Reverse electrodialysis powered greenhouse concept for water- and energy-self-sufficient agriculture

This paper documents the development of a sustainable greenhouse system which incorporates a greenhouse, reverse electrodialysis (RED), reverse osmosis, and a dehumidification desalination system aiming to support water and energy self-sufficient agriculture in arid regions with a saline groundwater feed. The system is referred to as the sustainable greenhouse (SGH). The aim is to generate enough fresh water to cover the irrigation load of the greenhouse, symbiotically cool the greenhouse environment to adequate temperatures, and create the energy needed for both. A computational model was first developed to aid in the design of the SGH, and determine its limitations. The model was validated at a commercial greenhouse farm in Abu Dhabi, UAE. Subsequent analysis of the SGH suitability for Abu Dhabi was undertaken, as a representative application region, with the use of a typical meteorological year (TMY) profile created under the study. The main finding from this analysis confirmed that the SGH system can operate if specific design criteria are met. Significant energy consumption in the dehumidification process rendered the system economically unviable if the dehumidifier (condenser) was to supply the full irrigation load. The optimal solution was found to be partial water recovery by the condenser unit, complemented with a reverse osmosis (RO) unit powered using an RED unit. The RED system was designed and tested at lab-scale. Its operation is based on the salinity gradient between seawater and shallow coastal hypersaline groundwater. Design parameters, such as the condenser unit, internal greenhouse shading and fan operations for maintaining suitable greenhouse temperatures were studied. Finally, economic feasibility analysis, which also considers crop selection, was conducted to probe the economic viability of the SGH system.