Newsletter and Technical Publications
<International Source Book On Environmentally Sound Technologies
for Wastewater and Stormwater Management>
Feasibility study for sewerage and drainage improvement in Phuket city,
Like other big cities in Thailand, in Phuket Municipality (the City), there
exists a public storm water drainage system which is also used for domestic
wastewater removal. However, there is no public sewage disposal system. (Source:
Project for Phuked Municipality in Kingdom of Thailand. Sewage Works in Japan)
In the city centre, the sullage from kitchens, washing and bathing is
discharged to rivers or canals through the existing stormwater drainage system,
and approximately one-third of the volume of septage from cesspools and septic
tanks is simply allowed to infiltrate into the ground. Therefore, the existing
stormwater drainage system is practically refered to as the combined sewage
collection system, even though it was not originally planned for such a purpose.
This has caused pollution not only of river and sea water, but also of
The evaluation of alternatives for planning the sewage collection system for
the study area was undertaken. Experience has shown that, for surrounding
environmental impact and water pollution control, a separate collection system
is advantageous compared with a combined system. However, further analysis shows
that under the following conditions, a combined system may be more desirable to
promote the diffusion of sewerage more economically.
- The degree of pollution of the receiving watercourses during rains is
- The existing public drainage system, which is collecting both surface
runoff and sewage can be intercepted to combined sewers to be constructed
thus resulting in a lesser need for lateral sewers.
Based on a comparative cost study, the combined system is less expensive than
the separate system in terms of construction cost and operation and maintenance
(O & M) cost. Construction cost and O & M cost in the combined system
are only 30% and 40% of those in the separate system, respectively.
Indonesian sewerage development plan
Because open drainage networks drain stormwater in some areas, two types of
sewerage collection systems are applicable depending on the terrain in the
collection area. One is the conventional separate system, and the other is the
interceptor collection system (Wastewater Disposal Jakarta 1994).
As a general rule, the conventional system is applied for the following
- Commercial and institutional areas located along main roads.
- Residential areas where redevelopment has been completed and the existing
road is wider than 2m, which is the minimum width required for laying sewer
lines and other dimensions.
The interceptor system is applied for high population density areas, which
cannot be covered by a conventional system. This system will collect only grey
water through the existing roadside ditches and other drains to the proposed
interceptor. Toilet waste is treated by septic tank systems and its overflow
flows into the interceptor. The proposed interceptor however, will not receive
storm water collected through ditches. Wastewater exceeding the dry weather flow
will overflow into rivers or canals in the vicinity.
Jakarta water quality suffers from combination of domestic and industrial
pollution. The backbone of the sanitation system is still an open ditch system
that serves as a conduit for all wastewater. While this system may have been
adequate for the city with a population of less than half a million, which was
the size of the city when the system was planned, it can not cope with the
wastes of the current 11.5 million residents.
Sewerage systems in more developed countries
Currently, more developed countries such as Australia, Hong Kong, Japan,
Korea, Singapore and Taiwan normally have separate systems for sewage, with two
types of collection system, one for stormwater and another for sanitary sewage
in the new development areas. As development and urbanisation has continued to
increase, the pollution load due to stormwater overflow has been found to be
significant. Many communities in the developed countries, therefore, provide
some degree of treatment to stormwater overflows or store stormwater for
treatment at the sewage treatment facilities.
Sewer systems in Australia
In Australia, the community collection system comprises a reticulation system
serving individual household properties. The sizes of the pipes, generally
gravity pipes, are such that the system can readily accommodate changes in the
residential development densities. More recently vacuum collection systems have
been introduced in Western Australia.
For local communities, the reticulation system conveys the wastewater to the
central treatment and reuse disposal facilities. For large community systems
there is generally a main sewer system that conveys wastewater to a large
central treatment and reuse/disposal facility. The main sewer system is
developed as catchment grows and its capacity can be increased to accommodate
Drainage systems in Japan.
There are two different systems for draining wastewater; namely, the combined
system and the separate system. The combined system was first developed in
Japan, but to prevent contamination of the receiving water, at present the
separate system is primarily used. In Japan, it is common to establish a
five-year medium term plan for structures such as sewers. The current five- year
plan is the seventh such plan.
The proportion of sewered population in Japan increased very quickly. In 1965,
only 8% of population was sewered. By 1970 the sewered population had increased
to 16%, in 1985 to 36% and in the year 1993 to 49%. Based on the progress made
during previous successive five-year plans the sewered population in Japan is
now estimated to be about 65%. Total length is about 11,858 km, with size from
200 to 5000mm.