New insights into the mechanisms underlying phosphorus removal from agricultural drainage water via eco-concrete ecological (ECE) ditches

This study examined the roles of eco-concrete, soil, and plants in phosphorus removal in an eco-concrete ecological (ECE) ditch employed to treat agricultural drainage water. To this end, a controlled laboratory experiment was conducted, and the phosphorus removal efficiency of a scaled-up ECE system was assessed using a practical ECE ditch. Results showed that significant phosphorus removals were achieved by both the experimental ECE systems and the practical ECE ditch (89.31–95.69 % over a 15-day treatment cycle). Soil and the plant ( Acorus calamus ) were found to have an insignificant impact on the final phosphorus removal in the ECE systems. The enhanced phosphorus crystallization on the eco-concrete surface weakened the role of the soil in phosphorus removal. The results demonstrated that eco-concrete alone captured more than 95 % of the phosphorus from the test water. However, Acorus calamus maintained healthy growth in the vegetated group using phosphorus from the test water as the only phosphorus source, implying either preferential phosphorus uptake by Acorus calamus or potential secondary phosphorus transfer from the eco-concrete to plant roots in the ECE system. This is the first study to propose and validate the induced crystallization of phosphate, rather than chemical adsorption, as the primary mechanism for phosphorus removal by eco-concrete, as evidenced by both laboratory tests and scaled-up experiments. • Induced phosphate crystallization occurred on the surface of eco-concrete. • Eco-concrete might weaken the role of soil in phosphorus removal. • Plants could grow well despite eco-concrete’s remarkable phosphorus trapping. • A scale-up ECE ditch still exhibited efficient phosphorus removal. • Phosphorus was removed at 89.31–95.69 % by the experimental ECE ditches.