Greywater Management in Low and Middle-Income Countries - SSWM

Moderately tolerant
Bean Cowpea Vigna unguiculata
Okra Abelmoschus esculentus Wheat
Onion Allium cepa Fig Ficus carica
Avocado Persea americana Olive Olea europaea
Lemon Citrus limon Papaya Carica papaya
Mango Pineapple Ananas comosus
Moderately sensitive
Maize Zea mays Barley
Rice, paddy Sugarbeet
Cabbage Brassica oleracea capitata Asparagus
Eggplant Date palm
Spinach
Tomato
Spinacia oleracea
Lycopersicon lycopersicum
can lead to the degradation of well-structured soils (dispersion of clay particles),
reducing soil porosity and aeration, and increasing the risk of poor water movement
through the soil. Depending on soil characteristics, greywater with a SAR as low as
3-4 can already lead to degradation of soil structure (Patterson, 1997, Gross et al.,
2005).
Sodium salts are soluble and cannot be removed under typical wastewater
treatment conditions. The best and by far cheapest strategy to avoid excessive
sodium loads on soils is the selection of low sodium laundry detergents (see Chapter
Source control).
Figure 4-10 can be used to evaluate irrigation water quality in relation to its
potential impact on soil structure as a function of EC and SAR values. In the event
of uncertainty regarding the potential effects of greywater irrigation on soil structure
stability, soil samples can be submitted for analysis to an accredited laboratory.
Other problems related to greywater irrigation may be caused by chloride and
boron toxicity. Although essential to plants in very low concentrations, boron and
chloride can cause toxicity to sensitive crops at high concentrations. Leaf burn at
the leaf tip is a typical toxicity symptom for high chloride concentrations. Similar
to sodium, high chloride concentrations cause more problems when applied with
sprinklers. Plant injuries must be expected with chloride concentrations as low as
140 mg/l (Bauder et al., 2004). Boron toxicity is likely to occur on sensitive crops at
concentrations lower than 1 mg/l. Gross et al. (2005) observed boron accumulation in
greywater-irrigated soils in Israel. After three years of irrigation, boron concentrations
in the soil reached 2.5 mg/kg. The risk of chloride and boron toxicity can best be
minimised by utilising cleaning agents poor in boron and chloride.
Low-cost Management and Treatment Options
48