Study of Filtralite Depletion and pH Influence on Nickel Removal

This work delves into the efficiency of Filtralite in managing Sustainable Urban Drainage Systems (SUDS) for nickel (Ni) removal from urban runoff water. It addresses the optimization of green infrastructure in relation to water pollution and public health, due to the toxicity of heavy metals in general and Ni in particular, and their potential accumulation in living organisms (Ricco et al., 2015). The study's relevance lies in the growing need for innovative and sustainable solutions in urban water management, particularly in semi-arid and urbanized areas where runoff carries heavy metals into water sources (Wang et al., 2017).

The experimental procedure was carried out using flow tests in 10 cm-length columns filled with Filtralite. This porous medium has proven effective in removing heavy metals, including Ni (Pla et al., 2021b) jointly with the requirement of a high hydraulic conductivity. A Ni pulse was introduced into the column and the breakthrough curve was continually monitored at the outflow. The laboratory experiment is underpinned by a numerical model in HYDRUS-PHREEQC-1D (HP1), incorporating three Ni removal processes: Dispersion, Chemical Precipitation, and Adsorption, achieving a determination coefficient (R2) of 98%. With the calibrated HP1 model, it is feasible to analyze the impact of pH as a key element in metal removal.

The interaction between the contaminated solution and Filtralite leads to a rapid and noticeable increase in the solution’s pH. Ni solubility is highly dependent on pH (Amiri & Nakhaei, 2021); an increase in pH causes the Saturation Index of Ni to decrease, thereby facilitating its precipitation as hydroxide. The results demonstrated that the final concentration of the pollutant directly depends on pH values, with the lowest concentrations occurring at the highest pH (Pla et al., 2021a).

Laboratory tests were conducted to analyze Filtralite's wear over time in its capacity to modify the pH of the circulating water. Distilled water circulated for 100 days in continuous flow. When Ni was injected at two different pH levels, 9.27 and 8.28, removal efficiencies of 94% and 47% were observed, respectively. This confirms the relationship between pH and pre-removal efficiency, underscoring the importance of pH control for process effectiveness. Representing Filtralite's depletion over time, a gradual decrease in pH is observed as water circulates. Polynomial adjustments with an R2 of 93% help to determine the relationship between pH, time, and flow rate.

This finding is significant for SUDS design, which aims not only for water regeneration but also for the reduction of metal pollution (Ghadim and Hin, 2017). The research underscores the importance of green infrastructure in managing urban risks, demonstrating how nature-based solutions can effectively mitigate complex environmental challenges. The Filtralite study provides a firm foundation for integrating these systems into a broader urban risk management framework, aligned with green infrastructure and sustainability guidelines.