There is a simple way to prevent this problem

Garbage bin, food court, City Square, Vancouver, BC (Detail)

Garbage bin, food court, City Square, Vancouver, BC

How hard should it be to prevent customers from throwing your trays in the garbage? This begs two questions.

1. Why would customers think that the plastic trays were single use items that should end up in the bin? 
2. Why do you have a bin opening that is big enough to fit a tray?

McDonald's solve this problem by using bigger trays and having a smaller opening at the top of the garbage bin. As a result there is no way that the consumer can throw away their tray.

Garbage bin, McDonald's, Vancouver, BC

Garbage bin, McDonald's, Vancouver, BC

A simple solution to a profit-reducing problem.