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CHAPTER 1

THE CHALLENGE OF WATER

TREATMENT PLANT DESIGN

Thomas J. Lane
Malcom Pirnie, Inc.
Jackson Heights, New York

When water treatment engineering first evolved in the early part of the twentieth century,
its main goal was to ensure that infectious organisms in drinking water supplies were re-
moved or inactivated. Chlorination and filtration practices were applied with tremendous
success to the point that major death-causing waterborne disease outbreaks in the United
States were virtually eliminated by the 1930s.
As a result, for engineers trained in the 1960s, 1970s, and 1980s, both education and
industry belief was that all concerns of microbiological contamination in surface waters
could be eliminated by providing filtration (with suitable pretreatment) to produce water
of sufficient clarity (turbidity less than 1.0 or 0.5 ntu) and then chlorinating. Groundwa-
ter was thought to be already filtered, requiring only chlorination to maintain a distribu-
tion system residual. Any additional treatment was generally considered necessary only
to address non-health-related parameters, such as excessive hardness or water discol-
oration caused by iron and manganese.
The principal challenge to water treatment engineers in the 1960s and 1970s was en-
gineering cost-effectiveness: how to accomplish these simple treatment goals at the low-
est total cost to the water utility. Thus, in these decades many new techniques and pro-
cesses were developed to clarify surface water economically. These developments included
improvements to sedimentation basin designs; high-rate clarification processes such as
tube settlers, plate settlers, and dissolved air flotation; high-rate filtration processes; and
proprietary preengineered or package equipment integrating flocculation, settling, and fil-
tration processes.
In the 1970s and 1980s a new drinking water concern arose: the potential long-term
health risks posed by trace amounts of organic compounds present in drinking water. A
wave of regulations ensued with new maximum contaminant levels (MCLs) established
for total trihalomethanes (TTHMs), pesticides, and volatile organic chemicals (VOCs).
This trend continues today. In response to this concern and resulting treatment needs, wa-
ter treatment engineers have successfully devised new methods of water treatment to re-
move organic compounds. These methods, such as air stripping, activated carbon ad-
sorption, and enhanced coagulation, have been a primary focus of water treatment
engineering over the last 20 years.

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