Greywater Management in Low and Middle-Income Countries - SSWM

is planted with Phragmites karka
and (see Photo
5-6). The treated greywater is
then collected in a 700-litre tank
range range average average
before it is used for irrigation,
washing vehicles and toilet
of greywater is treated daily.
Hydraulic retention time (HRT)
5
mg/l
100–400
177–687
52–188
mg/l
0–12
7–72
1–6
mg/l (SD)
200 (93)
411 (174)
98 (53)
mg/l (SD)
5 (4.6)
29 (20)
3 (2)
in the settling tank averages 24
NH 4
-N 4–26 0–2 13 (8) 0.5 (0.6)
hours and hydraulic loading rate
(HLR) of the constructed wetland
4
1–5 1–4 3 (1) 2 (1)
amounts to 8.3 cm/d. Assuming
an average BOD removal rate of 40–50% in the settling tank, the organic
loading rate of the constructed wetland totals 8–12 g BOD 5/m 2 /d.
4-N is transformed
to nitrate (NO 3
The system has been in operation since April 1998 and monitored from
The following maintenance was performed to ensure proper operation of
the system:
•
•
Annual sludge removal from the settling tank.
Regular inspection of dosing chamber to ensure operation of the siphon
and intermittently greywater-charged bed.
•
•
Annual plant cutting.
cleaned.
Costs
The construction costs of the system, including main treatment unit, settling,
dosing and storage tank amounted to USD 430 (i.e. USD 61/p). System costs are
to be negligible. The 500 litres of drinking water saved every day leads to an
annual reduction in household expenditure of USD 40 (water price in Kathmandu:
USD 0.23/m 3 ). Such a reduction in expenditure allows payback of the construction
Greywater Management in Low and Middle-Income Countries
67