Reducing the Required Area of Vertical-Flow Constructed Wetlands for Urban Wastewater Treatment Through Substrate Integration and Low Doses of Effective Microorganisms

This study evaluates the efficiency of several urban wastewater treatment configurations in reducing suspended solids (TSSs) and organic pollutants (BOD5 and COD) under Montenegrin conditions. The systems tested include combinations of primary treatment and vertical-flow constructed wetlands (VFCWs) in three different configurations (VFCW1–VFCW3), with and without the addition of low doses of effective microorganisms (EMs). The results show that the inclusion of EMs significantly improves pollutant removal efficiency and system stability. Suspended solid removal reached over 90%, while organic matter removal was also high. Among the evaluated systems, those integrating microorganisms and optimized substrates required the smallest land area to achieve high treatment performance, with some configurations reducing land demand by over 70% compared to traditional systems. Under Montenegrin climatic conditions, the smallest required wetland area to achieve 95% BOD5 removal was only 1.07 m2/PE in the PT-EM-VFCW3 system (primary treatment + effective microorganisms + vertical-flow constructed wetland configuration 3), which is comparable to or even more favorable than the best values reported in the literature. These findings suggest that enhanced wetland systems offer a sustainable and space-efficient solution for municipal wastewater treatment in areas with land constraints, such as Montenegro. Beyond treatment performance, the results highlight land-use reduction as the dominant economic benefit of the proposed configurations, while the integration of effective microorganisms provides additional operational flexibility under seasonal and variable loading conditions.