“The Biggest Loser” (8 p.m., NBC): In the two-hour season premiere of “The Biggest

“The Biggest Loser” (8 p.m., NBC): In the two-hour season premiere of “The Biggest Loser,” the contestants begin the competition in the middle of a desert, where trainers Bob Harper and Kim Lyons await them. The show features a new host in Alison Sweeney (“Days of our Lives”), as well as its first set of twins and oldest competitor ever at 62.

“Ground Zero: Search and Recovery” (9 p.m., History Channel): A full day of programming related to the anniversary of the Sept. 11, 2001, attacks is capped by this new special, which profiles investigators’ efforts to gather clues from the disaster scene.