Dr Francisco Gomez RiveraDept Chemical and Environmental Engineering

The University of Arizona (E-mail: fgomez@email.arizona.edu)

Fate of Cerium Oxide Nanoparticles During Activated Sludge Secondary Treatment

Outline

INTRODUCTION

OBJECTIVES

MATERIALS AND METHODS

RESULTS

CONCLUSIONS

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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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 Domestic WW on Stability of Nanoparticles

● Milli-Q water ● Wastewater

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

BioreactorOriginal sludge(t=0)

CeO2 Nanoparticles Associated with Sludge

(1) Bacterial cells(2) Extracellular deposits

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.

Acknowledgements

Dr James Field

Dr Reyes Sierra

MC Monica Rodriguez

Jeffrey Rotman

ISMI/Sematech

SRC/Sematech Engineering Research Center for Benign Environmental Semiconductor Manufacturing (ERC)

Mexican National Science and Technology Foundation (CONACyT)