This is briefly suggested in https://forum.airportceo.com/t/airline-meals-janitors-garbage-disposal/367?u=4b54
Here I would like to see that we have some form of waste management presented to the player. In the broadest sense, we have general garbage, recyclables, organic waste, and unique to the airport, international waste.
Let's deal with the simple stuff first...
1. At any place where there is a garbage bin, there should also be a separate bin for recyclables as an endorsement to the airport's recycling program (if it has one)
2. At any place where food is expected to be wasted e.g. cafes, restaurants, food fairs... there should also be a bin or manned workstation to allow organic waste to be sorted.
This waste will end up at some local 'behind-the-scenes' waste station where the waste is collected and prepared for delivery. These can be both indoors and outdoors. As your airport grows, there will be a need to build and allocate space for several local waste stations to facilitate the janitor's ability to collect and dispose of waste. You wouldn't want your janitor to waste precious working hours moving a bin of garbage from one end of the airport to the other end because of poorly placed waste stations. The means to collect and prepare might be a bin loader and compactor; multiple needed since there are different types of waste. Finally, the collected and prepared waste will need to be delivered off-site for downstream processing (landfill, incineration, composting, melting, etc.)
Now for international waste...
International waste is special because it presents the risk of introducing invasive plant/insect species or non-endemic pathogens when not properly processed. Waste collected from an arriving international flight will need to be directed to specially designated containers for further processing. It is essential that international waste not mix with domestic waste as discussed above. Processing could be as simple as compaction and direct delivery to an off-site incinerator, or in situ incineration within airport jurisdiction.