Environmental Engineering Reference
In-Depth Information
Another common misconception is that treatment plants can be operated and
maintained with a very low O&M budget, usually about one-third of the
minimum need 51 , so that, even if well designed, the plant cannot be expected
to function. Monitoring and acting on this problem, which is mandatory in
the ICs, does not exist in the DCs. DC officials and practitioners have paid
such little attention to O&M because of lack of performance monitoring
and because the project feasibility studies often do not include adequate
allowance in the economic analysis for O&M costs.
A typical example is the proposed expansion in 1992 of the municipal
sewage treatment plant of Chittagong (Bangladesh) 8 , justified on the basis
of public health protection and of correcting water pollution in the river
receiving the plant effluent. An evaluation showed that (1) the plant, even
when enlarged, would not receive the bulk of the city's excreta, (2) the
existing plant (built earlier by the British) had long since ceased to be
operated properly, and, hence, was doing little if any good, and this problem
was scarcely recognized in the project feasibility study, and (3) even if
the old and new plants were to be properly operated, the resulting benefit
both to public health and water pollution control would likely not be very
meaningful. All such proposed projects need to include an EIA, which will
call attention to such deficiencies and misconceptions.
An additional finding from the USEM experience in the DCs so far is the
need for standardization in design of facilities for the USEM system, to
standardize practices for all system components, but especially for treat-
ment plants. As it has been, individual designers use a variety of treatment
systems that are in the same ballpark in terms of costs 135 but that, because
of their differences in terms of parts replacement, go unrepaired for months
or even years. Replacement parts often takes months or even a year or two
to get, and finding people who are trained to make the repairs is another
problem. With standardization, parts replacement can be readily managed
and training requirements greatly simplified. Unfortunately, few if any DCs
have as yet adopted such standardization and, accordingly, O&M is usually
very inadequate.
Infiltration into sewers in the ICs used to be a serious problem but this
has been virtually eliminated over the past half-century by use of new pipe
jointing methodology. But jointing in existing DC sewers is often old-style
(bell and spigot pipes), which can result in significant infiltration, which
must be taken into account in the design.
Selection of treatment/disposal design criteria depends on the environmental
standards to be met, and the appropriate standards suited to the DC use may
be quite different from the IC standards. Care must be given to selecting
treatment levels that are appropriate/affordable.
Attention must be given in the project feasibility study to the institutional
and financial aspects — that is, the relationship between the central, provin-
cial, and local governments and their relative responsibilities. Common
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