Quern and sewage treatment plant: what they have in common

1. Step 1. Quern — is used in — Bread. Flour was ground on millstones.
2. Step 2. Bread — uses — Fermentation. Yeast dough rises through fermentation.
3. Step 3. Fermentation — is used in — Sewage treatment plant. Activated sludge is microbes.

Open Evothings