What does the arduino do? It looks like with an appropriate level shifting chip, you could talk directly to the device from VB via serial.
Assuming, of course, that people actually do the proper thing when removing a container.
Personally, I would put microswitches (Hall effect, reed, etc.) Under each bin location. When an Active bin was lifted, the staff would have 15 seconds to use their personal RFID card-tag to log the bin outbound. Reverse for inbound. Siren, red-fladhing lights, or other fun alarms would instill trustworthiness