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 Stretchable biofuel cells extract energy from sweat to power wearable devices
22.08.2017 | University of California - San Diego

nachricht Laser sensor LAH-G1 - optical distance sensors with measurement value display
15.08.2017 | 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: Fizzy soda water could be key to clean manufacture of flat wonder material: Graphene

Whether you call it effervescent, fizzy, or sparkling, carbonated water is making a comeback as a beverage. Aside from quenching thirst, researchers at the University of Illinois at Urbana-Champaign have discovered a new use for these "bubbly" concoctions that will have major impact on the manufacturer of the world's thinnest, flattest, and one most useful materials -- graphene.

As graphene's popularity grows as an advanced "wonder" material, the speed and quality at which it can be manufactured will be paramount. With that in mind,...

Im Focus: Exotic quantum states made from light: Physicists create optical “wells” for a super-photon

Physicists at the University of Bonn have managed to create optical hollows and more complex patterns into which the light of a Bose-Einstein condensate flows. The creation of such highly low-loss structures for light is a prerequisite for complex light circuits, such as for quantum information processing for a new generation of computers. The researchers are now presenting their results in the journal Nature Photonics.

Light particles (photons) occur as tiny, indivisible portions. Many thousands of these light portions can be merged to form a single super-photon if they are...

Im Focus: Circular RNA linked to brain function

For the first time, scientists have shown that circular RNA is linked to brain function. When a RNA molecule called Cdr1as was deleted from the genome of mice, the animals had problems filtering out unnecessary information – like patients suffering from neuropsychiatric disorders.

While hundreds of circular RNAs (circRNAs) are abundant in mammalian brains, one big question has remained unanswered: What are they actually good for? In the...

Im Focus: RAVAN CubeSat measures Earth's outgoing energy

An experimental small satellite has successfully collected and delivered data on a key measurement for predicting changes in Earth's climate.

The Radiometer Assessment using Vertically Aligned Nanotubes (RAVAN) CubeSat was launched into low-Earth orbit on Nov. 11, 2016, in order to test new...

Im Focus: Scientists shine new light on the “other high temperature superconductor”

A study led by scientists of the Max Planck Institute for the Structure and Dynamics of Matter (MPSD) at the Center for Free-Electron Laser Science in Hamburg presents evidence of the coexistence of superconductivity and “charge-density-waves” in compounds of the poorly-studied family of bismuthates. This observation opens up new perspectives for a deeper understanding of the phenomenon of high-temperature superconductivity, a topic which is at the core of condensed matter research since more than 30 years. The paper by Nicoletti et al has been published in the PNAS.

Since the beginning of the 20th century, superconductivity had been observed in some metals at temperatures only a few degrees above the absolute zero (minus...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

Event News

Call for Papers – ICNFT 2018, 5th International Conference on New Forming Technology

16.08.2017 | Event News

Sustainability is the business model of tomorrow

04.08.2017 | Event News

Clash of Realities 2017: Registration now open. International Conference at TH Köln

26.07.2017 | Event News

 
Latest News

What the world's tiniest 'monster truck' reveals

23.08.2017 | Life Sciences

Treating arthritis with algae

23.08.2017 | Life Sciences

Witnessing turbulent motion in the atmosphere of a distant star

23.08.2017 | Physics and Astronomy

VideoLinks
B2B-VideoLinks
More VideoLinks >>>