Supplemental Table 1 Comparison of the most widely used AMD treatment
Treatment method
Used materials
Active treatment
(addition of
alkaline chemicals
to raise pH and
precipitate metals)
Limestone,
hydrated lime,
pebble
quicklime,
caustic soda,
soda ash,
ammonia,
potassium
hydroxide,
magnesium
hydroxide, etc.
Passive treatment
Limestone,
clay, natural
soil, peat,
plant residue,
composted
organic
matter, etc.
Type of
treatment
Direct
addition of
chemicals
(e.g.,
limestone)
into the AMD
stream, lime
treatment
plant with a
mixer/aerator,
basket-hopper
system, etc.
Principle
Advantages
Disadvantages
References
Active treatment
systems collect AMD
into pond and apply
alkaline chemicals
which raise water pH,
neutralize acidity and
cause precipitation of
metals
Some materials (e.g.,
limestone) are cheap;
calcium sulphate and metal
hydroxide precipitate;
limestone is the safest and
easiest to handle of used
AMD chemicals; effective
treatment
Require continual additions of
chemicals; some materials (e.g., caustic
soda, ammonia) have high cost and are
danger in handling; limestone has low
solubility and is usually coated by
ferric hydroxide; hydrated lime powder
is hydrophobic and extensive
mechanical mixing is required;
formation of bulky sludge; needs vast
aria for sludge storage in ponds; long
term stability of neutralization sludge is
poorly understood; treated effluent has
high pH; scaling; sometimes needs
flocculants and oxidants; expensive
when the cost of equipment, chemicals,
and manpower are considered
GARD/INAP; Skousen
and Ziemkiewicz 1995;
Johnson and Hallberg
2005; Taylor et al.
2005; Gaikwad and
Gupta 2008
Open/Oxic
Chemical, biological Acid neutralization; remove
Long retention time and large surface
GARD/INAP; Johnson
limestone
and physical removal
metals from AMD by
areas*; residence time in the limestone
and Hallberg 2005;
drains, anoxic
processes occurring
physical, chemical and
layer is critical factor governing the
Taylor et al. 2005;
limestone
naturally in the
biological processes (uptake limestone dissolution rate; weather and
Gaikwad and Gupta
drain, aerobic
environment
by plants, adsorption on
streamflow are important factors;
2008; Zipper et al.
and anaerobic
organic substrates, oxidation clogging; construction cost can be high
2011
wetlands,
and precipitation, microbial
initially depending on the size and
vertical flow
reduction); improve water
specific design of the system; regular
systems,
quality; wetland are valuable
maintenance is required
permeable
ecological system; cost
reactive
effective; constant
barriers, etc.
operations are not required
*Vertical flow system generally requires shorter residence times and smaller surface areas comparing aerobic and anaerobic wetlands (Zipper et al. 2011)