Hiya, thanks for the note. Sounds like you know more about the site than my guess from the aerial imagery, so please feel free to amend the tagging to be more appropriate. :) If a suitable tag isn’t already documented on the wiki (see things linked from https://wiki.openstreetmap.org/wiki/Tag:man_made%3Dwastewater_plant) then feel free to make up a new one (see https://wiki.openstreetmap.org/wiki/Any_tags_you_like).

In any case, it might be worth keeping a link to https://waterprojectsonline.com/case-studies/kendal-wwtw-2019/ in a note on the reactor. :)