PHP session data

I'm using CodeIgniter 3.x with database session driver and i want to access data cloumn that BLOB type. Here my blob data:

__ci_last_regenerate|i:1435420891;identity|s:13:"[email protected] ";username|s:13:"johndoe";email|s:13:"[email protected] ";user_id|s:1:"5";old_last_login|s:10:"1435412865";
I tried with unserialize($string) but didnt work!

unserialize(): Error at offset 0

How can i access blob data element? For ex: $user['email']