Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

Wastewater produces electricity and desalinates water

10.08.2009
A process that cleans wastewater and generates electricity can also remove 90 percent of salt from brackish water or seawater, according to an international team of researchers from China and the U.S.

Clean water for drinking, washing and industrial uses is a scarce resource in some parts of the world. Its availability in the future will be even more problematic.

Many locations already desalinate water using either a reverse osmosis process -- one that pushes water under high pressure through membranes that allow water to pass but not salt -- or an electrodialysis process that uses electricity to draw salt ions out of water through a membrane. Both methods require large amounts of energy.

"Water desalination can be accomplished without electrical energy input or high water pressure by using a source of organic matter as the fuel to desalinate water," the researchers report in a recent online issue of Environmental Science and Technology.

"The big selling point is that it currently takes a lot of electricity to desalinate water and using the microbial desalination cells, we could actually desalinate water and produce electricity while removing organic material from wastewater," said Bruce Logan, Kappe Professor of Environmental Engineering, Penn State

The team modified a microbial fuel cell -- a device that uses naturally occurring bacteria to convert wastewater into clean water producing electricity -- so it could desalinate salty water.

"Our main intent was to show that using bacteria we can produce sufficient current to do this," said Logan. "However, it took 200 milliliters of an artificial wastewater -- acetic acid in water -- to desalinate 3 milliliters of salty water. This is not a practical system yet as it is not optimized, but it is proof of concept."

A typical microbial fuel cell consists of two chambers, one filled with wastewater or other nutrients and the other with water, each containing an electrode. Naturally occurring bacteria in the wastewater consume the organic material and produce electricity.

The researchers, who also included Xiaoxin Cao, Xia Huang, Peng Liang, Kang Xiao, Yinjun Zhou and Xiaoyuan Zhang, at Tsinghua University, Beijing, changed the microbial fuel cell by adding a third chamber between the two existing chambers and placing certain ion specific membranes -- membranes that allow either positive or negative ions through, but not both -- between the central chamber and the positive and negative electrodes. Salty water to be desalinated is placed in the central chamber.

Seawater contains about 35 grams of salt per liter and brackish water contains 5 grams per liter. Salt not only dissolves in water, it dissociates into positive and negative ions. When the bacteria in the cell consume the wastewater it releases charged ions -- protons -- into the water. These protons cannot pass the anion membrane, so negative ions move from the salty water into the wastewater chamber. At the other electrode protons are consumed, so positively charged ions move from the salty water to the other electrode chamber, desalinating the water in the middle chamber.

The desalination cell releases ions into the outer chambers that help to improve the efficiency of electricity generation compared to microbial fuel cells.

"When we try to use microbial fuel cells to generate electricity, the conductivity of the wastewater is very low," said Logan. "If we could add salt it would work better. Rather than just add in salt, however in places where brackish or salt water is already abundant, we could use the process to additionally desalinate salty water, clean the wastewater and dump it and the resulting salt back into the ocean."

Because the salt in the water helps the cell generate electricity, as the central chamber becomes less salty, the conductivity decreases and the desalination and electrical production decreases, which is why only 90 percent of the salt is removed. However, a 90 percent decrease in salt in seawater would produce water with 3.5 grams of salt per liter, which is less than brackish water. Brackish water would contain only 0.5 grams of salt per liter.

Another problem with the current cell is that as protons are produced at one electrode and consumed at the other electrode, these chambers become more acidic and alkaline. Mixing water from the two chambers together when they are discharged would once again produce neutral, salty water, so the acidity and alkalinity are not an environmental problem assuming the cleaned wastewater is dumped into brackish water or seawater. However, the bacteria that run the cell might have a problem living in highly acidic environments.

For this experiment, the researchers periodically added a pH buffer avoiding the acid problem, but this problem will need to be considered if the system is to produce reasonable amounts of desalinized water.

King Abdullah University of Science and Technology, Saudi Arabia and Ministry of Science and Technology, China, supported this work.

A'ndrea Elyse Messer | EurekAlert!
Further information:
http://www.psu.edu

More articles from Power and Electrical Engineering:

nachricht Fraunhofer Researchers Develop High-Pressure Sensors for Extreme Temperature
28.06.2017 | Fraunhofer-Institut für Zuverlässigkeit und Mikrointegration IZM

nachricht Touch Displays WAY-AX and WAY-DX by WayCon
27.06.2017 | WayCon Positionsmesstechnik GmbH

All articles from Power and Electrical Engineering >>>

The most recent press releases about innovation >>>

Die letzten 5 Focus-News des innovations-reports im Überblick:

Im Focus: Can we see monkeys from space? Emerging technologies to map biodiversity

An international team of scientists has proposed a new multi-disciplinary approach in which an array of new technologies will allow us to map biodiversity and the risks that wildlife is facing at the scale of whole landscapes. The findings are published in Nature Ecology and Evolution. This international research is led by the Kunming Institute of Zoology from China, University of East Anglia, University of Leicester and the Leibniz Institute for Zoo and Wildlife Research.

Using a combination of satellite and ground data, the team proposes that it is now possible to map biodiversity with an accuracy that has not been previously...

Im Focus: Climate satellite: Tracking methane with robust laser technology

Heatwaves in the Arctic, longer periods of vegetation in Europe, severe floods in West Africa – starting in 2021, scientists want to explore the emissions of the greenhouse gas methane with the German-French satellite MERLIN. This is made possible by a new robust laser system of the Fraunhofer Institute for Laser Technology ILT in Aachen, which achieves unprecedented measurement accuracy.

Methane is primarily the result of the decomposition of organic matter. The gas has a 25 times greater warming potential than carbon dioxide, but is not as...

Im Focus: How protons move through a fuel cell

Hydrogen is regarded as the energy source of the future: It is produced with solar power and can be used to generate heat and electricity in fuel cells. Empa researchers have now succeeded in decoding the movement of hydrogen ions in crystals – a key step towards more efficient energy conversion in the hydrogen industry of tomorrow.

As charge carriers, electrons and ions play the leading role in electrochemical energy storage devices and converters such as batteries and fuel cells. Proton...

Im Focus: A unique data centre for cosmological simulations

Scientists from the Excellence Cluster Universe at the Ludwig-Maximilians-Universität Munich have establised "Cosmowebportal", a unique data centre for cosmological simulations located at the Leibniz Supercomputing Centre (LRZ) of the Bavarian Academy of Sciences. The complete results of a series of large hydrodynamical cosmological simulations are available, with data volumes typically exceeding several hundred terabytes. Scientists worldwide can interactively explore these complex simulations via a web interface and directly access the results.

With current telescopes, scientists can observe our Universe’s galaxies and galaxy clusters and their distribution along an invisible cosmic web. From the...

Im Focus: Scientists develop molecular thermometer for contactless measurement using infrared light

Temperature measurements possible even on the smallest scale / Molecular ruby for use in material sciences, biology, and medicine

Chemists at Johannes Gutenberg University Mainz (JGU) in cooperation with researchers of the German Federal Institute for Materials Research and Testing (BAM)...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

Event News

Plants are networkers

19.06.2017 | Event News

Digital Survival Training for Executives

13.06.2017 | Event News

Global Learning Council Summit 2017

13.06.2017 | Event News

 
Latest News

Mice provide insight into genetics of autism spectrum disorders

28.06.2017 | Health and Medicine

New photoacoustic technique detects gases at parts-per-quadrillion level

28.06.2017 | Physics and Astronomy

Funding of Collaborative Research Center developing nanomaterials for cancer immunotherapy extended

28.06.2017 | Life Sciences

VideoLinks
B2B-VideoLinks
More VideoLinks >>>