Science and Technology for Sustainable Water Supply Menachem Elimelech Department of Chemical Engineering Environmental Engineering Program Yale University “Your Drinking Water: Challenges and Solutions for the 21 st Century”, Yale University, April 21, 2009
The “Top 10” Global Challenges for the New Millennium 1. Energy 2. Water 3. Food 4. Environment 5. Poverty 6. Terrorism and War 7. Disease 8. Education 9. Democracy 10. Population Richard E. Smalley, Nobel Laureate, Chemistry, 1996, MRS Bulletin, June 2005
International Water Management Institute
Regional and Temporal Water Scarcity National Oceanic and Atmospheric Administration
How Do We Increase the Amount of Water Available to People? § § Water conservation, repair of infrastructure, and improved catchment and distribution systems ― improve use, not increasing supply! Increase water supplies to gain new waters can only be achieved by: ü Reuse of wastewater ü Desalination of brackish and sea waters
Many Opportunities We are far from thermodynamic limits for separating unwanted species from water Traditional methods are chemically and energetically intensive, relatively expensive, and not suitable for most of the world New systems based on nanotechnology can dramatically alter the energy/water nexus
Wastewater Reuse
Reclaimed Wastewater in Singapore (NEWater) Source of water supply for commercial and industrial sectors (10% of water demand) 4 NEWater plants supplying 50 mgd of NEWater. 5 miles Will meet 15% of water demand by 2011
Reuse of Wastewater in Orange County, California www. gwrsystem. com Groundwater Replenishment System, GWR (70 MG/day)) Prado Dam Santa Ana River Facilities
GWR System for Advanced Water Purification (Orange County) Microfiltration (MF) OCSD Secondary WW Effluent Reverse Osmosis (RO) Ultraviolet Light with H 2 O 2 Recharge Basins
Namibia, Africa
Natural Beauty … but not Enough Water
Windhoek’s Solution: Wastewater Reclamation for Direct Potable Use Goreangab Reclamation Plant (Windhoek) “Water should not be judged by its history, but by its quality. ” Dr. Lucas Van Vuuren National Institute of Water Research, South Africa The only wastewater reclamation plant in the world for direct potable use
The Treatment Scheme: A Multiple Barrier Approach
Most Important: Public Acceptance and Trust in the Quality of Water Breaking down the psychological barrier (the “yuck factor”) is not trivial – Rigorous monitoring of water quality after every process step – Final product water is thoroughly analyzed (data made available to public) The citizens of Windhoek have a genuine pride in the reality that their city leads the world in direct water reclamation
Wastewater Reuse: Membrane Bioreactor (MBR)-RO System Shannon, Bohn, Elimelech, Georgiadis, and Mayes, Nature 452 (2008) 301 -310.
Fouling Resistant UF Membranes: Comb (PAN-g-PEO) Additives amphiphilic copolymer added to casting solution segregate & self-organize at membrane surfaces PEO brush layer on surface and inside pores Casting Solution Doctor Blade Coagulation Bath Heat Treatment Bath Fouling Resistance Asatekin, Kang, Elimelech, Mayes, Journal of Membrane Science, 298 (2007) 136 -146.
Fouling Reversibility (with Organic Matter) White: Pure water Gray: recovered flux after fouling/cleaning (following “physical” cleaning (rinsing) with no chemicals) Shannon, Bohn, Elimelech, Georgiadis, and Mayes, Nature 452 (2008) 301 -310.
AFM as a Tool to Optimize Copolymer for Fouling Resistance Kang, Asatekin, Mayes, Elimelech, Journal of Membrane Science, 296 (2007) 42 -50.
Wastewater Reuse: Membrane Bioreactor (MBR)-RO System Shannon, Bohn, Elimelech, Georgiadis, and Mayes, Nature 452 (2008) 301 -310.
One Step NF-MBR System? NF
Antifouling NF Membranes for MBR (PVDF-g-POEM) Filtration of activated sludge from MBR – PVDF-g-POEM NF: no flux loss over 16 h filtration – PVDF base: 55% irreversible flux loss after 4 h PVDF-g-POEM (●, ●) PVDF base ( , ) Asatekin, Menniti, Kang, Elimelech, Morgenroth, Mayes: J. Membr. Sci. 285 (2006) 81 -89
Wastewater Reuse: Osmotically-Driven Membrane Processes
Wastewater Reclamation with Forward (Direct) Osmosis Wastewater Concentrate Disposal
Osmotic MBR-RO: Low Fouling, Multiple Barrier Treatment OMBR SYSTEM RO DISINFECTION Wastewater Sludge Achilli, Cath, Marchand, and Childress, Desalination, 2009. Potable water
Reversible Fouling: No Need for Chemical Cleaning Mi and Elimelech, in preparation.
Desalination: Reverse Osmosis
Population Density Near Coasts
Seawater Desalination § Augmenting and diversifying water supply § Reverse osmosis and thermal desalination (MSF and MED) are the current desalination technologies § Energy intensive (cost and environmental impact) § Reverse osmosis is currently the leading technology
Reverse Osmosis § Major improvements in the past 10 years § Further improvements are likely to be incremental § Recovery limited to ~ 50%: § Brine discharge (environmental concerns) § Increased cost of pre-treatment § Use prime (electric) energy (~ 2. 5 k. Wh per cubic meter of product water)
Minimum Energy of Desalination § Minimum energy needed to desalt water is independent of the technology or mechanism of desalination § Minimum theoretical energy for desalination: § § 0% recovery: 0. 7 k. Wh/m 3 50% recovery: 1 k. Wh/m 3
Nanotechnology May Result in Breakthrough Technologies “These nanotubes are so beautiful that they must be useful for something. . . ”, Richard Smalley (1943 -2005).
Aligned Nanotubes as High Flux Membranes for Desalination? Hinds et al, “Aligned multi-walled carbon nanotube membranes”, Science, 303, 2004.
Research on Nanotube Based Membranes Mauter and Elimelech, Environ. Sci. Technol. , 42 (16), 5843 -5859, 2008.
Next Generation Nanotube Membranes Mauter and Elimelech, Environ. Sci. Technol. , 42 (16), 5843 -5859, 2008. Single-walled carbon nanotubes (SWNTs) with a pore size of ~ 0. 5 nm are critical for salt rejection Higher nanotube density and purity Large scale production?
Bio-inspired High Flux Membranes for Desalination Natural aquaporin proteins extracted from living organisms can be incorporated into a lipid bilayer membrane or a synthetic polymer matrix
BUT …. Energy is Needed Even for Membranes with Infinite Permeability § Minimum theoretical energy for desalination at 50% recovery: 1 k. Wh/m 3 § Practical limitations: No less than 1. 5 k. Wh/m 3 § Achievable goal: 1. 5 2 k. Wh/m 3 Shannon, Bohn, Elimelech, Georgiadis, and Mayes, Nature 452 (2008) 301 -310.
Desalination: Forward Osmosis
The Ammonia-Carbon Dioxide Forward Osmosis Desalination Process Nature, 452, (2008) 260 Energy Input Mc. Cutcheon, Mc. Ginnis, and Elimelech, Desalination, 174 (2005) 1 -11.
NH 3/CO 2 Draw Solution NH 3(g) CO 2(g) NH 4 HCO 3(aq) (NH 4)2 CO 3(aq) NH 4 COONH 2(aq) HEAT
High Water Recovery with FO (atm) 450 400 350 300 250 200 150 100 50 0 RO FO Seawater 0 10 20 30 40 50 60 70 80 90 100 Recovery (%)
Energy Use by Desalination Technologies (Equivalent Work) Contribution from Electrical Power Mc. Ginnis and Elimelech, Desalination, 207 (2007) 370 -382.
Waste Heat Geothermal Power
Concluding Remarks We are far from thermodynamic limits for separating unwanted species from water Nanotechnology and new materials can significantly advance water purification technologies Advancing the science of water purification can aid in the development of robust, costeffective technologies appropriate for different regions of the world
Acknowledgments
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