Waste Water: a source to produce hydrogen and energy.
Scientists have come accross with a method to kill two birds with one stone. With this technique, not only we generate electricity but waste water is cleaned as well.
This is due to the fact that waste water contains a big quantity of energy in form of organic matter.
According to Bruce Logan, director of the Hydrogen Energy Center and the Engineering Energy and Environment Institute at Pennsylvania State University in University Park, “Domestic waste water contains nine times more chemical energy than the energy required to treat it.[…] that amount added to the energy in waste water from livestock and food production, would be nearly enough energy to maintain the entire US water infrastructure”.
The conversion is carried out in microbial fuel cells. Organic matter is separated and oxidized by bacteria. In consecuence, electrons are released. Hydrogen ions pass through a proton-exchange membrane whereas electrons transfer from the anode to the cathode generating an electrical current. Electrons, hydrogen ions and ambient oxygen are combined in the cathode generating clean water.
In order to estimulate the power density, a second process takes place as well. Addresed electrodyalisis, electricity is generated utilizing the ionic discrepancy between fresh water and sea water. Water from both sources passes through a pair of membranes that accept positive or negative charges. Electrodes oppositely charged are linked to their respective membranes; as electrons get attracted to their respective electrodes an electrical current is generated.
Using an ammonium bicarbonate solution instead of sea water raises the power even more and makes the configuration more efficient. In this way, the equip reaches power densities of 3 watts per metre squared.
You may wonder: we clean water but microbial fuel cells are not a source of hydrogen generation.
The answer is that the system has evolved to the point that it can produce hydrogen. Logan’s bacterial hydrolysis cell has membranes (RED), mentioned above, that are used to split water molecules in oxygen and hydrogen.
This cells achieved such rates: 58 to 64 percent energy efficiency and 0.8 to 1.6 cubic meters of hydrogen production for every cubic meter of liquid.
After such results Logan claimed, «pure hydrogen gas can efficiently be produced from virtually limitless supplies of seawater and river water and biodegradable organic matter.»
So this may be a new renewable and carbon-free source of hydrogen with high efficiency as only one percent of that energy was used to pump water through the cells.
By Nora Etxezarreta.
Sources:
http://www.engadget.com/2011/09/22/microbial-fuel-cell-produces-hydrogen-from-wastewater-without-wa/
http://www.microbialfuelcell.org/www/index.php/News/
http://www.merit.unu.edu/itweekly/archive_search_article.php?nid=4467
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