Evaluation of porous concrete leachate to improve water quality.

Porous concrete is increasingly explored as a multifunctional material for water quality improvement, stormwater management, and emerging agricultural applications. However, uncertainties remain regarding nutrient and trace metal leaching, particularly for freshly cast concrete. This study investigated the time-dependent leaching behavior of a bio-receptive porous concrete substrate designed for ecological and hydroponic applications. Porous concrete tiles were immersed in distilled water for a 12-week period. Weekly leachate samples were analyzed to determine Ca, P, K, S, Mg, B, Fe, Zn, and Cu concentrations using inductively coupled plasma optical emission spectrometry. Leachate pH rose from 6.8 at Week 0 to a peak above 11.5 during Weeks 1-3, before declining progressively to approximately 9.7 by Week 12. Electrical conductivity peaked at over 3200 µS/cm at Week 4 before gradually decreasing. Most elements exhibited a pronounced first flush effect, characterized by elevated concentrations during the initial weeks (0-3 Weeks) followed by stabilization over time. Ca, K, S, and Mg showed significant (Weeks 0-3; linear mixed model, p < 0.05) early release linked to dissolution of readily soluble and surface bound phases. Trace metals, including Zn, Cu, and Fe, showed decreasing concentrations after the initial sampling period, with levels stabilizing at low concentrations (<0.05 µg/mL), suggesting progressive immobilization within the porous concrete matrix. Overall, results indicate short-term chemical reactivity but long-term elemental stability. These findings support the environmental compatibility of bio-receptive porous concrete and its potential application in hydroponic systems, green infrastructure, and decentralized water treatment.