“The solution is the development of easily degradable plastic. The problem to overcome is how to stop biodegradable plastic containers from biodegrading on the supermarket shelf.”
You’d probably need a 2-component process, like binary explosives that are stable until two elements are mixed together. Normally the plastic is nonbiodegradeable, but if you spray it with some agent, it starts degrading.
Or we can just burn it and generate power with it.
I do not suggest engineering bacteria to eat plastic, because that is just the beginning of a dystopian science fiction story.
Stories on that theme were not uncommon in 1950s "pulp" science fiction. They never ended well ...