Synthetic dye and sewage treatment plant: what they have in common

1. Step 1. Synthetic dye — is a kind of — Dye. A dye.
2. Step 2. Dye — uses — Fermentation. Some dyes (indigo) were obtained by fermenting plants.
3. Step 3. Fermentation — is used in — Sewage treatment plant. Activated sludge is microbes.

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