Direct thickening screen
Is it possible he’s using too high a dose of polymer?
Does the water treatment system process industrial effluent?
No, it's actually a typical municipal effluent with no industrial input.
If you perform an HEM test (hexane extractable content), you’ll be able to see if there is a variation in the oil and grease, and a microscopic analysis will tell you whether it contains filamentous bacteria..
High pressure cleaning of the screen wouldn't hurt.