Possible Fix to effluent ...

Possible Fix to effluent color

How are they disposing of the coffee grounds?  Hopefully not in the drain, but if so, the main contributor to the color may be coming from tannins associated with the coffee waste.  The simplest, proactive fix (if this is what they are doing) is not to dispose the grounds in the drain.  A reactive approach would be to try electrocoagulation as a means to remove the color as a polisher to existing treatment train.  The EC will also give a 3-5 log pathogen removal.  You can couple this with a Fentons reaction to break up short chain carbons if the EC does not work alone.  Typically EC by itself has difficulty removing carbon chains