B. Vestergård
In the past any form for sterilization has been considered too expensive, but recently new application techniques have given cause for a revaluation of the possibilities for sterilization of nutrient solutions and raw water. Experiments made by the author and results from trials made by other firms and institutes have shown that the possibilities for effective sterilization are present here and now. The following techniques have been tested and evaluated for both technical and economic feasibility. UV radiation, Gamma radiation, destructive ultra sonic, pasteurization, ozone and ozone combinations, hydrogen peroxide, chlorine and a number of approved and prohibited organic agents. The results indicate that if the quantity is small heat is the most economic agent specially if the heat can be considered waste e.g. from burning of gas for CO2 production or from heating the solution or greenhouse. If the heat can not be reused and the recirculation rate of the solution is high, UV sterilization must be considered the best alternative, and if the quantity of solution is very large, ozone and different combinations using ozone, will be the cheapest way to assure an adequate sterilization.

This paper has been written in order to give interested parties some background knowledge on sterilization and the related techniques available today. Please bear in mind that different techniques have different strength in different applications. This means that we must not try to make one system work for all applications. Up until now there has not been a great interest in the horticultural field for using sterilization but pollution problems have put a pressure on the agricultural sector as a whole in order to get less effluence containing pollutants.

On one side the horticultural industry is being infected from the outside. More and more raw water analysis with infection not only of human pathogens but also with specific plant pathogens such as phytium is being brought to our attention. It is not only from the outside this pollution originates. The more effluence the agricultural industry is discharging into the environment containing fertilizer ions such as nitrate, ammonium and phosphates, pesticides and fungicides, the more infection they are getting, when they pump the polluted water back again and use it without any form for precaution or treatment. With central irrigation systems and reuse of the nutrient solutions comes the danger of easy spreading of the phatogens.

The reasons for treating and reusing the water are:

Better plant quality

Higher plant production

Conservation of water and nutrients

Less pollution

Legislative dictation

The sterilization process should eliminate pathogens like fungus,

Vestergård, B. (1988). STERILIZATION OF WATER AND NUTRIENT SOLUTIONS. Acta Hortic. 221, 303-313
DOI: 10.17660/ActaHortic.1988.221.33

Acta Horticulturae