•
Se fed activated sludge has better settleability vis-à-vis control activated sludge
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Se fed activated sludge has more negative surface vis-à-vis control activated sludge
Graphical abstract Abstract Selenite containing wastewaters can be treated in activated sludge systems, where the total selenium is removed from the wastewater by the formation of elemental selenium nanoparticles, which are trapped in the biomass. No studies have been carried out so
far on the characterization of selenium fed activated sludge flocs, which is important for the development of this novel selenium removal process. This study showed that more than 93% of the trapped selenium in activated sludge flocs is in the form of elemental selenium, both as amorphous/ monoclinic selenium nanospheres and trigonal selenium nanorods. The entrapment of the elemental selenium nanoparticles in the selenium fed activated sludge flocs leads to faster settling rates, higher hydrophilicity and poorer dewaterability compared to the control activated sludge (i.e. not fed with selenite). The selenium fed activated sludge showed a less negative surface charge density as compared to control activated sludge. The presence of trapped elemental selenium nanoparticles further affected the spatial distribution of Al and Mg in the activated sludge flocs. This study demonstrated that the formation and subsequent trapping of elemental selenium nanoparticles in the activated sludge flocs affects their physicochemical properties. Keywords : selenium, nanoparticles, activated sludge, physicochemical, settleability, surface charge
1. Introduction Selenium is an essential element and is required in low doses for synthesizing selenoproteins, preventing cardiovascular disease, assisting in sperm mobility and avoiding miscarriage [1]. However, at higher doses selenium oxyanions (selenate and selenite) can cause toxicity to humans, but also to animals and aquatic organisms. Thus, they need to be removed from wastewaters prior to discharge [2–4]. Physicochemical remediation such as adsorption of selenite by nanoscale zero-valent iron [5],
magnetic nanoparticle-graphene oxide composite [6], maghemite [7] are successfully demonstrated However, physico-chemical remediation is expensive and yet sometimes ineffective in achieving the stringent selenium discharge criteria (less than 50 µg L–1) [3,8]. Anaerobic microbial reduction of selenium oxyanions to elemental selenium is often a recommended biological process for selenium oxyanions containing wastewater treatment [9,10]. However, biological anaerobic reduction of selenium oxyanions leads to the formation of biogenic elemental selenium nanoparticles (BioSeNPs) in the discharged wastewaters [11]. These BioSeNPs have to be removed prior to discharge, which requires an additional treatment step that further increases the remediation cost [12–14].
Aerobic reduction of selenium oxyanions to either volatilized selenium compounds followed by gas trapping [15] or to elemental selenium entrapment in microbial biomass would be a one-step process for the treatment of selenite containing wastewaters. The entrapment of selenium in the biomass is progressive as the selenium is then in the solid state and much easier to handle as compared to volatilized selenium trapped in concentrated HNO3 [15]. Aerobic reduction of selenite by microorganisms has been described for Bacillus cereus [16], Escherichia coli [17] and activated sludge [18]. The activated sludge is more suitable as compared to pure cultures for treating selenium rich wastewater as it can easily handle variation in the influent and the wastewaters need not be sterilized for continuous operations [19]. However, there are so far no studies on the characterization of selenium fed activated sludge. This characterization is important for the development of activated sludge based selenium remediation processes.
Therefore, the present work focused on the characterization of the selenium fed activated sludge.
In this study, activated sludge loaded with selenium was produced by aerobic reduction of selenite in batch reactors. The localization, speciation and crystallinity of selenium in the activated sludge flocs were identified by Scanning Electron Microscopy-Energy Disperse X-ray Spectroscopy (SEM-EDXS), Transmission Electron Microscopy (TEM), sequential extraction, X-ray Diffraction (XRD) and Selected Area Electron Diffraction (SAED). The elemental constituents, morphology, hydrophilicity, sludge volume index (SVI), capillary suction time (CST) and surface groups density of the selenium fed activated sludge were compared with a selenium-free control activated sludge.
2. Materials and methods 2.1 Production of selenium fed activated sludge The activated sludge used in this study was collected from a full scale domestic wastewater treatment plant in Harnaschpolder (The Netherlands). The synthetic wastewater was composed of (in mg L–1): Na2SeO3 (173), NH4Cl (600), MgCl2.2H2O (200) and CaCl2.2H2O (20). Glucose (2000 mg L–1) was used as electron donor and carbon source. The total suspended solid (TSS) concentration added was 1300 ± 100 mg L–1.
The selenite removal was carried out under continuous aeration by an air flow (15-20 L air h–1) in a 5L batch reactor. Mixing was carried out with a magnetic stirrer (500 rpm).
The pH was maintained at 7.5-8.0 by manual correction or addition of Na2CO3 when needed. After the reduction of selenite, selenium fed activated sludge was collected by settling and the supernatant was discarded. Control activated sludge without the addition of sodium selenite was produced using the same procedure and collected by settling as well.
2.2 Elemental composition Concentrated HNO3 (10 mL) was added to 0.5 g (TSS) of selenium fed activated sludge. The sludge was destroyed using microwave digestion (Duo Temp, MARS 5) operated at 1600 W. The program consists of heating first for 10 minutes to 165 oC, followed by raising the temperature to 175 oC and maintaining this temperature for 8 minutes, followed by 60 minutes cooling. The samples were appropriately diluted and elemental concentrations were measured by Inductively Coupled Plasma-Mass Spectrometry (ICP-MS). The experiments were done in triplicate. 2.3 Selenium localization and speciation analysis SEM-EDXS and TEM were carried out to locate selenium in the microorganisms and activated sludge flocs. For SEM-EDXS analysis, each sample was diluted in Milli-Q water (18 MΩ cm) and filtered using 0.22 µm pore-size polycarbonate membrane filters. Filters were deposited on carbon tape, dried at ambient temperature and finally coated with a thin carbon film. Samples for TEM were diluted in Milli-Q water, deposited on a copper TEM grid covered with a lacey formvar film and dried at ambient temperature.
Selenium speciation was determined by carrying out sequential extraction following the KCl based protocol described by Wright et al. [20], but using a 30 times higher extractant to solid ratio for complete selenium recovery. Sequential extraction analysis was carried out in quadruplicates. The crystallinity of the trapped selenium in the activated sludge flocs was determined by XRD and SAED associated with the TEM.
2.4 Physicochemical activated sludge properties The SVI and CST of the selenium fed and control activated sludge were determined as per standard methods [21]. For the SVI, 1.8 g L–1 of TSS was used. The relative hydrophilicity (RH) was measured following the protocol described in Laurent et al. [22].
Acid-base titration was carried out for determining the pKa of the functional groups using a Metrohm autotitrator unit. Selenium fed and control activated sludge (0.0266 g dry weight) was suspended in 30 mL of Milli-Q water with 1 mM of NaCl background electrolyte. The titration was carried out by automatic addition of 0.1 mL HCl (0.01214 M). The acid-base titration data were fitted using a PROTOFIT software [23] as described by Laurent et al. [24]. Briefly, a non-electrostatic model with four discrete acidic sites and an extended Debye-Huckel activity coefficient were used. Prior to simulation using PROTOFIT, the derivative of the acid-base titration versus moles of HCl added was plotted to determine the local minima. These local minima represent the pKa of the functional groups [25]. Taking these pKa as the initial guess, the data fitting was carried out.
2.5 Analytical methods Selenium measurements by ICP-MS and XRD analysis were carried out as described previously [26]. SEM was performed with a Field Emission Gun Scanning Electron Microscope (GEMINI ZEISS Ultra55) operated at 2 kV. SEM-EDXS analyses were done on the selected particles at 15 kV. TEM and SAED analyses were performed using a JEOL 2100F (FEG) operating at 200 kV and equipped with a field emission gun, a highresolution UHR pole piece, and a Gatan energy filter GIF 200.
3. Results 3.1 Elemental composition of selenium fed activated sludge The selenite was removed from aqueous phase in the batch reactor and more than 78% of the fed selenium was entrapped in the biomass. The concentration of trapped selenium in the activated sludge is 55 ± 2 mg of Se per g of TSS. The concentrations of Na, Mg Al, K, Ca and Fe in selenium fed activated sludge are presented in Table 1. Other elements such as Cu, Mn, Zn, Ba, Cr, V, Ni, Co, Pb and Mo were less than 1.0 mg per g of TSS.
Table 1.
3.2 Characterization of trapped selenium in the activated sludge Sequential extraction of selenium trapped in the activated sludge suggests that 94 ± 9% of the trapped selenium is in the form of elemental selenium. The sequential extraction method was able to account for 95.7% of the total selenium trapped in the activated
sludge. All other fractions, i.e. the soluble/exchangeable fraction, adsorbed fraction and residual fraction, were insignificant as they constitute only 2 ± 1% of the total trapped selenium.
SEM images showed the presence of two different morphologies of selenium: nanospheres and nanorods (Figure 1a). EDXS analysis confirmed that these morphologies are composed of selenium (Figure 1b1, b2). The presence of selenium nanorods and nanospheres was further confirmed in SEM images and its corresponding cartography (Figure 1.e, f). SEM images of the bacterial cells suggest that the selenium is partly trapped in the biomass and present inside the bacterial cells (Figure 1c). The white colored spheres and black dots in Figure 1c are selenium nanospheres and the pores of the filters, respectively. The TEM image showed that the selenium nanospheres are closely associated with the bacterial cells. Some of the spheres are indeed present at the surface of the bacteria, while others are possibly found inside the bacteria, confirming the SEM observations (Figure 1d).
Figure 1.
Elemental selenium exists mainly in trigonal, monoclinic or amorphous forms [11]. In order to determine the crystallinity of trapped elemental selenium, XRD was carried out on selenium fed activated sludge. XRD results showed the features at 2-theta values of 23.4 and 30.0, corresponding to, respectively, the 100 and 101 crystallographic planes of trigonal selenium, while the feature at 2-theta value 26.9 corresponds to 220 planes
of β-monoclinic selenium [27] (Figure 2a). The XRD also showed a hump like structure between 2-theta values of 15 to 40, suggesting the presence diffuse scattering related to the presence of aperiodic structures (nanocrystallized and/or “amorphous”). In contrast to selenium fed activated sludge, the control activated sludge showed no features in the XRD.
The diffuse SAED pattern of the spherical particles present in the selenium-fed activated sludge suggests that these nanospheres are amorphous or poorly crystalline (Figure 2b). Selenium nanospheres are known to be either aperiodic or monoclinic [26,28]. Thus, the SAED pattern of the Se nanospheres and XRD of selenium fed activated sludge suggest the presence of a mixture of amorphous and different crystalline
structures
of
elemental
selenium:
trigonal
(nanorods)
and
monoclinic/aperiodic (nanospheres) as also observed in the SEM images (Figure 1a, e). It is interesting to note that the biological conversion of selenium oxyanions always results in the formation of aperiodic or monoclinic nanospheres [28,29], which may later transform to trigonal nanorods [30].
Figure 2.
3.3 Spatial distribution of elements in selenium fed activated sludge flocs Figure 3a shows the SEM image of a single bacterium from the selenium fed activated sludge. Figure 3b indicates that the nanospheres observed in the SEM image of Figure 3a are mainly composed of selenium, but Al and Mg are also found to be closely
associated to the selenium particles (Figures 3c, d). Other elements such as Ca, Fe, Cu, Zn, Pb and Ba were not found to have gradient towards elemental selenium trapped in the sludge (data not shown).
Figure 3.
3.4 Functional groups in the activated sludges
To evaluate the surface charge present on the selenium fed activated sludge, an acidbase titration was carried out. The delta pH versus micromoles HCl added is plotted in Figure 4. The local maxima in Figure 4a represent the maximum shift in pH and hence the equivalence points. Similarly, the local minima represent the minimum change in pH and hence the pKa of the functional groups present [25,31] The local minima for selenium fed activated sludge were observed at pH 7.1, 6.9, 5.2, 3.7, 3.4 and 3.1 (Figure 4a). Similarly, the local minima for control activated sludge are observed at pH 7.2, 5.1 and 3.3. The local minima at 6.9-7.2 correspond to phosphoryl groups [31,32]. Carboxyl groups can be assigned to local minima at pH 5.1-5.2 [31,32]. The local minima observed at pH of 3.1-3.7 are due to the presence of phosphodiester/ carboxyl groups [31,33,34]. Figure 4.
The simulation of the acid-base titration data fitted well with the experimental data (Figure 4b). The surface charge density of the selenium fed activated sludge was twice
more negative than the control activated sludge at neutral pH (Figure 4c). The simulation of acid-base titration data predicted the pKa of the functional groups at pH 3.2, 5.2, 7.1 and 9.7 for selenium fed activated sludge (Figure 4d). For the control activated sludge, the predicted pKa values of the functional groups are at pH 3.9, 5.0, 7.2 and 9.5. Assignment of predicted pKa to various functional groups is presented in Figure 4d. It is important to note that we may not observe the local minima in the derivate of pH vs moles of acid graph at the start and end of the titration due to a small change in pH and hence the most acidic and basic groups may be missed out. But as shown above, these groups can be successfully predicted by the simulation.
3.5 Physical properties of selenium fed and control activated sludge The SVI of the selenium fed and control activated sludge was 61.1 ± 0.3 and 138.8 ± 0.1 mL g–1, respectively (Figure 5a). The CST of both the selenium fed and control activated sludge was in the range of 20 seconds at a TSS of 3 g L–1 (Figure 5b). With the increase in TSS, the CST of the selenium fed activated sludge increased to a value as high as 67.2 seconds as compared to 19.0 s for control activated sludge at TSS value of 9 g L–1. The RH of selenium fed activated sludge was 1.6 times higher than that of the control activated sludge (Figure 5c).
Figure 5.
4. Discussion
4.1 Entrapment of elemental selenium affects the physical properties of activated sludge flocs This study demonstrates for the first time the effect on the physicochemical properties of activated sludge flocs after treating the synthetic selenium contaminated wastewater. Sequential extraction procedure and XRD provided the experimental proof, for the first time, about the trapping of elemental selenium nanoparticles in the activated sludge flocs. The trapping of microbiologically produced elemental selenium nanoparticles lead to an improved settleability and relative hydrophilicity, but a negative impact on the dewaterability of the selenium fed activated sludge. Elemental selenium is 4.5 times denser than the activated sludge. The improved settleability can consequently be attributed to the dense elemental selenium nanoparticles that increase the density of activated sludge and thus, lead to better settling. The higher RH of activated sludge with entrapped elemental selenium as compared to the control activated sludge suggests the presence of more polar groups such as hydroxyl, carboxyl or phosphodiester groups in the flocs (Figure 4d and 5c) [22]. The higher CST of selenium fed activated sludge at high TSS values as compared to the control indicates a poorer dewaterability of the sludge (Figure 5b). The reason for the poor dewaterability can be due to the blockage of filter pores by elemental selenium nanoparticles (Figure 1c, d), thus, leading to a higher CST. The blocking of the filter pores by nanoparticles can be due to the agglomeration of selenium nanoparticles caused by their interaction with metals such as Al and Mg [26] (Figure 3c, d) or due to the presence of nanorods that can be micrometers in length. The poor dewaterability of the activated sludge with entrapped elemental selenium nanoparticles as compared to
control activated sludge can also be attributed to a different extracellular polymeric substances (EPS) content [35,36]. Selenite removal has been shown to cause stress on Bacillus sp., leading to the production of larger amounts of EPS, with a different composition, as compared non stressed microorganisms [37].
4.2 Entrapment of elemental selenium affects the surface properties of the activated sludge flocs The less negative surface charge density of the selenium fed activated sludge flocs as compared to the control activated sludge can be due to the higher concentration of phosphodiester groups as well as their lower pKa value (3.2 for selenium fed activated sludge as compared to 3.9 for control activated sludge) (Figure 4d). The difference in the EPS content can be a one of the reasons for the difference in the surface charge density of the selenium fed and control activated sludge. The other reason for the less negative selenium fed activated sludge is the presence of elemental selenium nanoparticles. Elemental selenium nanoparticles are known to have a negative ζpotential with an acidic iso-electric point (pH 3.5) due to the presence of organic moieties produced by microorganisms on their surface [4,38]. These negative ζpotential nanoparticles might contribute to the less negative surface density of the selenium fed activated sludge.
Due to the negative ζ-potential of these elemental selenium nanoparticles, the spatial distribution showed a higher concentration of Al and to some extent of Mg near the elemental selenium nanoparticles trapped in the activated sludge flocs (Figure 3), as
observed in case of Cu [39], Zn [26] as well as other cations such as Ca and Ba [12]. However, it is interesting to see that other than Al and Mg, all the other possible elements such as Ca and Fe did not show any concentration gradient towards elemental selenium.
The preference of any cation towards an adsorbent follows 1) a decrease in ionic radius, 2) an increase in electronegativity of the metal ion or 3) an increase in ratio of the ionisation potential and ionic radius [40]. In the previous study by the same authors, the preference of divalent cations at equimolar concentration (Zn, Ca and Mg) towards BioSeNPs followed ratio of ionization potential and ionic radius [26]. Fe has a higher ratio of ionization potential to ionic radius when compared to Al, Mg and Ca (–0.68 compared to –3.1, –3.3, 2.9, respectively), higher concentration in the activated sludge than Mg and Al (Table 1), would be present as a trivalent cation and still no gradient towards BioSeNPs was observed. This might be due to very low solubility of Fe3+ at the pH of this study and is precipitating as hematite as predicted by Visual MINTEQ. Hence, Fe is not available to compete for adsorption sites on the elemental selenium nanoparticles.
The ratio of ionization potential to ionic radius and the concentration in the selenium fed activated sludge was slightly higher for Ca when compared to Al, but as a trivalent ion, the tendency of Al for forming complexes with the protein coatings of EPS present on elemental selenium nanoparticles [38] would be higher than Ca, thus Al would outcompete other divalent cations including Ca and Mg. It is interesting to note that
though Mg has lower ionization potential to ionic radius and concentration in the selenium fed activated sludge than Ca, Mg showed a gradient towards BioSeNPs and Ca does not (Figure 3d). This might be again due to non availability of Ca which might be due to the precipitation of Ca as hydroxyapatite as predicted by the Visual MINTEQ.
4.3 Practical implications The presence of elemental selenium nanoparticles in the activated sludge flocs improves their settleability. This is important for the activated sludge process as gravity settling is a cost-effective method for industrial scale solid-liquid separation [41]. The poorer dewaterability of the selenium fed activated sludge might affect the activated sludge process, as the entrapped elemental selenium nanoparticles affect the CST at TSS concentrations (> 3 g L–1). As the selenium is a scarce resource and used as a fertilizer for selenium deficient soils [42], one of the possible uses of waste selenium fed activated sludge is a slow release selenium fertilizer [43]. Elemental selenium is known to adsorb heavy metals including mercury [44–46], copper [39] and zinc [26], thus selenium fed activated sludge can also be used for decontamination of heavy metal and specially mercury polluted soils [47]. However, further research is required to realize the full potential of selenium fed activated sludge as fertilizer or remediation agent.
5. Conclusions This study showed that most of the trapped selenium in activated sludge flocs is in the form of elemental selenium. SEM and TEM images suggest that elemental selenium is present both inside and outside the microbial cell. XRD and SAED suggest the
presence of aperiodic and β-monoclinic nanospheres as well as trigonal nanorods. The trapping of this elemental selenium in the activated sludge flocs improves the settleability and hydrophilicity of the sludge, but reduces the dewaterability of the activated sludge (only at higher TSS concentrations). The selenium fed activated sludge also showed a less negative surface charge density as compared to control activated sludge.
Acknowledgements The authors thank Ferdi Battles (UNESCO-IHE, The Netherlands) for ICP-MS analysis and Rohit Kacker (TU Delft, The Netherlands) for XRD analysis. Author Contributions The manuscript was written through contributions of all authors. All authors have given approval to the final version of the manuscript.
Funding Sources This research was supported through the Erasmus Mundus Joint Doctorate Environmental Technologies for Contaminated Solids, Soils, and Sediments (ETeCoS3) (FPA n°2010-0009). The purchase of the SEM facility of the Institut de Minéralogie, de Physique des Matériaux et de Cosmochimie (IMPMC) was supported by Région Ile-deFrance grant SESAME 2006 N°I-07-593/R, INSU-CNRS, INP-CNRS, University Pierre et Marie Curie – Paris 6, and by the French National Research Agency (ANR) grant no. ANR-07-BLAN-0124-01. The TEM facility at IMPMC was supported by Région Ile-de-
France grant SESAME 2000 E 1435, INSU-CNRS, INP-CNRS and University Pierre et Marie Curie (UPMC) – Paris 6. References [1] [2]
[3] [4]
[5]
[6]
[7] [8]
[9]
[10]
[11]
[12]
[13]
[14]
M.P. Rayman, The importance of selenium to human health., Lancet. 356 (2000) 233–41. L. Wu, Review of 15 years of research on ecotoxicology and remediation of land contaminated by agricultural drainage sediment rich in selenium., Ecotoxicol. Environ. Saf. 57 (2004) 257–69.. M. Lenz, P.N.L. Lens, The essential toxin: the changing perception of selenium in environmental sciences., Sci. Total Environ. 407 (2009) 3620–33. L.H.E. Winkel, C.A. Johnson, M. Lenz, T. Grundl, O.X. Leupin, M. Amini, et al., Environmental selenium research: from microscopic processes to global understanding., Environ. Sci. Technol. 46 (2012) 571–579. L. Ling, B. Pan, W. Zhang, Removal of selenium from water with nanoscale zerovalent iron: Mechanisms of intraparticle reduction of Se(IV), Water Res. 71 (2015) 274–281. Y. Fu, J. Wang, Q. Liu, H. Zeng, Water-dispersible magnetic nanoparticle– graphene oxide composites for selenium removal, Carbon N. Y. 77 (2014) 710– 721. N. Jordan, A. Ritter, A.C. Scheinost, S. Weiss, D. Schild, R. Hübner, Selenium(IV) uptake by maghemite (γ-Fe2O3)., Environ. Sci. Technol. 48 (2014) 1665–74. CH2MHILL, Review of available technologies for the removal of selenium from water, A final report published for North American Metals Council (2010), http://www.namc.org/docs/00062756.PDF (accessed date 28/11/2014). A.W. Cantafio, K.D. Hagen, G.E. Lewis, T.L. Bledsoe, K.M. Nunan, J.M. Macy, Pilot-scale selenium bioremediation of san joaquin drainage water with Thauera selenatis., Appl. Environ. Microbiol. 62 (1996) 3298–303. M. Lenz, E.D. Van Hullebusch, G. Hommes, P.F.X. Corvini, P.N.L. Lens, Selenate removal in methanogenic and sulfate-reducing upflow anaerobic sludge bed reactors., Water Res. 42 (2008) 2184–2194. R. Jain, G. Gonzalez-Gil, V. Singh, D. van Hullebuchs, Eric, F. Farges, P.N.L. Lens, Biogenic selenium nanoparticles : production , characterization and challenges, in: A. Kumar, N. Govil, J (Eds.), Nanobiotechnology, Studium Press LLC, USA, 2014: pp. 361–390. B. Buchs, M.W.-H. Evangelou, L. Winkel, M. Lenz, Colloidal properties of nanoparticular biogenic selenium govern environmental fate and bioremediation effectiveness., Environ. Sci. Technol. 47 (2013) 2401–2407. L.C. Staicu, E.D. van Hullebusch, M. A. Oturan, C.J. Ackerson, P.N.L. Lens, Removal of colloidal biogenic selenium from wastewater, Chemosphere. 125 (2015) 1–9. L.C. Staicu, E.D. van Hullebusch, P.N.L. Lens, E.A. Pilon-Smits, M. A Oturan, Electrocoagulation of colloidal biogenic selenium., Environ. Sci. Pollut. Res. Int. (2014). doi:10.1007/s11356-014-3592-2.
[15] T. Kagami, T. Narita, M. Kuroda, E. Notaguchi, M. Yamashita, K. Sei, et al., Effective selenium volatilization under aerobic conditions and recovery from the aqueous phase by Pseudomonas stutzeri NT-I., Water Res. 47 (2013) 1361–8. [16] S. Dhanjal, S.S. Cameotra, Aerobic biogenesis of selenium nanospheres by Bacillus cereus isolated from coalmine soil., Microb. Cell Fact. 9 (2010) 52. [17] J. Dobias, E.I. Suvorova, R. Bernier-latmani, Role of proteins in controlling selenium nanoparticle size, Nanotechnology. 22 (2011) 195605. [18] R. Jain, S. Matassa, S. Singh, E.D. van Hullebusch, G. Esposito, P.N.L. Lens, reduction to elemental selenium nanoparticles by activated sludge under aerobic conditions, Process Biochemistry. (Unpublished results). [19] Y. Chen, G. Gu, Preliminary studies on continuous chromium(VI) biological removal from wastewater by anaerobic-aerobic activated sludge process., Bioresour. Technol. 96 (2005) 1713–21. [20] M.T. Wright, D.R. Parker, C. Amrhein, Critical evaluation of the ability of sequential extraction procedures to quantify discrete forms of selenium in sediments and soils., Environ. Sci. Technol. 37 (2003) 4709–16. [21] APHA, Standard methods for examination of water and wastewater, 5th ed., American Public Health Association, Washington, DC, USA, 2005. [22] J. Laurent, M. Casellas, C. Dagot, Heavy metals uptake by sonicated activated sludge: relation with floc surface properties., J. Hazard. Mater. 162 (2009) 652– 60.. [23] B.F. Turner, J.B. Fein, Protofit: A program for determining surface protonation constants from titration data, Comput. Geosci. 32 (2006) 1344–1356. [24] J. Laurent, M. Casellas, M.N. Pons, C. Dagot, Flocs surface functionality assessment of sonicated activated sludge in relation with physico-chemical properties., Ultrason. Sonochem. 16 (2009) 488–94. [25] O. Braissant, a. W. Decho, C. Dupraz, C. Glunk, K.M. Przekop, P.T. Visscher, Exopolymeric substances of sulfate-reducing bacteria: Interactions with calcium at alkaline pH and implication for formation of carbonate minerals, Geobiology. 5 (2007) 401–411. [26] R. Jain, N. Jordan, D. Schild, E.D. Van Hullebusch, S. Weiss, C. Franzen, et al., Adsorption of zinc by biogenic elemental selenium nanoparticles, Chem. Eng. J. 260 (2015) 850–863. [27] Y. Ding, Q. Li, Y. Jia, L. Chen, J. Xing, Y. Qian, Growth of single crystal selenium with different morphologies via a solvothermal method, J. Cryst. Growth. 241 (2002) 489–497.. [28] R.S. Oremland, M.J. Herbel, J.S. Blum, S. Langley, T.J. Beveridge, P.M. Ajayan, et al., Structural and spectral features of selenium nanospheres produced by Serespiring bacteria, Appl. Environ. Microbiol. 70 (2004) 52–60. [29] C.I. Pearce, R.A.D. Pattrick, N. Law, J.M. Charnock, V.S. Coker, J.W. Fellowes, et al., Investigating different mechanisms for biogenic selenite transformations: Geobacter sulfurreducens, Shewanella oneidensis and Veillonella atypica., Environ. Technol. 30 (2009) 1313–26. [30] W. Zhang, Z. Chen, H. Liu, L. Zhang, P. Gao, D. Li, Biosynthesis and structural characteristics of selenium nanoparticles by Pseudomonas alcaliphila., Colloids Surf. B. Biointerfaces. 88 (2011) 196–201.
[31] H.-W. Luo, J.-J. Chen, G.-P. Sheng, J.-H. Su, S.-Q. Wei, H.-Q. Yu, Experimental and theoretical approaches for the surface interaction between copper and activated sludge microorganisms at molecular scale., Sci. Rep. 4 (2014) 7078. [32] M.G. Baker, S. V Lalonde, K.O. Konhauser, J.M. Foght, Role of extracellular polymeric substances in the surface chemical reactivity of Hymenobacter aerophilus, a psychrotolerant bacterium., Appl. Environ. Microbiol. 76 (2010) 102– [33] J. Tourney, B.T. Ngwenya, The role of bacterial extracellular polymeric substances in geomicrobiology, Chem. Geol. 386 (2014) 115–132. [34] R.E. Martinez, D.S. Smith, E. Kulczycki, F.G. Ferris, Determination of intrinsic bacterial surface acidity constants using a donnan shell model and a continuous pK(a) distribution method., J. Colloid Interface Sci. 253 (2002) 130–9. [35] X.Y. Li, S.F. Yang, Influence of loosely bound extracellular polymeric substances (EPS) on the flocculation, sedimentation and dewaterability of activated sludge., Water Res. 41 (2007) 1022–30. [36] F. Ye, Y. Ye, Y. Li, Effect of C/N ratio on extracellular polymeric substances (EPS) and physicochemical properties of activated sludge flocs., J. Hazard. Mater. 188 (2011) 37–43. [37] C.L. Xu, Y.Z. Wang, M.L. Jin, X.Q. Yang, Preparation, characterization and immunomodulatory activity of selenium-enriched exopolysaccharide produced by bacterium Enterobacter cloacae Z0206., Bioresour. Technol. 100 (2009) 2095–7. [38] R. Jain, N. Jordan, S. Weiss, H. Foerstendorf, K. Heim, R. Kacker, et al., Extracellular Polymeric Substances Govern the Surface Charge of Biogenic Elemental Selenium Nanoparticles, Environ. Sci. Technol. 49 (2015) 1713–1720. [39] Y. Bai, F. Rong, H. Wang, Y. Zhou, X. Xie, J. Teng, Removal of copper from aqueous solution by adsorption on elemental selenium nanoparticles, J. Chem. Eng. Data. 56 (2011) 2563–2568. [40] G. McKay, J.F. Porter, Equilibrium parameters for the sorption of copper, cadmium and zinc ions onto peat, J. Chem. Technol. Biotechnol. 69 (1997) 309– 320. [41] J. Wanner, Activated sludge: bulking and foaming control, Technomic Publishing Company, Inc, USA, 1994. [42] A. Haug, R.D. Graham, O.A. Christophersen, G.H. Lyons, How to use the world’s scarce selenium resources efficiently to increase the selenium concentration in food., Microb. Ecol. Health Dis. 19 (2007) 209–228. [43] M.R. Broadley, P.J. White, R.J. Bryson, M.C. Meacham, H.C. Bowen, S.E. Johnson, et al., Biofortification of UK food crops with selenium, Proc. Nutr. Soc. 65 (2007) 169–181. [44] N.C. Johnson, S. Manchester, L. Sarin, Y. Gao, I. Kulaots, R.H. Hurt, Mercury vapor release from broken compact fluorescent lamps and in situ capture by new nanomaterial sorbents., Environ. Sci. Technol. 42 (2008) 5772–5778. [45] S. Jiang, C.T. Ho, J.-H. Lee, H. Van Duong, S. Han, H.-G. Hur, Mercury capture into biogenic amorphous selenium nanospheres produced by mercury resistant Shewanella putrefaciens 200., Chemosphere. 87 (2012) 621–4. [46] J.W. Fellowes, R.A.D. Pattrick, D.I. Green, A. Dent, J.R. Lloyd, C.I. Pearce, Use of biogenic and abiotic elemental selenium nanospheres to sequester elemental
mercury released from mercury contaminated museum specimens, J. Hazard. Mater. 189 (2011) 660–669. [47] H. Zhang, X. Feng, C. Jiang, Q. Li, Y. Liu, C. Gu, et al., Understanding the paradox of selenium contamination in mercury mining areas: high soil content and low accumulation in rice., Environ. Pollut. 188 (2014) 27–36.
Table 1. Metal(loids) presence in the selenium fed activated sludge (As+Se).
Se
Na
Mg
Al
K
Ca
Fe
(mg per g TSS)
AS+Se
Table 1.
55
27
4.6
3.1
3
31
14.0
±2
±4
± 0.3
± 0.7
±2
±2
± 0.3
List of figures Figure 1. SEM (a) and EDX spectra of nanospheres (b1) and nanorods (b2) present in the selenium fed activated sludge. Zoomed in SEM image (c), TEM image (d) suggesting the presence of selenium inside the cells and flocs and (e) SEM images and (f) corresponding cartography (carbon red, phosphorous green and selenium blue) clearing showing the presence of selenium nanorods.
Figure 2. (a) XRD of selenium fed (▬) and control (without selenium, ―-―-) activated sludge and (b) SAED pattern of trapped elemental selenium nanospheres.
Figure 3. (a) SEM image of a single bacterium from selenium fed activated sludge and EDXS analyses corresponding to the spatial distribution of (b) Se, (c) Al and (d) Mg in the SEM image. Note that the distortion of one of the nanospheres of selenium observed in (a) is due to the damage by the electron beam while performing the measurements.
Figure 4. (a) Derivative of acid-base titration data of selenium fed (―) and control (― ―) activated sludge, (b) Titration data for selenium fed (◊ Raw, ― Simulated) and control (∆ Raw, ― ― Simulated) activated sludge, (c) Surface charge density of activated sludge trapping selenium (―) and control activated sludge (― ―) and (d) %
sites with corresponding pKa values of various functional groups for selenium fed and control activated sludge.
Figure 5. SVI (a), CST (b) and RH (c) of selenium fed (◊) and control (∆) activated sludge.
Figure 1.
Figure 2.
Figure 3.
Figure 4.
Figure 5.
