That is the wrong question -- if a juror is that certain, pre-trial, that a defendant is guilty, there is no way that the defendant can get a fair trial.
Sure they can, one nutjob juror cannot convict.
I've also been seated on juries where some of my fellow jurors were quite obviously biased against the defendant, and this really hurt their credibility with me. I wasn't the only one either, other jurors challenged some of the statements they made and it was clear to me that they also picked up on the bias and rejected it.
My first time on a jury a pleasant looking retired white man said he wanted to be foreman, for a trial of a Hispanic youth, and the guy started with "well he's obviously guilty right?" and he was serious. This was met with total outrage from several others on the jury and the foreman sat there meekly for the rest of the deliberations. The rest of us carefully reviewed the evidence and the defendant absolutely received a fair trial.
Combine this with the concept of jury nullification (something law enforcement DESPISES) and there are lots of situations where it would make sense for a juror to refuse to align with the rest of the jury.