Recent Advances in Nanotechnology for the Water Sector

Transcription

1 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

2 Water distribution uneven Sub-Saharan Africa Not enough water available Global Water Scarcity 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

3 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.

4 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)

5 Conventional Water Treatment Method Requirements 35% of Population in RSA

6 Solution Required Improved remediation technologies Degradation of POPs (vs physical removal) Cost efficient Environmentally friendly Not energy intensive Easy to operate

7 Nanotechnology a viable solution for water treatment? Nanotechnology: The study, processing and application of structures in the range 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

8 Nanotechnology: High Surface Area 2g of bulk gold surface area= 0.02m 2 2g of nanogold surface area = 100m times!!!

9 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

10 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

11 Commercial: Nanosorbent for Arsenic and Fluoride Removal AMRIT Indian Institute of Technology- Madras, India Gravity driven, regenerable, affordable

12 Nanocatalysts: Photocatalysts Activated by visible light or UV radiation Nanoparticles Target Pollutant Nanoscale TiO 2, Fullerenes Poliovirus 1, hepatitis B, herpes simplex virus, bacteriophage. Ammonia, Organic Pollutants (pesticides, drugs, dyes, pharmaceuticals, cosmetics) n-ag-doped TiO 2 Nanoscale ZnO E. Coli Organic Pollutants (aromatics, aliphatic, aromatic chloro compounds) Disinfection without harmful byproducts

13 Conventional Filtration Membranes Set-back: High pressures required for operation Not a viable option for rural areas No access to electricity

14 Conventional Filtration Membranes Semi-permeable barriers Work by blocking/retaining particles Water molecules Pollutant Membrane Water Flow x Problem Fouling: x energy and operation cost x production

15 Nano-enabled Catalytic Membranes Embedded with Nanoparticles Nanoparticles - Catalysts/particle reducers Water molecules Pollutant Benign molecules Reactive NPs Water Flow NPs-embedded Membrane Reduced fouling

16 Nano-enabled Catalytic Membranes Immobilization of catalytic NPs on membranes Catalytic membranes Gravity-driven membranes

17 Catalytic Membrane: with Fe/Ni NPs on Methyl Orange Degradation 0 min 10 min 50 min 200 min K. Sikhwivhilu and R.M. Moutloali., Materials Today 2 (2015)

18 Catalytic Membrane: with Fe/Pd NPs on PCB 77 Dechlorination Cycle 1 Cycle 2 Cycle 6 Contact time (min) L. Ndlwana, K. Sikhwivhilu, J.C. Ngila, R.M. Moutloali, submitted to Appl. Surf. Sc,

19 Commercial: Enhanced Membrane Filtration Incorporation of hydrophilic nanoparticles to increase water permeation Low driving force required e.g. UCLA/NanoH 2 O Reverse Osmosis Membrane for Sea Water Desalination 50% more permeable 25% less OPEX

20 Enhanced Membrane Filtration + Solar Energy Solution for energy-driven treatment in South Africa- Sisukumile Secondary School- Mpumalanga

21 Water re-use: Acid Mine Drainage Ultrafiltration NICMembrane TM Raw Permeate SANS 241 = 5NTU 280 NTU 3 NTU

22 Antibacterial Action - Coatings Disinfection and Biofilm growth retardation E. Coli 96% reduction S. Aureus 77% reduction Control (PES) PES-Nanocomposite B. Vatsha, P. Tetyana, P. Shumbula, J.C. Ngila, L. Sikhwivhilu, R.M. Moutloali, J. Biomater Nanotechnol, 4 (2013)

23 Potential: Improvement of existing Technologies Coating of interiors of water storage/transport containers The Hippo roller

24 End-Use Possibilities

25 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!!!!

26 Acknowledgements THE NETWORK/CONSORTIUM

27 Thank You