Closed hydroponic systems : operational parameters, root exudates occurrence and related water treatment

Greenhouse production of vegetables in closed hydroponic cropping systems is a resource-efficient technique for the production of high-quality produce with a high yield per unit area. Recently, there have been considerable progresses in the development of hydroponic culture. While this type of cropping system allows savings in terms of water and nutrient use, the recirculation of water increases the risk of root exudates dispersal. Plant roots often exude numerous organic acids, which are known to inhibit growth. So far several methods have been found to be effective in removing or degrading the phytotoxic substances released from plant roots during autotoxicity such as adsorption by activated carbon, electrodegradation of root exudates and TiO2 photocatalysis. In this review an overview will be presented of hydroponic systems and their related root exudates occurrence and removal