How to block Bittorrent ?
First you will need a legal document explaining your users that torrent use is forbidden.
You could use a 3 strike rule (popular expression these days). loose your Internet access or get fired as the end game.
As to implement a solution with pfSense you could combined/check out:
OpenDNS (Limit websites users can visit)
Captive Portal (Knowing who is using your net)
Traffic Shaper (Make traffic slow on none standard ports)
Add a untangle server.
Thank you so much .,,
I ever seen IPcop addon they setup L7 ipp2p to block all p2p..