The most convenient and economical way to get from the airport to the city centre is the local TRER shuttle service. They leave from the airport at 15-30 minute intervals from 5:18 to 23:36 daily. The journey time is about 18-20 minutes and costs 6 EUR. The train station is the end point of the route in Bologna.
Note that in addition to this route, intercity routes to Rimini, Ferrara, Florence and Modena run through the airport. The timetable and routes can be found at the airport information desk. The cost ranges from 15 EUR to 32 EUR depending on the distance.