Wizards of the water cycle

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S i nga p o r e ’ s s k y l i n eg l e a m s b e h i n d t h em a r i n a r e s e r voi r .T h e n e w ly e n c l o s e db ay i s f l a n k e d b ya t h r e e - p i l l a r e dr e s o rt b u i lt o nr e c l a i m e d l a n d.t i n y t e s t b e d ss i n g a p o r e n m a l t as p e c i a l r e p o r t n w a t e r v s . e n e r g yWizardsof theWater CycleSingapore’s toilet-to-taptechnology has saved thecountry from shortages—and a large electricity billb y s a n d r a U p s o np h o t o s b y D a r r e n S o hspectrum.ieee.orgjune 2010 • IEEE Spectrum • NA 57

3. t i n y t e s t b e d s n s i n g a p o r e n d e s a l i n a t i o n n m a l t as i N G a P o r e B e G a N i t s J o U r N e yto sovereignty with a mighty jolt. Theisland was still an exotic outpost of theBritish Empire when World War IIdelivered the shake-up. Japan’s armywas preparing to invade from the MalayPeninsula, and the British forces beat aretreat to Singapore across the one bridgeconnecting it to the mainland. To thwartthe Japanese troops, the Royal Engineersblew up the bridge behind them.The blast sealed the island’s doom, forit also ruptured a critical pipeline thatbrought water from Johor, a Malay state.The people of Singapore discovered theyhad only a few days’ water stored intheir meager reservoirs. The island wastruly defenseless. The Japanese swiftlyrepaired the bridge, bicycled across thestrait, and claimed victory.Sixty-eight years later, this port cityhas both gained territorial independenceand managed to bootstrap itsway to wealth in spite of a lack of waterand energy. And now, against all odds,complete water independence—fromboth Malaysia and even the weather—is within easy reach. Rather than flushingwaste into the sea, the water utilitycollects the country’s wastewater, cleansit to pristine levels, and returns it to thepublic supply. Singapore has thus shortcircuitedthe water cycle by reducing it toan island-ringing loop.At first, no one relished the idea ofdrinking wastewater. Rejuvenatingthe waste stream requires electricityto power an intensive cleaning process,and that investment makes the recycledwater more expensive than what’s usedby cities blessed with nearby freshwaterlakes, rivers, and aquifers. But presentedwith a set of tough choices, Singaporechose water recycling—and so far it hasworked admirably.W h e N S i N g a P o r e F i N a l ly S e Pa r at e dfrom Britain and then Malaysia in the1960s, water was at the top of the agenda.The government negotiated two treatieswith its mainland neighbor to guarantee awater supply, at a cost, for the next century.With a base supply in place, the waterutility went looking for more. The agencystarted with the one resource availabler e v e r S e - o S m o S i Sm e m b r a n e Sat a n e wat e rp l a n t, ov e r S e e nb y h a r r y S e a h[ t op r ight ] , p r o d u c et h e n e wat e r S a m p l e db y c h i l d r e n.to this tropical dollop of land, its amplerainfall—some 237 centimeters a year.It built dams to interrupt the flow of itsstreams and tiny rivers and built 15 reservoirsto store rain. Such reservoirsare crucial because they stand in for thegroundwater that Singapore lacks.Then the utility did a radical thing.After half a decade of research and tests ata pilot recycling plant, Singapore’s plannersunveiled their ultimate strategy forwater security. They would force wastewaterthrough filters under high pressureto remove all microbes, viruses, andlarger impurities. The utility called itsproduct NEWater, and it called the treatmentplant a factory. With great emphasison its sparkling newness, treatedwastewater made its public debut in 2003.The real work was about to start. Oneby one, the utility cajoled its customersinto accepting the water. Manufacturerswondered what residues the water mightNEWaterTASTETESTthree choices: NeWater,bottled water fromMalaysia, and a glass filled atthe tap. your correspondentsat down to drink. theNeWater was bland toa fault, like paper madepotable. the Malaysianwater delivered a cloying aftertaste—a perplexingblend of dryer lint and berries. the drink from thetap, however, was just right.leave in their factories, but Harry Seah, theutility’s director of technology and waterquality, pointed out that NEWater wascleaner than most drinking water. “At firstI had to convince them,” Seah recalls. Butsoon enough, he had signed on the island’s12 wafer-fabrication plants and other electronicsmanufacturers, and the utilitylaid dedicated pipes to deliver NEWater.Now Systems on Silicon ManufacturingCo., which uses ultrapure water to washits silicon wafers, champions NEWater.58 nA • ieee spectrum • june 2010 spectrum.ieee.org

s p e c i a l r e p o r t n w a t e r v s. e n e r g yThe company calculated that the recycledwater’s exceeding purity saves it morethan half a million dollars a year, in partby cutting out steps in its internal waterpurificationprocess.Singapore also started priming thepublic. The prime minister drank a bottleof NEWater at a national festival, andthe crowd cheered. The subtext wasclear—patriotic Singaporeans drinkwastewater. But the rest of Singaporewas slower to follow. A parody of a popularnationalist song, “Count on Me,Singapore,” cheerily urged residents to“Drink Our Pee, Singapore.”T he queasy reac t ions of someSingaporeans didn’t deter the utility,which built four more wastewater treatmentplants and is about to increase itsNEWater production to 555 megalitersa day. By the end of this year the plantswill treat enough sewage to cover nearlya third of Singapore’s water needs.spectrum.ieee.orgFor now, only a tiny fraction of thedrinking supply is NEWater. About40 ML are blended in with the city-state’spotable water each day, equivalent to2 percent of consumption. The utility alsobuilt a seawater desalination plant thatproduces 136 ML of water each day, or a bitless than one-tenth of Singapore’s supply.The city-state has all the water it needs.N at u r e ’ s h y d r o l o g i c a l c y c l e r e l i e son sunlight to evaporate water, leavingbehind salt and other impuritiesand returning freshwater to Earth inthe form of rain and snow. But it can becapricious: Most freshwater evaporatesfrom the oceans, where it rises throughthe atmosphere and then cools to formclouds. Winds push around the clouds,driving a few of them over land, wherethey deposit a mere tenth of the world’sprecipitation, according to the U.S.Geological Survey. Singapore decided tocut the atmosphere out of the transactionand to replace evaporation with speediermechanisms—membranes.Here’s how it works: First, a treatmentplant gathers up the city’s used water andseparates out the large, easily removableimpurities. About 60 percent of the wateris released into the sea. The rest gets sentto a NEWater factory. The water enterscontaminated with bacteria, viruses, andall sorts of carbon-based particles andemerges cleaner than what flows fromjust about any tap in the world.The main tactic of the water trade isto simply push water through tiny holes—the smaller the holes, the fewer the undesirablemolecules that can sneak through.The art is to do so without sending theelectricity bill skyrocketing or cloggingup the tiny holes with grime. Here, thefirst step is to force the water through amembrane that blocks particles of up to0.2 micrometers in size, catching mostbacteria and protozoa. The membranelooks like a cylinder filled with skinny,hollow tubes. The stream flows into theporous straws. Water molecules pushthrough the pores and collect outsidethe membranes, while the larger particlescontinue traveling inside the tubes,to be disposed of separately.The water still needs to be strippedof any viruses that might be adrift in theflow. For this the partially treated streamneeds a reverse-osmosis membrane. Inone configuration, paperlike sheets ofmembrane more than a meter long aresandwiched between sheets called spacers.The stack of membranes and spacersis wound up into a cylinder, like a thickroll of wrapping paper. The core of thecylinder is an empty channel where theclean water collects.As the stream is pushed into one endof the roll, the impurities slide along thespacers and never penetrate the polymermembrane. The water molecules, however,escape through the 0.0001-µm poresand slip into the central channel.These two steps remove just abouteverything, but in a third and final step,mercury lamps generate ultraviolet-lightrays that penetrate the water. The radiationscrambles the genetic material of anybacteria and other microorganisms thatjune 2010 • IEEE Spectrum • NA 59

3. t i n y t e s t b e d s n s i n g a p o r e n d e s a l i n a t i o n n m a l t aglacier or how much rain falls duringmonsoon season. Suddenly, Singapore iswater rich. The water that falls from thesky may have once washed the streets ofParis or filled Cleopatra’s bathtub. Nowit’s augmented with some of the waterused by Harry Seah, Asit Biswas, andeverybody else in Singapore. The utilityisn’t waiting for nature to turn its usedwater fresh again—it’s letting technologydo the job.might have slipped through, destroyingtheir ability to reproduce. Now the wateris ready for the tap.t h e S i g N i F i c a N c e o F N e Wat e r i S M u c hgreater than its literal contribution indrops or buckets or liters per person.“NEWater is key to our whole strategy,”Seah says.Seah is a soft-spoken, dapper manwith a face that collapses frequentlyinto a brassy laugh. He’s been with thePublic Utilities Board for almost twodecades, and he’s seen the NEWaterproject through to maturity. “The realbeauty of NEWater is its multiplyingeffect,” he explains. What he means isthat if the utility recycles 50 percent ofits wastewater, Singapore can squeezeone more drop out of every two it desalinatesor collects from the sky. “If I canachieve 100 percent recycling, I wouldn’teven need rain,” Seah says.That’s critical, given how few optionsSingapore has. Half of the island hasalready been converted into rainwatercatchment areas, and three new reservoirswill soon bring it to two-thirds. Theother source of freshwater is Singapore’sone desalination plant, which consumesso much energy it can cover only a fractionof the overall demand.Consider the details. To remove saltfrom seawater, Seah says the treatmentplant must apply a pressure of about7 megapascals. To remove impuritiest h e m a r i n ab a r r age t u r n Sa b ay i n t o ar e S e r voi r[at le f t ]p r o t e c t e d f r o mt h e S e a [ r ight ] .from wastewater, he requires less than1 MPa. That translates directly into theenergy cost for the whole plant—morethan 4 kilowatt-hours per thousand litersof water for seawater desalination, versus0.7 kWh for NEWater. “It’s a no-brainer,”says Seah, and his eyes crinkle into alaugh. “Win, win, win!” he says.Asit Biswas, an international waterpolicyexper t who splits his timebetween the National University ofSingapore and the Third World Centerfor Water Management, in Mexico, seesSingapore as one of the few places wherethe water authorities agree with his owncontroversial position—that water scarcitysimply does not exist. What doesexist, just about everywhere, is badwater management.The problem, he says, is that peopletend to assume that water is like oil orany other fossil fuel and that it behavesaccording to the same basic economicprinciples. “But water is not oil,” hesays. “Once we use oil, it breaks downinto various components. You can’tput it back together.” Water, despiteits tendency to evaporate and trickleout of reach, doesn’t change its molecularstructure. “There is no limit tohow many times water can be reused,”Biswas points out.That simple fact radically changes theway that water is counted. What’s availableto a city or country is not just a matterof how much ice sits in a HimalayanN o t e V e r y o N e c a N B e c a J o l e d i N t odrinking recycled urine. In Queensland,Australia, and in San Diego, public opinionhas thwarted local utilities’ water-recyclingambitions. But at least three sitesin the United States—Scottsdale, Ariz.;Orange County, Calif.; and northernVirginia—purify wastewater and blend itinto their drinking water.In fact, most places reuse water—justwithout meaning to do so. According toPeter Gleick’s The World’s Water 2002–2003, each drop in the Colorado Riveris used 17 times. Similarly, residents ofLondon drink water that was dischargedfrom numerous wastewater treatmentplants upstream on the Thames.In Singapore’s case, the deliberatereuse of water has played a prominentrole in the country’s development.Seetharam Kallidaikurichi is the directorof the Institute of Water Policy at theNational University of Singapore, and heargues that Singapore’s water strategyhas been the foundation of the country’seconomic success in the last 45 years.“The evidence is beginning to emerge,”he says, “that it’s not water among manyother things but water as central, the keyto unlocking the vicious cycles of deprivationand poverty into economic successand a good quality of life.”But prioritizing water means using aconsiderable amount of energy to makeit, clean it, and move it. The question ishow to optimize the juggle of resources.Because Singapore must import some290 billion cubic feet of natural gas to runits power plants, it can be said that thecountry has merely substituted one formof dependence for another.The consequences of that dependenceare starting to hit home. Darren60 nA • ieee spectrum • june 2010 spectrum.ieee.org

s p e c i a l r e p o r t n w a t e r v s. e n e r g yILLUSTRATION: BRANDON PALACIO; MAP: ANDREW ZBIHLYJSun, an associate professor of civil andenvironmental engineering at NanyangTechnological University, in Singapore,has seen an uptick in interest in his workon energy-efficient membranes. “In mostwater engineering, people didn’t careabout how much energy goes in—untilrecently. The energy crisis made thisa critical issue,” he says. Sun is investigatinga membrane design that usestitanium-dioxide nanofibers to filter waterand generate electricity simultaneously.But the research is far from mature,so for now the energy cost will remainhigh. That’s the price Singapore mustpay for a first-rate water supply and ahealthy country, says Kallidaikurichi.“You may argue that water here consumesmore energy, but the city needsmore water, because it’s the city that’sproducing more wealth.”The solution to making the trade-offwork, say Biswas and Kallidaikurichi, ispurely economic: Singapore charges allits customers the marginal cost of water—that is, the cost of producing another liter.For Singapore, that means desalination.So the Public Utilities Board has setthe price of water to pay for its energyintensiveoperations.As a result, the utility has enough cashto investigate new technologies. Seahwould like to cut the energy needed fordesalination by more than half, to 1.5 kWhper thousand liters, and the energy forNEWater to 0.4 kWh from 0.7 kWh.He ’s opt i m ist ic. A f ter a l l, t heNEWater processes would have consumedmore energy per liter had hisengineers not experimented with them.“The technologies came from everywhere,but I think our value is in how weexploit them,” Seah says. “How we putthem together. How we wrote the software.How we operate the plants.”For example, he and his colleaguesfound a way to introduce a bit of chloramine,a disinfectant, into the membranefi lt r at ion pro cess. T hat add it ionprevents the pores from clogging withoutdegrading the membrane material—achallenge that had stymied theindustry for some time. Clogged poresmean more pressure to drive the waterthrough, with a larger electricity bill asa result. Similarly, the utility’s engineershave found a way to use less pressurein operating a membrane bioreactor, amachine containing swarms of microorganismsthat snack on contaminantsin the water. That innovation will soonreplace the first filtration step, makingNEWater about 20 percent cheaper toproduce, Seah says.Other innovations are likely to trickleout of Singapore’s water sector, as companiesand academics seek to profitfrom the water utility’s interest in innovation.For example, researchers underSay Leong Ong, acting head of the environmentalsciences and engineeringdivision at the National University ofSingapore, are figuring out the mechanismsused by mangrove trees andtilapia fish to process the salt in seawater,with the hope of one day designingmembranes that mimic nature.Ultimately, Singapore will have truewater security only if it can reduce itsdependence on imported energy. A civilization’ssurplus energy, arising fromits trade and technological prowess, isReservoirsNEWater Plant77 ML/dayWater importedfrom MalaysiaPoweredByCrazyFree eNergy? uriNe lucK!you may not think of urine as avaluable resource—quite theopposite, probably—but ohiouniversity chemical engineergerardine Botte has come upwith a way to harness it forgood. Botte’s technologyefficiently produceshydrogen for fuel-cellpoweredcars, from urine.dry out that urine and you’re left with acompound called urea, a single molecule ofwhich contains four hydrogen atoms. thebonds that bind urea’s hydrogen are mucheasier to break than the hydrogen bonds inwater, which is typically used as the sourcefor hydrogen in fuel cells. experimentingwith human urine, Botte showed thatapplying a mere 0.37 volt did the trick,much less than the 1.23 V required to splitwater. What’s more, urea yields twice asmuch hydrogen per molecule.Botte’s research might lead to cheaperhydrogen for fuel cells as well as cheaperwastewater purification: a scaled-up versionof the technology could generate hydrogenwhile treating sewage.—Sally Adeewhat allows an economy to shift investmentaway from life-critical needs such aswater to education, art, and a rich civic life.An energy-secure water sector, then, willbe a major question for the next 50 yearsof the tiny island’s nationhood. ❏NEWater Plant23 ML/dayPacificO ceanI n d I aArea ofdetailC h I n aNOT JUSTTOILETS...NEWaterplants andreservoirsdot the island, providing anengineered stand-in for thegroundwater Singapore lacks.DesalinationPlantSouth TunnelSewerage System(incomplete)NEWater Plant145 ML/dayNorth TunnelSewerage SystemNEWater Plant82 ML/dayNEWater Plant227 ML/dayspectrum.ieee.orgieee spectrum • nA 61