The management of wastewater remains a challenge, particularly in developing countries. The potential use of constructed wetlands to treat wastewater is promising but their contaminant removal efficiencies, particularly in a tropical country such as Zimbabwe, are not fully understood. A pilot-scale study was undertaken in Zimbabwe to evaluate the efficiency of vertical-flow constructed wetlands planted with Typha latifolia in the treatment of domestic wastewater. Four pilot subsurface vertical-flow constructed wetland units (measuring 1 m × 1 m × 1.1 m) were built from concrete. The units were filled with waste rock from a nickel mine. Three units were planted with Typha latifolia while the fourth one was left unplanted, acting as the control. Each unit was loaded with wastewater at a rate of 220 dm³/day. Physico-chemical and bacteriological parameters were analyzed during the winter season. Physico-chemical and bacterial contaminant concentrations were significantly lower in the effluent than in the influent, and the system achieved maximum removals for BOD₅, COD, TDS, TSS, nitrates, phosphates, phosphate pentoxide, phosphorus, and E. coli of 56.01%, 82.87%, 30.61%, 90.40% 17.26%, 35.80%, 36.19%, 40.64%, and 90.28%, respectively. The study shows that constructed wetland systems can be successfully established for the removal of physical, chemical, and microbial contaminants from domestic wastewater.

Constructed wetlands are increasingly recognised for their potential in wastewater treatment, particularly in the removal of pathogenic microorganisms. However, the mechanisms of removal are not fully understood. This study investigated the role of endophytic and rhizosphere fungi and associated secondary metabolites in the removal of pathogenic bacteria from wastewater. Endophytic and rhizosphere fungi were isolated from roots of wetland macrophytes (T. latifolia, C. papyrus and P. mauritianus) and screened for their antimicrobial effects on E. coli, Shigella spp., Salmonella spp. and Vibrio spp. Secondary metabolites were extracted from fungal isolates (broth cultures) and tested for their antibacterial activity as a possible mechanism of pathogen removal. Antimicrobial activity of the fungi and their metabolites, measured as zones of inhibition, was analysed using ANOVA at a 5% significance level. Active secondary metabolites were identified using GC-MS techniques. Four fungal isolates (three endophytic, one rhizospheric) from the genus Candida exhibited antimicrobial activity against E. coli, Salmonella spp., Shigella spp. and Vibrio spp. in vitro. There were significant differences in inhibition zones (p < 0.0001) between the different species of fungi. Fungus RTGRS did not show any antibacterial activity on Vibrio spp. and Shigella spp. but showed the highest zones of inhibition of 21.17 ± 0.75 against Salmonella spp. This study demonstrated that the selected wetland macrophytes harbour both endophytic and rhizosphere fungi that can produce bioactive compounds that have antimicrobial properties, inhibiting the growth of pathogenic bacteria E. coli, Salmonella spp., Shigella spp. and Vibrio spp., contributing to pathogen removal in CWs. The findings have implications for the design and operation of CWs, as it is important to select macrophytes that harbour fungi with antimicrobial properties. More research is needed on the use of these fungi in wastewater treatment in full-scale CWs.