Organic Waste Recycling

370 Organic waste recycling: technology and management

Table 7.11 Summary of BOD 5 and SS removal from constructed wetlands (U.S. EPA
1988)

a Free Water Surface System
bSubsurface Flow System

Owing to the complex reactions occurring in wetland beds, it is very difficult
to develop a comprehensive model that would adequately describe or predict the
treatment efficiency. Nevertheless, Reed and Brown (1995) recommended a
first-order reaction for BOD 5 removal in constructed wetlands:

e ekTt

C

C.

0

= − (7.11)

Where,

Ce = Effluent BOD 5 concentration, mg/L

Co = Influent BOD 5 concentration, mg/L

kT = k 20 (1.06)T-20

T = liquid temperature, oC

k 20 = 1.104 day-1, for SF constructed wetlands,

k 20 = 0.687 day-1 for FWS constructed wetlands

t = hydraulic retention time in the wetland beds, days.

Project Flow, BOD 5 mg/L SS mg/l % reduction
m^3 /day

Wetland

type Influent Effluent Influent Effluent BOD 5 SS

Hydraulic
surface
loading
rate,
m^3 /(ha-day)
Listowel,
Ontario

17 FWSa 56 10 111 8 82 93 -

Santee, CA SFb 118 30 57 5.5 75 90 -
Sydney,
Australia

240 SF 33 4.6 57 4.5 86 92 -

Arcata, CA 11,350 FWS 36 13 43 31 64 28 907
Emmitsburg
, MD

132 SF 62 18 30 8.3 71 73 1,543

Gustine,
CA

3785 FWS 150 24 140 19 84 86 412