How does a trickling filter work and what are its design parameters?

Trickling filters are fixed-film biological reactors where wastewater is distributed over media (stones or plastic) covered with biofilm. Microorganisms in the biofilm degrade organic matter as wastewater trickles down. Design parameters include: hydraulic loading (1-4 m3/m2/day for low rate), organic loading (0.08-0.32 kg BOD/m3/day), media depth (1.5-3m for stone, up to 12m for plastic), and recirculation ratio. Ventilation is critical for oxygen supply. Achieves 60-85% BOD removal.