One thing I noted was how common tricking filters were for wastewater treatment. Of course these trickling filters typically were rock based versus modern plastic media. As a result of the rocks, the filters were relatively shallow in depth with no need for blowers to supply oxygen in the lower regions. They selected trickling filters over lagoons (the alternative common technology) because it had greater treatment efficiency and took up less space than a facultative or partially aerated lagoon.
This is very similar to today's fixed film systems including RBCs, MBBR, and even modern trickling filters. Our new systems are designed with added aeration for high DO residuals along with greater surface area per square meter which allows for more biomass per unit volume. Why did they abandon tricking filters for activated sludge in the 1960s - 70s. Well it was a case of more stringent permits and modern fixed film system not being fully developed at the time.
For you reading pleasure, I am including an old case history of parallel tricking filters with a bioaugmentation trial that was run over a 6 week period. Because of parallel setup, there was a control and experimental for the test.