Many intensively farmed soils show high phosphorus (P) contents compared to the thresholds required for agricultural production; 0.084 Mt of P year⁻¹ is leaving the European terrestrial system. This paper focuses mainly on non-point flows of P and provides an overview of the most promising and sustainable solutions for P recycling, centred on waste materials from agriculture. Given the global shortage of the primary resource of P, its management is critical for its efficient use. Nowadays, wastage and loss at every stage of the P cycle raise concerns about future supplies and especially about the resulting environmental problems, such as the eutrophication of surface water bodies and the reduction of biodiversity. Recovering P costs more than EUR 640 per tonne depending on the type of technique used. The opportunity for P recovery with green and sustainable technology is, therefore, a great challenge for the next years. Waste materials or by-products of agricultural processing have been considered ecologically safe, low-cost, and highly selective with high pollutant adsorption capacities, which would enable sustainable P recovery, both environmentally and economically. A realistic threshold for considering the reuse of P sustainably at the farm level is EUR 320 per tonne.

In this study, the potential of cactus pear pruning waste (CPPW) as a low-cost adsorbent biomass for phosphorus (P) removal from aqueous solutions was investigated in batch mode. Biomass samples derived from cactus pear were collected and analyzed to investigate their properties when enriched with either calcium (Ca) or iron (Fe). The examination focused on the capacity of these samples to remove P. The P removal capacities were determined to be 2.27 mg g⁻¹, 1.33 mg g⁻¹, and 1.87 mg g⁻¹ for Ca²⁺-enriched, Fe²⁺-loaded, and Fe³⁺-loaded biomass respectively. Among the various models studied, the Langmuir isotherm model was identified as the most appropriate for accurately describing the P adsorption the enriched biomass. The kinetics of the adsorption process were analyzed by applying the pseudo-first-order, pseudo-second-order, and intraparticle diffusion models. The pseudo-second-order model provided the best fit to the experimental data. Furthermore, the desorption and regeneration process was investigated, revealing minimal P desorption (less than 8%) from Ca or Fe-loaded biomass, indicating the strong stability of the biomass-cation-P system.

The increasing interest in sustainable and cost-effective options for containerized plant cultivation has driven research into the use of agricultural by-products and waste as alternative growing media. Cactus pear (Opuntia ficus-indica (L.) Mill.) pruning residuals, abundant in Mediterranean regions, represent a potential renewable resource. This study aimed to evaluate the suitability of cactus pear pruning residuals, enriched with calcium (Ca²⁺), iron (Fe²⁺ and Fe³⁺) ions, as a growing medium for basil (Ocimum basilicum L.) cultivation, with a focus on plant growth. From pots under greenhouse conditions, growth parameters (plant height, leaf area, number of leaves), chlorophyll content (SPAD), phosphorus availability in substrates (Olsen), and volatile compounds in leaves (HS-SPME coupled with GC-MS) were measured. Results suggest that incorporation of Ca- and Fe-enriched substrates significantly improved basil growth, with leading to better nutrient assimilation and higher growth metrics (plant height +23%; number of leaves +17%; leaf area +67%) compared to the untreated cactus pear substrate. Plants grown in Fe-enriched substrates exhibited increased plant height (+14%), leaf area (+48%), and number of leaves (+14%), along with improved phosphorus availability, compared to Ca²⁺ enrichments. The addition of 5% Fe³⁺ enriched cactus pear to the substrate resulted in increased plant height (+20%), number of leaves (+22%), and leaf area (+29%) compared to the control. Cactus pear pruning residuals, when enriched with Fe³⁺, show significant promise as a sustainable and cost-effective alternative to conventional growing media for basil cultivation, particularly in Mediterranean environments.