On Tue, 28 Jul 2020 12:12:49 +0100, NY wrote:

It's about the same noise at 100 yards as standing right next to a noisy
fridge. Maybe his sewage works is an early model and more noisy that
modern ones.

The latter. The active systems I've encountered have had noise levels
about that of a fridge when right next to them not 100 yds away.

They are more than just a motorised stirrer, there is a compressor to
bubble air through the contents as well.

--
Cheers
Dave.