An off-grid desalination technology that combines membrane distillation with light-harvesting nanophotonics is being developed by the Centre for Nanotechnology Enabled Water Treatment (NEWT) at Rice University.

 

Video: NEWT Centre will use nanotechnology to transform water treatment.

NEWT’s ‘nanophotonics-enabled solar membrane distillation’ technology, or NESMD, is described in an article in the Proceedings of the National Academy of Sciences (PNAS).
Direct solar desalination

More than 18,000 desalination plants operate in 150 countries, but NEWT says its desalination technology is unlike any other used today.

“Direct solar desalination could be a game changer for some of the estimated 1 billion people who lack access to clean drinking water,” says Rice scientist and water treatment expert Qilin Li, a corresponding author on the study. “This off-grid technology is capable of providing sufficient clean water for family use in a compact footprint, and it can be scaled up to provide water for larger communities.”

The oldest method for making freshwater from salt water is distillation, the research team explains. Salt water is boiled, and the steam is captured and run through a condensing coil. However, distillation requires complex infrastructure and is energy inefficient due to the amount of heat required to boil water and produce steam. More than half the cost of operating a water distillation plant is for energy.

Membrane distillation is an emerging technology for desalination. Hot salt water is flowed across one side of a porous membrane and cold freshwater is flowed across the other. Water vapour is naturally drawn through the membrane from the hot to the cold side. Because the seawater does not need to be boiled, the energy requirements are less than for traditional distillation, but still significant because heat is continuously lost from the hot side of the membrane to the cold.

“Unlike traditional membrane distillation, NESMD benefits from increasing efficiency with scale,” explains Rice’s Naomi Halas, a corresponding author on the paper and the leader of NEWT’s nanophotonics efforts. “It requires minimal pumping energy for optimal distillate conversion, and there are a number of ways we can further optimise the technology to make it more productive and efficient.”

NEWT’s new technology builds upon research in Halas’ lab to create engineered nanoparticles that harvest as much as 80% of sunlight to generate steam. By adding low-cost, commercially available nanoparticles to a porous membrane, NEWT has essentially turned the membrane into a one-sided heating element that heats the water to drive membrane distillation.

“The integration of photothermal heating capabilities within a water purification membrane for direct, solar-driven desalination opens new opportunities in water purification,” says Yale University ‘s Menachem ‘Meny’Elimelech, a co-author of the new study and NEWT’s lead researcher for membrane processes.
Modular system

In the PNAS study, researchers offered proof-of-concept results based on tests with an NESMD chamber about the size of three postage stamps and just a few millimetres thick. The distillation membrane in the chamber contained a specially designed top layer of carbon black nanoparticles infused into a porous polymer. The light-capturing nanoparticles heated the entire surface of the membrane when exposed to sunlight. A thin half-millimetre-thick layer of salt water flowed atop the carbon-black layer, and a cool freshwater stream flowed below.

Li says the water production rate increased greatly by concentrating the sunlight. “The intensity got up 17.5 kW/m2 when a lens was used to concentrate sunlight by 25 times, and the water production increased to about 6 l/m2 per hour.”

The NEWT team has already made a much larger system that contains a panel that is about 70 cm by 25 cm. Ultimately, they hope to produce a modular system where users could order as many panels as they needed based on daily water demands.

“You could assemble these together, just as you would the panels in a solar farm,” Li says. “Depending on the water production rate you need, you could calculate how much membrane area you would need. For example, if you need 20 l/hr, and the panels produce 6 l/hr per m2, you would order a little over 3 m2 of panels.”

Additional information:

In conventional membrane distillation (top image), hot saltwater is flowed across one side of a porous membrane and cold freshwater is flowed across the other. Water vapour is naturally drawn through the membrane from the hot to the cold side. In NEWT’s nanotechnology-enabled solar membrane distillation (lower image), a porous layer of sunlight-activated carbon black nanoparticles acts as the heating element for the process. (Image courtesy of P. Dongare/Rice University.)

 

Article Source: http://www.filtsep.com/view/46050/direct-solar-desalination-offers-modular-off-grid-water-treatment/

 

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Most fine filtration is measured in microns

Micrometer (micron) is a metric unit of measurement denoting one millionth of a meter. To give you some idea of how fine a micron is, consider that the smallest particle visible to the unaided human eye is about forty microns (you can see smaller particles through light diffraction).

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There are a few rules to remember when sizing a filtration system:

  • With in-depth cartridge filters, the slower the flow, the more efficient the cartridge is and the longer the user can go between change-outs. At Filters.com, we typically size housings to start out with a clean differential pressure of two pounds or less. You will find that many people in the filter business will quote housings that are undersized for an application so that they quote the lowest capital equipment cost.

 

  • The differential pressure (pressure drop) across both the cartridge and housing must be considered cumulatively. The pressure drop across the housing differs from housing to housing, but in most cases, it can be obtained from the housing manufacturer.

 

  • Assuming a cartridge vessel is designed for cartridges with a one-inch inside diameter, keep in mind that the flow through the bottom of each filter should not exceed 15-25 gallons per minute (for membrane pre-filters, try not to exceed 15 gpm). These flow rates should not be exceeded because turbulent flow is created on the interior core of the filter, which frequently cause unloading of contaminant from the filter media.

 

  • Always consider the viscosity of the material to be filtered when sizing filters or vessels. Also keep in mind that the viscosity of most materials varies depending on temperature. If you have an application where the customer does not want to go over a certain differential pressure and the temperature of the product can go through a wide swing, be careful to find out what the viscosity of the liquid is at both extremes of temperature.

 

Copyright 2008 Barney Corporation, Inc… www.Filters.com… Info@Filters.com…1.614.274.9069

 

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Particles to be filtered usually fall into one of two categories:

 

 

1.Non-deformable particles that under normal conditions (temperatures) do not deform. In some instances, non-deformable particles can become deformable with a temperature or chemistry change—an example of this would is a particle of resin, which at ambient temperatures may be solid, but at elevated temperatures turns liquid.

2. Deformable particles (frequently called gels) that deform when put under pressure. The amount of pressure needed to deform gels varies depending on the specific gel/particle. With deformable particles, if enough pressure is applied, the gel will deform, push out through the filter, and frequently re-agglomerate on the downstream side of the filter. Sometimes, when the particle re-agglomerates, it is larger than could be seen on the upstream side due to coalescence that may have occurred in the filter. In some instances, deformable particles can become non-deformable due to changes in temperature, chemistry, or other conditions.

Copyright 2008 Barney Corporation, Inc… www.Filters.com… Info@Filters.com…1.614.274.9069

 

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