Environ. Sci. Technol. 2010, 44, 8216–8222
Biogenic Nanoscale Colloids in Wastewater Effluents GUIXUE SONG, JUN WANG, CHAO-AN CHIU, AND PAUL WESTERHOFF* School of Sustainable Engineering and The Built Environment, Arizona State University, P.O. Box 5306, Tempe, Arizona 85287
Received April 15, 2010. Revised manuscript received August 23, 2010. Accepted September 8, 2010.
The size, surface area, metal complexation capacity, organic pollutant sorption potential, reactivity with disinfectants, and elevated nitrogen content of biogenic organic nanoscale material (BONM) can potentially affect aquatic environments. BONM in effluents from 11 full-scale wastewater treatment plants (WWTPs), which use a range of biological processes, were characterized in two ways. First, BONM was measured by hydrodynamic size-exclusion chromatography coupled with an online organic carbon and UV detector. Second, BONM was isolated from the wastewater using rotary evaporation and dialysis and then characterized by elemental analysis, transmission electron microscopy, and Fourier transform infrared spectroscopy. The wastewaters contained 6-10 mg/L of dissolved organic carbon (DOC). BONM accounted for 5%-50% of the DOC in wastewater effluent organic matter, and the largest size fraction (>10 kDa) of organic carbon correlated with the organic carbon content determined after rotary evaporation and dialysis. Membrane bioreactor WWTPs had the lowest fraction of BONM (10 kDa range. The confidence bands for the linear regression analysis using simulated data show that real data are mainly in the 95% confidence interval. Oval lower left, MBR; oval middle, activated sludge; oval circle upper right, trickling filter, reclamation water park. Inset: biogenic organic colloids isolated from HF treatment. VOL. 44, NO. 21, 2010 / ENVIRONMENTAL SCIENCE & TECHNOLOGY
9
8219
FIGURE 3. TEM images of the uranyl acetate-stained fibrillar network of biogenic nanomaterial and fibrils in concentrated wastewater effluents after HCl treatment (a) or after HF treatment (b) from the TR sample. Bars in the figure correspond to 0.2 µm (a) and 50 nm (b). nutrient loading, hydraulic and sludge retention times), as (6). The frequently detected peak at 1040 cm-1 is assigned indicated by the bulk water quality, which shows varying to O-H stretching and that at 1264 cm-1 to C-O stretching of polysaccharides or O-H bending of carboxylic acids. The degrees of nitrification and denitrification (Table 1). combination of these peaks is normally assigned to proteins Geometry of BONM. Dialyzed colloids were analyzed by and N-acetylamide structures, indicating amino sugar origins, TEM to visualize their morphology. Figure 3 shows typical possibly a contribution of bacterial cell walls (27). A shoulder morphological TEM images for the colloids collected from at approximately 1730 cm-1 contributes to carboxylic groups. the dialysis tubes. Several shapes are evident in the samples, The sharp peak at 2929 cm-1 and a shoulder peak at 2840 including long linear structures, branched aggregates, sphericm-1 are usually ascribed to the aliphatic methyl and cal objects, and inorganic aggregates (darker clumps). The methylene groups in long chain aliphatic groups from lipids shapes of elongated fibrils are similar to some polysaccharideor to the side chains of proteins/peptides. A strong peak at like colloids in the freshwaters (44, 45). 740 cm-1 may correspond to CH2 bending in long chain Improved visualization of polymeric fibrils and vesiclealiphatics from fatty acids or lipids, which are known to be like colloids by TEM analysis exist after HF dialysis, compared present in wastewater and may be one site that could bind against dialysis with only HCl (Figure SI-1, Supporting hydrophobic organic pollutants and lead to their facilitative Information). This is because inorganic colloids (likely transport. silicates) “masked” these fibrils. As a note, EDX analysis of A strong broad silicate spectral response was present in the TEM samples determined that “dark spots” were residual HCl-colloids at 1000-1200 cm-1 (not shown). As with EDX uranyl acetate, our TEM contrasting stain, and not silica or analysis, this could indicate either an association of silica other inorganic materials. As indicated in Tables 1 and SI-2 with BONM or simply that inorganic silicates were coisolated (Supporting Information),, dialysis against HF removed a with BONM. HF-dialysis significantly reduced the silicate significant mass of inorganic materials. High ash and silica peaks, and FTIR spectra could readily be obtained (Figure content were detected in the HCl-colloid samples. For SI-2, Supporting Information). example, the ash content of TR is high (>77% by mass) in Implications of BONM on WWTP Processes. In summary, which silica is dominant (about 58% by mass based upon the sizes and shapes of BONMs isolated from representative EDX analysis). Silica content was very low content in HClwastewater effluents employing different biological treatment colloids (Figures 3a and SI-1, Supporting Information), based (from less treated trickling filter, aerated lagoon to stateupon EDX analysis. The presence of silica materials in HClof-the-art membrane bioreactor) are similar, invariably colloids, but not HF-colloids, suggest that silica-based showing a nanoscale fibril entangled network structure. HDmaterials could either be directly associated with BONM SEC of raw effluent samples can be used quantify the amount surfaces or simply co-occur upon the basis of the isolation different sizes of BONM in the effluents, because we validated process and size separation (45). For example, plant cell walls the linear relationship (Figure 2) between BONM content and diatoms contain microscopic silica crystals to macromeasured by a rotary evaporation/dialysis method against scopic silica structures for rigidity and protection against the integrated response in high molecular weight range (>10 grazers, and both cases result in silica bound directly with kDa) of HD-SEC chromatographs. The association between organic materials. Upon the basis of EDX analysis, calcium silica and BONM is interesting and potentially affects WWTP appeared when higher levels of silica were detected in HCloperations employing MBR technology (see below), and colloids. It is possible that calcium acted as a bridge between further research into these associations could be productive. BONMs and silicate materials (46). Calcium content was The fibril entangled networks which BONMs create can ∼1.3% in the TR sample, while other potential chelating enhance aggregation and sedimentation of nanosize particles metals (e.g., iron) where not detected. in wastewater (47, 48) and impact the efficiency of wastewater FTIR Analysis. Overall, spectra for samples from all the treatment processes. Examples of nanosize pollutants in WWTPs were remarkably similar, indicating a high uniformity wastewater include clays, heavy metal precipitates (e.g., Ag2S), of BONM independent of the biological processes used to viruses, and perhaps even engineered nanomaterials (e.g., treat wastewater. FTIR spectral peaks at 1650 and 1540 cm-1 reflect functional groups of primary and secondary amides TiO2, CeO, Ag, fullerenes) (49-53). 8220
9
ENVIRONMENTAL SCIENCE & TECHNOLOGY / VOL. 44, NO. 21, 2010
The control and removal of BONMs may gain increased attention for two primary reasons. First, increasing attention is focused on limiting levels of organic nitrogen discharged from WWTPs into sensitive ecosystems (54, 55). BONMs represent a major pool of organic nitrogen (6) on a mass basis discharged from many types of WWTPs. Recent research shows that colloidal organic nitrogen can become biologically available and potentially lead to eutrophication (7). The second major reason for which BONM control may gain attention is related to increasing use of membrane technology. In wastewater treatment, microfiltration (MF) processes, with ∼0.2 µm cutoff, are alternatives to traditional sedimentation tanks and granular media filtration because of economics (56). Furthermore, the combination of higher biomass densities and improved separation capabilities offered by membrane bioreactors, compared to activated sludge systems with conventional sedimentation, leads to improved water quality performance (e.g., Tables 1 and SI-2, Supporting Information). Additionally, reverse osmosis (RO) systems are increasing being used in wastewater reclamation projects. However, membrane systems from MF to RO are prone to fouling (i.e., reduction in flux across the membrane and/or increased energy and operational costs required to operate the membrane). The most common foulants in MBRs are organic and silica-based (57-60). For example, silica and algenate were found to synergistically foul membranes (61). Our research shows an association between BONM and silica, suggesting that such interactions may play a complex role in fouling membranes. The morphological significance of colloids and silica matrices on membrane fouling could be important, because as our TEM images suggest, a network of nanoscale fibrils, lipid-rich vesicles, and aggregates will be present and could affect the morphology of the fouling layer on membranes used in MBR treatment systems. Water flux decline or increased pressure requirements to maintain water flux in these membranes is caused by the presence of organic materials similar to BONMs (11). Thus finding strategies to reduce levels of BONMs are desirable. In one case, the presence of Chloroflexi bacterium reduced levels of N-acetylglucosamine (62), a main substantial constituent of the cell wall peptidoglycan that is a major BONM component. Thus monitoring and managing the bacterial diversity in biological wastewater processes may aid in reducing BONM concentrations and thus minimize flux decline due to organic foulants and reduce organic nitrogen loading to the environment.
Acknowledgments This work is supported by a grant from the Paul L. Bush Award of the Water Environmental Research Foundation (WERF). The authors thank David Lowry for providing TEM support and WWTP utility operators for assisting in sampling.
Supporting Information Available Additional information as noted in the text. This material is available free of charge via the Internet at http://pubs.acs.org.
Literature Cited (1) USEPA. Clean Water Needs Survey; USEPA: Washington, DC, 1996. (2) Grossart, H. P.; Simon, M.; Logan, B. E. Formation of macroscopic organic aggregates (lake snow) in a large lake: The significance of transparent exopolymer particles, phytoplankton, and zooplankton. Limnol. Oceanogr. 1997, 42 (8), 1651–1659. (3) Logan, B. E.; Grossart, H. P.; Simon, M. Direct observation of phytoplankton, TEP and aggregates on polycarbonate filters using brightfield microscopy. J. Plankton Res. 1994, 16 (12), 1811–1815. (4) Passow, U. Transparent exopolymer particles (TEP) in aquatic environments. Progr. Oceanogr. 2002, 55 (3-4), 287–333.
(5) Bar-Zeev, E.; Berman-Frank, I.; Liberman, B.; Rahav, E.; Passow, U.; Berman, T. Transparent exopolymer particles: Potential agents for organic fouling and biofilm formation in desalination and water treatment plants. Desalin. Water Treat. 2009, 3 (13), 136–142. (6) Leenheer, J. A.; Dotson, A.; Westerhoff, P. Dissolved organic nitrogen fractionation. Ann. Environ. Sci. 2007, (1), 45–56. (7) Bronk, D.; Roberts, Q. N.; Sanderson, M. P.; Canuel, E. A.; Hatcher, P. G.; Mesfioui, R.; Filippino, K. C.; Mulholland, M. R.; Love, N. G. Effluent organic nitrogen (EON): Bioavailability and photochemical and salinity-mediated release. Environ. Sci. Technol. 2010, 44 (15), 5830–5835. (8) Pehlivanoglu, E.; Selak, D. L. Bioavailability of wastewaterderived organic nitrogen to the alga Selenastrum Capricornutum. Water Res. 2004, 38, 3189–3196. (9) Dotson, A.; Westerhoff, P.; Krasner, S. W. Nitrogen enriched dissolved organic matter (DOM) isolates and their affinity to form emerging disinfection by-products. Water Sci. Technol. 2009, 60 (1), 135–143. (10) Mitch, W. A.; Sedlak, D. L. Characterization and fate of N-nitrosodimethylamine precursors in municipal wastewater treatment plants. Environ. Sci. Technol. 2004, 38 (5), 1445–1454. (11) Amy, G. Fundamental understanding of organic matter fouling of membranes. Desalination 2008, 231 (1-3), 44–51. (12) Jarusutthirak, C.; Amy, G.; Croue, J.-P. Fouling characteristics of wastewater effluent organic matter (EfOM) isolates on NF and UF membranes. Desalination 2002, 145 (1-3), 247–255. (13) Rosenberger, S.; Laabs, C.; Lesjean, B.; Gnirss, R.; Amy, G.; Jekel, M.; Schrotter, J. C. Impact of colloidal and soluble organic material on membrane performance in membrane bioreactors for municipal wastewater treatment. Water Res. 2006, 40 (4), 710–720. (14) Theng, B. K. G.; Yuan, G. D. Nanoparticles in the soil environment. Elements 2008, 4 (6), 395–399. (15) Zhang, X. Z.; Sun, H. W.; Zhang, Z. Y.; Niu, Q.; Chen, Y. S.; Crittenden, J. C. Enhanced bioaccumulation of cadmium in carp in the presence of titanium dioxide nanoparticles. Chemosphere 2007, 67 (1), 160–166. (16) Esparza-Soto, M.; Fox, P.; Westerhoff, P. Transformation of molecular weight distributions of dissolved organic carbon and UV-absorbing compounds at full-scale wastewater-treatment plants. Water Environ. Res. 2006, 78 (3), 253–262. (17) Esparza-Soto, M.; Fox, P.; Westerhoff, P. Comparison of dissolved-organic-carbon residuals from air- and pure-oxygenactivated-sludge sequencing-batch reactors. Water Environ. Res. 2006, 78 (3), 321–329. (18) Laspidou, C. S.; Rittmann, B. E. A unified theory for extracellular polymeric substances, soluble microbial products, and active and inert biomass. Water Res. 2002, 36, 2711–2720. (19) Logan, B. E.; Wagenseller, G. A. Molecular size distributions of dissolved organic matter in wastewater transformed by treatment in a full-scale trickling filter. Water Environ. Res. 2000, 72 (3), 277–281. (20) Wingender, J.; Neu, T. R.; Flemming, H.-C. Microbial Extracellular Polymeric Substances: Characterization, Structure and Function; Springer: Berlin, 1999. (21) Buffle, J.; Leppard, G. G. Characterization of Aquatic colloids and macromolecules. 1. Structure and behavior of colloidal material. Environ. Sci. Technol. 1995, 29 (9), 2169–2175. (22) Buffle, J.; Leppard, G. G. Characterization of Aquatic colloids and macromolecules. 2. Key role of physical structures on analytical results. Environ. Sci. Technol. 1995, 29 (9), 2176–2184. (23) Gustafsson, O.; Gschwend, P. M. Aquatic colloids: Concepts, definitions, and current challenges. Limnol. Oceanogr. 1997, 42 (3), 519–528. (24) Lead, J. R.; Wilkinson, K. J. Aquatic colloids and nanoparticles: Current knowledge and future trends. Environ. Chem. 2006, 3 (3), 159–171. (25) Aiken, G.; Cotsaris, E. Soil and hydrologysTheir effect on NOM. J. Am. Water Works Assoc. 1995, 87 (1), 36–45. (26) Baalousha, M.; Kammer, F. V. D.; Motelica-Heino, M.; Baborowski, M.; Hofmeister, C.; Le Coustumer, P. Size-based speciation of natural colloidal particles by flow field flow fractionation, inductively coupled plasma-mass spectroscopy, and transmission electron microscopy/X-ray energy dispersive spectroscopy: Colloids-trace element interaction. Environ. Sci. Technol. 2006, 40 (7), 2156–2162. (27) Leenheer, J.; Dotson, A.; Westerhoff, P. Dissolved organic nitrogen fractionation. Ann. Environ. Sci. 2007, 1, 45–56. VOL. 44, NO. 21, 2010 / ENVIRONMENTAL SCIENCE & TECHNOLOGY
9
8221
(28) Lienemann, C. P.; Heissenberger, A.; Leppard, G. G.; Perret, D. Optimal preparation of water samples for the examination of colloidal material by transmission electron microscopy. Aquat. Microb. Ecol. 1998, 14 (2), 205–213. (29) Worms, I. A. M.; Al-Gorani Szigeti, Z.; Dubascoux, S.; Lespes, G.; Traber, J.; Sigg, L.; Slaveykova, V. I. Colloidal organic matter from wastewater treatment plant effluents: Characterization and role in metal distribution. Water Res. 2010, 44 (1), 340–350. (30) Buffle, J.; Wilkinson, K. J.; Stoll, S.; Filella, M.; Zhang, J. W. A generalized description of aquatic colloidal interactions: The three-colloidal component approach. Environ. Sci. Technol. 1998, 32 (19), 2887–2899. (31) Leenheer, J. A. Systematic approaches to comprehensive analyses of natural organic matter. Ann. Environ. Sci. 2009, 3, 1–130. (32) Rostad, C. E.; Leenheer, J. A.; Daniel, S. R. Organic carbon and nitrogen content associated with colloids and suspended particulates from the Mississippi River and some of its tributaries. Environ. Sci. Technol. 1997, 31 (11), 3218–3225. (33) APHA; AWWA; WEF. Standard Methods for the Examination of Water And Wastewater, 21st ed.; American Public Health Association: Washington, DC, 2005. (34) Leenheer, J. A.; Noyes, T. I.; Rostad, C. E.; Davisson, M. L. Characterization and origin of polar dissolved organic matter from the Great Salt Lake. Biogeochemistry 2004, 69 (1), 125–141. (35) Chen, K. L.; Mylon, S. E.; Elimelech, M. Enhanced aggregation of alginate-coated iron oxide (hematite) nanoparticles in the presence of calcium, strontium, and barium cations. Langmuir 2007, 23 (11), 5920–5928. (36) Her, N.; Amy, G.; McKnight, D.; Sohn, J.; Yoon, Y. M. Characterization of DOM as a function of MW by fluorescence EEM and HPLC-SEC using UVA, DOC, and fluorescence detection. Water Res. 2003, 37 (17), 4295–4303. (37) Allpike, B. P.; Heitz, A.; Joll, C. A.; Kagi, R. I.; Abbt-Braun, G.; Frimmel, F. H.; Brinkmann, T.; Her, N.; Amy, G. Size exclusion chromatography to characterize DOC removal in drinking water treatment. Environ. Sci. Technol. 2005, 39 (7), 2334–2342. (38) Krasner, S. W.; Westerhoff, P.; Chen, B. Y.; Rittmann, B. E.; Nam, S. N.; Amy, G. Impact of wastewater treatment processes on organic carbon, organic nitrogen, and DBP precursors in effluent organic matter. Environ. Sci. Technol. 2009, 43 (8), 2911–2918. (39) Krasner, S. W.; Westerhoff, P.; Chen, B. Y.; Rittmann, B. E.; Nam, S. N.; Amy, G. Impact of wastewater treatment processes on organic carbon, organic nitrogen, and DBP precursors in effluent organic matter. Environ. Sci. Technol. 2009, 43 (8), 2911–2918. (40) Rumpel, C.; Rabia, N.; Derenne, S.; Quenea, K.; Eusterhues, K.; Ko¨gel-Knabner, I.; Mariotti, A. Alteration of soil organic matter following treatment with hydrofluoric acid (HF). Org. Geochem. 2006, 37 (11), 1437–1451. (41) McKnight, D. M.; Harnish, R.; Wershaw, R. L.; Baron, J. S.; Schiff, S. Chemical characteristics of particulate, colloidal, and dissolved organic material in Loch Vale watershed, Rocky Mountain National Park. Biogeochemistry 1997, 36 (1), 99–124. (42) Her, N.; Amy, G.; McKnight, D.; Sohn, J.; Yoon, Y. M. Characterization of DOM as a function of MW by fluorescence EEM and HPLC-SEC using UVA, DOC, and fluorescence detection. Water Res. 2003, 37 (17), 4295–4303. (43) Namkung, E.; Rittmann, B. E. Soluble microbial products (Smp) formation kinetics by biofilms. Water Res. 1986, 20 (6), 795– 806. (44) Wilkinson, K. J.; Negre, J. C.; Buffle, J. Coagulation of colloidal material in surface waters: The role of natural organic matter. J. Contam. Hydrol. 1997, 26 (1-4), 229–243.
8222
9
ENVIRONMENTAL SCIENCE & TECHNOLOGY / VOL. 44, NO. 21, 2010
(45) Wilkinson, K. J.; Stoll, S.; Buffle, J. Characterization of NOMcolloid aggregates in surface waters: coupling transmission electron-microscopy staining techniques and mathematicalmodeling. Fresenius’ J. Anal. Chem. 1995, 351 (1), 54–61. (46) Muzzarelli, C.; Muzzarelli, R. A. A. Natural and artificial chitosaninorganic composites. J. Inorg. Biochem. 2002, 92 (2), 89–94. (47) Chen, K. L.; Mylon, S. E.; Elimelech, M. Aggregation kinetics of alginate-coated hematite nanoparticles in monovalent and divalent electrolytes. Environ. Sci. Technol. 2006, 40, 1516–1523. (48) Wilkinson, K. J.; Joz-roland, A.; Buffle, J. Different roles of pedogenic fulvic acids and aquagenic biopolymers on colloid aggregation and stability in freshwaters. Limnol. Oceanogr. 1997, 42, 1714–1724. (49) Adams, N. W. H.; Kramer, J. R. Determination of silver speciation in wastewater and receiving waters by competitive ligand equilibration/solvent extraction. Environ. Toxicol. Chem. 1999, 18 (12), 2674–2680. (50) Benn, T. M.; Westerhoff, P. Nanoparticle silver released into water from commercially available sock fabrics. Environ. Sci. Technol. 2008, 42 (11), 4133–4139. (51) Gottschalk, F.; Sonderer, T.; Scholz, R. W.; Nowack, B. Modeled environmental concentrations of engineered nanomaterials (TiO2, ZnO, Ag, CNT, fullerenes) for different regions. Environ. Sci. Technol. 2009, 43 (24), 9216–9222. (52) Kiser, M. A.; Westerhoff, P.; Benn, T.; Wang, Y.; Perez-Rivera, J.; Hristovski, K. Titanium nanomaterial removal and release from wastewater treatment plants. Environ. Sci. Technol. 2009, 43, 6757–6763. (53) Limbach, L. K.; Bereiter, R.; Mueller, E.; Krebs, R.; Gaelli, R.; Stark, W. J. Removal of oxide nanoparticles in a model wastewater treatment plant: Influence of agglomeration and surfactants on clearing efficiency. Environ. Sci. Technol. 2008, 42 (15), 5828–5833. (54) Bradley, P. B.; Lomas, M. W.; Bronk, D. A. Inorganic and organic nitrogen use by phytoplankton along Chesapeake Bay, measured using a flow cytometric sorting approach. Estuaries Coasts 2010, 33 (4), 971–984. (55) Bronk, D. A.; Glibert, P. M.; Ward, B. B. Nitrogen uptake, dissolved organic nitrogen release, and new production. Science 1994, 265, 1843–1846. (56) Shirazi, S.; Lin, C. J.; Chen, D. Inorganic fouling of pressuredriven membrane processessA critical review. Desalination 2009, 250 (1), 236–248. (57) Kennedy, M. D.; Tobar, F. P. M.; Amy, G.; Schippers, J. C. Transparent exopolymer particle (TEP) fouling of ultrafiltration membrane systems. Desalin. Water Treat. 2009, 6 (1-3), 169– 176. (58) Koo, T.; Lee, Y. J.; Sheikholeslami, R. Silica fouling and cleaning of reverse osmosis membranes. Desalination 2001, 139 (1-3), 43–56. (59) Lesjean, B.; Rosenberger, S.; Laabs, C.; Jekel, M.; Gnirss, R.; Amy, G. Correlation between membrane fouling and soluble/colloidal organic substances in membrane bioreactors for municipal wastewater treatment. Water Sci. Technol. 2005, 51 (6-7), 1–8. (60) Teychene, B.; Guigui, C.; Cabassud, C.; Amy, G. Toward a better identification of foulant species in MBR processes. Desalination 2008, 231 (1-3), 27–34. (61) Higgin, R.; Howe, K. J.; Mayer, T. M. Synergistic behavior between silica and alginate: Novel approach for removing silica scale from RO membranes. Desalination 2009, 250 (1), 76–81. (62) Miura, Y.; Watanabe, Y.; Okabe, S. Significance of Chloroflexi in performance of submerged membrane bioreactors (MBR) treating municipal wastewater. Environ. Sci. Technol. 2007, 41 (22), 7787.
ES101208B
