Dr Francisco Gomez RiveraDept Chemical and Environmental Engineering
The University of Arizona (E-mail: [email protected])
Fate of Cerium Oxide Nanoparticles During Activated Sludge Secondary Treatment
Introduction: Nanoparticles
Adapted from Andrew Schneider’s “Amid nanotech's dazzling promise, health risks grow”, 2010
• High surface area per unit mass (> 100 m2/g)• Chemical reactivity greatly different from macroscopic forms,e.g., gold• Quantum effects (dual behavior, wave- and particle-like)resulting in unique mechanical, electronic, photonic, andmagnetic properties.
Nanoparticles (NPs): Materials with at least one dimension of 1 to 100 nm
Introduction: Nanoparticles market
Semiconductor industry: CMP Photolithography
Automotive catalystsMagnetic recording media Sunscreens
Major nanomaterials consumers:
1 trillion dollar market by 2015NSF, 2001
Sporting goods Food packing materials Stain-resistant clothing Healthcare products Cosmetics
Household products containing nanomaterials:
Little is known about the fate of nanoparticles in the environment and possible toxic effects on living organisms
EPA’s Technology White Paper, 2007
Risk = Hazard x Exposure
Introduction: Potential risks
Nanoparticles Effects
Fullerenes (C60)Antibacterial; oxidative stress; may induce DNA damage in plasmids
Titanium dioxide (TiO2)Antibacterial; oxidative stress; may damage DNA; tissue thickening
Zinc oxide (ZnO)Oxidative stress; may damage DNA; pulmonary adverse effects
Cerium oxide (CeO2)Oxidative stress; thickening of heart tissue, could bind to cell membrane of Gram-negative bacteria
Introduction: Potential risks
Exposure: Inhalation Ingestion Dermal
Klaine et al, 2008
Industry Buildings
Homes
WWTP
Adapted from http://www.epa.gov
Are Wastewater Treatment Plants a Sink or aSource of Nanoparticles?
Brar et al, 2009
Industry Buildings
Homes
WWTP
Adapted from http://www.epa.gov
Muller and Nowack, 2008, estimated TiO2 and Nano-Ag reaching WWTP39% nano-Ag64% TiO2
WWTPs remove harmful organisms and pollutants
http://www.biosolids.com.au/what-are-biosolids.php
Primary treatmentRemove large solids (rags and debris) and smaller
inorganic grit
Secondary treatmentRemoves organic
contaminants using microorganisms to consume
biodegradable organics
Tertiary treatmentRemoves nutrients and may include disinfection of the
effluent
Introduction: Wastewater Treatment
Gravity Settling
Ad- and/or absorption
_ _ _ _ _ _ _ _ _ _ _ _
+ + +
+ +
Intake
Entrapment by A/S flocs
Introduction: Removal During Treatment
Possible removal mechanisms
No conclusive results have yet been obtained
Activated sludge process attained high removal of CeO2 from synthetic medium(Limbach et al. 2008)
Limbach et al, 2008
Iron oxide (Fe3O4) cored SiO2 NPs coated with a nonionic surfactant effectively removed during primary treatment. Unfunctionalized NPs escaped with the effluent (Jarvie et al, 2009).
Jarvie et al, 2009
Introduction: Removal During Treatment
Number of publications in different disciplines of nanoparticles, until December 2008Brar et al, 2009.
Assess the impact of wastewater components on theaggregation behavior of CMP nanoparticles
- Organic compounds: eg proteins, amino acids, humus, etc.- Polyelectrolytes- pH, salts, divalent cations
Investigate the removal of nanoparticles in CMPeffluent in a lab-scale wastewater treatment plant
- Lab-scale experiments with ceria slurry
Objectives
Methods
Microwave-Assisted Digestion:To reduce interference by organic matter and to convert metalsassociated with particulates to a form (usually free metal) that can be determined with ICP
ICP- OES:To determine very precisely the elemental composition of samples
COD, VFA, VSS:To characterize the municipal wastewaters
Scanning and Transmission Electron Microscopy(SEM and TEM)University of Arizona Spectroscopy and Imaging Facilities
ICP-OES
Virgin NanoparticlesAlumina: 50 nmCeria: 20 and 50 nm
Particle size: Dynamic light scattering (DLS)Malvern Zeta Sizer Nano ZS
Dispersion stability: Zeta potentialMalvern Zeta Sizer Nano ZS
Zeta Potential
Zeta potential: The electrical potential that exists across the interface of all solids and liquids
Isoelectric Point: Point during pH titration when zeta potentialapproaches zero
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+
+ ++++
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Zeta Potential
Stable dispersion
++
+
+ ++++
Lower pH
Repulsion
Higher pH
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Repulsion
Instable dispersion (pH ~ IP)
Significant Aggregation of CeO2 and Al3O2 Nanoparticles in Aqueous Solution
CeO2 and Al2O3 NPs showed significant aggregation in aqueous solutions even at pH values considerably different from their respective isoelectric point.
Fig. Particle size distribution of nano-CeO2 and Al2O3 in pH-5.2 and pH-4.5 aqueous solutions, resp. Titration experiments showed that the dispersions exhibit high stability at these pH values.
Significant Aggregation of CeO2 and Al3O2 Nanoparticles in Aqueous Solution
Transmission electron microscope images of the nano-sized ceria (upper panel) and alumina used in this study.
Impact Specific Compounds on CeO2 NPs Stability
Zeta potential (top)
Average Particle Size (middle)
Residual Ceria Concentration (lower)dilution (1/1, v/v) of a nanoceria dispersion with solutions of different additives (200 mg/L)
The final pH of the diluted dispersions was 6.8.
Additives:L-Asp = L-aspartic acid;Dispex = Ammonium polyacrylate dispersant;Hum = Humic acid;Coll = Collagen;BSA = Bovine serum albumin.
Fate of CeO2 and Al2O3 During Aerobic Activated Sludge Treatment of Domestic Wastewater
Laboratory-scale wastewater treatment plant utilized in this study. (1) Ceriastock; (2) peristaltic pump feeding ceria; (3) activated sludge bioreactor; (4) settling tank; (5) peristaltic pump feeding wastewater; (6) effluent; (7) influent; [8] aeration.
0
50
100
150
200
250
300
0 200 400 600 800 1000 1200 1400 1600 1800
Size
(d.n
m)
Time (min)
Average Diameter Size (nm) over time
[CeO2] = 200 ppm
pH = 3.46
Fate of CeO2 and Al2O3 During Aerobic Activated Sludge Treatment of Domestic Wastewater
Fate of CeO2 During Aerobic Activated Sludge Treatment of Domestic Wastewater
Figure. Concentration of a) total unfiltered and b) filtered Ce in the (●) influent and (■) effluent of activated sludge treatment operated with real domestic wastewater. Bold markers in second panel indicate CeO2 < 200 nm, while empty markers refer to CeO2 < 25 nm.
Fate of CeO2 During Aerobic Activated Sludge Treatment of Domestic Wastewater
Figure. Sorption of CeO2 to biomass. Total unfiltered Ce was measured from thesupernatant of each assay after 20 h. Two pH values were considered for this test.Treatments consisted of Milli-Q water at pH 3.0 and 6.0, sludge biomass at pH 3.0 and5.9, and rinse sludge at pH 2.7 and 6.0. The Milli-Q water treatment was sampled at thebeginning of the experiment (Water 0 h) to be used as a control.
COD Removal by Activated Sludge Treatment
Figure. Fate of a) soluble and b) total COD in the aerobic activated sludge system when feeding real wastewater, where (●) indicates the influent and (■) the effluent.Feeding of CeO2 to the reactor is represented by the continuous vertical line. Dashed line indicates fresh wastewater batches.
Acetate Removal by Activated Sludge Treatment
Figure. Acetate concentration in the influent, (●), and effluent, (■), of the secondary treatment when feeding real wastewater. Continuous vertical line indicates the addition of CeO2 to wastewater. Dashed vertical lines represent fresh wastewater batches.
CeO2 Nanoparticles Associated with Sludge
TEM image of CeO2 associated with sludge show the CeO2 NPs associated with the cells and extracellular deposits.
• Nanoparticles accumulate around cell structure and extracellular material
• Internalization difficult to determine
Conclusions
Nanoparticles are difficult to maintain in dispersion. CeO2 instable at neutral pH, and in domestic WW at any pH WW components change stability of nanoparticles in dispersions
Cerium oxide nanoparticles are highly removed from wastewater during activated sludge treatment. “Adsorption” and agglomeration/sedimentation
Treatment of effluents containing ceria NPs in conventional wastewater treatment plants is expected to result in a significant removal of the inorganic oxides from the treated effluent.
Presence and accumulation of cerium oxide did not seem to have an inhibitory effect on the activated sludge secondary treatment system.
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