The pvc piece is an air gap, more than likely for the softener that's there. Doesn't look like the stand pipe is long enough from the pic, but it's hard to tell. Hate to be the one to tell you, but the air gap is doing what it's designed to do by overflowing and preventing that nasty water from entering your softener.
Unfortunately it's probably a clog somewhere that's causing the back up. Might just be a partial that allows your normal usage to slowly drain, but the high flow of a regenerating softener will back it up fast. It dumps a ton of water. My recommendation would be getting someone to run a camera through it to find the cause. There could be a separation in your drain line somewhere that's letting roots in. It could be a backup from a clog. There's not really any way to tell without getting a visual.
The pvc piece is an air gap, more than likely for the softener that's there. Doesn't look like the stand pipe is long enough from the pic, but it's hard to tell. Hate to be the one to tell you, but the air gap is doing what it's designed to do by overflowing and preventing that nasty water from entering your softener. Unfortunately it's probably a clog somewhere that's causing the back up. Might just be a partial that allows your normal usage to slowly drain, but the high flow of a regenerating softener will back it up fast. It dumps a ton of water. My recommendation would be getting someone to run a camera through it to find the cause. There could be a separation in your drain line somewhere that's letting roots in. It could be a backup from a clog. There's not really any way to tell without getting a visual.