The presence of zinc in wastewater discharges from printing operations is
from the small amount of oil that contaminates the condensate water from the
compressors and vaccum pumps. The zinc is added by the oil supplier and even
if an oil/water seperator is used, enough oil can be found in the discharge
to exceed some local sewer codes. Also, copper has been found in excess
levels in this "blow down" from the compressors.