Fire crews couldn't get in to the unit to tackle the cause, so Superior Sanitation staff opened the container onto the pavement a safe distance away.
Firefighters extinguished the smouldering debris in the parking lot.
The store was evacuated as a precaution, but Chief Clay Moase said there was little risk of the fire spreading as it was contained to the outside unit.
Store sprinklers were soaking the inside of the machine.
"It's a really well-designed unit," said Moase.
Customers were allowed back inside around 4:15 p.m.
