Wetland collection / field note 01

Every clean ideastarts somewhere messy.

Before MudBottle had a clean name or a tidy diagram, we had to go where the microbes live: into reeds, wet boots, and dark sediment that looked ordinary until it started making electrons.

Mud and wetland plants during field collection for the MudBottle project

Origin / MudBottle idea

From curiosity to water-treatment concept

We were not only trying to prove that microbial fuel cells could make electricity. The harder question was whether that energy could be collected, saved, and spent on a real water-treatment step.

01 / question

Could electricity from mud help clean water?

The idea started with a simple question: could the slow energy produced by microbial fuel cells be harvested, stored, and used for electrochlorination?

02 / concept

MudBottle was our way of testing the idea.

The concept connects four jobs: MFCs generate electricity, a harvester collects it, storage holds it, and the stored energy is released to disinfect water.

03 / material question

Then the cathode became part of the story.

During MFC development, PTFE stood out as something worth improving. That led to testing whether chitosan could replace it as a cathode coating while keeping useful electrical performance.

Early microbial fuel cell test setup before the MudBottle form — Before the bottle / test cells

MudBottle prototype held by hand — The concept / first bottle form

Long-term vision

A bottle that powers its own treatment step.

MudBottle points toward a compact, decentralised system where microbial activity supplies the energy for water disinfection.

Minimal external energy

Useful where infrastructure is limited

Biology, storage and treatment in one loop

Further work

Optimizing chitosan coating

Redesign MudBottle to fit standard screw-cap bottles

Electrode optimization and design

Engineering / iteration

Harvest the Current, Treat the Water

The engineering challenge was making the whole chain work: harvest enough microbial energy, store it, discharge it into electrochlorination. During the process, a question arose: could we improve cathode sustainability?

Prepared microbial fuel cell electrode parts on the lab bench

Electrochlorination test setup in the lab

Prepare the cells

The work started with the physical cell parts: membranes, electrodes, wiring, and enough repeated units to construct an array.

Microbial fuel cell setup during early electrical testing

Assemble the units

The next step was turning individual parts into working MFC units, ready to be filled, sealed, wired, and compared. The first voltages were not exactly dramatic, but they were enough to show us where to iterate.

Wired microbial fuel cell array with voltage measurement

Measure the output

Once the cells were running, the focus shifted to wiring, measuring, and checking whether the array produced a usable electrical signal. After setup improvements, a total of 1.3 V and 15 mA was achieved with a 3S9P array.

Energy harvesting board connected to microbial fuel cells and supercapacitors

Harvest and store

The AEM00940 harvester and supercapacitors turned a weak, slow input into stored charge that could be released later.

Chlorine and pH test strip used after electrochlorination

Microbial fuel cell parts during assembly

Measure disinfection

The stored energy was discharged into 400 mg/L salt water, then checked with chlorine and pH measurements to see whether treatment had actually happened. We were excited to discover that a 200 mV discharge at 4 V produced 1-3 ppm chlorine.

Cathode coating material being applied in the lab

Rethink the cathode

Alongside the energy chain, the cathode became a material question: could chitosan replace persistent PTFE without losing useful performance?

Material turn

With the proof of concept working, the next challenge was making the cathode more sustainable.

Material decision

While the system had to harvest and store enough energy, the cathode raised a second question: could chitosan replace PTFE without losing useful electrical performance?

PTFE molecule visual — PTFE
Proven cathode coating, but fluorinated and highly persistent.

vs

Chitosan molecule visual — Chitosan
Bio-derived alternative tested for usable cathode performance.

The answer

At a 0.05 g/g loading, chitosan matched or beat PTFE's performance in early testing. A heavier 0.1 g/g loading underperformed both, so the useful range is narrow — worth confirming with more samples before calling it a replacement.

Read full report

Cathode performance comparison: PTFE vs chitosan at two loadings

People behind the project