Environmental Engineering Reference
In-Depth Information
light. Moreover these alternative methods, while more expensive, have the added
advantage of not generating trihalomethanes (THMs), which are a byproduct of
chlorination and which, if ingested in drinking water over a period of decades,
can result in some increase in THM-induced cancer. Hence, the international
waterworks literature of today (which is IC-oriented) gives major of attention to
use of these alternative disinfection methods.
Another important aspect of urban water supply systems in the United States
is that in the earlier decades many of these systems were privately owned, but
by the end of the twentieth century, most of these had shifted to municipal
ownership. Even so, the municipally owned systems have been well designed
and managed — and hence, profitable, including financing of return on investment
plus O&M plus profit. A basic reason for this success is that the municipal
and higher-level public health authorities had the real power to require effective
monitoring for the safety of drinking of water delivered to the tap and to enforce
the requirement that the routine testing of the tap water for coliforms meet the
prescribed safety levels.
A key question here is, what do these progressive improvements in U.S. urban
water supply systems (WSSs) mean for DCs?
Situation in Typical DCs
Sad to say, the urban municipal water supply systems for almost all cities in
DCs, with the exception of the capital cities, very much resemble the situation
in U.S. cities in the early 1900s. The typical DC systems maybe characterized
as follows:
Little if any attention to protecting the source of supply (the raw water
supply) from pollution contamination.
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Focus of interest of WSS managers is on delivering an adequate quantity of
water, with little, if any, attention paid to the safety of the water delivered
to the tap for drinking. Some attention is given to selected water quality
parameters including hardness or excessive color or turbidity, which would
result in massive complaints from householders.
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Use of treatment plants (usually rapid sand filters) designed to suit IC condi-
tions requiring sophisticated O&M. Hence, these plants (the most expensive
component in the overall WSS) function poorly, commonly producing efflu-
ents with turbidities in the range of 5 to 10 ppm, which are hardly amendable
to disinfection. This is due primarily to the fact that the plant design is
by IAA engineers not familiar with DC needs, and to the fact that IC
governments in their programs for helping DCs often try to do so by furnish-
ing/selling them the type of design/equipment utilized in the ICs, without
realizing the consequences.
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Although the treatment plant effluent is usually chlorinated, so the water
is safe to drink when leaving the plant, the WSS managers rarely have
training in sanitary engineering, so they often don't understand that the
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