Organic Waste Recycling

Land treatment of wastewater 387

Table 8.2 Comparison of typical design features for land treatment processes (U.S. EPA
1981)

Features Slow rate
Rapid
infiltration Overland flow
Application techniques

Annual loading rate, m
Field area required, hab
Typical weekly loading
rate, cm
Minimum preapplication
treatment provided in
the United States
Disposition of applied
wastewater

Need for vegetation
BOD 5 loadingf kg/ (ha-
year)

Sprinkler or surfacea

0.5 – 6

23 – 280

1.3 – 10

Primary

sedimentationd

Evapotranspiration

and percolation

Required

370-1,830

Usually surface

6 – 125

3 – 23

10 – 240

Primary

sedimentatione

Mainly

percolation

Optional

8,000–46, 000

Sprinkler or

surface

3 – 20

6.5 – 44

6 – 40c

Grit removal and

comminutione

Surface runoff and

evapotranspiration

with some

percolation

Required

2,000–7,500

a Includes ridge-and-furrow and border strip.

b Field area in hectares not including buffer area, roads, or ditches for 3,785 m (^3) /day (1
mgd) flow.
c Range includes raw wastewater to secondary effluent, higher rates for higher level of
preapplication treatment.
d With restricted public access; crops not for direct human consumption.
e With restricted public access.
f Range for municipal wastewater.
Adequately disinfected wastewater should pose no danger to health when it is
used for irrigation. Adequate disinfection, which can be very costly, requires
complete and rapid mixing and a specified contact time of the disinfectant in the
effluent. Any aerosolising of inadequately disinfected water produces possible
health risks to human, and these risks should be minimized. Before harvesting
of the irrigated crops, wastewater application must be stopped to allow for
drying of the soil and die-off of the pathogens that may be present on the crops.