Tenant moved out, left me keys plus garbage/things.

[Richard Krokodiliukas]

I closed on a property on 1/17. Apparently some day in a week before the 17th one of the tenants was served a 3 day quit notice for non payment of rent. Tenant moved out on 19th. I found out about it only when the tenant called me asking to open basement for utility company to shut down his gas. Also tenant told me over the phone that he left me the keys in the jar on the deck. He didn't give me his new address.
When I entered apartment next day I found out that tenant left a lot of junk. Most of it is garbage but also some old furniture. Can I dispose it right away or I have to wait 30 days?
I'm going to mail an itemized security deposit return letter to the last known address. Do I prorate security deposit to cover January rent till 19th or I can charge the full month? Property in PA.