Suppressing sediment nutrient release via electrokinetic drainage of porewater: apparent paradox and underlying mechanisms

Sediment nitrogen and phosphorus release drives internal eutrophication in many waterbodies, with nutrient-rich porewater serving as the key pathway for nutrient transfer to overlying water. In this study, electrokinetic geosynthetics (EKGs) were employed as electrodes to drain porewater and suppress sediment nutrient release. Five treatment groups with varying voltage gradients and power-on modes were tested. Nitrogen and phosphorus were primarily drained as ammonium (NH₄⁺) and phosphate (PO₄^3-), respectively. The total nitrogen removal from sediments was 16-20 times greater than that of phosphorus; however, the increase in nitrogen concentration in the overlying water was also nearly 10 times higher than that of phosphorus. This apparent paradox likely resulted from two key mechanisms. On one hand, NH₄⁺ was rapidly mobilized and drained under the electric field, whereas PO₄^3- required a series of acidification reactions before it could be released and transported. On the other hand, even when phosphate entered the overlying water, it was readily re-adsorbed or precipitated by the sediment, while nitrogen continued to accumulate through ongoing biogeochemical processes. Despite the differing removal efficiencies, electrokinetic drainage of porewater reduced sediment nutrient content in situ and suppressed nutrient enrichment in the overlying water, offering a promising strategy for the mitigation of internal eutrophication.