as long as the recir water is discharged to a sanitary sewer system (WWTP) you should have no issues, as this is not an "Industrial Discharge".
Be mindful, any flocking agent could cause some drain/pipe issues unless you use a lot of dilution when discarding it.
I use a home made flock agent (w Al) and have had no issues with putting it down the drain to the WWTP. Just as you say, "there are a lot worse things going down the drain"! In this case, any toxicity or turbidity issue is handled easily by the Advanced Waste Water Treatment in the city/county WWTP.