Elemental is not TPN. TPN as you are aware is Total Parenteral Nutrition.
Elemental is either drank or administered via a nasogastric tube that goes through the nose down into the stomach. It is designed to absorbed in the first metre of the small bowel. TPN is intravenous nutrition as you rightly say via a PICC line or another type of intravenous line like a central venous catheter.
Elemental is not generally used for UC patients because nutrition doesnt seem to have the same inpact - according to the last research I read - for UC patients as it does for Crohnies.
I really feel for you and your hubby. Its a tough thing to go through. Generally they gradually reduce the amount of TPN based on how much he can "regularly" eat and maintain eating over several days. His physical stomach will have shrunk in size due to not having the "bulk" of food so will take some time and discomfort initially for that to settle down again. Little and often would be my thought and something that is light, easy to digest and that he actually fancies. This will improve over time.
It should be done over a period of time that suits him and not because they think he should be at a certain point at a certain time. There is an element of goal setting but it should be flexible. Will also take some time for his appetite to pick up again and get used to having food in his mouth AND things like jaw ache from chewing which is often overlooked! ;-)
Its going to feel a bit foreign eating again but he will get there trust me. May have some abdominal cramping but its about him learning to listen to his body and also voice his concerns too. For example abdominal pains may be related to wind with new bulk travelling the gut or it could be an initial inflammatory response to food again which will settle OR could be something else like the UC getting a grip over a period of time. Unfortunately its a case of time will tell and although frustrating at times his own "instinct" will be a good guide.
Hope what I have said makes sense and helps in some small way. I am an ex ITU nurse so if I can help at all just PM me. I havent posted much of late as have had alot going on myself. But will help where I can.
Thinking of you both ((hugs))