The Biogas Digester

Why a biogas digester?

Every kitchen produces waste — peels, scraps, leftovers. In most homes that energy is thrown away. A small biogas digester captures it instead: feed in the food waste and cow dung, and out comes methane gas for cooking and a slurry that is excellent liquid fertiliser.

It's low pressure, has no moving parts, and is safer to run than an LPG cylinder. Enough to power a single burner for a couple of hours a day — the difference between buying gas and making your own.

What you will build

Over two days you'll build a small household biogas digester from scratch, with expert guidance, using the exact system we use at Karuna. By the end of the workshop, you will:

• Have assembled a working biogas digester and seen it begin to produce gas.
• Understand the biology of anaerobic digestion — what to feed it, what not to feed it, and why.
• Know how to plumb the gas line, manage pressure, and use the slurry safely in the garden.
• Leave with plans and a materials list so you can build the same system at home.

How the system works — step by step

Transforming waste to fuel

As gas prices rise and resources become scarce, self-sufficiency in the kitchen starts with how we manage our organic "waste." This workshop focuses on a floating-drum biogas digester — a time-tested design perfect for local materials and reliable daily cooking.

1. The engine — the digester & gas holder

The system is built using two heavy-duty plastic drums. The larger Digester Drum (1) is buried or insulated to keep the active bacteria warm. Inside, a slurry of kitchen waste and cow dung undergoes anaerobic digestion.

The smaller Gas Holder Drum (2) is inverted and sits inside the digester, floating on the liquid slurry. As the bacteria produce methane, the drum rises — a clear visual indicator of how much fuel you have ready for dinner.

2. The clean-up — the H₂S filter

Raw biogas contains moisture and hydrogen sulfide (H₂S), which can corrode your stove and create a "rotten egg" smell. To solve this, the gas passes through a simple inline scrubber (4):

• Steel wool core. The iron in the steel wool reacts with the hydrogen sulfide, scrubbing it from the gas stream.
• Desiccant layer. A replaceable layer of silica or similar material catches moisture to ensure a dry, clean burn.

3. The power — modified LPG stove

Biogas has a lower pressure and energy density than commercial LPG. To get a strong, efficient flame:

• Jet modification. We slightly enlarge the stove's gas injector. This allows a higher volume of biogas to flow through, maintaining a steady, hot flame.
• The result. A slightly taller, yellowish-blue flame that is perfect for traditional Indian cooking — fueled entirely by yesterday's leftovers.

4. The bonus — organic fertiliser

Nothing goes to waste. As new slurry is added, the fully digested material — now a nutrient-rich, pathogen-free sludge — is pushed out through the scrap outlet. This is liquid gold for your garden, completing the cycle from soil to plate.

Workshop note: This setup is designed for ease of maintenance. By using local hardware and simple modifications, we can turn a mounting resource crisis into a sustainable, closed-loop solution for the home.

Who it's for

• Rural families with a cow or two — and a steady supply of kitchen waste.
• NGOs and community workers introducing closed-loop waste systems in villages.
• Homesteaders and off-grid builders setting up a self-sufficient kitchen.
• Students and researchers in appropriate technology, sustainable energy, or rural development.

Format

A two-day, hands-on workshop. Mornings are teaching and theory. Afternoons are construction. Evenings are shared meals and questions around the fire. Group sizes are kept small so everyone gets real hands-on time.

The workshop runs periodically — typically in the drier months when outdoor work is easier.

Who leads it

The workshop is led by Karuna's long-time builders and natural-systems team — the same people who built the earthships, the cob cow shed, and the solar-hydro power network that keeps Karuna off-grid. Pragmatic, practical, unromantic about what works.

Accommodation & meals

Stay in one of our cottages (see rates) for the workshop. Three vegetarian meals a day at Govinda's are included in the workshop fee. The build materials — drums, pipe, fittings — are also included.

What to bring

• Old clothes you don't mind getting dirty (there is dung involved).
• Work gloves (we have some spares but bring your own if you have them).
• A notebook and pen. You'll want to write things down.
• The usual Karuna essentials — torch, jumper, waterproof layer.

Register your interest