It won't work in your septic system. Or rather, your septic won't continue to work with whey being put into it. The bacteria from cheesemaking cultures are very oxygen hungry, so you would end up killing off the system.
My home is an old cheese factory and the neighbors next door were farming while the factory was still in operation. The factory sprayed the whey on their fields for them and they have said that their fields have never been as fertile since those days.
Only you can investigate your local regulations regarding this. I don't even know if it is still legal here to spray it on the fields.