Editorial Feature

Microbial Fuel Cell Turns Human Waste into Power

A microbial fuel cell enables the conversion of chemical energy to electrical energy when microorganisms react by catalysis.

A microbial fuel cell includes cathode and anode compartments separated by a positively charged membrane. Fuel is oxidized in the anode section by micro-organisms and electrons, protons and carbon dioxide is generated.

The transfer of protons to the cathode compartment is done through the membrane and the transfer of electrons to the cathode is done through an external electric circuit. Protons and electrons are consumed in the cathode and combine with oxygen forming water.

Caitlyn Butler’s Green Pit Latrine

Environmental Engineering professor, Caitlyn Butler has come up with a novel green pit latrine that is capable of purifying human waste to supply power for a small village in Africa and at the same time converting the waste into healthy compost for farming purposes.

This new innovation is defined as the microbial fuel cell pit latrine. Dr Butler traveled to Ghana for the installation of a pilot version of the device in the tiny village of Agona Nyakrom.

She worked with graduate students Joe Goodwill and Cynthia Castro, collaborators Brad Rogers and Mark Henderson from Arizona State University. She is aiming at deploying this system at affordable prices throughout the developing world.

She believes that the deployment of her economical latrine will change the way human waste is treated in places where there are poor or non-existent sanitation facilities. The device will also play an important role in preventing waterborne diseases such as diarrhea.

Butler stated that a lot can be obtained from this system. Electricity is generated, compost is made and the ground water source is protected so that one gets enough returns for minimal investment.

According to her, the pilot model will be able to address key challenges faced by the village. These include the following:

  • The leaching of human waste into the ground water causes the introduction of deadly pathogens due to which waterborne diseases such as diarrhoea start spreading.
  • Healthy water systems can also be damaged due to the leaching of human waste into the ground water and may cause nitrate poisoning in the elderly and the young.
  • A number of villages in Africa have little amount of electricity and the fuel cell of Butler generates enough electricity to power a light in the latrine. This kind of centralized resource will help the whole community.

Butler’s latrine works similar to a battery and has a cathode and an anode. Here the fuel is the organic waste matter and the oxidant is the nitrate. The system includes a composting chamber in which solid wastes are initially filtered and oxidation of the dissolved waste organic matter is done in an anode chamber.

Bacteria on the anode surface assist the oxidation of organic matter and the metabolic reaction is completed by using the anode as an electron acceptor. This biological process releases electrons that are transmitted through a load-bearing circuit generating electricity to the cathode component.

The cathode is used as an electron donor by a different community of bacteria and the energy is captured from the electrons reducing harmful nitrates in the waste stream.

Ammonium is the key nitrogen compound found in human waste that can be decomposed by nitrification or oxidation. Bacteria present in the intermediate chamber between the anode and the cathode enables nitrification in Butler’s latrine.

This reaction causes effluent water that is low in nutrients and organic matter reducing the presence of pathogen in the environment. She also added that the objectives of her research are to develop energy-efficient treatment strategies for waste water and water treatment.

Currently, she is studying biofilms that can either use a cathode as an electron donor or an anode as an electron acceptor.

Oregon State University Microbial Fuel Cell

Oregon State University researchers have designed a microbial fuel cell that is capable of treating waste water and generating significant amounts of power at the same time.

The microbial fuel cell is similar to a normal fuel cell but uses waste water as a fuel and specially designed bacteria behave as a catalyst.

Hong Liu and her OSU colleagues developed this fuel cell in which waste water enters at the anode, bacteria oxidizes the organic compounds and spare electrons are produced through which only clean water can pass through, purifying the waste water.

The MFC produces 2 kW of power/m3 of bioreactor volume but around 10 – 50 times more power when compared to other MFC’s commercially available.

Ecobot III

The Ecobot III is a self-sustaining, lightweight robot that is developed for the cleaning of wastewater. The Ecobot III is powered by microbial fuel cells that use human waste as the fuel. The electricity produced helps the robot to generate electricity for performing cleaning.

Funding was done through the Engineering and Physical Sciences Research Council (EPSRC) and developed along with Wessex Water and the Bristol Robotics Laboratory in England.

The Director of Innovation and Research from Wessex Water, Dr Julian Dennis stated that this technology could be applied in remote areas where the robot is capable of running off organic waste.

The main goal of this project was to create a machine that is self sufficient having an on-board fluid circulation that will obtain energy from its environment and eliminate its own waste.

The robot is just 6 kg and includes artificial digestion, ingestion and solid waste excretion mechanism. Beneath the microbial fuel cells is an overflow collection tray that feeds back into the ingestion vessel.


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