Characterization of modified cactus pear (Opuntia ficus indica (L.) Mill) pruning waste as a sustainable and innovative solution to recycle phosphorus from agricultural streams

This thesis provides an overview of the most promising current solutions to recover lost phosphorus (P) fluxes in surface water, and focuses mainly on its recycling through the use of waste materials from agriculture. In this thesis, cactus pear pruning waste (henceforth, called biomass).The thesis evaluates i) the potential of biomass as an adsorbent biomass to remove P from an aqueous solution; ii) studies the hydraulic properties of soils in which this by-product is incorporated; iii) its use for growing potted plants. Many intensively farmed soils show high P contents compared to the thresholds required for agricultural production; 0.084 Mt of P y−1 is leaving the European terrestrial system. Given the global shortage of the primary resource of P, 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. 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. The removal Pcapacity in biomass enriched in Ca2+, Fe2+ and Fe3+ was 2.27, 1.33 and 1.87 mg g-1, respectively. The desorption/regeneration process revealed that less than 8% P desorption in Ca or Fe-enriched biomass and showing strong stability of the biomass-cation-P system. Therefore, cactus pear pruning waste, previously reduced to powder, and enriched with ions, could be a cheap adsorbent with a good P removal performance, which could be used directly in agriculture as a soil conditioner/fertilizer. The amendment of biomass shows positive effects on soil water retention. However, observable benefits require very high amendment proportions, more that 20% by volume. These quantities make use in the open field unrealistic but offer perspectives in the horticultural and floricultural sectors. The addition of Fe3+-loaded biomass to the growing media improves nutrient assimilation in basil, suggesting that the positive effects may be attributed to the presence of Fe in the biomass. These findings provide insights into the potential of recycled cactus pear waste as a valuable resource for P recycling,and for improving soil health and plant growth in horticultural settings. This approach can be particularly useful in Mediterranean environments where this biomass is largely available.