Recent Advances in Nanotechnology for the Water Sector

Keneiloe Sikhwivhilu, Ph.D Principal Scientist

DST/Mintek Nanotechnology Innovation Centre

Skills Drought in the Water Sector- NSTF Discussion Forum

Emperors Palace, 26 September March 2016

Global Water Scarcity

• Water distribution – uneven

• Sub-Saharan Africa

Not enough water available

Finding a reliable source of safe water

is time consuming and expensive

2004: Only 16% of people had access

to drinking water through a household

connection (an indoor tap or a tap in

the yard). (WHO)

Population growth: Water use has

been growing at > 2 x of population

growth in the last century

Difficult to control sanitation issues

Conventional of water treatment • Physical Methods: Sedimentation, screening,

aeration, fitration, flotation and skimming,

degasification, equalization.

• Chemical Methods: Chlorination, ozonation,

neutralization, coagulation, adsorption, ion

exchange.

• Biological Methods:

– Aerobic: Aerobic digestion, activated sludge,

filtration, oxidation ponds, lagoons, etc.

– Anaerobic: Anaerobic digestion, septic tanks,

lagoons, etc.

Conventional Water Treatment Methods: Challenges

• Flocculation / coagulation, precipitation, bioreactor, chlorination, for removal of heavy metals,

organics and bacteria.

Do not remove low pollutant concentrations

Chlorine added reacts with organic cations to form disinfection by-products

(DBPs) such as N-nitrosodimethylamine (NDMA) – Carcinogenic

Bacteria: fouling microcystins: therefore degradation is needed

Sludge disposal

• Membrane technology (RO/NF): Physical removal, High energy requirements

• Persistent organic pollutants (POPs) - low biodegradability

chlorinated organic compounds

emerging pollutants (e.g. hormones, drugs)

•

Conventional Water Treatment Method Requirements

35% of Population in RSA

Solution Required

• Improved remediation technologies

Degradation of POPs (vs physical removal)

Cost efficient

Environmentally friendly

Not energy intensive

Easy to operate

Nanotechnology a viable solution for water treatment?

Nanotechnology: The study, processing and application of structures in the range 1-

100 nm in size

Involves the ability to “see” and to “control” individual molecules and atoms

Higher Surface area on a mass basis

Unique electronic properties allow functionalization – new properties

Functionalization can increase affinity towards target compounds

Nanotechnology: High Surface Area

2g of nanogold surface area = 100m2

2g of bulk gold surface area= 0.02m2

5000 times!!!

Nanosorbents

Examples: Carbon Nanotubes, nano alumina,

zeolites, nanoclays,

Mode of Action: Physical Adsorption

Pollutants:

heavy metals ( e.g. As, Hg, Cd, Pb, Th, U)

Pathogens (viruses and bacteria)

Organic Pollutants, e.g. Dyes, pesticides

Regeneration: e.g. Acid treatment

Nanobiocides

Examples:

n-Ag , n-Au, Mg (OH)2 and MgO NPs

Pollutants: Removal of pathogens (viruses and bacteria)

E.Coli, Cholera, Giardia, Hepatitis, Staph. Aureus

Mode of Action: Deactivation/Destruction

Alternative for disinfectant methods such as chlorination

Commercial: Nanosorbent for Arsenic and Fluoride Removal

AMRIT – Indian Institute of Technology- Madras, India

Gravity driven, regenerable, affordable

Nanocatalysts: Photocatalysts

• Activated by visible light or UV radiation

Nanoparticles Target Pollutant

Nanoscale TiO2, Fullerenes Poliovirus 1, hepatitis B,

herpes simplex virus,

bacteriophage. Ammonia,

Organic Pollutants

(pesticides, drugs, dyes,

pharmaceuticals, cosmetics)

n-Ag-doped TiO2 E. Coli

Nanoscale ZnO Organic Pollutants

(aromatics, aliphatic,

aromatic chloro compounds)

Disinfection without harmful

byproducts

Conventional Filtration Membranes

• Set-back: High pressures required for operation

• Not a viable option for rural areas – No access to electricity

Conventional Filtration Membranes

• Semi-permeable barriers

• Work by blocking/retaining particles

Water molecules

Pollutant

Water Flow

Membrane

x Problem – Fouling:

x ↑energy and operation cost

x ↓production

Nano-enabled Catalytic Membranes

• Embedded with Nanoparticles

• Nanoparticles - Catalysts/particle reducers

Water Flow NPs-embedded Membrane

Water molecules

Benign molecules

Pollutant

Reactive NPs

Reduced fouling

Nano-enabled Catalytic Membranes

• Immobilization of catalytic NPs on membranes – Catalytic membranes

• Gravity-driven membranes

K. Sikhwivhilu and R.M. Moutloali., Materials Today 2 (2015) 4070-4080

Catalytic Membrane: with Fe/Ni NPs on Methyl Orange Degradation

0 min 10 min 50 min 200 min

Cycle 1

Cycle 2

Cycle 6

Contact time (min)

L. Ndlwana, K. Sikhwivhilu, J.C. Ngila, R.M. Moutloali, submitted to Appl. Surf. Sc,

Catalytic Membrane: with Fe/Pd NPs on PCB 77 Dechlorination

Commercial: Enhanced Membrane Filtration

• Incorporation of hydrophilic nanoparticles to increase water permeation

Low driving force required

• e.g. UCLA/NanoH2O Reverse Osmosis Membrane for Sea Water Desalination

50% more permeable

25% less OPEX

Enhanced Membrane Filtration + Solar Energy

Solution for energy-driven treatment in South Africa-

Sisukumile Secondary School- Mpumalanga

Water re-use: Acid Mine Drainage

Raw Permeate

280 NTU 3 NTU

Ultrafiltration NICMembrane TM

SANS 241 = 5NTU

Antibacterial Action - Coatings

96% reduction

77% reduction

Control (PES)

S. Aureus

E. Coli

PES-Nanocomposite

Disinfection and Biofilm growth retardation

B. Vatsha, P. Tetyana, P. Shumbula, J.C. Ngila, L. Sikhwivhilu, R.M. Moutloali,

J. Biomater Nanotechnol, 4 (2013) 365-373

Potential: Improvement of existing Technologies

• Coating of interiors of water storage/transport containers

The Hippo roller

End-Use Possibilities

Conclusion

Nanomaterials can be substituted for conventional materials that require more raw

material, are energy intensive to produce or are known to be environmentally harmful

Can allow decentralization of water treatment and supply

Can be incorporated to improve existing technologies

Can reduce energy requirements and high costs associated with membrane technology

However, risks of nanomaterials need to be thoroughly evaluated before rolling out for

public consumption !!!!

Acknowledgements

THE NETWORK/CONSORTIUM

Thank You

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