Plastic islands being used to restore African lake

One of the BioHaven Floating Islands, from a previous project

As the ever-growing giant flotilla of floating refuse known as the Great Pacific Garbage Patch will show us, we shouldn't be putting plastic waste in our waterways. A new project, however, is aimed at helping the environment by doing so ... in a roundabout way of speaking. The participants plan on taking several artificial floating islands made from post-consumer plastic, planting papyrus on them, and then using them to help rebuild the ecosystem of Africa’s Lake Naivasha.
Located in Kenya’s Rift Valley, the lake was crystal clear 30 years ago. Since then, a 20-fold increase in the local human population, along with foraging activity by water buffalo native to the region, has resulted in massive clearing of the lakeshore papyrus plants.
Like other aquatic plants, papyrus serve a vital role. Acting as biofilters, they trap suspended sediments, plus they remove toxic substances and excess nutrients from the water. Unfortunately, the destruction of much of the lake’s papyrus plants has led to a marked decline in its water quality.

One of the last stands of papyrus along Lake Naivasha (Photo: University of Leicester)

The restoration project is being funded by the German REWE Group. It involves the participation of UK tea producer and flower grower Finlays (which grows flowers in the region), and is being led by Dr. David Harper, a senior lecturer at the University of Leicester.
The team plan on introducing a new population of papyrus to the lake, at a spot where silty water from the Malewa River enters into it. Those papyrus will be planted on a series of BioHaven Floating Islands, made from recycled polyester drink bottles by North Carolina-based Floating Island Southeast.
Each BioHaven island is essentially a floating mat, made up of multiple layers of a plastic matrix bonded together with marine-grade foam. This provides a highly buoyant surface for plants to grow on, while allowing their roots (which dangle beneath the island) to both act as a sediment filter, and as a home for aquatic microbes. Those microbes feed on nutrients that might otherwise lead to excess algae growth – a service also provided by the plants themselves.
Additionally, the roots should serve as feeding grounds and nurseries for fish, while the five meter (16 foot)-tall stalks of the plants should make a good habitat for birds.
The islands have been ordered, and will be anchored in place once the papyrus is planted on them. If they prove successful at their first location, additional islands will be installed at other locations along the lake shore.
Sources: University of Leicester, Floating Island Southeast

World’s most efficient thermoelectric material developed

Thermoelectrics can be used to convert energy currently lost as heat wasted from industry and vehicle tailpipes into electricity

Approximately 90 percent of the world’s electricity is generated by heat energy. Unfortunately, electricity generation systems operate at around 30 to 40 percent efficiency, meaning around two thirds of the energy input is lost as waste heat. Despite this, the inefficiency of current thermoelectric materials that can convert waste heat to electricity has meant their commercial use has been limited. Now researchers have developed a thermoelectric material they claim is the best in the world at converting waste heat into electricity, potentially providing a practical way to capture some of the energy that is currently lost.
The new material, which is based on the common semiconductor telluride, is environmentally stable and is expected to convert from 15 to 20 percent of waste heat to electricity. The research team, made up of chemists, material scientists and mechanical engineers from Northwestern University and Michigan State University, say the material exhibits a thermoelectric figure of merit (or “ZT”) of 2.2, which they claim is the highest reported to date.
The higher a material’s ZT, the more efficient it is at converting heat to electricity. While there’s no theoretical upper limit to ZT, no known materials exhibit a ZT higher than 3. The researchers believe with a ZT of 2.2, the new material is efficient enough to be used in practical applications and could usher in more widespread adoption of thermoelectrics by industry.
"Our system is the top-performing thermoelectric system at any temperature," said Mercouri G. Kanatzidis, who led the research. "The material can convert heat to electricity at the highest possible efficiency. At this level, there are realistic prospects for recovering high-temperature waste heat and turning it into useful energy."
With the huge potential for thermoelectrics to recover some of the heat energy that is currently lost, they have been the focus of much research that has seen them improve significantly in recent years. So much so that the Mars rover Curiosity features lead telluride thermoelectrics, although its system only has a ZT of 1. BMW is also testing systems to harvest the heat from the exhaust systems and combustion engines of its cars.
Aside from capturing some of the wasted heat energy emitted through a vehicle’s tailpipe, the new material could be used in heavy manufacturing industries, including glass and brick making, refineries, and coal- and gas-fired power plants, and on large ships and tankers, where large combustion engines operate continuously. Such applications are seen as ideal as the waste heat temperatures in these areas can range from 400 to 600 degrees Celsius (750 to 1,100 degrees Fahrenheit),which is the sweet spot for thermoelectrics use.
The team’s paper describing the development of the new material is published in the journal Nature.
Source: Northwestern University

MIT researchers devise technique to clean up oil spills using magnets

The oil and water separation technique uses permanent magnets immersed in a reservoir containing oil and water

Possibly the only good thing to come out of the Deepwater Horizon disaster is the subsequent increase in research into finding more effective ways to clean up oil spills, including such initiatives as the X PRIZE Foundation's Wendy Schmidt Oil Cleanup X CHALLENGE. Joining the list is a new method devised by researchers at MIT who propose separating oil and water using magnets. The new technique would allow the oil to be recovered to help offset the costs of the cleanup operation.
Oil isn’t magnetic, but suspending magnetic nanoparticles within the oil turns it into a magnetic liquid known as a ferrofluid. Previous research efforts using ferrofluids typically involved pumping a water-and-ferrofluid mixture through a channel with magnets on the outside directing the flow of the water one way and the flow of the ferrofluid another. However, this technique will work only if the concentration of the ferrofluid is known beforehand and remains constant – neither of which is possible in water contaminated by an oil spill.
For their approach, the MIT researchers made two modifications to the existing method. Instead of placing the magnets on the outside of the stream, they were immersed within it, and instead of being oriented parallel to the flow of the stream, they run perpendicular to it.
Because the magnetic field of the cylindrical permanent magnets used by the MIT team is strongest at its edges, the oil is attracted to the tips of the magnets much more strongly than the sides. And as the bottoms of the cylindrical magnets were embedded under the waterline in the base of a reservoir and the tops of the magnets were positioned above water level, the oil didn’t collect around them. Rather, it shot up the sides of the magnets to form beaded spheres at the top.
Shahriar Khushrushahi, a postdoc in MIT’s Department of Electrical Engineering and Computer Science and lead author on a paper describing the approach says the technique provides excellent separation between oil and water. Additionally, its simplicity makes it feasible for large scale manufacture and deployment at sea for days or weeks a a time, where electrical power and maintenance facilities are limited.
While the team is yet to determine the most practical way to remove the oil from the magnets in an actual oil-recovery system, in their experiments they used a Halbach array. This is a special arrangement of permanent magnets where the magnetic field on one side is augmented, while the magnetic field on the other side is canceled out to near zero. This allowed the oil in the reservoir to remain unattracted to the bottom of the array, while the oil attached to the magnets was pulled off by the top of the array.
The team says that adding magnetic nanoparticles to oil mixed with water to produce a ferrofluid aboard a ship is not a challenge. Additionally, removing the nanoparticles can be achieved using a technique known as high-gradient magnetic separation. This has been done on a small scale and would allow the recovery of both the nanoparticles and the oil.
One remaining challenge is to determine how much water gets dissolved in the oil and the best way to remove it. “To our eye, you don’t see much moisture in there, but I’m sure that there is some moisture that adheres to it,” says team member Markus Zahn. “We might have to run it through multiple cycles.”
On a commercial scale, the magnetic separation method could be used in conjunction with existing oil recovery techniques such as skimming, which would perform an initial separation. The magnetic separation technique could then be used to finish the job.
The research team will present a paper detailing their work at the 13th International Conference on magnetic Fields (ICMF13) being held in New Delhi, India, in January 2013. The team has also filed two patents on its work.
MIT researchers Zahn and Khushrushahi explain the magnetic separation technique in the video below.
Source: MIT