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A greenhouse
To increase food production we can cultivate crops in controlled-environment greenhouses.

Researchers from the Birmingham Energy Institute have reviewed desalination technologies to support greenhouse food production.  

Our global population is expected to grow from 7.7 billion to 8.5 billion by 2030 and 9.7 billion by 2050, consequently increasing the demand for food production.

One way to increase food production is to cultivate crops in controlled-environment greenhouses, which boost productivity and extend the productive crop season. Large-scale greenhouses require cooling technologies to maintain temperatures of the crops, particularly in extreme climatic conditions where the humidity and high external temperatures limit cooling and dehumidification effectiveness.

Traditionally, greenhouses were cooled via evaporative cooling, but this process consumes large quantities of freshwater and does not perform adequately in hot and humid conditions.

Liquid desiccant air conditioning (LDAC) is an emerging technology, powered by solar energy that can mitigate the high water requirement and maintain optimal growing conditions in self-sustained greenhouses. However, LDAC technology depends on constant availability of a low vapour pressure liquid desiccant (LD), which is creating a bottleneck for this technology.

Co-author of the article and Professor of Water Technologies, Philip Davies, explains: "Despite having large amounts of sunlight, many arid countries like Saudi Arabia have to import food from cooler countries, because their climate is too hot and arid for crops to be grown locally. Global heating will make this even more difficult. Liquid desiccant technology promises to make arid countries more self-sufficient by providing cooling and irrigation water in greenhouses"

The authors of the article are Professor Davies, Dr Pasqualin and Dr Mahmoud from the School of Engineering at the University of Birmingham and Dr Lefers from King Abdullah University of Science and Technology (KAUST) in Saudi Arabia.

Dr Pasqualin adds: “We investigated alternative regeneration technologies which could make agriculture in arid counties sustainable, practical and economical. Contrary to conventional cooling greenhouse technologies that require high amounts of water, the technologies we investigated produce water which can be used for the irrigation of the crops, leading to water savings. Moreover, the investigated technologies require less energy than the conventional cooling technologies.”

The article investigates six desalination technologies – membrane distillation (MD), reverse osmosis (RO), nanofiltration (NF), forward osmosis (FO), thermoresponsive (TR) solutions and electrodialysis (ED) – that may be employed for LD regeneration.

The technologies are compared and evaluated on a number of criteria including achievable LD concentration, energy requirements, system efficiency, and availability of the technology.