When a post or comment is deleted in your WordPress site or blog, it goes to the trash instead of being permanently deleted. WordPress permanently delete the posts or comments in the trash after 30 days automatically.
You can set when to empty the WordPress trash by adding the following code in wp-config.php file, located at blog/site root directory.
define('EMPTY_TRASH_DAYS', 7); // Where 7 is number of days
The number 7 refers to how many days between WordPress trash Empty. You can set ‘Trash Day’ interval to 1 for daily empty the trash automatically.