Greywater Management in Low and Middle-Income Countries - SSWM

SAR
The fate of surfactants in irrigated soils in not yet
fully understood and requires further research. Most
studies conclude that biodegradable surfactants are
unlikely to accumulate in soil and biota (e.g. Doi et
al., 2002; Jensen, 1999). One study conducted in
Israel indicates that long-term irrigation of arid loess
soil with greywater may result in the accumulation of
LAS (linear alkylbenzene sulfonate) and AE (alcohol
ethoxylate), two of the most frequently used surfactants
in household detergents. The study concludes that
soils irrigated with greywater may turn hydrophobic
due to a reduction in capillary rise (Gross et al., 2005;
Shafran et al., 2005). According to Barber (2002), the
fate of surfactants and other organic contaminants in
the subsurface depends on geochemical and nutrient
conditions, with low dissolved oxygen and low nutrient
conditions favouring long-term persistence.
20
15
10
5
0
Soil structure
problems likely
Depends
0.1 0.2 1 2 10
EC (dS/m)
on soil type
Stable
soil structure
Although solar radiation destroys pathogens on crops within a few days, irrigation
systems should try to avoid contact of greywater with the edible part of the crop.
Sprinkler installations enhancing direct contact of greywater with above-ground plant
parts are therefore not recommended.
Drip irrigation systems have shown to be highly effective if well-designed and
maintained. Simple hoses release the water directly at the point of need. The
pathogen contamination risk of plants by irrigation water is therefore markedly
reduced. Drip irrigation systems normally need a dosing pump and, consequently,
also a reliable power supply. Mofoke et al. (2004) also successfully
tested an alternative, gravity-driven drip irrigation system (see
Photo 4-11). This system was constructed exclusively from
form of the medical infusion set as emitter. Maintenance has
to be ensured, as the emitters tend to clog frequently. Polak et
al. (1997) tested another low-cost drip irrigation system whose
movable dripper line can irrigate ten plant rows and thus reduce
investment costs by 90 percent. Farmers reported that this lowcost
drip irrigation system cut labour requirements by half and
doubled the area irrigated with the same amount of water. Use
of greywater in drip irrigation requires an appropriate primary
treatment to remove oil, grease and suspended solids and thus
prevent clogging of the dripper holes.
The mulch trench system is a simple and promising irrigation
leaves, rice, spelt, wood or other mulch material is laid around a
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