Bologna’s plant limits are different from the regulation: ammonia nitrogen mg/l; COD 160 mg/l; TSS 80 mg/l. For the Imola plant, where there is a final lagoon, the TSS limit is 150 mg/l. The efficiency in removing pollutants in compliance with the legal limits, as expressed by the indicator in the graphic, is related to the purification capacity of the plant and the technologies adopted.