What type of figurative language is a new world of bustling factories?

If this is the entire example, and there is not something following the comma to which the new world of bustling factories is being compared, there are two possibilities, depending on the definition of "bustling". Metaphor or personification.
(If there is something following the comma to which the new world of bustling factories is being compared, the figure of speech is most likely a metaphor.)
METAPHOR is when two different things are compared as if they are literally alike, even though they are not. In this case, "bustling" means a place that is full of activity, so the factory is busy and full of activity. We could imagine that to be a place full of things and people that are actively moving about, creating things, making things, etcetera, like a factory where cars are produced. That place would be loud and probably dirty, full of parts being put together, machinery operating, and people assembling things. This is quite unlike what people might imagine a "new world" to be like. A new world would be one that is undiscovered by people, so activity would be limited, it would most likely be quieter than a factory. It would most likely be pristine and clean and devoid of the markings of man. A new world and a bustling factory, then, would not be literally alike at all.

Another possibility is PERSONIFICATION in which a non-human thing is treated as if it were human and given human characteristics. If you take the word "bustling" to mean 'a person scurrying about' then the phrase bustling factories could also be giving the factories the human ability to "bustle" or "scurry about", which a factory can't actually do on it's own. This figure of speech would allow a person/reader to imagine the factories as a people, bustling about and running themselves, creating things on their own, and doing the work of people, as if the city were full of workers.