Water reuse in closed hydroponic systems : comparison of GAC adsorption, ion exchange and ozonation processes to treat recycled nutrient solution

In this study, the removal of root exudates from recycled nutrient solution (RNS) in hydroponic systems was investigated by using alternative advanced treatment processes. In particular, the performance of adsorption on granular activated carbon (GAC adsorption), ion exchange (using Amberlite IRA96) and ozonation was evaluated. The characterization of a RNS from a lettuce hydroponic company showed the occurrence of several organic acids including benzoic, maleic, palmitic, stearic, phthalic, succinic, acrylic, adipic, myristic, mannonic, oleic, arachidic and acetic acid. Furthermore, benzoic, acrylic, myristic and palmitic acid were detected even after the RNS treatment by GAC adsorption, ion exchange or ozonation. Further experiments were performed to evaluate the removal efficiency of root exudates from RNS by the selected treatment processes. For this purpose benzoic acid (BA), which is a potent growth inhibitor, was selected as target compound. Benzoic acid occurring at 23 lig/L in the RNS was completely removed by GAC adsorption, ion exchange or ozonation process. In addition, GAC adsorption was the most efficient technique for organic matter removal. Indeed, the COD removal efficiency was 74%, 67% and 22% for GAC adsorption, ozonation and ion exchange treatments, respectively. The results from UV vis absorbance measurements corroborated the best performance of activated carbon in organic compounds removal from RNS. For instance, the absorbance removal at 280 rim reached 82%, 51% and 27% after GAC adsorption, ozonation and ion exchange treatments, respectively

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