WASHINGTON (AP) — Senate appointee Roland Burris will be sworn into office Thursday, his office said, closing a painful and protracted certification process ensnared in the federal corruption investigation of Illinois Gov. Rod Blagojevich. Senate Democrats have reversed course, grudgingly accepting the former Illinois attorney general into their exclusive club as the person who will replace the Senate seat vacated by President-elect Barack Obama. “I really never doubted that I would be seated,” Burris said in a nationally broadcast television interview Tuesday. “It was just a matter of going through the process and making sure that the Senate rules were abided by,” he said.