Recent reports from university researchers highlight work in developing more energy-efficient, energy-generating, and environmentally sound technologies for treating wastewater. While these technologies are still being tested, the research suggests realistic potential for changing how future wastewater treatment plants are designed and operated.
Fuel cell technologies
Engineers at Oregon State University (OSU) in Corvallis, Ore., recently announced a breakthrough in the performance of microbial fuel cells that can produce electricity directly from wastewater. The new technology can now produce 10 to 50 times the electricity per volume than most other approaches using microbial fuel cells, researchers said, and 100 times more electricity than some. This eventually could replace the activated sludge process that has been in use for almost a century.
"If this technology works on a commercial scale the way we believe it will, the treatment of wastewater could be a huge energy producer, not a huge energy cost," said Hong Liu, an associate professor in the OSU Department of Biological and Ecological Engineering. Experts estimate that about 3 percent of the electrical energy consumed in the United States and other developed countries is used to treat wastewater.
With new concepts – reduced anode-cathode spacing, evolved microbes, and new separator materials – the technology can now produce more than 2 kilowatts per cubic meter of liquid reactor volume. This amount of power density far exceeds anything else done with microbial fuel cells.
The OSU system has now been proven at a substantial scale in the laboratory, Liu said, and the next step is a pilot study. Once advances are made to reduce high initial costs, researchers estimate that the capital construction costs of this new technology should be comparable to that of the activated sludge systems now in widespread use today – and even less expensive when future sales of excess electricity are factored in.
In this new technology, bacteria oxidize the organic matter and, in the process, produce electrons that run from the anode to the cathode within the fuel cell, creating an electrical current. Almost any type of organic waste material can be used to produce electricity, including grass straw, animal waste, and byproducts from operations such as the wine, beer, or dairy industries.
On a smaller scale, Caitlyn Shea Butler, a civil engineering professor at the University of Massachusetts Amherst, has designed and is now field-testing a "green latrine" that purifies human waste, turning it into compost for farming and generating electricity. Her multipurpose invention is called a "Microbial Fuel Cell Latrine."
Butler's latrine is similar to a fuel cell where a fuel is oxidized at an anode and an oxidant is reduced at a cathode. After solid wastes are first filtered in a composting chamber, dissolved waste organic matter is oxidized in an anode chamber. Oxidation is assisted by bacteria on the anode surface and uses the anode as an electron acceptor to complete their metabolic reaction. Electrons released in this biological process are conveyed through a load-bearing circuit, producing electricity, to the cathode compartment. There a different community of bacteria uses the cathode as an electron donor, capturing the energy from the electrons, to reduce harmful nitrates in the waste stream.
Butler said her inexpensive green latrine can be deployed in places such as rural Africa, transforming the way human waste is treated in areas where sanitation facilities are poor or nonexistent. At the same time, the device can play a key role in preventing waterborne diseases, including diarrhea.
The primary nitrogen compound found in human waste is ammonium, which can be broken down by oxidation, or nitrification. In Butler's latrine, nitrification takes place thanks to bacteria living in an intermediate chamber that separates the anode and cathode chambers. The result is effluent water that is quite low in organic matter and nutrients.
A professor at Michigan State University is part of a team developing a new method of removing phosphorous from wastewater – a problem seriously affecting lakes and streams across the country. Steven Safferman, an associate professor of biosystems and agricultural engineering, and colleagues at Columbus, Ohio-based MetaMateria Technologies, are devising a cost-effective way of recovering the phosphorous, which then can be reused for fertilizer products.
During the last 10 years, MetaMateria Technologies and Safferman have tested methods to produce a media, enhanced with nanoparticles composed of iron, that can more efficiently remove larger amounts of phosphorous from water.
"Phosphorous that is dissolved in wastewater is hard to remove," Safferman said. "We found that a nano-media made with waste iron can efficiently absorb it, making it a solid that can be easily and efficiently removed and recovered for beneficial reuse."
The material should be commercially available for use within two years, said J. Richard Schorr, MetaMateria CEO. "Phosphorous is a finite material," Schorr said, "Analyses show that the supply of phosphorous may become limited within the next 25 to 50 years. This is an economical way to harvest and recycle phosphorous."