A pilot unit was constructed and operated to study the ability of treating polluted water using biological treatment. The experimental unit consists of water sprayer unit that ensure wetting of the filtered media and distributing water in a homogenous manner as well as increasing the dissolved oxygen concentration in water. The sprayer unit is followed by a biological filter; the area of the filtered media was (13) m2. The developed biological film placed on the filtered media will dismantle the organic matter, which reduce nitrates to nitrite then to a nitrogen gas. The filter was connected to an aeration basin where the suspended growth was archived. The pilot unit was operated depending on the water was taking from a manhole nearby the residential unit number 18. The average efficiency of BOD5 removing was 69.4% and of nitrate, removing was 34%. The results showed that this system can improve water's characteristics.