The RO units aren't very efficient. I love mine but for every gallon it generates about six go down the drain. I still haven't implemented a reclamation method.
1:6 = 14% recovery. You're right, that isn't very efficient, but you'll never have to worry about scaling up your membranes.
At 14% recovery your concentrate waste has nearly the same mineral content as your feedwater. Run the waste line from your RO unit to a rain barrel and irrigate with it.
In my case, since the wastewater from the RO unit will have a high sodium content, wouldn't this have immediate benefits but also cause an accumulation of salt in the soil leading to problems down the road?
I couldn't really find much info about watering with this type of water.
You soften your water with a salt softener and then use that as feedwater for your RO unit?
At 14% recovery, and assuming 100% salt rejection -
If your RO feedwater has a TDS of 100ppm your concentrate waste will have a TDS of 117ppm. I would guess that your membrane salt rejection is more in the 90%-95% range so the concentrate waste TDS would be even lower.
I operate RO systems that use brackish water (high in sea salt) wells to provide landscape irrigation and swimming pool makeup for homes. The product water (permeate used to water plants and fill pools) has TDS in the 500ppm - 650ppm range with no ill effect on the plants. The pool operators like this high TDS water because the pools use salt water chlorination. They save on salt.
Your RO waste should be fine to irrigate with.
FWIW the concentrate waste from these irrigation RO systems is injected back into the ground. Since most of the irrigation water percolates back into the ground too, the net salt increase in the brackish aquafer is near zero (immeasurable). The brackish wells are close to the ocean and are under tidal influence. Groundwater salinity is monitored continuously. There was concern that irrigation water would dilute the brackish water in the aquafer and nearby anchialine ponds, disrupting the environment in those ponds. This has not been the case.