The most convenient and economical way to get from the airport to the city center is by shuttle buses operated by the local company TPER. They depart from the airport every 15–30 minutes from 5:30 AM to 11:30 PM daily. The journey takes about 18–20 minutes and costs 11 EUR. The final stop in Bologna is the central railway station.
Note that in addition to this route, intercity buses also pass through the airport to Rimini, Ferrara, Florence, and Modena. You can find schedules and routes at the airport information desk. The cost of such trips ranges from 15 to 35 EUR depending on the destination.