The reason why the researcher(s) is(are) interested in the topic is that the hotel industry, which is one of the largest polluters, implements green programmes to reduce operating costs and protect their properties.
If you use interest as a verb, there should not be any preposition but if you use it as an adjective, you need a verb to be in front of it.
Operating costs, not operation cost.
Green program should be in plural (i.e. green programmes), or else you need an artcile "a" in front of it.
I do not quite understand what "protect their properties with guests" means.