Emerging Contaminants and Nano-Enabled Solutions

Summary: The point of this lesson is to introduce students to the importance of groundwater as a source of drinking water and the issue of contamination. Students will become more aware of what are the common types of groundwater contaminants, how they enter the subsurface, and how they move and spread due to groundwater flow. They will also become more aware of common remediation techniques and why they are limited due to issues with subsurface complexity. They will be provided with an example of enhanced nanoparticle reactivity, as well as consider how engineered nanomaterials can provide novel nano-enabled approaches to remediation, including applications with challenging emerging contaminants.

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Nanoscience Connection: Surface and subsurface contamination threatens freshwater supplies at sites worldwide. Engineered nanomaterials can be developed to overcome challenges to conventional remediation strategies including targeting and selectivity, as well as treating emerging contaminants that resist degradation. By learning about the importance of groundwater and the threats and challenges to remediation, students are ready to build on these concepts and explore nano-enabled solutions.

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Learning Objectives:

• Explain what is the water table and what determines the movement of water in the subsurface
• Give an example of a point source of contamination and describe two mass transport processes in groundwater
• Explain why contamination of groundwater supplies is an important problem
• Explain the enhanced reactivity of nanomaterials can cause them to dominate a chemical systems
• Describe how the enhanced reactivity and other selected properties of nanomaterials can be used to develop new remediation agents and treatment strategies

Emerging Contaminants and Nano-Enabled Solutions

Key Concepts:

• Groundwater
• Conventional Remediation & Subsurface Complexity
• Emerging Contaminants
• Nano-Enabled Solutions

Google images

Module: Environmental Nanoscience

2022 Nanoscience Professional Development Workshop

Credit: NASA

Zhang et al. 2019 Env Sci Nano

Credit: Lumen Learning

Water table: the underground boundary between the soil surface and the area where groundwater saturates the spaces between sediments and within rock

Groundwater and the Water Table

Credit: Lumen Learning

Groundwater and the Water Table

Credit: USGS

Credit: Lumen Learning

Groundwater and the Water Table

Groundwater flow: Flow direction generally follows surface topography (flows downhill)

Flow

Credit: Lumen Learning

Groundwater and the Water Table

Wells: Vertical pipes with openings in sides that is used to monitor water table (height, flow direction, composition, etc.) and extract water

Credit: Uobabylon

Credit: Ligavha-Mbelengwa & Gomo (2020) Env Earth Sciences 79, 196.

Groundwater Flow

Contaminant Plumes

Contaminants migrate from a point source (e.g., leaking underground storage tank) via mass transport processes in subsurface

Mass Transport

Advection: Mass transport due to flow of water

Advection only

Time

Image Credit: M. Saatsaz (Researchgate)

Concentration

“Slug” or volume of contaminated groundwater

Mass Transport

Diffusion & Dispersion: Spreading of contaminants over time from molecular to macroscale

Advection: Mass transport due to flow of water

Advection only

Advection with diffusion and dispersion

Time

Image Credit: M. Saatsaz (Researchgate)

Concentration

Groundwater from public and private wells is an important source of drinking water in the U.S.

2005 data, water.usgs.gov

U.S. EPA

Groundwater and Soil Contamination by Hazardous Substances

• Many U.S. sites contaminated with heavy metals, oxyanions (e.g., nitrate, arsenate), organic chemicals, radionuclides, etc.
• Negative impacts to soil, water, and air quality

Contaminated U.S. Superfund Sites located in areas that may be impacted by flooding, storm surge, wildfires or sea level rise

Conventional Remediation

Google images

Leaking due to corrosion

Conventional Remediation

Google images

Conventional Remediation

Some common techniques:

• Excavate and off-site disposal
• Containment barriers
• Pump/dig and on-site treatment
• Chemical reduction/oxidation

Google images

In Situ Remediation

• Remediation in situ or ”in place” is the only option for some scenarios
• Chlorinated solvents, pesticides, coal tar, etc.
• Injection of chemical oxidants, reduction, bioremediation

Example of in situ thermal treatment combined with vacuum extraction

Treatment system

Wells

ISOTEC

Large-Scale Contamination

• Trichloro-ethylene or ”TCE” is a known carcinogen
• 13 trillion-gallon GW plume
• Conventional remediation approaches not feasible

https://www.michiganradio.org/post/northern-michigan-community-tries-stay-ahead-massive-contaminated-plume

Large-Scale Contamination

• Trichloro-ethylene or ”TCE” is a known carcinogen
• 13 trillion-gallon GW plume
• Conventional remediation approaches not feasible

https://www.michiganradio.org/post/northern-michigan-community-tries-stay-ahead-massive-contaminated-plume

What makes subsurface remediation (cleanup) difficult?

Zhang et al. 2019 Env Sci Nano

• Plume size & depth
• Partitioning of contaminants and inaccessible zones
• Preferential flow paths
• Complex and dynamic chemistry (pH, ionic strength, gradients, organic matter, life, etc.)

What makes subsurface remediation (cleanup) difficult?

• Inability to characterize and effectively target contaminant source zones
• Low efficiency of remediation agents
• Inability to monitor performance

Contaminant “Rebound”

Credit: Regenesis

What can innovative nano-enabled remediation strategies offer?

What makes subsurface remediation (cleanup) difficult?

• Inability to characterize and effectively target contaminant source zones
• Low efficiency of remediation agents
• Inability to monitor performance

Contaminant “Rebound”

Credit: Regenesis

Nano-Enabled Remediation Agents

Enhanced Nanoparticle Reactivity

Madden & Hochella (2005) Geochim. Cosmochim. Acta, 69, 389-398.

Surface area-normalized

oxidation rate of Mn²⁺

• Hematite catalyzes reaction of dissolved Mn²⁺ to Mn³⁺OOH (solid)

Nano-Enabled Remediation Agents

Enhanced Nanoparticle Reactivity

Madden & Hochella (2005) Geochim. Cosmochim. Acta, 69, 389-398.

Surface area-normalized

oxidation rate of Mn²⁺

• Hematite catalyzes reaction of dissolved Mn²⁺ to Mn³⁺OOH (solid)
• Oxidation rate increases 1-2 orders of magnitude with decreasing size

Nano-Enabled Remediation Agents

Enhanced Nanoparticle Reactivity

Madden & Hochella (2005) Geochim. Cosmochim. Acta, 69, 389-398.

Surface area-normalized

oxidation rate of Mn²⁺

• Hematite catalyzes reaction of dissolved Mn²⁺ to Mn³⁺OOH (solid)
• Oxidation rate increases 1-2 orders of magnitude with decreasing size
• Due to fundamental change in electronic properties with size

Madden & Hochella (2005) Geochim. Cosmochim. Acta, 69, 389-398.

• Tested binary mixtures made of different amounts of 7 and 37 nm particles

Reaction progress due to�7 nm particles

Nano-Enabled Remediation Agents

Enhanced Nanoparticle Reactivity

Madden & Hochella (2005) Geochim. Cosmochim. Acta, 69, 389-398.

• Tested binary mixtures made of different amounts of 7 and 37 nm particles

Reaction progress due to�7 nm particles

Nano-Enabled Remediation Agents

Enhanced Nanoparticle Reactivity

Madden & Hochella (2005) Geochim. Cosmochim. Acta, 69, 389-398.

• Tested binary mixtures made of different amounts of 7 and 37 nm particles
• It takes just 1-2% of 7 nm particles to dominate reactivity

Reaction progress due to�7 nm particles

Nano-Enabled Remediation Agents

Enhanced Nanoparticle Reactivity

Madden & Hochella (2005) Geochim. Cosmochim. Acta, 69, 389-398.

• Tested binary mixtures made of different amounts of 7 and 37 nm particles
• It takes just 1-2% of 7 nm particles to dominate reactivity
• Demonstrates how important highly reactive nanoparticles can be in chemical systems

Reaction progress due to�7 nm particles

Nano-Enabled Remediation Agents

Enhanced Nanoparticle Reactivity

Multifunctional Engineered Nanomaterials (ENMs) can be designed to…

Target multiple contaminants

Zhang et al. 2019 Env Sci Nano

Zhang et al. 2019 Env Sci Nano

Be selective towards contaminants

Multifunctional Engineered Nanomaterials (ENMs) can be designed to…

Zhang et al. 2019 Env Sci Nano

Break down emerging contaminants

Poly- and per-fluoroalkyl substances (PFOA, PFOS, etc.)

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Human-made chemicals manufactured for use in food packaging (e.g., pizza boxes), nonstick products (e.g., Teflon), stain-repellent fabrics, etc.

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Multifunctional Engineered Nanomaterials (ENMs) can be designed to…

Key Takeaways…

• Groundwater is a critical source of drinking water that is threatened by contaminated sites worldwide
• Conventional remediation techniques are limited due to subsurface complexity and in cases of emerging contaminants
• Nanomaterials enhanced reactivity can dominate processes in chemical systems
• Nano-enabled remediation agents have the potential to overcome challenges of traditional approaches