We provide Bio-Filter mechanism upto 200' diameter and above to meet varying process requirement with plastic media or any other conventional media to achieve high level of BOD removal at very low operating cost generally in the primary stage. The key to the performance of Bio-Filter, beside the media is the Rotary Distributor which is installed at the centre of the circular Bio-Filter tank and these are designed to deliver consistent performance by uniformly distributing the wastewater over the media across the tank diameter. The simulated design allows the distributor to rotate with a very low hydraulic head of the wastewater and thus extremely low power cost. The Rotary Distributor is attached to number of arms, mostly two or four, and each of these arms are fitted with spreader nozzles to deflect and distribute the wastewater on the media while the arm is rotating due to the hydraulic head.