Well, if you don't count small concerts.
Then it was Laundry day, the biggest DJ festival in Belgium.
Over 150 Dj's on 13 stages and over 65.000 visitors.
There allso where a lot of styles.
-Techno
-Elektro
-Drum n' Base
-Hardstyle
...
Here is some extra info (if you would be interested).
http://www.laundryday.be/