Greywater Management in Low and Middle-Income Countries - SSWM

When considering irrigation with treated greywater, its microbial and biochemical
properties should be evaluated and compared with reuse standards. Focus should
be placed on the irrigated crop, soil properties, irrigation system used, and crop
evaluate the treated greywater in terms of chemical criteria such as dissolved salts,
greywater treatment systems will most probably not cause any toxic effects on the
crop or pose increased health risks. Caution is recommended in households with low
water consumption or with greywater potentially contaminated by pathogens. High
pathogen loads may be attributed to an acute illness of one or several household
members, or use of critical chemicals such as solvents and disinfectants. Use of
problematic chemicals, such as solvents or disinfectants combined with low amounts
of greywater generated, may lead to the accumulation of some chemicals in the soil
environmental sustainability (Shafran et al., 2005).
Compared with domestic wastewater, greywater will generally contain a reduced
number of pathogenic viruses, bacteria, protozoa or helminth eggs. However, as
indicated in Chapter 3, washing of babies and their soiled clothing and diapers
may substantially raise the pathogen load in greywater. Irrespective of pathogen
load or treatment system used, it should be noted that some pathogenic life forms
may pass the treatment unaffected and cause a potential health risk if greywater is
used for irrigation. Although treatment plant removal rates of 99% or even 99.9%
may appear impressive, survival rates nevertheless amount to 1% or 0.1%. This
contaminated by an acute illness of one or several household members. In low and
middle-income countries, where greywater may exhibit high pathogen concentrations,
survival of more than one percent is generally considered inadequate.
Not only the presence of pathogens but also their survival time in the water, soil
and on irrigated crops are important. Feachem et al. (1983) summarised pathogen
behaviour in warm climates (20–30 °C) as shown in Table 4-12. Due to degradation
processes caused by sunlight and/or desiccation, pathogen survival time on crops is
much shorter than in water or soil.
During primary treatment in grease and grit traps and septic tanks, helminth
eggs, protozoal cysts and viruses (attached to settable solids) tend to settle and
accumulate in the sludge. However, helminth eggs may survive for several months
in this sludge and therefore still pose a health risk when the sludge is removed.
sites for mosquitoes, important vectors of diseases such as malaria or Bancroftian
may form puddles where mosquito larvae can develop in the absence of natural
enemies. Even if greywater is led into open stormwater drains, mosquito problems
may occur. Drains, built for occasional stormwater events are often used for sewage
Low-cost Management and Treatment Options
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