I have thought about running the waste water back thru too. And yes you can, but, eventually that water is not going to have much H2O in it as it will be concentrated with minerals and metals so it won't yield anything. At work we have a system that does not have much waste, but, you need huge resin towers for that - like the size of a home water softener would be, but more towers. You could do that, a home DI water softener system from a commercial company and have it serviced monthly or as needed and then run that water thru the RO/DI. We only have a slight drip of waste water with a system like that.

Some use UV's. I don't because I want the planktons to stay alive. I use a variety filter feeders to clean things up as well as unshielded lights on the tank. Combined with the refugium, skimmer, sump and great congregations of filter feeders on and in the rocks, I don't see the need for sterilizing the water. You may have to if you just used the holey rock and didn't add any microbs to do the job. The ultimate goal of adding DT's or other phytoplankton is to establish an on-going life cycle just like the ocean has. When you run a sterilizer, that cycle is not possible which means you MUST feed filter feeders, anemones of all kinds, LPS, etc., all the time. Still others use it to cure and keep diseases like ick under control. IMO, this is not necessary if you have all the bio-diversity in place and have added the proper bacteria cultures to kick off all the waste breakdown cycling and if you have a stabile tank chemiclly as well as physically.