MartinR has it. It's actually the Southern Water Sewage Treatment Works at Sittingbourne, although it's actually in Milton Regis. The photo is of the flow-rate meter at the old inlet works.
It measured the incoming flow in the millions of gallons per day. This part of the works is actually derelict now, having been replaced by a new inlet works built in the early 2000's, as part of an overall expansion in the capacity of the plant. In addition to building a new inlet works, some new settlement tanks and a new sludge works were built. The expansion was necessary because of all the new housing built around Milton Regis and Kemsley. Also, more stringent environmental controls meant that the inlet works needed better and higher capacity screens designed to handle all the "rag". "Rag" is what Sewermen call the mass of wet wipes, sanitary towels, tampons, condoms and ear buds which seem to be finding their way into the drains in ever greater amounts these days.
The old inlet works at Sittingbourne is now completely derelict and overgrown with brambles and bushes, but is easily visible from the Saxon Shoreway as it follows Milton Creek up towards the Nature Reserve. I took this photo amongst others while doing some work on the Storm Tank at Sittingbourne.
Over to you MartinR.....