MFC (Microbial fuel cell)

 

Several technologies have been studied as alternatives to petroleum-based fuels. Among these stands out the technology of fuel cells due to their diverse field of application extends from portable devices to generate stationary, including automotive use. Although the high cost still prevents the application of such devices on a large scale, reduced cost, weight and increase efficiency, will provide a rapid growth in the use of fuel cells. The technology of fuel cells is divided into two categories electrochemical fuel cells (also called conventional) and biocells fuel (or fuel cell biological - MFC), the latter having received extensive attention in the past three years.  For the production of electricity, the MFC operates with two sections (one cathode-anode-aerobic and anaerobic), separated by an ion selective membrane H. Micro-organisms are used to catalyze the oxidation of organic matter, generating electricity by transfer of electrons to an external circuit, introduced before the step of reducing an electron acceptor. In the anaerobic compartment is the oxidation of organic material, with formation of CO2, protons and electrons. The generated protons migrate to the aerobic compartment (cathodic chamber) permeating through the proton exchange membrane. The produced electrons are transferred to the cathode through the external circuit, and this surface is the reduction of oxygen to water. This flow of electrons through the external circuit generates an electrical current that can be measured and used to do work. The overall cell reaction is the conversion of biodegradable organic material to carbon dioxide and water, generating electricity in the process. The electrodes can not colonized by a few species of bacteria. Electroactive bacteria can transfer electrons to the electrode surface without the need for redox mediators. Some of the micro-organisms known more electrochemical active Shewanella putrefaciens and Shewanella oneidensis, the Gamma-proteobacteria, Geobacter sulfurreducens, Geobacter metallireducens and Desulfuromonas acetoxidans all Deltaproteobacteria and Rhodoferax ferrireducens the Betaproteobacteria. The MFCs form a promising technology for sewage treatment, as a method of recovering energy in the form of hydrogen or electricity. In 2004, there was a change in the relationship between electricity production and sewage treatment, when it was shown that wastewater can be treated at practical levels parallel to power generation. The amount of energy generated in the study, although low, can be considered high compared to previous studies. Reimers, 2001, demonstrated that inorganic and organic materials present in marine sediments could be used in a new type of MFC, with the use of variety of substrates, new materials and structural arrangements in the construction of the MFCs.

 

MFC CONSTRUCTION

Materials

á4 PLATES ACRYLIC 120x120mm, 5mm thick

á2 PLATES ACRYLIC 100X75mm, 5mm thick

á2 PLATES 120X75mm, 5mm de thick

á24 screw-nut M6

á24 washer/bezant M6

á6 tubes of 20g of cyanoacrylate (superglue)

á6 connectors 1/4''

áHose 1/8''

áStraight connectors 1/8''

á3 valves d

_ácarbon fiber

_á10x10cm de NAFION^¨  MEMBRANE117

Procedures

1)            Machining of acrylic pieces.

The acrylic pieces were cut according to the specifications.

 

Assembly

 

á               Plates were united in order to form a rectangle with cyanoacrylate based glue as shown below:

 

https://igem.org/File:8.png

 

 

Electrode:

Aluminum wire was wound and coated with a carbon fiber for the anode.

A heat sink aluminum was used as the counter electrode to the cathode

 

 

 

SETUP OF MEASUREMENT DEVICE

The electrodes were connected to a resistor of 0.9620 K½, and then connected to an Agilent U1252A multimeter. The potential was measured at intervals of 15 minutes by 9hrs30min, and stored. From the same may construct the table below, where the MFC produced watts / hour.

Time	Potential with charge (mV)	Resistence ½	Current(mA)	Potencia (uW)	Energy (uW-h)
1	65,00	153,38	0,424	27,546	6,886
2	121,29	153,38	0,791	95,914	23,978
3	222,90	153,38	1,453	323,930	80,983
4	120,89	153,38	0,788	95,282	23,821
5	161,97	153,38	1,056	171,041	42,760
6	139,97	153,38	0,913	127,732	31,933
7	124,67	153,38	0,813	101,334	25,333
8	96,71	153,38	0,631	60,978	15,245
9	67,01	153,38	0,437	29,276	7,319
10	172,65	153,38	1,126	194,341	48,585
11	212,42	153,38	1,385	294,186	73,547
12	320,00	153,38	2,086	667,623	166,906
13	358,00	153,38	2,334	835,598	208,899
14	147,53	153,38	0,962	141,903	35,476
15	333,00	153,38	2,171	722,969	180,742
16	357,00	153,38	2,328	830,936	207,734
17	293,00	153,38	1,910	559,714	139,929
18	260,95	153,38	1,701	443,962	110,991
18	150,40	153,38	0,981	147,478	36,869
20	178,94	153,38	1,167	208,759	52,190
21	177,45	153,38	1,157	205,297	51,324
22	95,06	153,38	0,620	58,915	14,729
23	97,04	153,38	0,633	61,395	15,349
24	50,00	153,38	0,326	16,299	4,075
25	167,00	153,38	1,089	181,829	45,457
26	155,85	153,38	1,016	158,360	39,590
27	108,30	153,38	0,706	76,469	19,117
28	145,80	153,38	0,951	138,595	34,649
29	153,26	153,38	0,999	153,140	38,285
30	230,11	153,38	1,500	345,225	86,306
31	122,04	153,38	0,796	97,104	24,276
32	91,73	153,38	0,598	54,860	13,715
33	64,22	153,38	0,419	26,889	6,722
34	15,11	153,38	0,099	1,488	0,372
35	37,67	153,38	0,246	9,252	2,313
36	76,50	153,38	0,499	38,155	9,539
37	20,48	153,38	0,134	2,734	0,684
38	8,75	153,38	0,057	0,499	0,125
39	45,22	153,38	0,295	13,330	3,333

 

This means that the MFC produced is necessary to feed our own meter for approximately 5.6 minutes. The calculations below demonstrate our conclusion:

Current battery power meter = 2.8mA = I.

Supply voltage meter = 7.38 V = V

Power generated by the MFC = 1930.085 μW

Power required by multimeter:

P = VXI = 7.38V x 0.0028 = nd = 0.020664W 20664μW

PMFC / Pmultimetro = 0.093405 h Å 5.6 minutes

 

The electricity generated is measured as follows:

The MFC electrodes are connected in parallel with the multimeter, whose terminals are also placed in parallel with screw terminals, so that there is overhang of the screws engaged in the junction, in order to connect, also in parallel with a resistor (15 k) with sole purpose of measuring its power.

The voltage produced by the full MFC suffers a fall due to the consumption of the load. With a quarter of a period of time, it is checked potential difference "up" resistor, so in the end of 8 hours of perform the integration of the power to obtain energy.

Through the knowledge of Ohm's law, we know that the voltage produced undergoes substantial decrease before the presence of the load, which does not affect the efficiency of the system.