Which all IITs have a course related to environmental engineering ?And how can I get admission into IITs containing this course ?
B.Tech in environmental engineering is offered by IIT Kanpur & Delhi, to name a few. For admissions, you need to have a good score in JEE Advanced and for M.Tech, admission is through good GATE scores.

B.Tech in environmental engineering is offered by Indian School of Mines (ISM), Dhanbad, whereas,
IIT Kanpur offers Environmental Engineering & Management under its inter-disciplinary courses.
IIT Kanpur & IIT Delhi offers M.Tech in environmental engineering.