Periodicly Executed Contract Relating To Mechanical And/Or Electrical Maintenance Services Of Electric Pumps, Mixers, Agitators, Automatic Grids, Screw Screens, Auger Screens, Electric Motors, Gear Motors, Compressors And, In Any Case, Any Type Of Machine Present On The Lifting Stations Of Sewerage And On The Purification Plants Managed By Asa Spa