Conventional WWTP Design question

Hi everyone, Can anyone tell me, for a domestic treating WWTP, what would be a generally accepted peak coefficient for nitrogen? Also, can anyone tell me (again for a conventional WWTP) what an approximate proportion of overall construction costs nitrogen treatment represents? I know there are sooooooooooooooo many variables that would come into play, but I don't have all the data to make it representative, so I'm looking for a general idea.   TIA!