Treatment method



Design factors


Net alkaline water



Aerobic wetlands

Net alkaline water

Overland flow with cattails

10 - 20 g Fe/m2/day 0.5 - 1 g Mn/m2/day

Anaerobic wetlands

Net acidic water Low flow

Flow over and within the substrate

3.5 g acidity/m2/day

Sulfate-reducing bioreactors

Net acidic water

low flow

Flow through the substrate

Residence time of 24 h


Net acidic water

low DO, Al, Fe contents

Flow through buried limestone

Residence time of 15 h


Net acidic water

Vertical flow

15 - 30 cm of organic matter,

residence time of 15 h,

20 g acidity/m2/day

Open limestone drain

Slope > 10%

Rock-lined channel

Acid load and residence time

Limestone leach bed

Inflow pH < 3.0

Flow through limestone

Residence time of 1.5 h

Slag leach bed

Water without metals

Flow through steel slag fine aggregate

Residence time of 1 - 3 h