Hello, congrats on getting the interview! You'll probably be asked what interests you about the topic, what skills and knowledge you bring, and to talk about your masters or BA project so you could do some preparation in these areas. Perhaps you could read a couple of papers on the topic as well. Before my interview I read some papers my supervisor wrote on the topic which helped to inform me about the area. I was asked which particular aspects interested me most, and I was asked questions about my research skills.
It certainly sounds like you are enthusiastic, that helps loads!! Good luck!