Environmental Engineering Reference
In-Depth Information
Fig. 2
Metabolic scheme
for the degradation of
complex organic matter,
culminating in methano-
genesis (Megonigal et al.
2004)
lignin and hemicellulose, are resistant to
decomposition (i.e. recalcitrant). Biopolymers
are degraded in a multistep process (Fig.
2
).
water column (Kadlec and Knight
1996
).
Filtration is primarily mechanical straining where
the particles larger than the pore size of the
strainer (filtering medium) are separated from the
bulk of the liquid. Sedimentation is separation of
suspended particles that are heavier than water by
gravitational settling (Metcalf and Eddy
2003
).
3.4
Phosphorus Removal
Based on the phosphorus cycle, the only means
of removing phosphorus from wastewater by a
constructed wetland is through accumulation of
phosphorus within the system. This accumula-
tion of phosphorus can occur physically, biologi-
cally or chemically.
3.4.2 Biological Removal
Mechanisms
Biological storage of phosphorus occurs through
uptake by plants and microbes; though this quan-
tity maybe small. During the start-up phase,
phosphorus is taken up by biomass as it becomes
established (Mander and Jenssen
2002
). However,
as wetlands mature to steady state, there is little
net removal through uptake. By carefully manag-
ing the growing and harvesting of vegetation,
bioretention of phosphorus can be controlled
(Davies et al.
2006
). Cooke (
1992
) found that
11 % of the phosphorus in the wetland was taken
up by the plants. Another study found that uptake
by cattails was 40 % of the total phosphorus input
(Weng et al.
2006
).
3.4.1 Physical Removal Mechanism
Physical processes function by removing phos-
phorus in suspended solids and in precipitates by
filtration, with subsequent sedimentation in the
substrate media within the wetland. Suspended
particles in the influent may combine with a num-
ber of soluble and insoluble phosphorus forms in
the wetland. However, if the solid matter filtered
from the wastewater is planktonic, its decompo-
sition can release dissolved phosphorus into the
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