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The two researchers coated the scrap metal with copper to improve its effectiveness, then ran lab experiments and conducted a successful pilot test at the Taopu plant. The city of Shanghai approved construction of a full-scale reactor with 2 million pounds of iron shavings, the largest test in history to use iron in an environmental application. The results were immediately positive. When the ZVI reactor was connected to the existing biological treatment plant, removal rates improved for biological oxygen demand, nitrogen, phosphorus, and colors and dyes.
The “green” iron, Zhang reported in an article published by The Economist in November 2008, enhanced the treatability of the industrial wastewater by reducing the toxicity and increasing the biodegradability of recalcitrant organic compounds.
“This project,” he says, “has uncovered a fascinating use for recycled materials.”
Extracting value from scum
Not far from the Taopu Industrial District, in the delta of the lower Yangtze River, lies Lake Tai, third-largest body of fresh water in China. The lake’s misty vistas and peaceful waters have inspired centuries of artists. Millions of Chinese depend on the lake for food – rice, fish and world-famous crab and shrimp – and for drinking water.
Today, much of Lake Tai is veiled in green, covered from April to October with algae feeding on agricultural, municipal and industrial wastes. Two million people, The New York Times recently reported, have had to stop using water from the lake, and stench from the algae can be smelled a mile from Tai’s shores.
In the past two years, Zhang has helped the city of Wuxi build a $25-million plant that filters and recovers 45,000 pounds of algae a day from Lake Tai. The goal is to develop new technologies that utilize algae. Possible uses range from organic fertilizer to diesel fuel to methane, and from pharmaceutical compounds to insecticides to fungicides. The organism could even be converted into a tofu-like food.
Nanoparticles of solid peroxide, a whitening agent in toothpaste, transform oil into water-soluble fats and alcohols.
The government invited Zhang to take part in the project in hopes that his iron-based nanoparticles would help remove algae from Lake Tai. But the nanoparticles proved too expensive for the size of the job. As he had with the Taopu wastewater project, Zhang came up with a homegrown technology. Nanoparticles of clay, he found, neutralize the electric charge that causes algae particles to shun each other, thus allowing the algae to aggregate into clumps that can be skimmed from the water.
“Algae is a strange organism,” says Zhang. “It is 10 to 100 microns in size, and its density is nearly identical to that of water. So it is very difficult to separate from water.
“The clay gives the algae a life-preserver vessel. And it’s literally dirt cheap.”
A peroxide’s double life
Back in Hoboken, Zhang watches as technicians use a hydraulic machine to drill 3-inch holes to a depth of 40 to 50 feet in the soil around the corroded heating oil tank. The workers have mixed Zhang’s nanoparticles into a granular slurry for easier injection. They are drilling 10 holes in front of the house today and will drill another dozen tomorrow through the basement, where heating oil has also leaked. Altogether, the workers will inject 600 pounds of the slurry through the holes. They will finish the job in two days. In three weeks, the New Jersey Department of Environmental Protection will inspect the soil and groundwater.
For this job, Zhang is using nanoparticles of a solid peroxide – the whitening agent in most toothpastes. The particles are more than 1,000 times smaller than those in Colgate. Instead of dissolving coffee stains, they transform oil’s long hydrocarbon chains into water-soluble fats and alcohols. Zhang developed the nano-peroxide three years ago and has used it to remediate the soil beneath oil storage tanks at gas stations. Recently, he and his students showed in the lab that the nanoparticles can quickly break up oil spilled into water bodies like the Gulf of Mexico and the Bohai Sea off China’s coast.
“Guys, we have something special today,” Zhang says as he opens the trunk of his car. He lifts out two white five-gallon pails and carries them to the engineers operating a hydraulic drill. The pails contain a catalyst he believes will make the peroxide nanoparticles more reactive.
Zhang does not reveal the composition of the catalyst, except to say that it contains four or five materials.
“I’ll let you know,” he says, “when I get it patented.”