08-02-2010, 11:54 AM
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Production Of Bioelectricity
INTRODUCTION:
Fossil fuels have supported the industrialization and economic growth of countries during the past century, but it is clear that they cannot indefinitely sustain a global economy. The infrastructure changes needed to address our global energy needs will be far more extensive and will likely require changes not only to our infrastructure but also to our lifestyle. Changes will affect everything from home heating and lighting, to where we prefer to live and work and how we get there. The costs of energy and how much energy we use will come to dominate our economy and our lifestyle in the coming decades.
A microbial fuel cell (MFC) or biological fuel cell is a bio-electrochemical system that drives a current by mimicking bacterial interactions found in nature. A microbial fuel cell is a device that converts chemical energy to electrical energy by the catalytic reaction of microorganisms. A typical microbial fuel cell consists of anode and cathode compartments separated by a membrane. In the anode compartment, fuel is oxidized by microorganisms, generating electrons and protons. Electrons are transferred to the cathode compartment through an external electric circuit, and the protons are transferred to the cathode compartment through the membrane. Electrons and protons are consumed in the cathode compartment, combining with oxygen to form water. In general, there are two types of microbial fuel cells, mediator and mediator-less microbial fuel cells.
International scenario
1) Microfabricated Microbial Fuel Cell Arrays Reveal Electrochemically Active Microbes
Huijie Hou, Lei Li, Younghak Chop, Paul de Figueiredo, Arum HanTexas A&M University, College Station, Texas, United States of America
o Microbial fuel cells (MFCs) are remarkable green energy devices that exploit microbes to generate electricity from organic compounds.
o MFC devices currently being used and studied do not generate sufficient power to support widespread and cost-effective applications.
o Most of the MFC devices are not compatible with high throughput screening for finding microbes with higher electricity generation capabilities.
o Here,the development of a micro fabricated MFC array, a compact and user-friendly platform for the identification and characterization of electrochemically active microbes.
o The MFC array consists of 24 integrated anode and cathode chambers, which function as 24 independent miniature MFCs and support direct and parallel comparisons of microbial electrochemical activities.
2) Microbial fuel cells: novel biotechnology for energy generation
A work was done by Korneel Rabaey and Willy Verstraete at Laboratory of Microbial Ecology and Technology (LabMET), Ghent University, Coupure Links 653, B-9000 Ghent, Belgium
o Microbial fuel cells (MFCs) provide new opportunities for the sustainable production of energy from biodegradable, reduced compounds. MFCs function on different carbohydrates but also on complex substrates present in wastewaters.
o Depending on the operational parameters of the MFC, different metabolic pathways are used by the bacteria. This determines the selection and performance of specific organisms.
o The MFC technology is evaluated relative to current alternatives for energy generation.
National scenario
1) Bioelectricity production by mediatorless microbial fuel cell under acidophilic condition using wastewater as substrate: Influence of substrate loading rate
A work on bioelectricity production had been carried out by S. Venkata Mohan, S. Veer Raghavulu, S. Srikanth and P. N. Sarma at Bioengineering and Environmental Engineering Centre, Indian Institute of Chemical Technology, Hyderabad 500 007, India
o Microbial fuel cell employing low-cost materials without any toxic mediators was evaluated under acidophilic conditions using anaerobic mixed consortia to enumerate the influence of substrate loading rate on bioelectricity generation from anaerobic wastewater treatment at ambient temperature.
o Experimental data showed the feasibility of power generation from wastewater treatment.
o Maximum power yield (274 mW/g CODR; 50 ), was observed at operation OLR of 0.574 kg COD/m3-day
o The study documented the advantage of both wastewater treatment and electricity production in a single system.
2) Growth with high planktonic biomass in Shewanella oneidensis fuel cells.
A work by Martin Lanthier, Kelvin B Gregory, and Derek R Lovley was carried at Eastern Cereal and Oilseed Research Center, Agriculture and Agri-Food Canada..
o Shewanella oneidensis MR-1 grew for over 50 days in microbial fuel cells, incompletely oxidizing lactate to acetate with high recovery of the electrons derived from this reaction as electricity.
o Electricity was produced with lactate or hydrogen and current was comparable to that of electricigens which completely oxidize organic substrates.
o These results demonstrate that S. oneidensis may conserve energy for growth with an electrode serving as an electron acceptor and suggest that multiple strategies for electron transfer to fuel cell anodes exist.
Local scenario
1) Biological fuel cells and their applications
A work was done by A. K. Shukla1, P. Suresh, S. Berchmans1 and A. Rajendran1 at
Central Electrochemical Research Institute, Karaikudi 630 006, India.
o One type of genuine fuel cell that does hold promise in the long-term is the biological fuel cell.
o Unlike conventional fuel cells, which employ hydrogen, ethanol and methanol as fuel, biological fuel cells use organic products produced by metabolic processes or use organic electron donors utilized in the growth processes as fuels for current generation.
o A distinctive feature of biological fuel cells is that the electrode reactions are controlled by biocatalysts, i.e. the biological redoxreactions are enzymatically driven, while in chemical fuel cells catalysts such as platinum determine the electrode kinetics.
o This article provides a brief introduction to biological fuel cells along with their envisaged applications
Materials and methods:
Materials:
2 1x1x1 PVC Schedule Tee.
3 1" PVC Schedule Connector.
1 1" PVC Schedule Slip Cap.
2 1" PVC Schedule Plug.
1 1x1/2 Slip vs. FPT threaded adapter.
Titanium fishing lead.
Clear plastic wrap.
Rubber bands.
Salt Bridge Medium.
Household salt.
Drill Press or Drill with bits
Soldering iron with solder
Measuring cups
Skewer ( wood or metal )
Sample
Method
MFC design:
Step 1: Collection of materials.
Step 2: Create the salt bridge.
To create the salt bridge we will use gelatin in place of the more common agar. Start some water to boil, we don't need and actually won't use more than a couple of tablespoons. Take one of the coupler sections. Place the plastic wrap firmly over one end and secure with a rubber band to form a tight seal. Place the coupler open end up in a bowl. Take one packet of gelatin and pour it into the coupling. Fill the rest of the way with salt. Pour this mixture into a dry measuring cup and pour back into the coupling and notice that settling left a little more room. Top off with salt, pour back into the measuring cup and add an extra tablespoon. Mix the dry ingredients thoroughly and pour back into the upright coupler. When the water is at a strong boil pour a bit into the measuring cup and use this to gently fill the salt bridge. The mixture will settle and allow you to "top off" the water; this will disclose air bubbles flushed out and help judge when the bridge is full. Carefully picking it up and examining the bottom can also help make sure that the entire column is saturated. Allow to stand for a few minutes and pour off any tiny bit of standing water on the top. Then place the bowl in the refrigerator for 3-4 hours. This is the salt bridge, it should be left in the refrigerator until final assembly.
Step 3: Assemble the electrodes
First we will use one wire and one carbon brush to make a carbon electrode Now taking the DRY sponge cut a strip 3/4" wide and about an inch long. This piece should fit smoothly into the neck opening of the screw top. Now take it back out and using a skewer, nail or other suitable object punch a hole big enough for the wire to pass through.
Using the smallest drill bit we have equal to or greater than the size of the wire drill a small hole in the center of the screw cap. Thread the electrode lead through the sponge and slide the sponge into the the neck of the screw top. Thread the wire through the cap, it should pass more or less freely. Screw the top down lightly and add water to the sponge. It will expand to fill the neck and provide a slight overcover at the base.
This is the anode assembly. It is used for the anaerobic (microbe cell). The small gap will allow the decomposition gasses to escape while the sponge will inhibit the passage of air into the chamber. To add nutrients to the anode chamber simply unscrew the top and gently pour the nutrient medium through the sponge.
For the cathode we are using a different approach. The cathode is inserted into the sponge (actually placed between two pieces of sponge) where air can circulate freely.
To make the cathode assembly remove the coil wire from the remaining brush.
From the remaining section of the sponge cut a strip 1" wide by 4" inches long, then cut this into two strips. Please the remaining carbon brush between the two strips so that only the top is exposed. Insert this into one of the 1" connectors. Wet the sponge and it will expand to hold the electrode in place.
Step 4: Assemble the fuel cell
Once the salt bridge has cooled and solidified its time to assemble the device. For easier dis-assembly and maintenance we recommend coating the PVC with the graphite powder when assembling.Take the two remaining couplers and insert the end caps fully into them. Insert these into the base of the tees to provide feet for standing.Insert the salt bridge into the center tee. When properly seated the tees will meet and the salt bridge connector will not be visible.
Now the fuel cell is now complete and ready to be charged.
Step 5: Charging and Operating
Pick on chamber to be the anode (microbe) chamber and one to the cathode chamber.
Fill a measuring cup with about 2 ozs of warm water and add salt to it until no more will dissolve ( a saturated solution ). Stirring and shaking should be constant. Allow the water to completely cool. Remove the sponge slices from the cathode assembly and we make sure they are thoroughly soaked in the salt solution. We pour the rest into the cathode chamber until only the salt slurry remains. Place the carbon electrode on top of one sponge, cover gently with the slurry and then use the remaining slice to complete the sandwich. Place this gently back into its connector and insert into the cathode tube. The tube will overflow as the cathode is inserted, but thatâ„¢s okay we want the carbon electrode to come into contact with the air so pour off a bit of water as well.
Fill the anode chamber 1/2-3/4 full of the septic tank treatment. We also added a couple of teaspoons of sugar and some shredded paper to provide carbon and nitrogen. Fill the chamber the rest of the way with pure, dechloronated water. Insert the anode assembly fully into the anode tube.
We began measuring voltage on the open circuit. Within 15 minutes it
was generating measurable voltage . Once the output voltage seems to stabilize we will measure under load and update.
Method 2: Bio-electricity generation using a microbial fuel cells- the process of electrogenesis.
Method 3: New bottle reactor MFC.
Conclusion
MFCs represent a viable technology for simultaneous electricity generation and waste water treatment. Even though microbial fuel cells are not yet able to compete with other types of chemically-generated electricity, advancements in this area render this a possibility. Two key challenges in the quest for sustainable societies are energy generation and waste disposal; electrochemical fuel cells. As the applications of MFCs are ever-growing, feasible, economical and ecofriendly, the MFCs prove to be the most efficient fuel cells contemporarily available. The technology now exits for system scale up-pilot testing is needed.
