You can configure Bitdefender to automatically delete quarantined items after a certain number of days (default 30 days).
To access thse settings:
Double-click on the BitDefender icon in the Windows System tray.
Click on "SWITCH TO ADVANCED VIEW".
Go to Antivirus > Quarantine
Click on the Settings button.
In the dialog that opens up, modify the value next to "Delete files older that [ ]"