The detoxification of agro-industrial effluents using superabsorbent polymers is a new and innovative process. Olive mill wastewater constitutes a major environmental problem in Mediterranean countries due to the large volumes generated, the seasonality of the industry, and the high content of polyphenols and organic matter. The application of superabsorbent polymers allows olive mill wastewater to be used as a fertilizer, as it is immobilized, increasing the biological activity that decreases its phytotoxicity, thus making its water, organic matter and mineral content usable for plant nutrition. Various parameters that characterise olive mill wastewater were evaluated after absorption in 2 different superabsorbent polymers (SAP1 and SAP2). The organic matter was equally distributed in both phases, while there was a concentration of protein and sodium in solution. The K:Na ratio decreased from 70:1 to 2:1. The polyphenol desorption from the gel into solution was found to follow Fick's law. The mass transfer coefficients were 0.147 min(-1) and 0.0085 min(-1) for SAP1 and SAP2, respectively. Phytotoxicity tests were carried out with SAP2. Olive mill wastewater in SAP2 with polyphenol concentrations up to 200 mg l(-1) revealed no phytotoxicity, and even stimulated Lepidium sativum growth, while olive mill wastewater without superabsorbent polymer revealed growth inhibition for all concentrations tested. Caffeic acid degradation by the immobilised biomass followed zero order kinetics. Degradation constants of 0.087 mg l(-1) min(-1) gSAP2(-1) and 1.156 mg l(-1) min(-1) gSAP2(-1) were found. Fungi that developed in the plant growth medium were identified as Aspergillus sp. and Penicillium sp.