Civil Engineering Reference
In-Depth Information
However, increasingly more stringent turbidity limits and concern regarding removal
of pathogens such as
Giardia
and
Cryptosporidium
may require that pretreatment be
provided to ensure compliance with the regulations.
Provisions should be made in plant design to disinfect both filter influent and ef-
fluent. Disinfectant applied ahead of a filter is a great aid in maintaining clean filters.
Disinfection of the finished water makes the most effective use of the disinfectant
because of the reduced disinfectant demand at this point in treatment. Provisions
should also be made for application of a filter aid such as alum, activated silica, or a
polymer ahead of the filters so that the water can be adjusted to optimize filterability.
Where there is no full plant operating experience with a particular water to be
treated, or where the records are not adequate to determine the best treatment processes
to be used, pilot plant studies are a valuable aid in producing the most efficient and
economical scheme of treatment. Pilot studies can be used to determine the kind and
extent of pretreatment that may be required ahead of filtration. A pilot filter can reveal
through its operation the characteristics of floc particles and filter media that achieve
optimal removal efficiency and length of filter runs. While filter-cleaning requirements
are well standardized, it is prudent to check them through pilot plant operation on a
particular water to be treated. In conducting pilot plant tests, the necessity to operate
under all raw-water conditions must not be overlooked. Unless the pilot plant is op-
erated under the most severe conditions, the full-scale plant may be underdesigned
and ill-equipped to produce the desired water quality at all times.
FILTRATION TECHNOLOGIES
Filtration systems employed at water treatment facilities utilize a porous medium
through which the water passes to remove suspended solids. A number of methods
have been developed to accomplish this purpose. Currently, the most commonly used
approach to filtration in water treatment plants is rapid rate gravity filtration. However,
developments in filtration technology have increased the popularity of other types of
filter systems.
Types of Filters Available
A number of types of filtration systems are technically feasible, depending on the
application. System types that have been identified for possible consideration for most
water treatment facilities are:
Gravity Filtration Systems
Rapid rate gravity filtration
•
Slow-sand filtration
•
Pressure Filtration Systems
Rapid rate pressure filtration
•
Diatomaceous earth filtration
•
Membrane filtration
•
Cartridge filtration
•
