Presentation on theme: "Science and Technology for Sustainable Water Supply"— Presentation transcript:
1 Science and Technology for Sustainable Water Supply Menachem ElimelechDepartment of Chemical EngineeringEnvironmental Engineering ProgramYale UniversityThank you for the kind introduction.My talk will be on the “Science and Technology for Sustainable Water Supply”, a subject which has a great societal impact, and in which engineering can play a very important role.“Your Drinking Water: Challenges and Solutions for the 21st Century”, Yale University, April 21, 2009
2 The “Top 10” Global Challenges for the New Millennium EnergyWaterFoodEnvironmentPovertyTerrorism and WarDiseaseEducationDemocracyPopulationIt is not surprising that water and energy are on the top of this list.In fact, as you will see later in my talk, water and energy are interrelated.Several of the other top challenges are also indirectly related to water and energy.Richard E. Smalley, Nobel Laureate, Chemistry, 1996, MRS Bulletin, June 2005
3 1) 25% of world population, 33% of developing world population – will live in areas of water scarcity2) Areas shown as not water scarce will need to greatly increase their fresh water productivity (catchment, distribution, etc)3) Areas shown as not water scarce have regional scarcityInternational Water Management Institute
4 Regional and Temporal Water Scarcity We need to look at regional and temporal water scarcity – not average for the entire country.The IPCC report tells us that dry areas getting drier, wet areas wetter, flow more seasonal (less storage in snow and ice).Improved catchment and redistribution are needed, but these will have environmental impacts (such as those of dams on river systems and fisheries), and can be energy intensive.National Oceanic and Atmospheric Administration
5 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:Reuse of wastewaterDesalination of brackish and sea waters
6 Many OpportunitiesWe are far from the thermodynamic limits for separating unwanted species from waterTraditional methods are chemically and energetically intensive, relatively expensive, and not suitable for most of the worldNew systems based on nanotechnology can dramatically alter the energy/water nexusWe are far from the thermodynamic limits for separating unwanted species from water. This will be analyzed in our discussion on desalination where thermodynamics dictates the minimum theoretical energy to desalinate a saline solution.6
7 Co-authored a review paper with colleagues in the Center for Advanced Materials for Purification of Water with Systems.The paper discusses a few of the issues addressed in my presentation.
9 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.Will meet 15% of water demand by 2011To give an example of a successful implementation of relaimed water, I am citing the example of NEWater. NEWater is produced from the reclamation of treated used water. It is now a reliable source of water supply for the commercial and industrial sectors, accounting for about 10% of Singapore’s water demand. Currently there are four NEWater plants supplying 50mgd of NEWater. From the figure, you can see the locations of the 4 NEWater plants and the pipeline system supplying reclaimed water to the industrial and commercial areas for direct non-potable usage and to the reservoirs for indirect potable usage. The long-term target is to meet 15% of our water demand through NEWater by the year 2011.5 miles
10 Reuse of Wastewater in Orange County, California Groundwater ReplenishmentSystem, GWR (70 MG/day))Prado DamSanta Ana River FacilitiesAnother example is the Groundwater Replenishment System in Orange County, California.This is a major upgrade of Water Factory 21 that was completed in 1975.Treated wastewater is used to recharge groundwater in Orange county, that later used for drinking water. This is a classic example of wastewater reclamation for indirect potable use.
11 GWR System for Advanced Water Purification (Orange County) Microfiltration(MF)Reverse Osmosis(RO)Ultraviolet Light with H2O2OCSD Secondary WW EffluentRecharge BasinsThe treatment scheme of the GWR system – which is considered nowadays as state-of-the-art.MF (pretreatment)RO oxidation/disinfection
14 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 VuurenNational Institute of Water Research, South AfricaThe only wastewater reclamation plant in the world for direct potable use
15 The Treatment Scheme: A Multiple Barrier Approach
16 Most Important: Public Acceptance and Trust in the Quality of Water Breaking down the psychological barrier (the “yuck factor”) is not trivialRigorous monitoring of water quality after every process stepFinal 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
17 Wastewater Reuse: Membrane Bioreactor (MBR)-RO System Future wastewater reuse will use MBRSkip MF/UF used in the previous schemeLess energy/cost, smaller footprintShannon, Bohn, Elimelech, Georgiadis, and Mayes, Nature 452 (2008)
18 Fouling Resistant UF Membranes: Comb (PAN-g-PEO) Additives amphiphilic copolymer addedto casting solutionsegregate & self-organizeat membrane surfacesPEO brush layer on surface and inside poresDoctor BladeCoagulation BathCasting SolutionHeat TreatmentBathCastingSolutionDoctorBladeCoagulationBathHeatTreatmentFor successful and cost/energy effective operation of MBR and wastewater reuse we need membranes with low fouling propensity.In this study, polyacrylonitrile-graftpoly(ethylene oxide) (PAN-g-PEO), an amphiphilic comb copolymer with a water-insoluble polyacrylonitrile (PAN) backbone and hydrophilic poly(ethylene oxide) (PEO) side chains, was used as an additive in the manufacture of novel PAN UF membranes.During casting, the PAN-g-PEO additive segregates to form a PEO brush layer on all membrane surfaces, including internal pores.Fouling ResistanceAsatekin, Kang, Elimelech, Mayes, Journal of Membrane Science, 298 (2007)
19 Fouling Reversibility (with Organic Matter) White: Pure waterGray: recovered flux after fouling/cleaning (following “physical” cleaning (rinsing) with no chemicals)Wettability, pure water permeability, and resistance to irreversible fouling increased when either the amount of PAN-g-PEO added to the membrane or the PEO content of the comb copolymer was increased. In this the PEO content of the comb copolymer was fixed (50%)In 24-h dead-end filtration studies, blend membranes prepared with 20 wt% PAN-g-PEO (comb PEO content: 39 wt%) were found to resist irreversible fouling by 1000 ppm solutions of bovine serum albumin (BSA), sodium alginate, and humic acid, recovering the initial pure water flux completely by a pure water rinse, or a backwash in the case of humic acid.Shannon, Bohn, Elimelech, Georgiadis, and Mayes, Nature 452 (2008)
20 AFM as a Tool to Optimize Copolymer for Fouling Resistance Kang, Asatekin, Mayes, Elimelech, Journal of Membrane Science, 296 (2007)
21 Wastewater Reuse: Membrane Bioreactor (MBR)-RO System Shannon, Bohn, Elimelech, Georgiadis, and Mayes, Nature 452 (2008)
23 Antifouling NF Membranes for MBR (PVDF-g-POEM) Filtration of activated sludge from MBRPVDF-g-POEM NF: no flux loss over 16 h filtrationPVDF base: 55% irreversible flux loss after 4 hCommercial polyvinylidene fluoride (PVDF) UF membranes were coated with the amphiphilic graft copolymer poly(vinylidene fluoride)-graft-poly(oxyethylene) methacrylate, PVDF-g-POEM, to create thin film composite (TFC) nanofiltration membranes.The PVDF UF base membrane served as the control in filtration experimentsActivated sludge from aerobic MBR. Tests at 40 psi for coated, 10 psi for base.Pure water permeabilities up to 56 L/m2 hMPa were obtained at pressures of 0.21MPa (30 psi). The new TFC NF membranesexhibited no irreversible fouling in 10-day dead-end filtration studies of model organic foulants bovine serum albumin, sodium alginate and humic acid at concentrations of 1000 mg/L and above. Dead-end filtration of activated sludge from an MBR (1750 mg/L volatile suspended solids, VSS) resulted in constant flux throughout the 16 h filtration period. Fouling performance of the TFC NF membrane and effluent water quality were substantially improved in all cases over that for the base PVDF UF membrane.PVDF-g-POEM (●,●)PVDF base (,)Asatekin, Menniti, Kang, Elimelech, Morgenroth, Mayes: J. Membr. Sci. 285 (2006) 81-89
33 Seawater Desalination Augmenting and diversifying water supplyReverse osmosis and thermal desalination (MSF and MED) are the current desalination technologiesEnergy intensive (cost and environmental impact)Reverse osmosis is currently the leading technology
34 Reverse Osmosis Major improvements in the past 10 years Further improvements are likely to be incrementalRecovery limited to ~ 50%:Brine discharge (environmental concerns)Increased cost of pre-treatmentUse prime (electric) energy (~ 2.5 kWh per cubic meter of product water)
35 Minimum Energy of Desalination Minimum energy needed to desalt water is independent of the technology or mechanism of desalinationMinimum theoretical energy for desalination:0% recovery: 0.7 kWh/m350% recovery: 1 kWh/m3
36 Nanotechnology May Result in Breakthrough Technologies “These nanotubes are so beautiful that they must be useful for something. . .”, Richard Smalley ( ).
37 Aligned Nanotubes as High Flux Membranes for Desalination? Hinds et al, “Aligned multi-walled carbon nanotube membranes”, Science, 303, 2004.
38 Research on Nanotube Based Membranes Mauter and Elimelech, Environ. Sci. Technol., 42 (16), , 2008.
39 Next Generation Nanotube Membranes Mauter and Elimelech, Environ. Sci. Technol., 42 (16), , 2008.Single-walled carbon nanotubes (SWNTs) with a pore size of ~ 0.5 nm are critical for salt rejectionHigher nanotube density and purityLarge scale production?
40 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
41 BUT …. Energy is Needed Even for Membranes with Infinite Permeability Minimum theoretical energy for desalination at 50% recovery: 1 kWh/m3Practical limitations: No less than 1.5 kWh/m3Achievable goal: 2 kWh/m3Shannon, Bohn, Elimelech, Georgiadis, and Mayes, Nature 452 (2008)
48 Concluding RemarksWe are far from the thermodynamic limits for separating unwanted species from waterNanotechnology and new materials can significantly advance water purification technologiesAdvancing the science of water purification can aid in the development of robust, cost-effective technologies appropriate for different regions of the world