Exegesis on ornamental phytoremediation substrates in engineered wetland systems by deciphering three decades of progress

Constructed wetlands (CWs) have emerged as a promising and sustainable alternative to conventional wastewater (WW) treatment methods over the past three decades. This comprehensive review critically analyzes global trends in substrate innovation and ornamental plant integration within CWs. It clarifies the distinctions between various CW types, such as vertical subsurface flow CWs (VSSFCWs) and horizontal subsurface flow CWs (HSSFCWs), and their respective pollutant removal efficiencies. It details the crucial roles of plant species in treatment processes, emphasizing their indirect mechanisms like providing surface area for microorganisms, enhancing oxygenation, and facilitating nutrient uptake. The document also categorizes and discusses various innovative substrates, highlighting their composition, advantages, and limitations in pollutant removal and microbial support. We analyzed 364 peer-reviewed articles published between 1993 and 2023 from the SCOPUS database using VOSviewer to map co-occurrence of key terms and identify thematic clusters. For instance, Canna and Phragmites emerged as the most frequently studied ornamental plant genera, while gravel-based and sand-based substrates were predominantly utilized. The type of CW significantly affects pollutant removal efficiency, with hybrid systems often outperforming single types due to a combination of aerobic and anaerobic processes. This study highlights the critical need for optimizing CW performance for diverse WW types and environmental conditions. Our findings offer valuable insights for future sustainable CW designs, integrating aesthetic appeal with high treatment efficiency.