How can I study for a career in Waste Management with a bachelors degree in Business Management?

Sure. What school has the degree in waste management? It could be the Civil Engineering Department. If so, you will have to meet the requirements to get that degree, which would mean additional semester hours to level/qualify. It could be several years of additional work because you would have to go back to physics, chemistry, biology courses plus the basic engineering courses. Or the degree could be in some other department, such as environmental science which is more of a science degree. More heavy in biology, chemistry, etc and not the engineering. You will probably still require leveling work of a year or more. You might consider graduating as is to get a degree, then go back for a masters in waste management. You would still have to level for about a year and then a second year for a Masters. But, I would get a ticket (degree) being as close as you are before risking a bigger endeavor and perhaps ending up with no ticket. Anyway go talk to the department head for waste management at your school and see what he says. They might have special cross over programs.   Consider the possibility of getting you current degree and then some courses in waste management, but no degree.  You have a ticket that will get you to the door for working in that field.

Why ask a bunch of strangers with no clue which University or which Country.

ASK the Uni yourself. Why are you kids so lazy?