Michael Misha's Public Library

"I said to myself, well, lithium ion batteries in my cell phone, in my iPod," – his daughter had given him one – "I wonder how much coal we burn to charge those guys up at the end of the day. Because that's one of the big drivers for portable power, to get all this stuff off the grid." After making some very conservative calculations, he arrived at an answer, which he shared with the class: "You burn about a quarter of a pound of coal per charge of your lithium ion battery, and you generate about half a pound of CO2 per charge, per battery, per day

Wastewater Produces Electricity And Desalinates Water

www.sciencedaily.com/...090806112601.htm - Preview

Desalinization Clean Water Clean Energy

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.
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.
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- The researchers
- 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.
- 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.
- 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
- 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.