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                KARNAL TECHNOLOGY        

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

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.

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). 

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. 

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.

 Source : Summarised from the topic "Waste Water as Source of Irrigation" by Ranbir Chhabra, Author, Soil Salinity & Water Quality

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