Water Treatment in Microbial Fuel Cell - A Sustainable Technology!

Water is referred to as waste water when it is highly polluted. It comprises liquid waste discharged by domestic residences, commercial properties; industry, agriculture and can encompass a wide range of potential contaminants and concentrations. In the most common usage, it refers to the municipal wastewater that contains a broad spectrum of contaminants resulting from the amalgamation of wastewater from diverse sources. When we talk about the waste water in Karachi, the conditions are worst. Being the most industrialized and urbanized city of Pakistan, Karachi is considered as the back bone of the Pakistans economy. According to Karachi Water & Sewerage Board (KWSB), more than 350 million gallons of wastewater is generated per day by different types of industrial processes and human operations. There are only three wastewater treatment plants in Karachi working at Haroonabad (TPl), Mahmoodabad (TP2) and Mauripur (TP3), which can treat less than 30% of the total wastewater generated. SITE, KIA and LIA are important industrial sites of Karachi in fluxing their wastewater directly into the Arabian Sea without any treatment. In addition untreated industrial effluents and domestic wastewater from other resources is also being discharged into the Arabian Sea. Therefore, more than 70% of the wastewater goes into the Arabian Sea without any treatment because the treatment process is very expensive which cant be afforded by our government without really achieving any advantage. So, the best possible solution is the waste water treatment in microbial fuel cell that can also help generate electricity.

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 cation (positively charged ion) specific 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, while 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.

Mediator-free microbial fuel cells do not require a mediator but use electrochemically active bacteria to transfer electrons to the electrode (electrons are carried directly from the bacterial respiratory enzyme to the electrode). Among the electrochemically active bacteria are, Shewanella putrefaciens, Aeromonas hydrophila, and others. Some bacteria, which have pili on their external membrane, are able to transfer their electron production via these pili. Mediator-free microbial fuel cells can, besides running on wastewater, also derive energy directly from certain aquatic plants. These include reed sweet grass, cord grass, rice, tomatoes, lupines, and algae. These microbial fuel cells are called Plant Microbial Fuel Cells (Plant-MFC). Given that the power is thus derived from a living plant (in situ-energy production), this variant can provide extra ecological advantages.

Electricity in these cells are produced according to the following reaction

C12H22O11 + 13H2O ---> 12CO2 + 48H+ + 48e-

MFC consists of two cells separated by a thin proton/cation exchange membrane. Microorganisms oxidize the substrate and produce electrons and protons in the anode chamber of MFC. Electrons collected on the anode are transported to cathode by external circuit and protons are transferred through the membrane internally. Thus, potential difference is produced between anode and cathode chamber due to dissimilar liquid solutions. Electrons and protons are consumed in the cathode compartment by utilizing oxygen from water and produce electricity.

The technology is widely used for waste water treatment and production of electricity. This MFC technology is cheap and very useful because with the use of this technology we cant only treat the water but also produce electricity. In a country like Pakistan, facing load shedding as one of the major problems, this technique can help bring some revolutionary changes. The government should encourage the companies so that they may use the MFC technology for the treatment of their waste water and thus, produce their own electricity.