Page 204 - Facility Piping Systems Handbook for Industrial, Commercial, and Healthcare Facilities

WATER TREATMENT AND PURIFICATION

4.40 CHAPTER FOUR

TABLE 4.9 Water Treatment Technology for Small Potable Water Systems
Technology Advantages Disadvantages
Filtration
Slow sand Operational simplicity and Not suitable for water with high
reliability, low cost, ability to turbidity, requires large land
achieve greater than 99.9 percent areas
Giardia cyst removal
Diatomaceous earth Compact size, simplicity of Most suitable for raw water
(septum filter) operation, excellent cyst and with low bacterial counts
turbidity removal and low turbidity (< 10 ntu),
requires coagulant and
filter aids for effective virus
removal, potential difficulty
in maintaining complete
and uniform thickness of
diatomaceous earth on filter
septum
Reverse osmosis membranes Extremely compact, automated Little information available
to establish design criteria or
operating parameters, most
suitable for raw water with
turbidity < 1 ntu, usually must
be preceded by high levels of
pretreatment, easily clogged
with colloids and algae, short
filter runs, concerns about
membrane failure, complex
repairs of automated controls,
high percent of water lost in
backflushing
Rapid sand/direct filtration Compact, treats a wide range Chemical pretreatment
package plants of water quality parameters and complex, time consuming, cost
variable levels
Chlorine Very effective, has a proven Potential for harmful
history of protection against halogenated by-products under
waterborne disease, widely used, certain conditions
variety of possible application
points, inexpensive, appropriate
as both primary and secondary
disinfectant
Ozone Very effective, no THMs formed Relatively high cost, more
complex operation because
it must be generated on-
site, requires a secondary
disinfectant, other by-products
Ultraviolet radiation Very effective for viruses and Inappropriate for surface
bacteria, readily available, no water, requires a secondary
known harmful residuals, simple disinfectant
operation and maintenance for
high-quality waters
(Continued)

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