I don't see why not. Check with your physician. As long as your one kidney works, you are in good physical condition, and you can meet the physical standards you should be fine.
I don't know if this matters or not, but I have never been asked if I had two kidneys... I figure as long as you are able to meet the physical requirements, there should be no issue. I have known folks that have had many different types of physical ailments, and have returned to the fire service afterward. These ailments include knee replacements, cancer, liver dysfunction and many more. It is all about your ability to do the job and the opinion developed between you and your physician.
In 1981 my father had one kidney removed due to a malignant tumor in it. He never had any problems with activity or diet or anything with just one kidney. The doctor told him the one would enlarge and take over function of the one that was removed. He passed away in 2005, and not from kidney dysfunction.
I think that donating one of your kidneys to your father is a very noble thing to do, sir.
I would not accept any notion that you would be disqualified from fire service with only one kidney.