A two-step approach to recycling hydroponics waste nutrient solutions using fertiliser drawn forward osmosis and chemical precipitation

Hydroponic waste nutrient solutions (HWNS) present significant environmental and economic challenges due to their high phosphorus content and potential for eutrophication. Addressing these issues requires innovative approaches that mitigate environmental impacts and recover valuable resources. This study introduces a novel two-step approach that combines Fertiliser Drawn Forward Osmosis (FDFO) and chemical precipitation to recycle HWNS effectively. In the first phase, FDFO was employed to concentrate HWNS using a commercial hydroponic fertiliser as the draw solution. This process resulted in a diluted fertiliser solution (potentially suitable for reuse in hydroponics irrigation) and a concentrated HWNS rich in phosphorus. The concentrated HWNS was then subjected to chemical precipitation in the second phase, where phosphorus was recovered as calcium phosphate by adding sodium hydroxide at an optimised pH of 9.5. Bench-scale experiments demonstrated a 93% water recovery rate using FDFO and an impressive 99.5% phosphorus removal efficiency through chemical precipitation. These results indicate that the combined FDFO and chemical precipitation processes effectively recover water and phosphorus from HWNS and reduce reliance on synthetic fertilisers and freshwater in hydroponic systems. The findings of this study demonstrate that the two-step approach not only enhances water and phosphorus recovery but also improves the efficiency of the chemical precipitation process by achieving higher recovery rates resulting in more sustainable hydroponic systems.