That is completely dependant on the individuals body, there is no study that proves that no human can use more than 30g protein per sitting, I myself take in a minimum of 60 over 5 meals a day, on 30 I would not be able to grow, 1g per pound bodyweight and I stagnate, and thats even less than that.
It depends on the subject, there are those who take in 500g per day, and its not because they like wasting the stuff.