Upstream of the reducing agent addition a pH meter 12 feeds {TAIL ~ output} to controller 21 which acts to control {HEAD ~ automatic valve} 13 to feed 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 chromium alone and 9.5 being preferable for total heavy metal removal 
Upstream of the reducing agent addition a pH meter 12 feeds { TAIL ~ output } to controller 21 which acts to control { HEAD ~ automatic valve } 13 to feed 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 chromium alone and 9.5 being preferable for total heavy metal removal
OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH 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 OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH