Organic Waste Recycling

Aquatic weeds and their utilization 371

Table 7.12 Summary of wetland design consideration (WPCF 1990). Reproduced by the
permission of the Water Environment Federation

Constructed

Design consideration free water surface submerged bed Natural

Minimum size

requirement, ha/1000

m^3 /d

3 – 4 1.2 – 1.7 5- 10

Maximum water

depth, cm

50 Water level

below ground

surface

50; depends on native

vegetation

Bed depth, cm Not applicable 30 – 90 Not applicable

Minimum aspect ratio

(L/W)

2:1 Not applicable Prefer 2:1

Minimum Hydraulic

residence time, days

5 – 10 5 – 10 14

Maximum hydraulic

loading rate, cm/day

2.5 – 5 6 – 8 1 – 2

Minimum pre

treatment

Primary;

secondary is

optional

Primary Primary;

Secondary;

Nitrification,

TP Reduction

Configuration Multiple cells in

parallel and series

Multiple beds in

parallel

Multiple discharge

sites

Distribution Swale; perforated

pipe

Inlet zone (> 0.5

m wide) of large

gravel

Swale; perforated

pipes

Maximum loading,

kg/ha-day

BOD 5 100 – 110 80 – 120 4

TN 60 60 3

Additional

consideration

Mosquito control

with mosquito fish;

remove vegetation

once each 1 to 5

years

Allow flooding

capability for

weed control.

Natural hydro period

should be > 50 %;

no vegetation harvest