Environmental Engineering Reference
In-Depth Information
Situation in Typical DCs
In contrast with the United States/ICs, the typical DC city, including even many
capital cities, has yet to achieve satisfactory management of community excreta
and other wastes posing public health/environmental hazards, including indus-
trial wastewaters discharged to municipal sewers. However, in recent decades
the IAAs have made many grants/loans intended to help the DCs to get a handle
on this problem, but with generally ineffective results and wastage of investments.
The first (and almost remarkable) finding in reviewing DC/USEM experience to
date shows a lack of understanding of the three components of a comprehen-
sive municipal sewerage system as previously described. It especially fails to
recognize that the most important component is use of sewers to collect/export
the sewage, not the subsequent treatment. A large number of IAA-sponsored
projects of the past several decades have been formulated on the assumption that
provision of treatment per se is the answer to the problem, without recognition
that treatment plants are not effective without sewers to collect and transport the
waste to the treatment plant.
The most comprehensive analysis of the USEM problem in the DCs known
to the author is the study on “Sewerage Prioritization” in Thailand completed
in 1995
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. This evaluated the ongoing situation in all of the larger cities
in the country (more than 100), with the key findings. These who plan/
design/manage urban sewerage systems must recognize that the DC approach
must be quite different from the IC approach, as follows:
A common notion (already noted) in both the IAAs and the DCs is that urban
sewage problems can be solved simply by building a treatment plant, which
receives only a portion of the area's excreta, with much of the remainder
reaching the waterway without adequate treatment, without recognizing that
such plants may do little good for protecting either public health or receiving
water quality.
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In the ICs, virtually all buildings in the sewerage service areas are served
by sanitary or combined sewers. When the public sewer system is built, all
buildings connect up and existing on-site units are abandoned. Generally in
the DCs, only the affluent areas (which can afford them) are served and the
bulk of the population continues to depend on on-site units. Many of these
on-site units do not function satisfactorily due to inadequate design and lack
of periodic servicing, resulting in frequent excreta overflows into the commu-
nity environment, which pose very serious disease transmission risk hazards,
not only to the nonaffluent subareas but to the entire service area. Hence, the
argument that is often made by IAAs that improving service to the affluent
subareas can be justified in terms of protecting overall community health is
hardly correct. If the planners are really interested in overall community pub-
lic health protection, the project plan must include “equal attention” to the
nonaffluent subareas (the same is true for provisions of improved urban water
supply) if these are to be justified in terms of public health).
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