On-site sanitation provisions in urban slums
rarely prioritise grey water management, yet it forms the
largest fraction of wastewater. This study was carried out to
characterise grey water and quantify its pollutant loads in
Bwaise III (Uganda) and to provide data for grey water
management in urban slums of developing countries.
Samples were collected for analysis from ten representative
households as well as from four tertiary drains and the
main drainage channel for 7 months in two dry seasons.
Grey water production was found to comprise 85 % of the
domestic water consumption. The chemical oxygen
demand (COD) concentration in the grey water generated
by laundry, in the kitchen and in the bathroom was
9,225 ± 1,200 mg L
-1, 71,250 ± 1,011 mg L
-1 and
4,675 ± 750 mg L
-1, while the BOD
5 (biochemical oxygen
demand) to COD ratio was 0.24 ± 0.05, 0.33 ± 0.08
and 0.31 ± 0.07, respectively. The maximum concentration
of
Escherichia coli
and total coliforms was 2.05 × 10
7
cfu (100 mL)
-1 and 1.75 × 10
8 cfu (100 mL)
-1, respectively,
in grey water from the bathroom, while that of
Salmonella
spp. was 7.32 × 10
6 cfu (100 mL)
-1 from
laundry. Analysis of variance (ANOVA) showed a
significant difference in the concentration of COD, total
suspended solids (TSS), total organic carbon (TOC), dissolved
organic carbon (DOC), total phosphorus (TP),
sodium adsorption ratio (SAR), oil and grease, and
Salmonella
spp. in grey water from laundry, bathroom and
kitchen (
p < 0.05). The high loads of COD
(>500 kg day
-1), TSS (>200 kg day
-1), nutrients (8.3 kg
TKN day
-1 and 1.4 kg TP day
-1) and microorganisms
(10
6 to 10
9 cfu c
-1 day
-1) originating from grey water in
Bwaise III show that grey water poses a threat to the
environment and a risk to human health in urban slums.
Therefore, there is a need to prioritise grey water treatment
in urban slums of developing countries to achieve adequate
sanitation.
