Apparently they play their games at home in this round however it may not be at their PL ground.
"5.1.2 Round of 32.
(i) The eight winners and eight runners up of the north and south group stages qualify for the round of 32. All other Clubs are eliminated from the Competition.
(ii) The round of 32 pairings are determined by means of a draw whereby the winner of a group will be drawn at home and will play a runner up of a group from the same region (but not from the same group)
(iii) Subject to the requirement above, the League shall determine the format of, and conduct, the draw to determine the round of 32.
(iv) Matches will be of ninety minutes duration, with no extra time. If the scores are level then the winners shall be determined by the taking of kicks from the penalty mark in accordance with procedures as approved by IFAB."
Didn't Peterborough play Chelsea's U21s last year at Stamford Bridge?