Improvement of nitrogen removal in a large municipal wastewater plant

The wastewater treatment plant utilized in the metropolitan area of Turin is connected to the Po river near the town, in an area that has been considered very critical for potential eutrophication phenomena. This fact led to the requirement of very high nitrogen removal performances for the plant; with this purpose an examination of water treatment line and sludge system has been performed, in order to identify potential interventions suitable to obtain the required improvement. First of all an analytical screening of the nitrogen concentrations in different flows interesting the plant was performed. The experimental results have been used to construct a nitrogen mass balance in the plant and to identify the removal capacities that the treatments operating in the system are able to realize. On the basis of the performed observations, two fundamental technological solutions in order to improve the nitrogen removal have been identified. The first one, to be realized on the waste water treatment system, doesn't require plant innovations, but only interventions on the biological treatment tanks. The second technological solution, necessarily connected with a plant innovation, consists in the realization of a system of autotrophic anoxic removal of nitrogen operating on the internal recycle, with the adoption of a fixed specialized biomass bioreactor operating on the recycle flux that is very rich in ammonia nitrogen, and poor in organic carbon. The two solutions are discussed and compared, with reference to operations and performances.