Project Summary

Greenhouse horticulture in the Mediterranean area was passing a period of enormous growth during the last 20 years as being a very successful method of crop production. This is mainly based on the combination of the mild climate during winter and a relatively simple and cost effective construction method, making the process viable. The fact of enhanced water efficiency, caused by a higher air humidity, a reduced air velocity compared to open field horticulture and effective possibilities of rainwater harvesting from the roof did also contribute to the growth, as available water sources in the arid climate could be exploited relatively effectively.

Now, as at many places groundwater basins are more and more overexploited or even fading, the specific possibilities of greenhouses for water saving are getting into the focus of general interest. The attention is now changing from production rates calculated by square meters to production rates calculated by litres of water. To further improve the water efficiency, there are two major directions of technological development :

• Closing the greenhouse means to provide internal cooling and dehumidification processes instead of climate control driven by air exchange. A closed greenhouse theoretically does not need any water input as it is cycling within the closed internal atmosphere. In reality, there will always be some remaining losses, but water efficiency has already been approved at below 0,5 litres/m² daily water demand for intensive cultivation. A closed greenhouse also allows to accumulate carbon dioxide to a level of plant optimum which also contributes to a higher production rate per water used.
• The use of sea - or brackish water can be an infinite water source if it is available from the surrounding area. Greenhouse integrated seawater desalination can be realised in different ways. The major approaches are either desalination in a separated volume over the greenhouse cover (like in a solar still), or as an input/output system with evaporation at the greenhouse air inlet and condensation or absorption at the air outlet. A further possibility is evaporation of saline water in the roof area of a closed greenhouse, where the air is hotter than in the crop area and can uptake more water.

Both practices, the closed greenhouse and the input/output system are aimed at recovering water from air humidity and also allow to recycle the water evaporated and transpirated by the plants. This is where a third major method can be integrated : An adapted and secure use of wastewater for greenhouse irrigation will allow to recycle these water sources into drinkable fresh water, using the vegetation's root membranes as the most effective and self-renewing water filter ever available.

The new technologies have the potential :

• to make greenhouse cultivation much more independent from drought and irregular rainfall and by this also more economic
• to use the content of plant nutrients in wastewater as a fertilizer
• to explore saline water sources for greenhouse integrated evaporative cooling and solar desalination
• to extremely reduce the pressure on freshwater resources and the pollution of surface and groundwater
• to up-grade and to re-use wastewater at the same time, which allows to change greenhouse horticulture from a water consuming to a water producing cultivation method
• to add value to otherwise unproductive land and by providing water and food, reaching a more sustainable level of water and food supply for growing urban areas

However, these research activities have not been fully implemented in the Mediterranean Partner Countries so far. The main reasons for that are :

• costs of the special water cycling greenhouse technology and - architecture
• insufficient information about Mediterranean Partner Countries wastewater collection systems and actual waste water qualities
• insufficient knowledge about the socio-economical benefits and risks to upgrade wastewater and saline water within greenhouses
• insufficient knowledge about the market potential of applicable crops that can be used in combination with greenhouse internal wastewater treatment

Project objectives :

In this context, the objectives of the CYCLER-SUPPORT project are :

• to provide major elements of the above mentioned missing information by accomplishing a CYCLER-SUPPORT study
• to provide a clear overview of further research demand
• to discuss the proposed options with different stakeholders from greenhouse horticulture, water supply, sanitation, policy-makers within the CYCLER-SUPPORT-Workshop
• to strengthen the exchange of know-how and co-operation between scientists from the European Union and Mediterranean Partner Countries
• to support the establishment of sustainable business-relations