Water recycling in greenhouse horticulture
Water disinfection and reuse in greenhouse horticulture.
The production in European greenhouse horticulture is not yet as water efficient as it could be. Soil-less growing systems are becoming common in horticultural practice in most of the European countries, although not in each country on a large scale yet. The advantages of soil-less growing systems compared to soil grown crops are as follows: 
The disadvantages of these systems are:
In most cases open or run-to-waste systems are adopted. In such open systems, superfluous nutrient solution freely leaches to ground and surface water. Because of economical motives and environmental concerns closed soil less systems can be applied. These closed systems are more efficient with the use of water and fertilizers, and cause less damage to the environment. The disadvantage of the closed systems is the risk of a rapid dispersal of soil-borne pathogens by the recirculating nutrient solution. To eliminate these pathogens, several disinfection methods can be used:
Ozone treatment can be used to disinfect the drain water . Ozone is the second most powerful sterilant in the world and its function is to destroy bacteria, viruses and odors. An ozone supply of 10 g/h/m3 water with an exposure time of 1 h is sufficient to kill all pathogens .
Another way to disinfect the drain water is the use of UV-radiation . Ultra-violet radiation (or UV) is a proven process for disinfecting water, air or solid surfaces that are microbiologically contaminated. For eliminating bacteria and fungi an energy dose is recommended of 100mJ/cm2. For viruses a dose of 250 mJ/cm2 is recommended.
When heat treatment is applied, a solution is heated for about 30 seconds to a temperature of 95˚C. At this temperature all pathogens are killed. A disadvantage of heat treatment is the consumption of gas. Also warm drain water contains less oxygen.
 Van Os, E.A. Closed soilless systems for more efficient and environmental friendly production. Acta horticulturae, Wageningen, The Netherlands (1994)
Information about water treatment and reuse of oily wastewater
Should you know of any other interesting or more recent book, report, article or publication, concerning water reuse in greenhouse horticulture. Please let us know, so that we can include reported case-studies in the above overview.