Alternatives for city sewer for a 12 unit building?

[Melissa Uppelschoten]

I am about to close on a 1.2 acre lot in Atlanta that I would like to ideally build affordable housing on. My builder and I have sketched out a 12 unit building (three stories high, 4 units per floor). The main drawback I have is that there isn't city sewer. I am going to contact my city council and lobby for sewer to be installed (I realize this is a LONG process) but I also was curious of alternatives to sewer. Is anyone aware of a septic tank system that can handle 12 units? Or another eco-friendly approach? Thanks in advance...Melissa