Wizards of the water cycle

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