Eutrophication is reported as the most important water quality issue around the world. The potential death of Lake Winnipeg, the world's ninth largest lake, is a dramatic exampe of this ecological disater in Canda. Property price devaluation, tourist repulsion, and toxicity due to eutrophication cause the annual economic losses over $3 billion in Europe, South and North America. The objective of this thesis is to develop an efficient biological nutrient removal reactor to be commercialized and used in the water/wastewater treatment industry. This bioreactor has a unique configuration which is filed as a US patent technology called "Compact Upright Bioreactor for the Elimination of Nutrients", invented by M. Alvarez Cuenca and M. Reza. It consists of four stages including Deaeration, Anoxic, Anaerobic and Aerobic where Do removal, denitrification and phosphorus removal processes take place respectively. The bioreactor performs very well obtaining 100% Do removal and 98% nitrate removal efficiency. The phosphorus removal process requires much longer operational period to reach steady state. The phosphorus removal process shows variable results having a maximum of 60% removal success.