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Newsletter and Technical Publications
<International Source Book On Environmentally Sound Technologies
for Wastewater and Stormwater Management>

3.3.2 Large scale treatment (domestic wastewater treatment)

Suitable treatment methods have been selected for most of the developing countries as shown below:

1- Stabilisation Pond
2- Aerated Lagoon
3- Oxidation Ditch
4- Conventional Activated Sludge

In the developing world, it is estimated that more than 90% of sewage is discharged directly into rivers, lakes, and coastal waters without treatment of any kind. Of India's 3,119 towns and cities, only 109 cities have full wastewater collection and treatment facilities. In Vietnam only the city of Hue has a primary treatment plant with a capacity of 300 m3/day, which is only 6% of the total municipal wastewater flow. A primary treatment plant for domestic wastewater has been installed in Kim Lien district in Hanoi. The operation of this plant was stopped, presumably due to lack of necessary funds for operation and maintenance.

In Vietnam some ponds, lakes, canals and rivers are used to receive water. They provide natural purification of wastewater, but analyses of water quality from the lakes in Hanoi indicate that the purification capacity has been exceeded. All the surface water bodies are considered enthrophic or polluted by wastewater. During the dry season the bottom layers and sediments are anaerobic. There is danger that many of these natural water bodies will turn anaerobic unless the pollution load is reduced. The canals in HCMC are already overloaded and septic. There are no known operational industrial wastewater treatment plants.

Some Chinese cities have secondary wastewater treatment plants built, but not in operation, one of the reasons being the incomplete status of the associated wastewater collection system. The investment required to establish a complete wastewater system with adequate piping and pumps is much higher than the expenditure on the treatment plants themselves.

In the Philippines there are 1500 cities but only 1% of there cities have domestic and industrial wastewater treatment facilities. Table 3.8 shows details of treatment plants for selected cities in the Philippines.

For small-scale treatment operations in urban and rural areas of Indonesia, the septic tank is commonly used. Large-scale treatment of domestic wastewater could incorporate biological filtration techniques. However, in view of the existing Indonesian situation, it appears that stringent effluent standards will need to be met, meaning that inevitable additions to the primary and secondary domestic treatment processes will be required.

Table 3.8: Water treatment plants in the Philippines
Cities Capacity of the wastewater treatment m3/day Type of the treatment Remark
Ayala 40,000 Activated sludge Operating
South Manila 207,000 Aerated lagoon Under construction
Central Manila 162,000 Oxidation ditch Under construction
North Manila 282,000 Aerated lagoon Under construction
Dagut 12,600 Aerated lagoon Under construction
Banguio 20% wastewater Oxidation pond Operating
Cauayan Isabela 30% wastewater Activated sludge Operating

At present, only five large cities in Indonesia operate centralised sewerage treatment plants: Jakarta, Bandung, Medan, Yokjakarta and Cirebon. Construction of the Jakarta treatment plant was completed in 1992. However, it serves less than 5% of the population. Bandung started the construction of its plant in 1980 and was completed in 1990, serving nearly the whole population. Medan started construction of its system in 1985 and was completed in 1995, covering 75% of the population. Cirebon required three years for the construction of its plant which was completed in 1991.

Thailand is one of the Asia Pacific developing countries with more extensive treatment facilities in its cities. Table 3.9 shows the sewerage plan for 2011 in Thailand.

Table 3.9: Outline of Sewerage Plan and Cost Estimates (facility for 2011), Thailand

Service Area Design Capacity  Treatment Method

No. of  Operators (person)

Construction
(Million Baht)

O&M
(Million Baht)

(m3/d) WW sludge

Chai Nat 5,900 SP DB 13 190.30 0.952

Sing Buri East
              West
Sub-total
3,000
8,200
11,200
SP
AL
N/A
DB
DB
N/A
11
16
27
185.66
171.56
357.22
1.286
1.524
2.810

Lop Buri 16,500 AL DB 21 372.16 4.902

Ang Thong East
                 West
Sub-total
N/A
N/A
3,700
SP
N/A
N/A
DB
N/A
N/A
N/A
N/A
11
93.36
60.39
153.75
0.666
0.429
1.095

Pa Mok East
            West
Sub-Total
2,000
1,700
3,700
SP
SP
N/A
DB
DB
N/A
8
8
16
117.97
97.34
215.31
0.432
0.313
0.745

Sena  2,600 SP DB 9 84.80 0.241

Rang Sit Preli.
Rang Sit Others
Sub-Total
N/A
N/A
75,000
AS
N/A
N/A
DU
N/A
N/A
N/A
N/A
50
182.18
1,065.19
1,747. 37
19.123
29.854
48.977

Bang Bua Thong Preli
North Others
Sub-Total
N/A
N/A
23,600
AS
N/A
N/A
DU
N/A
N/A
N/A
N/A
30
352.28
237.33
589.61
8.189
5.523
13.712

Bang Bua Thong South
Bang Bua Thong Total
7,900
N/A
OD
N/A
 DB
N/A
15
45
307.55
897.16
6.751
20.463

Note : SP - Stabilization Pond
OD - Oxidation Ditch
DB - Drying Bed
AS - Activated Sludge
AL - Aerated Lagoon
N/A - No Answer
 DU - Dewatering Unit

At present, there are 18 Common Effluent Treatment Plant (CETP) sites for tannery clusters in five districts of Tamil Nadu, viz. North Arcot Ambedkar, Erode Peruya, Dindigul Anna, Trichy and Chengai. Out of these, eleven CETPs are in operation, and the remaining are under construction.

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