Newsletter and Technical Publications
<International Source Book On Environmentally Sound Technologies
for Wastewater and Stormwater Management>
3.1.2 Characteristics of wastewater
Most of the wastewater in the Asia Pacific Region originates from residential
and industrial areas. Septic tanks are the most popular technology in the urban
areas of Asia Pacific developing countries, because of its practicality, being
easier and cheaper to implement in densely populated areas. About 80 % of the
total population in the urban areas have septic tanks.
Septic tanks are the most prevalent form of on-site urban sanitation in the
developing countries, for both flush and pour flush toilets. Some pit latrines
are also used. Because of small lot sizes in typical urban areas, septic tank
effluents over flow in to roadside drains even where subsoil soakage is
attempted. Some of these roadside drains are clogged by domestic and commercial
solid waste and other debris. In urban areas with waste disposal systems, human
excreta and bathing wastewater are directed predominantly to septic tanks.
Sullage waste (kitchen and laundry wastewater) may or may not be conveyed to
Characteristics of wastewater, including organic, solid, nutrient, and
inorganic substance loads typically result from domestic, commercial and
industrial waste. The characteristics vary between countries and also according
to location within countries over a period of time. Table 3.3 shows the typical
quality of wastewater in some Asia Pacific countries.
Table 3.3: The quality of wastewater in some countries in the Asia
|Oxygen mg O2/l
|Phosphorus mg P/l
|Total Nitrogen, mg N/l
|Ammonia, mg NH3/l
|Suspended solid, mg/l
|Source: International Specialized Conference
on Water Quality and its Management 1988, New Delhi.
Note: COD* Chemical Oxygen Demand
BOD**5 5 days of Biochemical Oxygen Demand
For example in Vietnam, Table 3.4 shows that the percentage of households
using flush toilets, which dispose of their wastewater on-site, appears to
increase with city size. It was expected that the effluents from septic tanks
would be infiltrated into the ground. However wastewater in many urban areas is
discharged directly into streets, drainage ditches or natural water areas.
Table 3.4: Disposal of domestic wastewater, % of households in
||Disposal to publicsewers/drain
from septic tanks
|City Class I
|City Class II
|City Class III
|Source: Vietnam National Urban Wastewater
and Sanitation Strategy Nov. 1995
At present, the average number of urban households without their own sanitation
facilities is about 14%. This corresponds roughly to the percentage of temporary
houses (about 19% in 1992 - 1993). Some improvements have probably taken place
since then, meaning the share of temporary housing should be lower now. If there
is a correlation between households living in temporary houses and households
without toilet facilities, then it is likely that households living in temporary
housing neither can afford nor are willing to invest in improved sanitation
facilities. The population living in this type of housing may be served by communal
or public facilities.
Households in large cities generally enjoy a higher sanitation standard than
households in small cities. The share of households that rely on bucket latrines
and other simple toilet facilities, or do without, is much higher in Class II
and III cities.