Septic Tanks vs Septic Treatment Plant

I am looking to purchase my 2nd park that is on 17+ acres and has several septic systems. I have been told that the park is maxed out in terms of adding more homes b/c the existing septic tanks can’t hold anymore homes. The owners are ready to retire and didn’t want to take on the hassle of building a septic treatment plant. How involved is that process and do you know anyone who has done this?

The benefit of adding the septic treatment plant is that I will be able to add an additional 50 homes over the next few years. I have been told it could cost 200K. I have done a small amount of due diligence but wanted to see if anyone had any experience with this. The property is also on a well but has city water at the end of the property that we can easily run throughout the property so that we could sub meter each home. This is a park with huge potential but needs some work to be a multi-million dollar property.

Any feedback or comments is welcomed.