Italy, Energy Efficiency of the Wastewater Treatment Plant Monza

The WWTP San Rocco is designed to treat the wastewater of 700,000 PE and a maximum flow of 900,000 m³/d. The effluents are rejected about 2 km downstream into the river Lambro. As the Lambro is a tributary to the river Po that leads into the Adriatic Sea, it is declared as sensitive water body. This means that the effluent of the WWTP has to meet strict effluent values.

The plant has been constructed in 1965 and constantly been extended and rehabilitated during the last 30 years. Latest rehabilitation measures executed were the complete reconstruction of the mechanical pre-treatment except from the primary sedimentation in 2010 and the new construction of an additional sludge treatment step (Biothelis process).

The treatment process consists of mechanical pretreatment with sand and grit removal, biological treatment with the elimination of carbon and to some extent nitrogen as well as phosphor, and anaerobic sludge stabilization. The digester gas is used in gas engine driven ventilators for the aeration of the biological treatment. The cooling water of the engines in turn is used to heat the sludge. Especially the aeration system and the sludge stabilization showed significant savings potential.

After data collection and analysis, the present power consumption was evaluated. Based on this, measures to save energy were proposed, which were checked for plausibility and practicability, and weighted according to their cost efficiency. Recommendations were given for measures which would require more investment and/or detailed planning, but which should add to a considerable reduction of energy consumption.