Greywater Management in Low and Middle-Income Countries - SSWM

eduction in capillary rise and build-up of hydrophobic soils (Doi et al., 2002; Gross
et al., 2005).
During greywater irrigation, toxicity problems may occur if boron ions (similarly to
sodium ions) are taken up by plants and accumulate to concentrations high enough
to cause crop damage or reduced yield. Detergents are the main sources of boron
in greywater. Although boron is an essential micronutrient for plants, excessive
amounts are toxic. Gross et al. (2005) observed boron concentrations reaching
3 mg/l in laundry greywater. The recommended maximum value for irrigation water
amounts to 1.0 mg/l for sensitive crops such as lemon, onion or bean (FAO, 1985).
Bleach, disinfectants and solvents are further substances of concern in greywater.
Inhibition of the biological process by bleach begins at concentrations as low as
1.4 ml/l, with quite a substantial inhibition occurring at 3 ml/l. By using environmentallyfriendly
household chemicals and refraining from pouring hazardous substances
(paint, solvents etc.) into the sink, the levels of toxic substances in greywater can
be maintained low (Ridderstolpe,
2004). Since many environmentallyfriendly
detergents are available on the
market, the problems with greywater
71 70 13.2 4.6 Total load, g/p/d
treatment, reuse and disposal systems
can be minimised (see section Source
33% Blackwater
53%
control).
74%
88%
Even though greywater is less
polluted than toilet wastewater, it is an
67% Greywater undeniable fact that due to the large
47%
volumes of greywater produced, its
26%
contribution to the total pollution load in
12%
domestic wastewater is considerable.
BOD 5
SS Total N Total P
According to different studies, greywater
makes up on average more than
half of the BOD load, up to two thirds of the total phosphorous load (where phosphatecontaining
detergents are used) and one fourth of the total suspended solids load
(see Figure 3-1). This clearly reveals the importance of including greywater in
sanitation programmes. Focussing only on blackwater will not meet the objective of
providing adequate sanitation and reducing public health risks and environmental
degradation.
16
Greywater Characteristics