Ecological Concrete-Based Modular System for Heavy Metal Removal in Riparian Transition Zones: Design, Optimization and Performance Evaluation

This study presents the development and evaluation of an innovative modular ecological transition zone system for riparian restoration. Through systematic optimization, we developed a C25-grade ecological concrete module (100 mm × 100 mm × 100 mm) with a specialized cavity design (φ61 mm × H60 mm) that achieves optimal balance between structural integrity (20–30 MPa compressive strength) and environmental functionality (>15% porosity, >1 × 10−4 cm s−1 permeability). The module incorporates precisely calibrated proportions of cement (378 kg m−3), reinforcing agent (12 kg m−3), aggregate (1650 kg m−3), and water (137 L m−3), creating a robust platform for environmental remediation. The system was evaluated at two scales: module-scale experiments in 25 L containers (833:1 mL g−1 ratio) and kinetic studies (10:1 mL g−1 ratio), revealing a sophisticated three-phase removal process. The initial rapid surface adsorption phase (0–4 h) achieved removal rates of 0.28–0.42 mg g−1 h−1, followed by pore diffusion (4–24 h) and chemical fixation phases, with removal patterns effectively modeled using a modified pseudo-second-order equation. The system demonstrated exceptional heavy metal removal capabilities across varying concentration ranges, achieving removal efficiencies of 95.6% for Pb2+ ions, 92.3% for Cd2+ ions, 84.2% for Cr3+ ions, 89.7% for Cu2+ ions, and 84.8% for Zn2+ ions under optimal conditions. Performance remained robust across two orders of magnitude in concentration ranges, with removal efficiencies maintaining above 80% at both experimental scales. The modular design’s cost-effectiveness is demonstrated through material costs of USD 45–60 m−3, with operational costs 40–60% lower than conventional systems. This research provides a practical, cost-effective solution for riparian zone restoration, combining structural durability with efficient pollutant removal capabilities while maintaining consistent performance across varying environmental conditions.