Increasing the hydrophyte removal rate of dissolved inorganic phosphorus using a novel Fe-Mg-loaded activated carbon hydroponic substrate with adsorption-release dual functions

Abstract

At present, the plant floating bed is mostly used to remediate aquaculture tail water since its obvious advantage of eco-friendly. However, there is still the problem of low phosphorus removal efficiency due to the balance between the floating bed coverage area and the aquaculture area, as well as the phosphorus content fluctuation in water. To solve this problem, a phosphorus-controlling hydroponic substrate prepared from granular activated carbon loaded with nanoiron-magnesium hydroxide (AC-Fe-Mg) was prepared, and the phosphorus adsorption and slow-release performance of AC-Fe-Mg were evaluated. Moreover, the effect of the combination of AC-Fe-Mg and I. pseudacorus L. on phosphorus purification was studied. AC-Fe-Mg exhibited superior adsorption and release ability for phosphorus without substantial interference from coexisting substances such as Cl−, NO3−, HCO3− and humic acid (HA) within the pH range of 5–9. Finally, the phosphorus removal rate reached 98.66% under the combined effect of I. pseudacorus L. and AC-Fe-Mg at the initial P concentration of 20 mg L−1. At a high P-level, phosphorus was sequestered by AC-Fe-Mg and consumed as a growth nutrient by I. pseudacorus L. At a low P-level, phosphorus was released from AC-Fe-Mg and provided to I. pseudacorus L. The regulatory ability of AC-Fe-Mg can provide plants with continuous and stable phosphorus, and maintain the nitrogen-phosphorus ratio for plant demand. Thus, the dissolved inorganic phosphorus was controlled and efficiently removed. Accordingly, the novel AC-Fe-Mg with adsorption and slow-release dual functions can be used as a hydroponic substrate of emergent plants to improve water purification.