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Like many of its counterparts around the world, the College of Engineering is seeking to better understand how energy can be best utilized and incorporated into daily lives. Yet, the impact of energy — clean, safe, and renewable energy — is such that no single institution can focus on all of the potential aspects of energy. For this reason, the college and its researchers have selected five areas — energy efficiency; safe nuclear waste storage; clean coal technologies; carbon dioxide separation, storage, and usage; and renewable resources — in which they have considerable expertise and through which they will continue to focus their efforts. The college also offers several courses highlighting energy technologies, as well as the social, political, and moral aspects associated with energy usage.

Making the Most of WindProfessors Corke & Nelson

Wind turbine blades (rotors) work in the same way as do airplane wings. The wind flowing over the blade produces lift. This makes a windmill turn, but wind turbulence can affect the performance of a turbine. If the wind is blowing smoothly, there are no problems. If the wind becomes unsteady, this not only affects the efficiency of a turbine (how much energy it is able to generate) but can also physically damage the turbine blades because of aerodynamic loads caused by the turbulence.

Researchers in the Institute for Flow Physics and Control — Clark Equipment Professor Thomas C. Corke, director of the center, and Professor Robert C. Nelson — are investigating distributed active flow control as a way to improve wind turbine performance. By placing plasma actuators, developed at Notre Dame, on a turbine blade, researchers can change the flow, and thus the aerodynamic load, of air around the blade in real time. This promotes continuous operation of a turbine at near optimal conditions in both steady and unsteady wind conditions, making the turbine more effective and more cost efficient. Other benefits of the actuators include that they are fully electronic with no moving parts, can withstand high-force loading, and can be laminated onto the blade surface.

More Efficient Wastewater Treatment with Less Energy


Robert NerenbergWastewater treatment is essential to protecting human health and the environment, but because of the burgeoning global population, and the increasing need to reuse wastewater, treatment plants are being required to meet even more stringent standards. Most plants will need upgrades to comply with these new regulations. Not only do the changes mean significant capital investments, higher chemical costs, and the production of more green-house gases, but they also signal increased energy requirements. A Notre Dame team has developed a novel water treatment technology that helps existing plants meet the new standards using less space, less energy, and less capital, while producing fewer emissions. Equally important, this technology may be adapted to convert a full-sized wastewater treatment plant from an energy sink into an energy source.
HMPB biofilm
Wastewater treatment plants discharge enormous volumes of water, exceeding 100 million gallons of water per day in some larger cities. Although the treatment process varies depending upon the sophistication and age of a plant, it requires a tremendous amount of energy, mainly to aerate the chambers and pump the water.

Conventional wastewater treatment systems use approximately three percent of all of the electrical energy produced in the United States. With the new regulations for nitrogen and phosphorus removal, the process will become even more of an energy drain. It will require larger facilities and more chemicals, making the process more expensive. Greater amounts of greenhouse gases will also be produced as a result of meeting the new standards.

Associate Professor Robert Nerenberg and his team of researchers may have a solution. They have developed a process that reduces the energy requirements for a treatment plant by up to 50 percent while minimizing emissions of nitrous oxide (N2O), a potent greenhouse gas. The Hybrid Membrane-Biofilm Process (HMBP) they have designed features air-filled hollow-fiber membranes, which are incorporated into a plant’s activated sludge tank. Once in the tank, a nitrifying biofilm develops on the membranes, producing nitrite and nitrate. By suppressing bulk aeration (instead of supplying it), the liquid becomes anoxic, and the nitrite/nitrate can be reduced with influent bio-chemical oxygen demand (BOD).

Its hybrid nature is what distinguishes the HMBP from other membrane-aerated processes. Heterotrophic bacteria are kept in suspension by maintaining low bulk liquid BOD concentrations, while nitrifying bacteria form a biofilm on the fiber, getting their oxygen by passive diffusion through the air-filled fibers. Thus, the HMBP can save up to 50 percent of the electrical energy required to run the plant, while preventing
N2O emissions and reducing the need for additional chemical additives. Another major advantage is the ability to retrofit existing infrastructure, rather than expand it or replace it with new systems.

After a successful bench-scale study, the team built a pilot reactor, which was tested at the 26th Ward Water Pollution Control Plant in Brooklyn in conjunction with New York’s Applied Research Facility. The pilot study confirmed the ability of the HMBP to achieve total nitrogen removal from an actual wastewater treatment plant in scalable concentrations. Ongoing research, funded by the National Science Foundation, will provide a more basic understanding of the unique microbial processes used in the HMBP.

According to Nerenberg, with a few tweaks the HMBP can also function like a microbial fuel cell, so that in addition to removing the nitrogen and other impurities from the water, it could convert the chemical energy contained in biodegradable compounds into electrical energy. This could allow wastewater treatment plants to send electrical power back to the grid.


SUGGESTED READING

Shea, Caitlyn and Nerenberg, Robert, “Performance and Microbial Ecology of Air-Cathode Microbial Fuel Cells with Layered Electrode Assemblies,” Applied Microbiology and Biotechnology, 2010, 86, 5, 1399.

Downing, Leon S.; Bibby, Kyle J.; Esposito, Kathleen; Fascianella, Tom; Tsuchihashi, Ryujiro; and Nerenberg, Robert, “Nitrogen Removal from Wastewater Using a Hybrid Membrane-biofilm Process: Pilot-scale Studies,” Water Environment Research, 2010, 82, 3, 195-201.

Downing, Leon S. and Nerenberg, Robert, “Effect of Bulk Liquid BOD Concentration on Activity and Microbial Community Structure of a Nitrifying, Membrane-aerated Biofilm,” Applied Microbiology ­­­­and Biotechnology, 2008, 81,153-162.

Downing, Leon S. and Nerenberg, Robert, “Total Nitrogen Removal in a Hybrid, Membrane-aerated Activated Sludge Process,” Water Research, 2008, 42, 3697-3708.

Downing, Leon S. and Nerenberg, Robert, “Effect of Oxygen Gradients on the Activity and Microbial Community Structure of a Nitrifying, Membrane-aerated Biofilm,” Biotechnology and Bioengineering, 2008, 101, 1193-1204.

Nanomagnetic Devices Present an Attractive Solution

Michael NiemierFor the last 40 years conventional electronic technology (CMOS) has relied on shrinking transistors to produce smaller, faster, and cheaper devices (cell phones, laptop computers, iPods, and more). The laws of physics prevent these devices from working below a certain size. Because of this, researchers across the country have been searching for a new logic device to either replace or augment CMOS technology. University of Notre Dame researchers have achieved a series of firsts, including their most recent accomplishment, that may well prove to be a giant leap toward achieving a new type of processing system, one driven by nanomagnets and their interactions rather than electric current flow.

In 1997, Notre Dame researchers were the first to physically demonstrate Quantum-dot Cellular Automata (QCA), a transistorless approach to computing that moves and processes information via nearest-neighbor interactions rather than electric current. Less than ten years later, researchers at Notre Dame were the first to demonstrate logic gates with a magnetic implementation of this device architecture. This was an important first step toward showing that nanoscale magnets could ultimately perform more complex computations, computations that would require much less energy than equivalent CMOS  circuits.

Assistant Professor Michael Niemier and a team from the departments of computer science and engineering and electrical engineering have been pursuing the design of circuit elements constructed with nanoscale magnets and using the QCA device architecture. In magnetic QCA (MQCA), logical operations and data flow are accomplished by manipulating the polarizations of nanoscale magnets. Niemier and his team are moving toward another “first”; they have designed MQCA structures that should facilitate more complex, circuit-level tasks. They have also demonstrated how these structures interact with the on-chip drive circuitry currently envisioned for MQCA-based systems through simulations and are proceeding to prototype testing.

Previous efforts of this nature had suggested the components required for a functionally complete logic set, but there was still a large gap between basic MQCA devices and computationally interesting MQCA systems. The Notre Dame team narrowed this gap by designing unique circuit structures essential for building MQCA systems. They used physical level simulation to demonstrate how external stimuli affect the logic state of individual magnets of various sizes and shapes. Within this study, they (a) ensured that all of the structures required to build a circuit could be controlled with implementable, on-chip drive circuitry, (b) designed structures that allowed data to flow orthogonally in the direction of the external stimuli, and (c) have proposed designs for crossing two logical signals with nanomagnets.

These studies revealed a number of physical and external design parameters, such as nanomagnetic shapes and sizes and clocking field (the external stimuli) strengths and shapes, which are key to circuit-level behavior. Careful selection of these parameters helps not only to facilitate computationally interesting circuits but can also improve circuit performance.

According to Niemier, the next step is fabricating MQCA-based systems, which should be fairly straightforward. “Nanomagnets can be made using conventional lithography or by leveraging electron beam lithography and liftoff to form specific patterns of magnetic material.” Researchers could also employ imprint lithography where the imprint is used to make molds, and then the molds can be used to make the nanomagnet shapes. Niemier and his team believe that these methods should be compatible with, and can take advantage of, advances in current CMOS fabrication techniques.

Another advantage to nanomagnetic technology is that the magnets are inherently resistant to radiation. Thus, any type of MQCA system placed in space would be immune to the effects of radiation, which eventually destroy traditional CMOS chips.

Still in the fundamental stages of research, Notre Dame is on the road to another first: developing an all-magnetic system that offers more complex computations and uses less energy.

SUGGESTED READING

Niemier, M., Dingler, A., Hu, X. Sharon, Alam, M. Tanvir, Bernstein, G.H., and Porod, W., “Bridging the Gap between Nanomagnetic Devices and Circuits,” in the 26th IEEE International Conference on Computer Design, Lake Tahoe, CA, Oct. 12-15, 2008, 506-513.

Niemier, M., Crocker, M., and Hu, X. Sharon, “Fabrication Variations and Defect Tolerance for Nanomagnet-based QCA,” in the 23rd IEEE International Symposium on Defect and Fault Tolerance in VLSI Systems, Cambridge, MA, Oct. 1-3, 2008, 534-542.

Orlov, A., Imre, A., Csaba, G., Ji, L., Porod, W., and Bernstein, G.H., “Magnetic Quantum-dot Cellular Automata: Recent Developments and Prospects,” Journal of Nanoelectronics and Optoelectronics, 2008, 3, 1-14.

Imre, A., Csaba, G., Ji, L., Orlov, A., Bernstein, G.H., and Porod, W., “Majority Logic Gate for Magnetic Quantum-dot Cellular Automata,” Science, 2006, 311, 5758, 205-208.