You are in charge of the garbage. What can you do with the milk bottle you just finished?
Recycling may be a good option : you just have to check the instructions on your empty bottle, it will guide you on how to recycle it.
In the future, you can also think about not buying single-use milk plastic bottles, and start reducing trash in general : there exists zero-waste shops where you can bring your own bottles (glass bottles for instance) and fill them with what you need : milk, juice, honey, shampoo... this can be done with most products in fact! It helps reducing trash, so it helps the environment.
Thank you in advance ;)
