What is the normal practice in pharma industry?
Are they using same sterilizer for preparing & disposal of media?
If yes, how to prove that disposal is not causing any contamination when we go to next media cycle.
Is there any guideline suggesting the validation for use of same autoclave to achieve the dual purpose?
Please provide references.

Are they using same sterilizer for preparing & disposal of media?

Can you dispose of media in this manner?

I had seen many waste disposal manuals/procedures for labs but not seen one that says you can do it this way. Check your lab manual to see what it says.

I would like to know that is there any guideline available which states that we can use the same sterilizer after doing appropriate validation?

Currently, we are using different sterilizers for preparation of media & disposal of media.

The only thing important is to prove that the contamination from waste cycle is not carried forward in next cycle. But, how to do that, is not that clear.

I don't know of any guideline for this situation. If you can separate the autoclaves and keep them separate for sterilization and wast disposal, that would surely seem the way to go and then you will not have this situation to worry about.