Water Treatment
Summary: The point of this lesson is to introduce students to a conventional method for treating contaminated water. Students will become more aware of drinking water sources, common types of contaminants in source water, and treatment using coagulation/sedimentation. They will also consider how particle size relates to surface area, as well as how the charges of metal oxide nanoparticle surfaces and contaminants are essential for explaining how they interact with one another during the treatment process.
Nanoscience Connection: Coagulation and sedimentation is widely used for water treatment because it is relatively cheap and effective at removing a variety of contaminants. The process involves formation of nanosized iron and/or aluminum hydroxides that react with contaminants through surface adsorption and other processes. The properties of nanoparticle surfaces including area, charge, reactivity, and adsorption are key concepts in nanoscience and nanotechnology. By learning about conventional water treatment, students are ready to understand alternative treatment strategies, as well as how contaminants interact with nanoparticles in environmental systems e.g., soils.
Learning Objectives:
Water Treatment
Key Concepts:
Google images
Module: Environmental Nanoscience
2022 Nanoscience Professional Development Workshop
What is the original source of the drinking water in your area?
Where does the water from your tap come from?
Surface Water Sources
Streams, Rivers, Lakes, Reservoirs
The New River
Credit: ReNew the New – Regional New River Cleanup
Surface Water Sources
Streams, Rivers, Lakes, Reservoirs
The New River
Credit: ReNew the New – Regional New River Cleanup
Surface Water Sources
Streams, Rivers, Lakes, Reservoirs
Cleanwisconsin.org
The New River
What types of natural and anthropogenic contaminants are common in raw source water?
Credit: www.blacksburg.gov
What types of natural and anthropogenic contaminants are common in raw source water?
Credit: www.blacksburg.gov
What types of natural and anthropogenic contaminants are common in raw source water?
Credit: www.blacksburg.gov
What types of natural and anthropogenic contaminants are common in raw source water?
Credit: www.blacksburg.gov
What types of natural and anthropogenic contaminants are common in raw source water?
Credit: www.blacksburg.gov
What types of natural and anthropogenic contaminants are common in raw source water?
Credit: www.blacksburg.gov
Dissolved vs. Solids
Credit: Western Oregon University
Sodium Chloride
SOLID PARTICLES
Dissolved vs. Solids
Credit: Western Oregon University
Sodium Chloride
SOLID PARTICLES
Sodium Chloride
DISSOLVED IONS
Size Classification of Contaminants
Credit: Maarten Bloemen
water
DISSOLVED IONS
Size Classification of Contaminants
Credit: Maarten Bloemen
water
CLAY
SILT
SAND
GRAVEL
DISSOLVED IONS
SOIL PARTICULATES
Size Classification of Contaminants
Credit: Maarten Bloemen
water
CLAY
SILT
SAND
GRAVEL
DISSOLVED IONS
SOIL PARTICULATES
What methods are there to remove contaminants that vary so widely in size?
Filtration
Filtration
Challenges:
Credit: Wikipedia
How is source water made safe for consumption?
?
Credit: Google images
A common treatment method is deactivating contaminants by surface adsorption
How is source water made safe for consumption?
Credit: Google images
A common treatment method is deactivating contaminants by surface adsorption
Conventional Water Treatment
Example: The New River
New River
Blacksburg, VA
NRV Regional Water Authority
Credit: www.blacksburg.gov
Credit: Google maps
http://www.blacksburg.gov/
NRV Regional Water Authority
Total capacity ~12.5 million gallons/day
Credit: Google maps
Conventional Water Treatment �is a multi-stage process that removes dissolved and particulate contaminants and disinfects source water
Conventional Water Treatment �is a multi-stage process that removes dissolved and particulate contaminants and disinfects source water
Conventional Water Treatment �is a multi-stage process that removes dissolved and particulate contaminants and disinfects source water
Credit: www.safewater.org
Small particles take longer to settle than larger particles.
Increasing particle size through aggregation and growth speeds up the process.
Big particle
Medium particles same overall size 20x more surface area
Tiny particles same overall size 60x more surface area
Nanoparticle Size vs. Surface Area
Big particle
Medium particles same overall size 20x more surface area
Tiny particles same overall size 60x more surface area
Nanoparticle Size vs. Surface Area
Big particle
Medium particles same overall size 20x more surface area
Tiny particles same overall size 60x more surface area
Nanoparticle Size vs. Surface Area
Phase | Surface Area (m2/g) | Site Density (per nm2) |
Ferric hydroxides | Up to 500 | 2-20 |
Aluminum hydroxides | Up to 150 | 2-12 |
One (1) gram of material can have more surface area than a full-size basketball court!
Credit: Good Food Grower
Credit: Virginia Tech
Surface Chemistry
Metal oxide surfaces are amphoteric: can react both as an acid or base (+ or -)
Schematic representation of the distribution of positive, negative, and neutral surface hydroxyl groups on an iron oxide surface
Image Credit: The Iron Oxides by Cornell & Schwertmann. © 2003 Wiley-VCH
Surface Chemistry
Metal oxide surfaces are amphoteric: can react both as an acid or base (+ or -)
Schematic representation of the distribution of positive, negative, and neutral surface hydroxyl groups on an iron oxide surface
Image Credit: The Iron Oxides by Cornell & Schwertmann. © 2003 Wiley-VCH
Surface Chemistry
Metal oxide surfaces are amphoteric: can react both as an acid or base (+ or -)
Schematic representation of the distribution of positive, negative, and neutral surface hydroxyl groups on an iron oxide surface
Image Credit: The Iron Oxides by Cornell & Schwertmann. © 2003 Wiley-VCH
Surface Chemistry
Metal oxide surfaces are amphoteric: can react both as an acid or base (+ or -)
Image Credit: The Iron Oxides by Cornell & Schwertmann. © 2003 Wiley-VCH
Schematic representation of the distribution of positive, negative, and neutral surface hydroxyl groups on an iron oxide surface
Zeta potential (ζ) refers to the electrical charge at the surface of the hydrodynamic shear layer surrounding a particle.
Image Credit: Science Direct
Neutral
Surface Charge
pH determines whether the net surface charges of particles can be negative, positive, or neutral (zero)
Image Credit: Wiese & Healy (1975) J. Colloid Interface Sci. 51, 427
Surface Charge
+
−
Neutral
Surface Charge
pH determines whether the net surface charges of particles can be negative, positive, or neutral (zero)
Image Credit: Wiese & Healy (1975) J. Colloid Interface Sci. 51, 427
Surface Charge
+
−
Neutral
pH Point of Zero Charge
Surface Charge
pH determines whether the net surface charges of particles can be negative, positive, or neutral (zero)
Image Credit: Wiese & Healy (1975) J. Colloid Interface Sci. 51, 427
Mineral Surfaces
Mineral Surfaces
AsO43-, PO43-, SO42-, NO3-
Organic molecules
Transition metals �e.g., Cr(H2O)63+
Complex cations �e.g., uranyl UO22+
Opposites Attract!
Dissolved species, molecules, and particles interact due to similarities and differences in net charges
Mineral Surfaces
Mineral Surfaces
AsO43-, PO43-, SO42-, NO3-
Organic molecules
Transition metals �e.g., Cr(H2O)63+
Complex cations �e.g., uranyl UO22+
Opposites Attract!
Dissolved species, molecules, and particles interact due to similarities and differences in net charges
Adsorption vs. Absorption
In chemistry, absorption is the diffusion of particles of gas or liquid into a material (e.g., water into a sponge)
Google images
Shutterstock
Adsorption
Separation of a substance from one phase accompanied by its accumulation or concentration at the surface of another
Mineral
Outer-sphere complex
weaker, electrostatic attraction (hydrogen bonding important)
Inner-sphere complex
Strong, bonded directly to surface (bridging oxygens)
Adsorption
Separation of a substance from one phase accompanied by its accumulation or concentration at the surface of another
Mineral
Outer-sphere complex
Weak, electrostatic attraction (hydrogen bonding important)
Inner-sphere complex
Strong, bonded directly to surface (bridging oxygens)
Adsorption
Separation of a substance from one phase accompanied by its accumulation or concentration at the surface of another
Mineral
Outer-sphere complex
Weak, electrostatic attraction (hydrogen bonding important)
Inner-sphere complex
Strong, bonded directly to surface (bridging oxygens)
Credit: Genesis Water Technologies
Conventional Water Treatment
Coagulation/flocculation & sedimentation remove a majority of organic and inorganic contaminants, but not all…
Anthracite coal
Fine sand
Coarse sand �& stone
Filtration
Removes remaining flocs, algae, and dissolved cations
Key Takeaways…