Water Treatment Technologies and Their Costs - Global Drinking Water Management and Conservation - page 34

Table 3.2 Proposed water treatment classes
Class Typical treatment

technology

Contaminants removed

Class
1

Chlorination Water disinfection; removal of most pathogens

Class
2

High Rate Clari cation
& Filtration

Disinfection plus suspended solid removal

Class
3

Ultra Violet Class 2 plus removal of Protozoa

Class
4

Ozonation Class 3 plus removal of dissolved organic matter

(no DPB a precursors)

Class
5a

Activated carbon, pow-
dered or granular

Class 3 plus removal of geosmin and other taste and
odor compounds, DBPs, Volatile Organic Compounds,
Endocrine Disruptors, micro-pollutants, pesticides, phar-
maceuticals and personal care products

Class
5b

Advanced oxidation
process

Class 5a plus higher ef cacy of the removal of chemicals
and other micro-pollutants (e.g. pesticides, pharmaceuti-
cals, taste and odor concerns)

Class
6

Reverse Osmosis OR
Distillation

Class 5 plus removal of salinity

a

DPB stands for “ disinfection byproducts. ” See footnote 2

higher treatment class indicates a greater removal of contaminants. However, this
classi cation scheme is fairly broad in scope, an initial attempt, although other more

cations are possible. Note that we are classifying treatment
categories or classes, not

finely graded classi

final water quality. What emerges from this classi cation

is a way of comparing final water quality indirectly, on the basis of what treatment

systems are used, and also assessing any possible long-term health threats.
In North America, most drinking water comes from surface water, which needs
to be treated adequately. The data presented in the introduction to this chapter
shows the dominant role played by chlorine and chlorine derivatives in North
America, where this Class 1 technology is concerned almost exclusively with the
removal of pathogens, although we know that chlorine is not effective against
protozoa and other pathogens. However, for most large cities and populations, the
conventional water treatment method is coagulation, flocculation, clari cation, and

filtration, and is typically followed by disinfection by chlorine or chlorine deriva-
tive. But the failure of a flocculator led to an outbreak of cryptosporidiosis in

Carrollton Georgia in 1987; the failure of a chlorinator led to an outbreak of
giardiasis in Bradford Pennsylvania in 1979. Thus, the conventional treatment train
is best described as being Class 3 if it removes all protozoa; it cannot be classi

ed
as Class 4 as chlorination will leave DBP precursors in the water. For this reason, in
Ontario and indeed in the whole of North America, the main DBPs, called Triha-
lomethanes (THMs), nitrosamines and Haloacetic Acids (HAAs) are regulated with
maximum contamination limits. But

there are also many other DBPs, called

Halides, that are not regulated at all.