Upstream of the reducing agent addition a pH meter 12 feeds output to controller 21 which acts to control automatic valve 13 to feed {HEAD ~ an alkali stream} 8 such as sodium hydroxide to raise the pH of the stream 1 to between 7.5 and 9.5 with 7.5 being adequate for removal of {TAIL ~ chromium} alone and 9.5 being preferable for total heavy metal removal 
Upstream of the reducing agent addition a pH meter 12 feeds output to controller 21 which acts to control automatic valve 13 to feed { HEAD ~ an alkali stream } 8 such as sodium hydroxide to raise the pH of the stream 1 to between 7.5 and 9.5 with 7.5 being adequate for removal of { TAIL ~ chromium } alone and 9.5 being preferable for total heavy metal removal
OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH