Activated sludge systems ...

Activated sludge systems along the coast often get saltwater intrusion and in the worst cases chloride levels can be greater than 3,000 mg/L.   I have had the impression that below 3,000 mg/L or so the systems are not terribly effected (the microbiology adapts) but that at levels of 4, or 5,000 mg/L and up there are negative impacts.  The levels you're describing are quite low and I'd expect little impact.