A series of filtration steps was used to separate iron (Fe) and mangan
ese (Mn) into soluble, colloidal, and particulate fractions. Two case
studies demonstrate how fractionation data can improve understanding o
f the origins and removal of Fe and Mn. The Mn species present in one
water source were shown to be regulated by a biogeochemical cycle in w
hich the natural oxidation and reduction of Mn appeared to be microbia
lly mediated. Mn removal was improved by adjusting the application of
potassium permanganate to account for this cycle. A groundwater treatm
ent plant was suffering from high postfilter Fe and Mn concentrations.
Fractionation data identified the problem as inadequate solids captur
e, not oxidant dosage, allowing a quick solution. The unexpected oxida
tion of Mn with chlorine (Cl-2) was attributed to Fe oxide surface cat
alysis. Without adequate particle removal (no coagulant added), applyi
ng Cl-2 on top of the filters exhibited superior removal to adding Cl-
2 before a detention basin.