Agriculture Reference
In-Depth Information
Adsorption
Adsorption is the process of removing soluble contaminants by attachment to a
solid. A common example is the removal of soluble organic compounds via adsorp-
tion onto granular activated carbon (GAC). GAC is useful for its ability to remove a
wide range of contaminants. Certainly, if pesticides were a concern for the drainage
water being examined, the use of GAC adsorption would be a leading candidate for
treatment.
Another treatment for removing volatile compounds for water is air stripping.
In a conventional counterpart of air stripping operation, the contaminated water is
distributed at the top of a tall reactor vessel that is packed with materials or structures
with a high surface area. As the water moves downward, clean air is introduced at
the bottom of the reactor and moves upward. As the water and air make contact,
volatile compounds are transferred from the liquid phase to the gas phase according
to gas transfer theory.
Distillation
Distillation is a thermal process used for salt removal. Heat is used to vaporize
the water, leaving the salts behind. The water vapor is condensed to a high quality
water. The process is energy intensive. Reverse osmosis is used for desalination
applications.
9.10 Economic Considerations in Drainage Selection
and Installation
Economic analysis should be carried out before undertaking a drainage project. The
result of economic analysis will help in deciding whether drainage system instal-
lation is feasible from economic point of view, or which type of drainage (e.g.,
surface (deep drain) or subsurface, or, random field lateral or uniform drainage) is
more economical. Sometimes, the economic criterion is not only deciding criteria,
but also depends on the national/regional food security issue, national priority, and
government policy.
Detail procedure for performing economic analysis and decision criteria (along
with sample example) has been discussed in Chapter 11 ( Economics in Irrigation
Management ), Volume 1.
9.11 Performance Evaluation of Subsurface Drainage
9.11.1 Importance of Evaluation
Subsurface drainage is instrumental in the improvement of non-productive soils,
and it can assist in avoiding unsuitable soil conditions during farming opera-
tions. Knowledge of subsurface drainage performance is important in order to use
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