The most common types of urine that people think go into the making of urea for DEF – urine from cows and bats, which is not correct. Contrary to popular myth, cow and bat urine and DEF are not a thing. The urea used in the manufacture of DEF is synthetically derived from ammonia and carbon dioxide, and urea production plants are often adjacent to other sites where ammonia is produced, such as coal and natural gas refineries. This allows for the capture of hydrocarbons from ammonia plant feedstocks to be used in the manufacture of urea, rather than allowing harmful emissions to enter the atmosphere, and eliminating the need to purchase ammonia as a separate commodity. In short, it is easier and more economical to manufacture urea on-site or nearby where ammonia is already being produced.
Where It Comes From
https://www.sclubricants.com/urine-and-def/