AnodeThe negative electrode. The bacteria on it give up electrons.
CathodeThe positive electrode. Electrons, protons and oxygen meet here.
Proton exchange membraneIt lets protons through and keeps the two liquids apart.
Bacteria (biofilm)A layer of bacteria that lives on the anode.
Organic matterThe fuel. The bacteria break it down for energy.
ElectronsThey flow along the wire, anode to cathode.
ProtonsHydrogen ions that cross the membrane to the cathode chamber.
Carbon dioxideA gas the bacteria give off as they break down the fuel.
Anode chamberThe side kept free of oxygen, where the bacteria live.
Cathode chamberThe side supplied with oxygen, where water forms.
Wastewater inDirty water that carries organic matter into the cell.
Treated water outThe water leaves with less organic matter in it.
NanowiresThin conducting threads that carry electrons from bacteria to the anode.
How this list was compiled: Every name and fact checked on 2026-10-03, a name kept only where two independent texts use it. (1) Wikipedia, text only, Microbial fuel cell: bacteria that pass electrons to the anode; a biofilm-covered anode; an anode chamber sealed from oxygen and a second chamber with the positively charged cathode; a wire between the electrodes; a salt bridge or ion-exchange membrane, such as a proton exchange membrane, that lets protons pass from anode chamber to cathode chamber; carbon dioxide, protons and electrons from the fuel; oxygen at the cathode; wastewater and its organic matter as fuel, and clean water as a product; electron transfer by pili. (2) S. Roy and others, Microbial Fuel Cell Construction Features and Application for Sustainable Wastewater Treatment, Membranes, 2023 (open access review): an anodic chamber kept without oxygen, a cathodic chamber and a proton exchange membrane; microorganisms that generate electrons and protons, with carbon dioxide as a byproduct; electrons passed by an external circuit; protons that reach the cathodic chamber through the membrane and react with oxygen to give water; biofilm on the anode; organic matter in wastewater; nanowires. (3) J. Greenman and others, Microbial fuel cells and their electrified biofilms, Biofilm, 2021 (open access review): two chambers split by a membrane that lets ions cross; a biofilm of bacteria on the electrode; organic substrates; the anode chamber and cathode chamber; oxygen from air at the cathode; bacterial nanowires. (4) C. Santoro and others, Microbial fuel cells: from fundamentals to applications, Journal of Power Sources, 2017 (open access review): electroactive biofilm on the anode; organic compounds from wastewater as fuel while the water is cleaned; conductive pili, also called bacterial nanowires. Licence: own work
The drawing: Drawn for this site on 2026-10-03 from plain geometry; not to scale; nothing traced or copied. Licence: own work
How it works
A microbial fuel cell uses bacteria to turn the organic matter in wastewater into electric current. This diagram of a microbial fuel cell shows a two-chamber cell.
Read the full guide
At the anode
The anode chamber is kept free of oxygen. Bacteria in a biofilm on the anode break down organic matter and release carbon dioxide, protons and electrons. The electrons pass to the anode, some along nanowires, and flow through the wire to the cathode. That flow is the electric current, and here it lights a lamp.
At the cathode
The protons cross the proton exchange membrane into the cathode chamber. There they meet the electrons and oxygen from the air and form water. The oxygen, the water and the lamp are drawn but not asked.
The quiz takes biofilm for the bacteria, PEM for the membrane and hydrogen ions for protons.
Questions and answers
How does a microbial fuel cell work?
Bacteria on the anode break down organic matter and release electrons and protons. The electrons travel through a wire to the cathode as electric current, and the protons cross a membrane. At the cathode both join oxygen to form water.
What are the parts of a microbial fuel cell?
An anode chamber and a cathode chamber, each with an electrode, a proton exchange membrane between them and a wire that joins the electrodes. The anode carries a biofilm of bacteria, and the liquid around it holds their fuel.
Why is there no oxygen in the anode chamber?
With oxygen present the bacteria would pass their electrons to it and not to the anode, so no current would flow through the wire.
Which bacteria are used in a microbial fuel cell?
Electrochemically active bacteria, which can pass electrons to an electrode. Shewanella and Geobacter are two kinds that are often studied.
What can a microbial fuel cell run on?
Almost any organic material, including the organic matter in wastewater. A cell fed with wastewater cleans the water while it produces a little electricity.