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1.2 CHAPTER ONE

In the 1990s the old concern about microbiological contamination reemerged as a pri-
mary focus of water treatment engineers. The main driving forces behind this develop-
ment were:
• The promulgation of the Surface Water Treatment Rule and Total Coliform Rule by
the U.S. Environmental Protection Agency (USEPA) and the monitoring and enforce-
ment actions that have occurred since 1989, when they went into effect
• Recent documented cases of contamination of drinking water supplies by waterborne
diseases, mainly giardiasis and cryptosporidiosis, caused by cysts rather than bacteria
New approaches and processes began to be applied and continue to evolve to address
these concerns. These approaches include renewed emphasis on source water protection,
optimizing plant performance, and recycle stream management, plus consideration of new
technologies, especially membrane treatment and ozonation.
Recently, new health effects research has led to reconsideration of the safe drinking
water concentrations for several inorganic contaminents. In the United States the MCL
for arsenic was reduced dramatically--from 50 to 10 ppb. This has created new treatment
challenges for many utilities.
The effects of planned and unplanned recycling of municipal wastewater into raw wa-
ter sources are gaining increased attention. A new class of constituents emanating from
modern human life has been discovered in trace amounts in water supplies. These include
pharmaceutical compounds and personal hygiene products. Additionally, new "emerging"
pathogens are being discovered and their potential occurrence and treatability in water
supplies evaluated. The potential impacts of these developments on the design require-
ments for water treatment facilities have yet to be determined.
In the last decade, new water treatment technologies have continued to be developed
and older technologies improved. Notable developments have been
• The sudden emergence of ultraviolet (UV) radiation as a viable and economic process
for achieving inactivation of cryptosporidium and other protozoan pathogens.
• The continued development and maturing of membrane technologies. Microfiltration
and ultrafiltration are being used frequently for particulate removal in lieu of granular
media filtration. Nanofiltration is being used increasingly for water softening and re-
moval of organic carbon. Reverse osmosis has new emphasis for desalination applica-
tions and for removal of inorganic contaminents (e.g., arsenic).
Finally, since September 1 l, 2001, there has been increased recognition of the vul-
nerability of municipal water systems to acts of terrorism and vandalism. New approaches
to siting and designing critical system components, including water treatment plants, are
evolving to reduce this vulnerability.

TODAY'S CHALLENGES

Engineers who design water treatment systems today face many challenges. The most im-
portant of these are described as follows.

Integrated Treatment Systems
Traditional treatment engineering has focused on the treatment plant as the sole vehicle
for controlling drinking water quality. The engineer's role was to characterize the qual-