Home biogas digesters: cooking gas from scraps, not electricity

What it makes

A digester is a sealed tank where bacteria break down food scraps or manure without air. They give off biogas: 50 to 75% methane, the same main ingredient as natural gas (EPA). It burns in a gas stove.

Setup	Fed	Cooking gas a day
In-ground bag digester (NCAT)	~10 gallons a day	~4 hours
HomeBiogas 2 kit (maker's rating)	Kitchen scraps	2 hours, one burner
HomeBiogas 7 kit (maker's rating)	Kitchen scraps	6 hours

For a household that cooks on propane, that's a real saving. You also get a liquid fertilizer out the other end.

Why it isn't a power source

Running a generator on biogas means cleaning the gas first: its hydrogen sulfide corrodes engines and pipes. NCAT's verdict is that this takes money and full-time attention that only pays at farm scale. At home, burn it directly: a stove, a water heater, a gas light.

For electricity, solar sized for your darkest month does the job: see what yours needs. A digester can still help it: every meal cooked on biogas is one that isn't on an induction cooktop drawing from your battery.

It needs warmth

The bacteria work best from about 60°F to over 100°F. Above-ground kits slow down a lot in cold weather. In a cold climate, a digester goes in the ground (the earth holds a steady temperature), in a greenhouse, or gets a heater. Plant scraps tend to keep going in the cold better than manure.

Safety

• Biogas burns like any fuel gas. Never look for leaks with a flame; use soapy water.
• Its hydrogen sulfide corrodes metal pipes and fittings over time. Check them.
• Never climb into a digester or a closed tank. The air inside has no oxygen and can kill.