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 {TAIL ~ 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 
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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 { TAIL ~ 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 OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD OTH REL REL TAIL TAIL TAIL TAIL TAIL 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