In the PAN Journal of Water and Land Development, Yah Loo Wong and co-authors Yixiao Chen, Anurita Selvarajoo, Chung Lim Law, and Fang Yenn Teo explored an integrated approach to urban stormwater management by combining a vortex-driven hydrodynamic separator with nature-based solutions (NbS) at a commercial urban site in Malaysia. This hybrid system, designed to address the inadequacies of conventional stormwater management in rapidly developing, tropical urban catchments, utilized a continuous deflective separation (CDS) unit for gross pollutant removal, followed by filtration through biochar and green zeolite beds, and a floating wetland planted with Vetiver grass. .

The CDS unit served as the first stage of treatment, effectively removing gross pollutants (greater than 99%) and coarse sediments (greater than 95%), while reducing TSS by 85% to 90% under variable inflow rates. This initial hydrodynamic separation is critical because it minimizes the pollutant load on the downstream components, reducing maintenance and minimizing the risk of clogging common in traditional mesh systems.

The subsequent nature-based components delivered the final polishing required to meet high water quality standards. The hybrid system demonstrated an overall contaminant removal efficiency between 85% and 95%. The palm kernel-based biochar filtration bed was particularly effective, contributing most significantly to the removal of dissolved ions and achieving 57% reduction in TDS. It also accounted for most of the oil and grease removal, confirming its strong affinity for organic pollutants, contributing to a greater than 50% reduction in the final effluent. Biochar’s high porosityPorosity of biochar is a key factor in its effectiveness as a soil amendment and its ability to retain water and nutrients. Biochar’s porosity is influenced by feedstock type and pyrolysis temperature, and it plays a crucial role in microbial activity and overall soil health. Biochar More, large specific surface area, and near-neutral pHpH is a measure of how acidic or alkaline a substance is. A pH of 7 is neutral, while lower pH values indicate acidity and higher values indicate alkalinity. Biochars are normally alkaline and can influence soil pH, often increasing it, which can be beneficial More supported this efficient adsorption of micro- and near-nano-sized particles, heavy metals, and organic pollutants.

The integrated system achieved a 78% nitrate removal efficiency, reducing concentrations from an inlet of 1.9 mg⋅dm⁻³ to 0.4 mg⋅dm⁻³ in the final effluent. This effective denitrification resulted from the combined action of the floating wetland, biochar, and zeolite filtration. While the floating wetland planted with Vetiver grass is recognized for its extensive phytoremediationThis is a technique that uses plants to clean up contaminated soil or water. Biochar can enhance phytoremediation by improving soil conditions and promoting plant growth, allowing plants to absorb and break down pollutants more effectively.   More potential, the addition of green zeolite (clinoptilolite), a natural mineral with high cation exchange capacity (CEC), further improved ammonium and nitrate removal rates by 65% and 60% respectively, by preferentially adsorbing cations like ammonium and heavy metals. Moreover, the floating wetland facilitated additional removal of heavy metals (cadmium and lead) and refractory organic contaminants, with observed reductions ranging from 40% to 50%.

Despite the strong performance in other areas, the study noted a temporary increase in phosphate concentrations by 58%. Investigation revealed this anomaly was due to two synergistic factors: overflow from the nearby sewage treatment plant (STP) during heavy rainfall, introducing untreated sewage, and internal loading caused by decomposition of dead Vetiver plants and the unwashed roots of new Vetiver plants which released stored phosphorus.

The hybrid nature of the system extends to sustainability and resource management, promoting circularity by integrating carbon sequestration and resource reuse. Harvested Vetiver grass is processed, and its residue is converted into new biochar via pyrolysisPyrolysis is a thermochemical process that converts waste biomass into bio-char, bio-oil, and pyro-gas. It offers significant advantages in waste valorization, turning low-value materials into economically valuable resources. Its versatility allows for tailored products based on operational conditions, presenting itself as a cost-effective and efficient More to replace saturated biochar, which is then repurposed as compost. This process is estimated to sequester up to 2.8 (Mg CO_²​)⋅ha⁻¹⋅year^−1.

The system incorporates a cost-effective Internet of Things (IoT) monitoring system using Raspberry Pi and Python software with seven strategically placed sensors to provide supplementary real-time performance tracking and early anomaly detection. Though the system faced some sensor breakdowns due to extreme rainfall, the real-time data collected, coupled with accredited laboratory analyses, was crucial for optimizing the system and validating its consistent removal performance.

The innovative integration of CDS technology and nature-based solutions created a robust, multi-layer pollutant attenuation system capable of significantly improving stormwater quality and reducing the carbon footprint of urban catchment management.

Source: Wong, Y. L., Chen, Y., Selvarajoo, A., Law, C. L., & Teo, F. Y. (2025). Enhancing urban catchment management using integrated CDS technology and nature-based solutions for stormwater quality improvement. PAN Journal of Water and Land Development, 2025(Special Issue), 53-63.