Treating Water at the Source. Treatment of water supplies is generally
done at a treatment plant where positive monitoring and control is possible.
Sometimes, however, providing treatment at the source (in situ treatment) is more
economical or practical. Treating reservoirs for algae or zebra mussel control is an
example of in situ treatment. For detailed information on specific in situ treatment
techniques, see pars. 2.1.3, 2.1.5, 2.2.6, and 2.2.14).
Unit Treatment Processes. For each process, guidance and information
is provided on fundamentals of how water treatment facilities and related equipment
operate, common operating problems, process control tests, applicable regulations,
recordkeeping, and safety precautions. General maintenance routines and procedures
for mechanical equipment can be found in Section 11 of this handbook.
Preliminary Treatment. Preliminary treatment (pretreatment) is used to
remove objects or grit that could clog or damage downstream equipment. Pretreatment
includes several processes that may be used alone or together. For information on the
most common processes, screening, presedimentation, and microstraining, see
Coagulation and Flocculation. Suspended material that is too fine to be
removed by plain sedimentation can be clustered into settleable particles through the
process of coagulation and flocculation. Coagulation and flocculation, along with
filtration, are sometimes referred to as "conventional" treatment. Consult par. 2.1.5 for
general information on coagulation and flocculation.
Specific information on chemical reactions, selection of coagulants,
conducting jar tests, and help with calculating chemical dosages can be found in
pars. 2.1.1, 2.1.2, 2.2.26, 2.2.58, and 2.2.59.
Maintenance of rapid mix and flocculation facilities is included in par.
Sedimentation Basins and Clarifiers. In conventional water treatment,
sedimentation is the step between flocculation and filtration. Sedimentation (or
"clarification," as it is sometimes called), is also used to remove the large quantities of
chemical precipitates formed during lime softening.
Refer to par. 2.1.5 for a general description of the sedimentation process.
This reference also gives specific information on basin types (conventional rectangular
basins, center-feed basins, peripheral-feed basins, spiral-flow basins, and shallow
basins), as well as plate and tube settlers. Information on other clarification processes
found in this reference include solids-contact basins, dissolved-air flotation, and