Summary of implementation guide

The Cycler Support project, funded by the 6th Framework Programme of the European Union was aimed at bringing together knowledge from different research areas, mainly from greenhouse horticulture and water management, to investigate the potential of growing food on the base of unconventional water sources. This includes on one hand the integrated crop production using the urban water and matter cycle as a base for water and plant nutrients. On the other hand, also technologies of rainwater harvesting and water desalination are investigated.

A long term scenario is described, that shall envisage a future sustainable economic base and the development of 100 % of the surface in the perimeter of urban areas in arid and hyper-arid regions. This includes high productive crop production within a new generation of water efficient greenhouses, but also reflects the development of the open landscape, that can be developed e.g. by changing the relief and by adding non-degradable carbon being generated as a waste product from the urban matter cycle.

New generation greenhouses: A group of new greenhouse technologies allows to collect condensed water from air water vapour within greenhouses. This means, that much less conventional water has to be used. Together with rainwater collected from the roof tops of the greenhouses, it is possible to reach a water autonomous situation of irrigation water supply in many regions of the world.

Urban greywater can be used as an additional water source in irrigation and can be recycled back as fresh water in the urban areas.

Saline water can be used in the greenhouses for evaporative cooling in a way, that also the condensed water yield is increased. Seawater can be directly used for irrigation directly, if it’s sufficiently mixed with condensed water, so that the salinity is decreased and can be managed by salt uptake of the vegetation and periodical flushing of drainage water.

A first example for the new technology is the Watergy greenhouse, a closed air environment. There is an internal, buoyancy driven air circulation with rising hot and humid air, that flows up into a tower. Within a cooling duct, the air then is cooled downd by a heat exchanger, that makes the the air cooler and heavier, so it flows down, back into the greenhouse. The water that has been evaporated by the plants in the greenhouse and by additional air humidifiers in the greehouse roof is condensed back by the cooling process.

A specific advantage of a closed greenhouse is, that no insects can enter, so that pesticides can be ambundant. Additionally, carbon dioxide can be accumulated in the closed system as a plant fertilizer. Already now, a 100% additional crop productivity has been approved within this prototype, mainly due to the CO2 enrichment. Growing larger amounts of crops at higher quality means  a big economical advantage for farmers.

Another new generation greenhouse type is the seawater greenhouse. It has been developed by the british company  “Seawatergreenhouse”. It is an open system with a linear air flow. There is a fan that blows air out of the greenhouse. Fresh air is comig in but is cooled by evaporation pads at the greenhouse air inlet using seawater for evaporation. This means that cool air can be provided relatively cheap, if seawater is availlable in the local neighbourhood. The water, that has been evaporated by the plants and the water vapour from the pads can be condensed out of the air by a cooling wall. In this way, a large amount of water intorduced into the system can be recycled.

To go beyond the stage of using ventilators, that are very energy consuming, it is proposed to develop a new kind of slope greenhouse, that can use the buoyancy effect to induce air exchange. Again, it is possible to use seawater for evaporative cooling of the incoming air and greenhouse crop production can be performed in the area behind the cooling pads.  In a second compartment along a mountain slope, the growing air temperatures can be used to evporate more seawater from ponds, that can be placed within several terraces. This part can be combined with algae production as these species, compared with higher plants, can tolerate hotter temperatures as well as increased water salinity. Finally, a simple air to air  heat exchanger can be placed at the upper outlet of the greenhouse system to cool down the hot and humid air and to force condensation.

The greenhouse could change both, the surface heating effect and the related desiccation of the air, and by this will contribute to fight against the negative climatic effect of hot spots, hindering rainfall in coastal areas due to insufficient evaporative cooling of vegetation surfaces.

Productive system using the urban water and matter cycle. A general risk in Mediterranean countries and other arid and hyper-arid areas on the world is growing drought and water scarcity, that destroys the base of food supply and the most important export business for many regions. Insufficient waste water treatment is also the base for groundwater contamination and related problems with diseases.

Treated wastewater from clearage fields can be filtered with a specific gravel filter. The drainage from these filters can be used for irrigation water supply of the new generation greenhouses. The risk of food contamination until now hinders applications like this in the official agricultural policies. It is proposed to first evaluate the quality of the water before and after the new gravel filter and within the final crops in detailed field studies

For the case of insufficient crop quality, it is proposed to use membrane ultra filtration, which is a more expensive method than the gravel filter, but still much less expensive than for example sea water desalination with reverse osmosis. Both filters have the specific advantage, that plant nutrients can remain in the water and can be used for crop production.

An alternative for the treated waste water from clearage fields is the direct separation of greywater and urine within the households. In this case, the water can be directly treated by the gravel filter or even can be used directly for irrigation and the greenhouse irrigation system itself is used as a treatment facility.

The final product is fresh food and clear water, that can be sold on the local market as well as for export.

For the case, that gravel filter or ultra filtration does not allow a sufficient crop quality, it is also possible to irrigate non-food crops within the greenhouses, that can for example be used as a base for construction materials. Here we have the risk concerning an insufficient value of non-food products, that would not allow capital intensive greenhouse production. For that case, it is proposed to further develop greenhouse integrated solid state fermentation, that allows to produce industrial raw materials like improved textiles and cellulose, materials that have a much higher value than just raw biomass. Bamboo could replace steal and biologically treated hemp could replace cotton, but both products could be produced with obviously lower energy and water consumption, compared to the products that can be substituted. 

Solid state fermentation can also be used to produce protein enriched food from oil or starchy crops like soy, peanut, rice or potatoes that can provide a valuable substitute for fish and meat. Again, these products can be produced with obviously lower energy and water consumption, compared to the products that can be substituted. These examples show the potential of increased surface productivity, far beyond just using biomass as an energy source, that can launch up totally new markets for the greenhouse business.

Integrating saline water in the greenhouse water cycle: Seawater can be used as an additional water source, especially for coastal areas, that could even allow a total independency from rain. In the closed greenhouse, seawater can be used for humidification of greenhouse air in the roof area as well as during night, using the stored thermal energy with having condensation yields on the greenhouse roof. For the open slope greenhouse, seawater can be used for the cooling of the incoming air as well as for the slope greenhouse, for the solar still in the slope part behind the crop area. In this way, a much more water independent production of crops and biomass can be introduced.

A specific problematic wastewater in coastal areas is coming from the fish industry, as it increases the total salinity of urban wastewater, thus making it problematic for reuse in irrigation. It is here proposed to separate this kind of wastewater and to use it as a nutrient source for aqua farming. Seawater can be used to dilute this wastewater to decrease its salinity. The runoff water from the aqua farming can still be used as a nutrient source for algae production, thus allowing a total removal and use of the organic residues. Algae production can be integrated into the solar still part of the slope greenhouses.

Pyrolysis, as a pollutant sink in the urban matter circuit, producing a non-degradable soil improver as a by-product: Looking at the waste stream after the product’s life cycle, the wastewater has already been mentioned. Organic solid waste can be divided into agricultural waste, which for example can be contaminated with pesticides and domestic waste, that can also contain toxic constituents.

The risk of accumulation of pollutants in closed matter circuits can be minimised by having pyrolysis as a general treatment method for solid waste. Beside having the possibility of producing oil and gas with this method, residues from the process like charcoal and carbon dioxide can be redirected into the greenhouse areas.

How does pyrolysis work? Agricultural residues, domestic solid waste and sludge has to be dried, using solar energy. This can be done as a common method either on open fields or in open greenhouses. The dried biomass is transported to a centralised pyrolysis device, where it is processed into oil, gas and solid charcoal. The oil can be used as an export good. It needs post processing, that can be done in a more decentralised unit. The gas can be used locally in combustion units, while the produced carbon dioxide from that units can be used for CO2 supply in closed greenhouses. The charcoal can be used as a permanent, non degrading soil improver at the productive land, that , as a positive feedback enhances the production of the biological resources.

Combined recovery of water from greenhouse irrigation and of cooling water from concentrating solar thermal power stations (CSP): On the scale of a whole region, greenhouse areas can be placed on the perimeter of cities, producing food for export and for the local market. Electricity can be produced by concentrating solar power stations, that can be used in combination with the greenhouses, using common heat storages for cooling purposes, without increasing the volume of these storages, as it is possible to just increase the temperature amplitude, which for the greenhouses ranges between 25 and 40°C and for the power stations between 40° and ~45° C. The stored heat can be used in combination with seawater desalination in the solar still of the slope greenhouse or in closed greenhouses during night with water condensation on the inside greenhouse cover. The size of the steam turbine of a concentrated solar power unit also triggers the size of one surrounding greenhouse unit.

Agadir as one off the exemplary regions: The central structure of Agadir is already attached to  neighboured greenhouse areas, that could be improved to provide the functions of the closed urban water and matter circuit. For the further growth of the urban region, it is proposed to have a kind of decentralised concentration instead of further growth out of the centre. There  is an area along the coastal main road with several larger villages, there is Biugra as the largest satellite town and there is a chain of villages along the road to the city of Taroudant. These areas have direct contact to the surrounding landscape. They can be further developed for the integration of the urban matter circuits and energy flows, providing a sufficient supply of labour, food, water and energy.  Finally a supply system for seawater is proposed. It can be used as an additional water source in the greenhouse areas, that will allow the regional production system to be more or less totally independent from rainfall. Agadir, the metropolitan area of Southern Morocco at the edge of the desert by this could be an example for new cities southbound the coast and for other hyper arid regions of the world.

Policy and Research recommendations: . The innovative, multifunctional character of the new proposed systems as a productive unit for food/non-food crops and clean water on the one hand, and a treatment system for wastewater and saline water on the other, requires support on policy and administrative level to speed up the implementation of these technologies. Starting up programmes to support implementation of the ECOSAN approach (incl. wastewater separation and safe reuse) are proposed. Based on the implementation of existing standards on wastewater reuse, a supporting development of adapted standards for new generation greenhouse systems is discussed. Recommendation for regional action plans, enabling wastewater reuse are given.

For the context of greenhouse horticulture, a label for sustainable agricultural production including sustainable use of water is proposed. Closed greenhouses in combination with pyrolysis waste treatment shall officially confirmed as carbon sink in the international carbon trade system. Cooling water recovery (including water surplus concepts) of concentrated solar power units and methods for using the waste thermal energy for solar desalination processes within greenhouses should be supported by specific CSP directives and should be included in related subventions. Coastal saline water supply networks can be developed as a part of regional infrastructure planning. Greenhouses shall be envisaged as a specific category in urban master plans or landscape development plans.

For near term measures, a number of 10 model research areas are proposed, being (1) closed greenhouse research for food crops, (2) closed greenhouse research for non-food crops including greenhouse integrated solid state fermentation, (3) open greenhouse research with natural convection, built on mountain slopes, using saline water from the sea for evaporative cooling, (4) integrated aqua farming for fish and algae production using waste water and solid waste from fish processing, (5) formation of model urban areas for wastewater pre-selection with related use of greywater and treated urine in greenhouse projects (6) wastewater post treatment systems adapted to reuse of water and solved plant nutrients in horticultural production systems, (7) sea- and brackish water desalination systems adapted to use in horticultural production, (8) pyrolysis model project for treatment of urban waste, sludge and agricultural waste with charcoal as a main output product to be used as a soil enhancer, (9) rain fed cultivation in arid areas based on charcoal soil supply and surface rainwater harvesting and (10) concentrated solar power projects with cooling water recycling in closed greenhouses.

For more information : http://www.a.tu-berlin.de/GtE/forschung/Cycler/Recent/Implementation Guide.pdf