Microbial Electrochemical Systems
The living battery hiding in wastewater
Certain bacteria breathe by pushing electrons onto solid surfaces. Give them an electrode and they turn sewage, sediment, and CO₂ into electricity, hydrogen, clean water, and recovered nutrients. This is the science — and the machines it makes possible.
- 1911
- first observed by M.C. Potter
- 5
- physics families
- 14
- system types
- 21
- interactive reactors
Follow one electron
The journey of a single electron
Forget the whole cell for a moment. Follow one electron from the acetate a bacterium just split, out through the wire that lights a lamp, and home again to make a drop of water — one step at a time.
A bacterium in the anode biofilm oxidizes acetate and releases an electron.
How it works
One skeleton, fourteen machines
Every microbial electrochemical system shares the same core: bacteria trading electrons with an electrode, ions crossing a membrane, a reaction completing on the other side. Change the cathode, the membranes, and the voltage, and that one architecture generates power, makes fuel, desalinates, recovers metals, or senses. The taxonomy sorts them into five physics families — explore each below.
Microbes oxidize fuel at the anode; electrons do useful work on the way out.
The canonical system. Electroactive bacteria oxidize organic matter and hand their electrons to the anode; the electrons power an external load on the way to the cathode, where oxygen becomes water.
- Anode
- Organics → CO₂ + H⁺ + e⁻
- Cathode
- O₂ + 4H⁺ + 4e⁻ → 2H₂O
- Power density
- up to ~3 W/m²
One architecture, many outputs
Watch one cell change its job
A microbial anode, a cathode, a membrane, a wire. Change one thing at a time — the cathode reaction, the applied voltage, the number of chambers — and the identical skeleton becomes a fuel cell, a hydrogen plant, a chemical factory, a desalinator, or a metal mine. Scroll to watch it transform.
MFC
Electricity
Cathode
O₂ + 4H⁺ + 4e⁻ → 2H₂O
Power density
up to ~3 W/m²
MFC
Electricity
01 · Microbial Fuel Cell
Start with electricity
Electroactive bacteria oxidize organic waste at the anode and release their electrons. Wired through an external load on the way to an air cathode — where oxygen simply becomes water — that current is harvested directly as power. One chamber, one membrane, no voltage supplied. This is the skeleton every other device inherits.
MEC
Hydrogen
02 · Microbial Electrolysis Cell
Add a nudge, make hydrogen
Keep the anode identical, but seal the cathode away from air and apply about 0.4 V — a tenth of what plain water electrolysis demands. Starved of oxygen, the cathode now reduces protons instead: 2H⁺ + 2e⁻ → H₂. The load became a power supply, and the waste stream becomes a clean, storable fuel.
MES
Chemicals
03 · Microbial Electrosynthesis
Reverse it to synthesize chemicals
Move the biofilm to the cathode and run electrons the other way. Fed CO₂ and a small applied voltage, cathodic microbes fix carbon into acetate, ethanol, and other platform chemicals. The anode now oxidizes water; the device is a biological power-to-X reactor that builds molecules instead of burning them.
MDC
Fresh water
04 · Microbial Desalination Cell
Split the cell to desalinate
Return to the microbe-powered fuel cell, then insert a third chamber between the electrodes, bounded by an anion- and a cation-exchange membrane. No extra voltage is needed — the electric field the bacteria already generate pulls Na⁺ and Cl⁻ out of the middle stream, desalinating water on the energy in the waste, with no pumping pressure.
MMRC
Recovered metal
05 · Microbial Metal Recovery Cell
Aim the cathode to recover metal
Collapse back to two chambers and feed the cathode a metal-laden effluent. The same electrons that once made water now reduce dissolved copper, silver, or chromium to their solid form, plating them onto the electrode. The reactor becomes a mine — pulling value out of mining runoff and electroplating waste while still treating it.
Applications
21 reactors, one living principle
Each card below is a real, interactive 3D reactor from the MESSAI lab — spanning microlitre chips to full municipal plants. Filter by what they do, then open one to spin the model and see its performance envelope.
Perspectives
The same reactor, five different stories
A microbial fuel cell is a science experiment, a business case, a permit strategy, a climate lever, and a classroom demo — all at once. Choose who’s reading and the story reframes itself.
Read as: Researcher
A hypothesis you can finally test against the whole literature.
“You see an experiment waiting for its priors.”
MES research is gloriously noisy — power-density coefficients of variation run past 1,000%. MESSAI treats that honestly: it extracts parameters from thousands of open-access papers, sorts every system into five physics families, and fits hierarchical Bayesian priors so a point estimate always arrives with its uncertainty attached.
- Reproducibility
- n, units & CoV on every number
- Physics families
- 5 — not 3 hard-coded types
- Uncertainty
- hierarchical priors, calibrated CIs
Start with these
Settings
The same tech, five settings
A microbial reactor that thrives on the seafloor is a different machine in a megacity treatment plant, a brewery, or a spacecraft. Choose where it’s deployed and the binding constraint — and the story — reframes itself.
Deployed in: Off-grid village
With no grid to lean on, a microbial system earns its keep by being self-powered and stubbornly simple. A jar of sediment and two electrodes treats local waste, powers a sensor, and asks for nothing back — no pumps, no chemical inventory, no service truck. The reward is decentralized treatment and trickle power exactly where centralized infrastructure never reaches.
What dominates here: self-sufficiency — every watt and every part has to be local.
- Power budget
- 1–50 µW per device — enough for a sensor
- Infrastructure
- zero grid, zero dosed chemicals
- Maintenance
- buildable and repairable at the bench
Start with these
Impact calculator
What could a plant recover?
Move the inputs — or start from a scenario — to see live, order-of-magnitude estimates of what a microbial-electrochemical treatment train might recover from a waste stream. These are illustrative figures for building intuition, not design numbers for any specific plant.
Start from a scenario
Inputs
Illustrative organic (COD) load: 150 kg/day. Estimated installed capital: $60,000.
Illustrative recovery
Energy recovered
60
kWh / day
from 120 kg COD removed / day
CO₂ avoided
19
t CO₂ / year
recovered + avoided-aeration electricity
Recovered value
$8k
per year
energy sold + aeration saved + resources
Simple payback
8
years (rough)
undiscounted, pilot-era capex ±2×
Order-of-magnitude only. Real microbial-electrochemical performance varies by more than one order of magnitude with substrate, temperature, geometry, and biofilm maturity.
From a curiosity in a petri dish to infrastructure that treats, powers, and recovers.
MESSAI turns the published literature on these systems into models you can query, compare, and design against.