No, human waste has too much bacteria from the types of foods we eat. That's why we only use cow waste because they graze open fields and eat grass and some animals eat hay.
It is possible, but the waste must be treated first. Otherwise, it is very hazardous, as human waste is mostly bacteria, many of which are harmful. It is not as effective as animal waste.
Yes, it can, but often it does not contain enough nutrients or plant matter to be helpful. If the person is a healthy eater or vegetarian, it may work well.
