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<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 septic tanks.

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 Pacific Region
Parameter Bangladesh Vietnam India Taiwan
pH 6-7.4 7-7.5 9.51-9.62 6.72-7.08
Oxygen mg O2/l 0.1-5.0 0-6 - 0.7-7.2
Turbidity, FTU 25-300 20-300 18-31  -
Conductivity,ÁS/cm2 - 200-750 1040-2040 493-2040
Phosphorus mg P/l 0.6-5.36 0.2-8 0.16-0.8 0.02-0.96
Total Nitrogen, mg N/l 6.7 35 - 3.56-9.47
Ammonia, mg NH3/l - 14.53 - 0.6-35
Suspended solid, mg/l 9-80 50-1700 18-340 -
COD*, mg/l 4-382 25-400 90-400 42.4-78.4
BOD**5, mg/l 1-150 100-400 70-220 11.0-27.9
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 Vietnam
  Flush toilets Disposal to publicsewers/drain On-site disposal
from septic tanks
City Class I 84 48 37
City Class II 75 44 31
City Class III 14 25 24
Average North 41 27 14
Average South 91 52 39
Average All 76 44 32
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.

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