rexresearch.com
Naomi
HALAS, et al.
Nanoparticle Solar Steam
Nanoparticle Solar Steam
1. David Brown : Making steam without boiling water, thanks to nanoparticles
2. Jade Boyd : Off-grid sterilization with Rice U.’s ‘solar steam’
3. Jade Boyd : Rice unveils super-efficient solar-energy technology
4. Oara Neumann, et al. : Solar Vapor Generation Enabled by Nanoparticles
5. YouTube : Researchers create solar steam using nanoparticles at Rice University
6. Zheyu Fang, et al. : Evolution of Light-Induced Vapor Generation at a Liquid-Immersed Metallic Nanoparticle
7. YouTube : Solar-Powered Steam Generation -- Solar steam used to clean human waste in the developing world
8. Oara Neumann, et al, : Compact solar autoclave based on steam generation using broadband light-harvesting nanoparticles
9. Patents
http://www.washingtonpost.com/national/health-science/making-steam-without-boiling-water-thanks-to-nanoparticles/2012/11/19/3d98c4d6-3264-11e2-9cfa-e41bac906cc9_story.html
Making
steam without boiling water, thanks to nanoparticles
By David Brown
By David Brown
It is possible to create steam within seconds by focusing sunlight on nanoparticles mixed into water, according to new research.
That observation, reported Monday by scientists at Rice University in Texas, suggests myriad applications in places that lack electricity or burnable fuels. A sun-powered boiler could desalinate sea water, distill alcohol, sterilize medical equipment and perform other useful tasks.
"We can build a portable, compact steam generator that depends only on sunlight for input. It is something that could really be good in remote or resource-limited locations," said Naomi J. Halas, an engineer and physicist at Rice who ran the experiment.
Whether the rig she and her colleagues describe would work on an industrial scale is unknown. If it does, it could mark an advance for solar-powered energy more generally.
"We will see how far it can ultimately go. There are certainly places and situations where it would be valuable to generate steam," said Paul S. Weiss, editor of the American Chemical Society's journal ACS Nano, which published the paper online in advance of the journalís December print publication.
The experiment is more evidence that nanoscale devices -- in this case, beads one-tenth the diameter of a human hair -- behave in ways different from bigger objects.
In the apparatus designed by the Rice team, steam forms in a vessel of water long before the water becomes warm to the touch. It is, in effect, possible to turn a container of water into steam before it gets hot enough to boil.
"There is a disconnect between what happens when we heat a pot of water and what happens when we put nanoparticles in that water," said Weiss, who is a chemist and director of the California Nanosystems Institute at UCLA.
"This is a novel proposed application of nanoparticles," said A. Paul Alivisatos, director of the Lawrence Berkeley National Laboratory and a nanotechnology expert. ìI think it is very interesting and will stimulate a lot of others to think about the heating of water with sunlight."
In the Rice experiment, the researchers stirred a small amount of nanoparticles into water and put the mixture into a glass vessel. They then focused sunlight on the mixture with a lens.
The nanoparticles -- either carbon or gold-coated silicon dioxide beads -- have a diameter shorter than the wavelength of visible light. That allows them to absorb most of a wave of light's energy. If they had been larger, the particles would have scattered much of the light.
In the focused light, a nanoparticle rapidly becomes hot enough to vaporize the layer of water around it. It then becomes enveloped in a bubble of steam. That, in turn, insulates it from the mass of water that, an instant before the steam formed, was bathing and cooling it.
Insulated in that fashion, the particle heats up further and forms more steam. It eventually becomes buoyant enough to rise. As it floats toward the surface, it hits and merges with other bubbles.
At the surface, the nanoparticles-in-bubbles release their steam into the air. They then sink back toward the bottom of the vessel. When they encounter the focused light, the process begins again. All of this occurs within seconds.
In all, about 80 percent of the light energy a nanoparticle absorbs goes into making steam, and only 20 percent is "lost" in heating the water. This is far different from creating steam in a tea kettle. There, all the water must reach boiling temperature before an appreciable number of water molecules fly into the air as steam.
The phenomenon is such that it is possible to put the vessel containing the water-and-nanoparticle soup into an ice bath, focus light on it and make steam.
"It shows you could make steam in an arctic environment," Halas said. "There might be some interesting applications there."
The apparatus can also separate mixtures of water and other substances into their components -- the process known as distillation -- more completely than is usually possible. For example, with normal distillation of a water-and-alcohol mixture, it isn't possible to get more than 95 percent pure alcohol. Using nanoparticles to create the steam, 99 percent alcohol can be collected.
Halas said the nanoparticles are not expensive to make and, because they act essentially as catalysts, are not used up. A nanoparticle steam generator could be used over and over. And, as James Watt and other 18th-century inventors showed, if you can generate steam easily, you can create an industrial revolution.
The research is being funded in part by the Bill & Melinda Gates Foundation in the hope it might prove useful to developing countries. Halas and her team recently spent three days in Seattle demonstrating the apparatus.
"Luckily," she said, "it was sunny."
The solar steam device developed at Rice University has an overall energy efficiency of 24 percent, far surpassing that of photovoltaic solar panels.
It may first be used in sanitation and water-purification applications in the developing world. Photo by Jeff Fitlow
... But how to deal with
residual solids fouling the system ? Hunh ? Eh ?
Riddle me that ...
http://news.rice.edu/2013/07/22/off-grid-sterilization-with-rice-u-s-solar-steam-2/
July 22, 2013
Off-grid
sterilization with Rice U.’s ‘solar steam’
by
Jade Boyd
Solar-powered sterilization technology supported by Gates Foundation
by
Jade Boyd
Solar-powered sterilization technology supported by Gates Foundation
Rice University nanotechnology researchers have unveiled a solar-powered sterilization system that could be a boon for more than 2.5 billion people who lack adequate sanitation. The “solar steam” sterilization system uses nanomaterials to convert as much as 80 percent of the energy in sunlight into germ-killing heat.
The technology is described online in a July 8 paper in the Proceedings of the National Academy of Sciences Early Edition. In the paper, researchers from Rice’s Laboratory for Nanophotonics (LANP) show two ways that solar steam can be used for sterilization — one setup to clean medical instruments and another to sanitize human waste.
“Sanitation and sterilization are enormous obstacles without reliable electricity,” said Rice photonics pioneer Naomi Halas, the director of LANP and lead researcher on the project, with senior co-author and Rice professor Peter Nordlander. “Solar steam’s efficiency at converting sunlight directly into steam opens up new possibilities for off-grid sterilization that simply aren’t available today.”
In a previous study last year, Halas and colleagues showed that “solar steam” was so effective at direct conversion of solar energy into heat that it could even produce steam from ice water.
“It makes steam directly from sunlight,” she said. “That means the steam forms immediately, even before the water boils.”
Halas, Rice’s Stanley C. Moore Professor in Electrical and Computer Engineering, professor of physics, professor of chemistry and professor of biomedical engineering, is one of the world’s most-cited chemists. Her lab specializes in creating and studying light-activated particles. One of her creations, gold nanoshells, is the subject of several clinical trials for cancer treatment.
Oara Neumann and Naomi Halas -- Rice University graduate student Oara Neumann, left, and scientist Naomi Halas are co-authors of a new study about a highly efficient method of turning sunlight into heat. They expect their technology to have an initial impact as an ultra-small-scale system to treat human waste in developing nations without sewer systems or electricity. Photo by Jeff Fitlow
Solar steam’s efficiency comes from light-harvesting nanoparticles that were created at LANP by Rice graduate student Oara Neumann, the lead author on the PNAS study. Neumann created a version of nanoshells that converts a broad spectrum of sunlight — including both visible and invisible bandwidths — directly into heat. When submerged in water and exposed to sunlight, the particles heat up so quickly they instantly vaporize water and create steam. The technology has an overall energy efficiency of 24 percent. Photovoltaic solar panels, by comparison, typically have an overall energy efficiency of around 15 percent.
When used in the autoclaves in the tests, the heat and pressure created by the steam were sufficient to kill not just living microbes but also spores and viruses. The solar steam autoclave was designed by Rice undergraduates at Rice’s Oshman Engineering Design Kitchen and refined by Neumann and colleagues at LANP. In the PNAS study, standard tests for sterilization showed the solar steam autoclave could kill even the most heat-resistant microbes.
“The process is very efficient,” Neumann said. “For the Bill & Melinda Gates Foundation program that is sponsoring us, we needed to create a system that could handle the waste of a family of four with just two treatments per week, and the autoclave setup we reported in this paper can do that.”
Halas said her team hopes to work with waste-treatment pioneer Sanivation to conduct the first field tests of the solar steam waste sterilizer at three sites in Kenya.
“Sanitation technology isn’t glamorous, but it’s a matter of life and death for 2.5 billion people,” Halas said. “For this to really work, you need a technology that can be completely off-grid, that’s not that large, that functions relatively quickly, is easy to handle and doesn’t have dangerous components. Our Solar Steam system has all of that, and it’s the only technology we’ve seen that can completely sterilize waste. I can’t wait to see how it performs in the field.”
Paper co-authors include Curtis Feronti, Albert Neumann, Anjie Dong, Kevin Schell, Benjamin Lu, Eric Kim, Mary Quinn, Shea Thompson, Nathaniel Grady, Maria Oden and Nordlander, all of Rice. The research was supported by a Grand Challenges grant from the Bill & Melinda Gates Foundation and by the Welch Foundation.
http://news.rice.edu/2012/11/19/rice-unveils-super-efficient-solar-energy-technology-2/
November 19, 2012
Rice
unveils super-efficient solar-energy technology
by
Jade Boyd
‘Solar steam’ so effective it can make steam from icy cold water
by
Jade Boyd
‘Solar steam’ so effective it can make steam from icy cold water
Rice University scientists have unveiled a revolutionary new technology that uses nanoparticles to convert solar energy directly into steam. The new “solar steam” method from Rice’s Laboratory for Nanophotonics (LANP) is so effective it can even produce steam from icy cold water.
Details of the solar steam method were published online today in ACS Nano. The technology has an overall energy efficiency of 24 percent. Photovoltaic solar panels, by comparison, typically have an overall energy efficiency around 15 percent. However, the inventors of solar steam said they expect the first uses of the new technology will not be for electricity generation but rather for sanitation and water purification in developing countries.
Rice University graduate student Oara Neumann, left, and scientist Naomi Halas are co-authors of new research on a highly efficient method of turning sunlight into heat. They expect their technology to have an initial impact as an ultra-small-scale system to treat human waste in developing nations without sewer systems or electricity. Photo by Jeff Fitlow
“This is about a lot more than electricity,” said LANP Director Naomi Halas, the lead scientist on the project. “With this technology, we are beginning to think about solar thermal power in a completely different way.”
The efficiency of solar steam is due to the light-capturing nanoparticles that convert sunlight into heat. When submerged in water and exposed to sunlight, the particles heat up so quickly they instantly vaporize water and create steam. Halas said the solar steam’s overall energy efficiency can probably be increased as the technology is refined.
“We’re going from heating water on the macro scale to heating it at the nanoscale,” Halas said. “Our particles are very small — even smaller than a wavelength of light — which means they have an extremely small surface area to dissipate heat. This intense heating allows us to generate steam locally, right at the surface of the particle, and the idea of generating steam locally is really counterintuitive.”
To show just how counterintuitive, Rice graduate student Oara Neumann videotaped a solar steam demonstration in which a test tube of water containing light-activated nanoparticles was submerged into a bath of ice water. Using a lens to concentrate sunlight onto the near-freezing mixture in the tube, Neumann showed she could create steam from nearly frozen water.
Steam is one of the world’s most-used industrial fluids. About 90 percent of electricity is produced from steam, and steam is also used to sterilize medical waste and surgical instruments, to prepare food and to purify water.
Most industrial steam is produced in large boilers, and Halas said solar steam’s efficiency could allow steam to become economical on a much smaller scale.
People in developing countries will be among the first to see the benefits of solar steam. Rice engineering undergraduates have already created a solar steam-powered autoclave that’s capable of sterilizing medical and dental instruments at clinics that lack electricity. Halas also won a Grand Challenges grant from the Bill and Melinda Gates Foundation to create an ultra-small-scale system for treating human waste in areas without sewer systems or electricity.
“Solar steam is remarkable because of its efficiency,” said Neumann, the lead co-author on the paper. “It does not require acres of mirrors or solar panels. In fact, the footprint can be very small. For example, the light window in our demonstration autoclave was just a few square centimeters.”
Another potential use could be in powering hybrid air-conditioning and heating systems that run off of sunlight during the day and electricity at night. Halas, Neumann and colleagues have also conducted distillation experiments and found that solar steam is about two-and-a-half times more efficient than existing distillation columns.
Halas, the Stanley C. Moore Professor in Electrical and Computer Engineering, professor of physics, professor of chemistry and professor of biomedical engineering, is one of the world’s most-cited chemists. Her lab specializes in creating and studying light-activated particles. One of her creations, gold nanoshells, is the subject of several clinical trials for cancer treatment.
For the cancer treatment technology and many other applications, Halas’ team chooses particles that interact with just a few wavelengths of light. For the solar steam project, Halas and Neumann set out to design a particle that would interact with the widest possible spectrum of sunlight energy. Their new nanoparticles are activated by both visible sunlight and shorter wavelengths that humans cannot see.
“We’re not changing any of the laws of thermodynamics,” Halas said. “We’re just boiling water in a radically different way.”
Paper co-authors include Jared Day, graduate student; Alexander Urban, postdoctoral researcher; Surbhi Lal, research scientist and LANP executive director; and Peter Nordlander, professor of physics and astronomy and of electrical and computer engineering. The research was supported by the Welch Foundation and the Bill and Melinda Gates Foundation.
ACS Nano, 2013, 7 (1), pp 42–49
DOI: 10.1021/nn304948h
November 19, 2012
Solar
Vapor Generation Enabled by Nanoparticles
Oara Neumann, Alexander S. Urban, Jared Day, Surbhi Lal, Peter Nordlander, and Naomi J. Halas
Oara Neumann, Alexander S. Urban, Jared Day, Surbhi Lal, Peter Nordlander, and Naomi J. Halas
Solar illumination of broadly absorbing metal or carbon nanoparticles dispersed in a liquid produces vapor without the requirement of heating the fluid volume. When particles are dispersed in water at ambient temperature, energy is directed primarily to vaporization of water into steam, with a much smaller fraction resulting in heating of the fluid. Sunlight-illuminated particles can also drive H2O–ethanol distillation, yielding fractions significantly richer in ethanol content than simple thermal distillation. These phenomena can also enable important compact solar applications such as sterilization of waste and surgical instruments in resource-poor locations.
https://www.youtube.com/watch?v=ved0K5CtmsU
Nov 19, 2012
Researchers
create solar steam using nanoparticles at Rice University
Rice University scientists have unveiled a revolutionary new technology that uses nanoparticles to convert solar energy directly into steam. The new "solar steam" method from Rice's Laboratory for Nanophotonics is so effective it can even produce steam from icy cold water. Details of the solar steam method were published online today in ACS Nano. The technology's inventors said they expect it will first be used in sanitation and water-purification applications in the developing world.
http://pubs.acs.org/doi/abs/10.1021/nl4003238
Nano Lett. 2013, 13, 1736-1742
Evolution
of Light-Induced Vapor Generation at a Liquid-Immersed
Metallic Nanoparticle.
Zheyu Fang, Yu-rong Zhen, Oara Neumann, Albert Polman, F. Javier Garcia de Abajo, Peter Nordlander, and Naomi J. Halas.
Zheyu Fang, Yu-rong Zhen, Oara Neumann, Albert Polman, F. Javier Garcia de Abajo, Peter Nordlander, and Naomi J. Halas.
When an Au nanoparticle in a liquid medium is illuminated with resonant light of sufficient intensity, a nanometer scale envelope of vapor—a “nanobubble”—surrounding the particle, is formed. This is the nanoscale onset of the well-known process of liquid boiling, occurring at a single nanoparticle nucleation site, resulting from the photothermal response of the nanoparticle. Here we examine bubble formation at an individual metallic nanoparticle in detail. Incipient nanobubble formation is observed by monitoring the plasmon resonance shift of an individual, illuminated Au nanoparticle, when its local environment changes from liquid to vapor. The temperature on the nanoparticle surface is monitored during this process, where a dramatic temperature jump is observed as the nanoscale vapor layer thermally decouples the nanoparticle from the surrounding liquid. By increasing the intensity of the incident light or decreasing the interparticle separation, we observe the formation of micrometer-sized bubbles resulting from the coalescence of nanoparticle-“bound” vapor envelopes. These studies provide the first direct and quantitative analysis of the evolution of light-induced steam generation by nanoparticles from the nanoscale to the macroscale, a process that is of fundamental interest for a growing number of applications.
https://www.youtube.com/watch?v=J2DbVQ6AnDs
Jul 22, 2013
Solar-Powered
Steam Generation -- Solar steam used to clean human waste
in the developing world
Researchers at Rice University's Laboratory for Nanophotonics (LANP) have unveiled a solar-powered sterilization system that could be a boon for more than 2.5 billion people who lack adequate sanitation. LANP's "solar steam" sterilization system converts as much as 80 percent of the energy in sunlight into germ-killing heat that can be used for off-grid sterilization. In a July 8 study in the Proceedings of the National Academy of Sciences, LANP researchers showed they could use the technology to sterilize human waste, an application that could improve public health in areas that lack reliable electric power.
http://www.pnas.org/content/110/29/11677.full?sid=1c7d56d7-0281-4ddb-9edc-76e1713a91a7
PNAS 2013 110 (29) 11677-11681
Compact
solar autoclave based on steam generation using broadband
light-harvesting nanoparticles
Oara Neumann, Curtis Feronti, Albert D. Neumann, Anjie Dong, Kevin Schell, Benjamin Lu, Eric Kim, Mary Quinn, Shea Thompson, Nathaniel Grady, Peter Nordlander, Maria Oden, and Naomi Halas
Oara Neumann, Curtis Feronti, Albert D. Neumann, Anjie Dong, Kevin Schell, Benjamin Lu, Eric Kim, Mary Quinn, Shea Thompson, Nathaniel Grady, Peter Nordlander, Maria Oden, and Naomi Halas
Abstract
The lack of readily available sterilization processes for medicine and dentistry practices in the developing world is a major risk factor for the propagation of disease. Modern medical facilities in the developed world often use autoclave systems to sterilize medical instruments and equipment and process waste that could contain harmful contagions. Here, we show the use of broadband light-absorbing nanoparticles as solar photothermal heaters, which generate high-temperature steam for a standalone, efficient solar autoclave useful for sanitation of instruments or materials in resource-limited, remote locations. Sterilization was verified using a standard Geobacillus stearothermophilus-based biological indicator.
According to the World Health Organization, healthcare-associated infections are the most prevalent adverse consequence of medical treatment worldwide (1⇓–3). Although this problem is disconcerting and costly in developed countries, its impact in developing regions is devastating (4). More than one-quarter of the human population worldwide lacks access to electricity, let alone the high power requirements necessary for modern sterilization systems. Because more than one-half of all people in developing regions lack access to all-weather roads, the channeling of a consistent supply of disposable sterilizing resources into these areas presents an even more daunting challenge (5). Consequently, addressing the problem of resource-constrained sterilization can be viewed as an effort to provide solutions to both power and supply chain constraints.
The underlying cause of healthcare-associated (nosocomial) infections is prolonged or focused exposure to unsanitary conditions. Such conditions can be ameliorated through the use of sanitation and sterilization methods. Sterilization involves the destruction of all microorganisms and their spores, whereas disinfection is a less robust process that involves the removal of microorganisms without complete sterilization (6). One of the simplest, most effective, and most reliable approaches for the sterilization of medical devices and materials is the use of an autoclave. The fundamental concept of an autoclave is to expose the media to be sterilized to saturated steam at an elevated temperature. On coming into contact with the medium to be sterilized, the saturated steam condenses from the gas phase to the liquid phase, transferring its latent heat of vaporization to the material to be sterilized and thus, any associated microbes on its surface. Such a rapid transfer of heat is extremely effective for denaturing proteins and may be used to destroy most known types of infectious agents, including bacteria, viruses, or viral spores.
Steam-based autoclave systems neutralize potentially infectious microorganisms localized on solid surfaces or in liquid-phase media by exposing them to high-temperature pressurized steam. The process of steam sterilization relies on both steam temperature and time duration of steam exposure to ensure irreversible destruction of all microorganisms, especially bacterial endospores, which are considered particularly thermally stable. Although steam-based sterilization is the primary method of choice for the processing of medical waste in the developed world, the large energy requirement for operation is the fundamental limitation for its adoption in developing countries, with limited or nonexistent access to sources of electricity sufficient to power such systems.
Recently, we reported the use of broadband light-absorbing particles for solar steam generation (7). A variety of nanoparticles such as metallic nanoshells, nanoshell aggregates, and conductive carbon nanoparticles, when dispersed in aqueous solution and illuminated by sunlight, has been shown to convert absorbed solar energy to steam at an efficiency of just over 80%, where less than 20% of the energy contributes to heating the liquid volume (7). This effect depends on the highly localized, strong photothermal response of these types of nanoparticles, a characteristic that is being used to effectively ablate solid tumors by irradiation with near-IR laser light with near-unity tumor remission rates (8⇓⇓⇓⇓⇓⇓⇓–16). In the solar steam generation process, broadband light-absorbing nanoparticles create a large number of nucleation sites for steam generation within the fluid. As light is absorbed by a nanoparticle, a temperature difference between the nanoparticle and the surrounding fluid is established because of a reduced thermal conductivity at the metal–liquid interface: this local temperature increase may become sufficient to transform the liquid in the direct vicinity of the nanoparticle into vapor. On sustained illumination, the vapor envelope surrounding the nanoparticle grows, eventually resulting in buoyancy of the nanoparticle–bubble complex. When this complex reaches the surface of the liquid, the vapor is released, resulting in vigorous nonequilibrium steam generation that does not require the bulk fluid temperature to have reached its boiling point. If the fluid is kept in an ice bath, steam is produced, even when the fluid temperature remains at 0 °C (7). Over prolonged exposure to sunlight, however, both the more-efficient process of nanoparticle-based steam generation and the less-efficient process of bulk fluid heating occur, eventually resulting in simultaneous nanoparticle-based steam generation and boiling of the bulk fluid. The combination of these two processes results in solar steam production that occurs at higher steam temperatures than can be achieved using nonparticle-based fluid heating (Fig. 1). The nanoparticles are neither dispersed into the vapor phase nor degraded by the steam generation process.
Fig. 1.
Temperature evolution of solar steam generation. (A) Temperature vs. time for Au nanoshell-dispersed water (i, liquid; ii, vapor) and water without nanoparticles (iii, liquid; iv, vapor) under solar exposure. (Au nanoparticle concentration sufficient to produce an optical density of unity.) (B) Photograph of system used in the temperature evolution of solar steam generation: (a) transparent vessel isolated with a vacuum jacket to reduce thermal losses, (b) two thermocouples for sensing the solution and the steam temperature, (c) pressure sensor, and (d) 1/16-in nozzle.
The temperature–time evolution of the nanoparticle-dispersed fluid and steam produced during solar irradiation is shown in Fig. 1A with and without the presence of nanoparticles. A detailed characterization of the nanoparticles is shown in Fig. S1. With nanoparticle dispersants, temperatures of both the liquid and the steam increase far more rapidly than the temperature of pure water (Fig. 1A, i and ii), with the liquid water reaching 100 °C more rapidly with nanoparticle dispersants than water without nanoparticles. Measurable steam production occurs at a lower water temperature for the case with nanoparticle dispersants, because nanoparticle-dispersed steam generation can occur at any fluid temperature. For the case shown here, measurable steam production appears at a water temperature of ∼70 °C, well below the steam production threshold for pure water. Perhaps most importantly, however, is the large difference in steady-state temperature achieved for the two systems: with the inclusion of nanoparticle dispersants, the temperature of both the water and the vapor increase well above the standard boiling point of water. In this case, an equilibrium temperature of 140 °C is easily achieved in the nanoparticle-dispersed water–steam system. This elevated temperature enables the use of nanoparticle-generated solar steam for medical sterilization applications.
The evolution of solar steam generation from Au nanoshells dispersed in water was quantified in an open-loop system (Fig. 1B) consisting of a 200-mL vessel isolated with a vacuum jacket to prevent heat loss, a pressure sensor, and two thermocouples to monitor both the liquid and vapor temperatures. The vessel was illuminated with solar radiation focused by a 0.69-m2 Fresnel lens into the glass vessel containing 100 mL nanoparticles at a concentration of 1010 particles/m3 or alternatively, water with no nanoparticles as a control. On solar illumination, vapor was allowed to escape through a 16-µm-diameter nozzle, while the pressure and temperature were recorded.
Here, we show two different compact solar autoclaves driven by nanoparticle-based solar steam generation that are well-suited to off-grid applications. Using a solar concentrator (Fresnel lens or dish mirror) to deliver sunlight into the nanoparticle-dispersed aqueous working fluid, this process is capable of delivering steam at a temperature of 115–135 °C into a 14.2-L volume for a time period sufficient for sterilization. Sterilization was verified using a standard Geobacillus stearothermophilus-based biological indicator.
Experimental Section
Two solar sterilization designs have been developed. One is a portable, closed-loop solar autoclave system suitable for sterilization of medical or dental tools; the second design is a solar dish collector autoclave system that can serve as a standalone, off-grid steam source suitable for human or animal waste sterilization systems or other applications. Steam from the closed-loop system (Fig. 2A) is produced under solar illumination, transported into the sterilization volume, condensed, and then delivered back into the fluid vessel. The design consists of three main subsystems: the steam generation module (Fig. 2A, I), the connection module (Fig. 2A, II), and the sterilization module (Fig. 2A, III). More detailed schematics of the system are presented in Figs. S1, S2, and S3.
Fig. 2.
(A) Schematic and photograph of the closed-loop solar autoclave showing (I) the steam generation module, (II) the connection module, and (III) the sterilization module. The components of the system are (a) sterilization vessel, (b) pressure sensor, (c) thermocouple sensor, (d) relief valve, (e and f) control valves, (g) solar collector containing the nanoparticle-based heater solution, (h) check valve, and (k) solar concentrator (a plastic Fresnel lens of 0.67-m2 surface area). (B) Schematic and photograph of the open-loop solar autoclave: the components of the system are (i) solar concentrator (44-in dish mirror), (ii) heat collector containing metallic nanoparticles, and (iii) sterilization vessel that contains a pressure sensor, two thermocouple sensors, a steam relief valve, and two hand pumps and valves that control the input and output of waste. The solar concentrator dish system has a dual tracking system powered by a small car battery recharged by a solar cell unit.
The particle solution is contained in a custom-built insulated glass vessel with two inlets that lead to the connection module. Solar collection is accomplished with a relatively small and inexpensive Fresnel lens. The hot solar steam generated within this module is channeled out one nozzle of the connection module into the sterilization module, where it condenses on the objects to be sterilized, returning as condensate to the steam generation module. A check valve at one port of the steam generation module ensures a unidirectional flow of steam throughout the entire system.
The sterilization module consists of an insulated pressure vessel (a converted stovetop autoclave with a 14.2-L capacity). A condensate return hole (diameter of 0.86 cm) was milled on the bottom face of the autoclave vessel 10 cm away from the center. Similarly, a steam inlet hole (diameter of 0.86 cm) was milled on the lid of the sterilizing vessel 10 cm away from the center. A finite element analysis (SolidWorks using the Tresca maximum) was performed to identify the mechanically weakest portions of the pressure vessel when placed under high-stress conditions (Fig. S3). By varying the radial position of the hole in the base of the pressure vessel, a minimum factor of safety (vessel material strength/design load) under many different machining configurations was determined. A 0.86-cm-diameter hole positioned 10 cm from the center of the pressure vessel was determined to be the optimal location, with a minimum factor of safety of 3.35. To minimize heat losses from the steam generation module and the sterilization module, the system was insulated with a sealant (Great Stuff Fireblock Insulating Foam Sealant) applied to the surfaces of the vessels and covered with aluminum foil to further minimize heat loss.
The connection module consists of two parts: the steam connection, which allows steam to flow from the steam generation module to the sterilization module, and the condensate connection, which returns the condensate from the sterilization module (Fig. S3). The steam connection consists of polytetrafluoroethylene (PTFE) tubing insulated in fiberglass pipe wrap and a ball valve; the condensate connection consists of a ball valve, PTFE tubing insulated in fiberglass pipe wrap, a check valve, and a pressure release valve. Both units contain an adaptor to connect to the steam generation module.
The solar-generated steam enters the sterilization module at the top of the vessel, forcing the unsterile air down and out of the vessel through the air exhaust tube, which is connected to the control valve. Trapped unsterile air can have an insulating effect and prevent complete sterilization; therefore, it is critical that as much air as possible be removed from the sterilization module. After the unsterile air is purged from the system, the control valve is closed to allow pressure to build up in the vessel. The cycle is maintained at a minimum of 115 °C and 12 psig and a maximum of 140 °C and 20 psig in all regions of the sterilization module throughout the duration of a sterilization cycle. The condensate is channeled back to the steam generation module by a check valve when the hydrostatic pressure exceeds the maximum pressure of the valve (rated at 0.3 psi).
An optimized, open-loop, prototypical compact solar autoclave for human waste sterilization is presented in Fig. 2B. Using a 44-in solar dish collector to focus sunlight into the nanoparticle-dispersed aqueous working fluid, we deliver steam into a 14.2-L capacity sterilization volume (a commercially available stovetop autoclave). This volume could easily accommodate the 10-L capacity volume of a mobile sanitation (moSAN) toilet, for example (a personal-use toilet designed for Deutsche Gesellschaft für Internationale Zusammenarbeit GmbH and originally developed for the urban poor in Bangladesh), and if operated three times per week, it could process the weekly amount of both solid and liquid waste produced by a household of four adults (∼35 L). Solar energy is supplied to this unit through a reflective parabolic dish that tracks the sun, is powered by a small car battery, and is rechargeable with a small solar panel. The generated steam is transmitted to the autoclave through silicon tubing. Unprocessed waste is delivered to the autoclave by means of a mechanical hand pump, which can be easily operated by a single person. After the sterilization process, the sanitized waste is removed by gravity. Because of its simple, modular design, the system can easily be expanded to provide high-temperature steam for larger-scale applications.
The nanoparticle solution is contained in a custom-designed vacuum-insulated vessel positioned at the focus of the parabolic reflector. The steam generated within this module is channeled into the waste sterilization module. Under typical operation, the steam temperature is maintained at 132 °C for 5 min, the duration of time required for an International Organization for Standardization (ISO) standard sterilization cycle. The steam temperature was monitored at the output of the steam generation module, and the waste solution temperature was monitored inside the sterilization module. These two locations are expected to reach the sterilization temperature with slight thermal (gas and liquid phases) differences inside the sterilization module during the sterilization process.
The steam temperature was monitored in both geometries at the steam connection and the condensate connection directly adjacent to the sterilization module. These two locations are expected to have the highest and lowest steam temperatures, respectively, allowing us to measure the overall temperature gradient generated inside the sterilization module during the sterilization process. The steam temperature before and during a sterilization cycle is shown in
Fig. 3.
The autoclave temperature distribution of the (A) closed-loop and (B) open-loop solar autoclaves. The temperature of steam vs. time measured in two different locations in autoclave: top (red curve) and respective bottom (blue curve). The dashed line indicates temperature required for sterilization, and the red box indicates the sterilization regime (115 °C for 20 min or 132 °C for 4.6 min). The ambient temperature (green) was monitored as reference.
The red curve in Fig. 3 is the temperature of the steam at the inlet valve to the sterilization vessel, the blue curve in Fig. 3 is the temperature of the condensate at the sterilization vessel output, and the ambient temperature in Fig. 3 is the green curve. The dashed gray line in Fig. 3 represents the temperature required for sterilization (115–132 °C). In the case of the closed-loop system (Fig. 3A), the irregular spikes in the temperature curves correspond to when the steam begins to enter the vessel. The bottom thermocouple shows two major spikes during warm-up that are generated by the release of unsterilized air from the sterilization module. The first spike induced turbulence into the system, which exposed the thermocouple briefly to hotter steam. The second jump in the temperature data of the output thermocouple corresponds to the release of the remaining unsterilized insulated air. The monitoring data clearly show that the autoclave is easily capable of maintaining a temperature over 115 °C for more than 30 min of the sterilization time required at that temperature. In the case of the open-loop system (Fig. 3B), the red curve is the gas temperature of the steam measured at the vessel inlet valve, the blue curve is the temperature inside the vessel contents (artificial fecal material), and the ambient temperature is the green curve. The dashed gray line represents the desired temperature required for sterilization (132 °C). After an initial ramp-up period of ∼20 min, the sterilization temperature is reached, and the temperature–time curve continues to oscillate around this value because of the frequent release of steam from the sterilization vessel through the pressure safety valve. The solar thermal evolution data show that the autoclave is capable of maintaining a temperature around 132 °C for more than 5 min.
To test whether our systems can achieve the Sterility Assurance Level defined by the Food and Drug Administration (17), we operated the system through a cycle with the sterilization vessel containing commercial biological indicator strips for G. stearothermophilus (EZTest Self-Contained Biological Indicator Strips; SGM Biotech), a reference strain commonly used for sterilization testing. The test strips were secured in the sterilization module near the inlet stream and outlet stream taps or immersed in a fecal simulator solution. After completion of the cycle, the strips were incubated for 36 h at 55–60 °C. The results are shown in Fig. 4.
Fig. 4.
The color change shown by the vials in Fig. 4, relative to the control vial, indicates that sterilization is achieved by operating the solar autoclave through one 30-min cycle at 115 °C for the closed-loop system and one 5-min cycle at 132 °C for the open-loop system. If some spores survive a sterilization cycle, the biological indicator culture medium undergoes a color change from purple to yellow. The observed color change indicates that spore survival did not occur.
In conclusion, we have shown two compact solar autoclaves enabled by solar steam generation using broadband, light-absorbing nanoparticles. The systems maintain temperatures between 115 °C and 132 °C for the time period sufficient to sterilize the contents of a 14.2-L volume, which is in accordance with Food and Drug Administration sterilization requirements. Using a parabolic dish solar collector enables a faster heat-up time and higher operating temperatures, which shorten the sterilization cycle time significantly (from 15 min at 121 °C to 5 min at 132 °C). The nanoparticles are not consumed by the heating process and can be reused indefinitely; the only consumable is water, which need not be sterilized before use. This type of system can easily be expanded to provide direct steam generation for additional applications, which may include distillation-based water purification, cooking, waste remediation, or electricity generation.
Figs. S1, S2, and S3 show extensive schematics of the configuration system and characterizations of metallic nanostructures.
References
World Health Organization (2010) The Burden of Health Care-Associated Infection Worldwide. Available at http://www.who.int/gpsc/country_work/burden_hcai/en/index.html. Accessed June 18, 2013.
World Health Organization (2002) Prevention of Hospital-Acquired Infections: A Practical Guide. Available at http://apps.who.int/medicinedocs/documents/s16355e/s16355e.pdf. Accessed June 18, 2013.
World Health Organization (2010) Solar Powered Autoclaves in Low Resource Settings. Available at www.who.int/medical_devices/poster_a18.pdf. Accessed June 18, 2013.
Orrett FA, Brooks PJ, Richardson EG (1998) Nosocomial infections in a rural regional hospital in a developing country: Infection rates by site, service, cost, and infection control practices. Infect Control Hosp Epidemiol 19(2):136–140.
Pacific UNEaSCfAat (2006) Transport Infrastructure. Available at http://www.unescap.org/pdd/publications/themestudy2006/9_ch3.pdf. Accessed June 18, 2013.
Rutala WA, Weber DJ, Healthcare Infection Control Practices Advisory Committee (HICPAC) (2008) Guideline for Disinfection and Sterilization in Healthcare Facilities, (Center for Disease Control and Prevention, Atlanta). Available at www.cdc.gov/hicpac/pdf/guidelines/disinfection_nov_2008.pdf. Accessed June 18, 2013.
Neumann O, et al. (2013) Solar vapor generation enabled by nanoparticles. ACS Nano 7(2013):42–49.
Govorov AO, Richardson HH (2007) Generating heat with metal nanoparticles. Nano Today 2(1):30–38.
Huhn D, Govorov A, Gil PR, Parak WJ (2012) Photostimulated au nanoheaters in polymer and biological media: Characterization of mechanical destruction and boiling. Adv Funct Mat 22(2):294–303.
Richardson HH, Carlson MT, Tandler PJ, Hernandez P, Govorov AO (2009) Experimental and theoretical studies of light-to-heat conversion and collective heating effects in metal nanoparticle solutions. Nano Lett 9(3):1139–1146.
Hirsch LR, et al. (2003) Nanoshell-mediated near-infrared thermal therapy of tumors under magnetic resonance guidance. Proc Natl Acad Sci USA 100(23):13549–13554.
O’Neal DP, Hirsch LR, Halas NJ, Payne JD, West JL (2004) Photo-thermal tumor ablation in mice using near infrared-absorbing nanoparticles. Cancer Lett 209(2):171–176.
Huang X, Jain PK, El-Sayed IH, El-Sayed MA (2008) Plasmonic photothermal therapy (PPTT) using gold nanoparticles. Lasers Med Sci 23(3):217–228.
Lal S, Clare SE, Halas NJ (2008) Nanoshell-enabled photothermal cancer therapy: impending clinical impact. Acc Chem Res 41(12):1842–1851.
Lee JY, Peumans P (2010) The origin of enhanced optical absorption in solar cells with metal nanoparticles embedded in the active layer. Opt Express 18(10):10078–10087.
Otanicar TP, Phelan PE, Prasher RS, Rosengarten G, Taylor RA (2010) Nanofluid-based direct absorption solar collector. J Renew Sustainable Energy 2(3):033102–033113.
Branch ICD (1993) Guidance on Premarket Notification [510(k)] Submissions for Sterilizers Intended for Use in Health Care Facilities. Available at http://www.fda.gov/downloads/MedicalDevices/DeviceRegulationandGuidance/GuidanceDocuments/UCM081341.pdf. Accessed June 18, 2013.
PATENTS
A method of producing bioethanol that includes receiving a feedstock solution that includes polysaccharides in a vessel comprising a complex is described. The complex may be copper nanoparticles, copper oxide nanoparticles, nanoshells, nanorods, carbon moieties, encapsulated nanoshells, encapsulated nanoparticles, and/or branched nanostructures. The method also includes applying electromagnetic (EM) radiation to the complex such that the complex absorbs the EM radiation to generate heat. Using the heat generated by the complex, sugar molecules may be extracted from the polysaccharides in the feedstock solution, and fermented. Then, bioethanol may be extracted from the vessel.
WO2012082364
Distilling a Chemical Mixture using an Electromagnetic Radiation-Absorbing Complex
[ PDF ]
WO2014127345
Solar Steam Processing of Biofuel Feedstock...
[ PDF ]