Posttreatment of Effluents From UASB Reactors Through Vertical Flow Wetlands Coupled With Coagulant-Free Double...

Water reuse is increasingly adopted to address global water scarcity, particularly for nonpotable applications. This study evaluated a pilot-scale treatment train consisting of a vertical flow constructed wetland (VFCW) followed by sequential double filtration (DF) consisting of a sand filter followed by activated carbon and clinoptilolite media as posttreatment of domestic wastewater previously treated in an upflow anaerobic sludge blanket (UASB) reactor. The system was operated under three hydraulic loading rates (200, 400, and 600 mm/day), corresponding to organic loading rates of 26.8 to 94.9 g COD/m²·day. The VFCW provided effective polishing of organic matter, achieving COD and BOD removals of up to 78% and 87%, respectively, relative to the UASB effluent, while additional total suspended solids removal ranged from approximately 25% at low and intermediate loadings to about 11% at the highest loading rate. Total nitrogen removal remained moderate and variable (~30%-65%), reflecting the predominance of aerobic conditions and limited denitrification potential within the wetland. Phosphorus removal in the VFCW was variable, with low efficiencies under low and high loadings (~14%-18%) and evidence of phosphorus remobilization under intermediate loading conditions. Microbial attenuation in the VFCW resulted in Escherichia coli removals of 90%-96% at low to intermediate hydraulic loads, with reduced performance at the highest loading rate. In contrast, the downstream DF consistently provided additional E. coli removal exceeding 99%, yielding final effluent concentrations on the order of 10² CFU/100 mL and complying with international reuse guidelines. Overall, the integrated VFCW-DF configuration functioned as a robust multibarrier system, enhancing operational reliability and demonstrating the potential of combined nature-based and low-cost filtration processes for decentralized wastewater reuse. Importantly, the results demonstrate that coagulant-free double filtration acts as a stabilizing barrier, transforming variable wetland performance into consistent and reuse-compliant effluent quality.