Many years ago, I went to a plant manufacturing cooking oil. We were installing new fatty acid deodorizers. Damn, they needed them.

Pulp and paper plants are pretty nasty; and food processing plants with wet/rotting grains are vile. I used to get highly amused by auditors puking. Raw sewage generally smells better - lol.

Without hesitation, the smell of persons who didn’t took a shower for a long time, the only smell so far able to make me puke.