Drush sql-sync: Access denied; you need the SUPER privilege for this operation
The user defined in settings.php on one or both sides of the sync lacks the SUPER privilege on the database.

Log in as the mysql root user and do

GRANT SUPER ON [db_name] TO '[username]'@'localhost' IDENTIFIED BY '[password]';


If you are security-conscious (as you should be), it's worth taking the following into account: 


  Do not grant the PROCESS or SUPER privilege to nonadministrative users. The output of mysqladmin processlist and SHOW PROCESSLIST shows the text of any statements currently being executed, so any user who is permitted to see the server process list might be able to see statements issued by other users such as UPDATE user SET password=PASSWORD('not_secure').