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The Karnal
Technology involves growing tree on ridges 1m wide and
50cm high (see Fig. 1) wand disposing of the untreated
sewage in furrows. The amount of the sewage/ effluents to
be disposed off depends upon the age, type of plants,
climatic conditions, soil texture and quality of
effluents. The total discharge of effluent is so
regulated that it is consumed
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within 12-18 hours and there is no
standing water left in the trenches. Through this technique,
it is possible to dispose off 0.3 to 1.0 ML of effluent per
day per hectare. This technique utilizes the entire biomass as
living filter for supplying nutrients to soil and plant;
irrigation renovates the effluent for atmospheric re-charge
and ground storage. Further, as forest plants are to be used
for fuel wood, timber or pulp, there is no chance of
pathogens, heavy metals and organic compounds to enter into
the human food chain system, a point that is a limiting factor
when vegetables or other crops are grown with sewage.
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Though most of the plants are
suitable for utilizing the effluents, yet, those tree
species which are fast growing can transpire high
amounts of water and are able to with stand high
moisture content in the root environment are most
suitable for such purposes. Eucalyptus is one such
species, which has the capacity to transpire large
amounts of water, and remains active through out the
year (see Fig. 2 & 3).
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Other species suitable for this
purpose are poplar and leucaena. Out of these three
species, eucalyptus seems to be the best choice as poplar
remains dormant in winter and thus cannot bio-drain
effluent during winter months (see Fig. 4). However, if
area is available and the volume of effluent is small, a
combination of popular and eucalyptus is the best
propagation.
This technology for sewage water use is relatively cheap
and no major capital is involved. The expenditure of
adopting this technology involves cost of making ridges,
cost of plantation and their care.
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This system generates gross returns
from the sale of fuel wood. The sludge accumulating in
the furrows along with the decaying forest litter can be
exploited as an additional source of revenue.
As the sewage water itself provides nutrients and
irrigation ameliorates the sodic soil by lowering the pH,
relatively unfertile wastelands can be used for this
purpose. This technology is economically viable as it
involves only the cost of water conveyance from source to
fields for irrigation and does not require highly skilled
personnel as well. This technology seems to be most
appropriate and economical viable proposition for the
rural areas as this technology is used to raise forestry,
which would aid in re-storing environment and to generate
biomass.
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| Source
: Summarised from the topic "Waste Water as Source of
Irrigation" by Ranbir Chhabra, Author, Soil Salinity & Water
Quality |
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