Performance of Vertical Subsurface Flow Constructed Wetlands for Mixed Wastewater Treatment: Physicochemical and Microbiological Assessment

The growing generation of mixed domestic wastewater necessitates effective decentralized treatment approaches. This study evaluated the treatment performance of vertical subsurface-flow constructed wetlands (VSSFCWs) receiving real mixed black and greywater from an institutional campus. Three comparable pilot-scale systems were operated under identical hydraulic and substrate conditions, comprising wetlands planted with Phragmites australis, Arundo donax, and an unplanted control. Treatment performance was assessed using physicochemical, nutrient, and microbiological indicators, with statistical and multivariate analyses to evaluate treatment consistency and pollutant interrelationships. All systems concurrently attenuated organic matter, solids, nutrients, and microbial indicators, confirming the multifunctional treatment capacity of the VSSFCW configuration. The P. australis-planted system exhibited the strongest treatment response, with mean removal efficiencies of 81.18% for chemical oxygen demand (COD), 75.29% for biochemical oxygen demand (BOD), 67.68% for total suspended solids (TSS), 65.50% for nitrate, and 67.25% for phosphate. The A. donax system showed intermediate performance, whereas the unplanted control exhibited comparatively lower removal. The treatment hierarchy remained statistically consistent across sampling events, and strong positive associations among water-quality parameters indicated coordinated pollutant attenuation. Principal component analysis further differentiated influent and treated wastewater, with the first principal component explaining 98.53% of the total variance. Overall, the findings demonstrate that vegetation can enhance the treatment functionality of VSSFCWs through the combined influence of the substrate, rhizosphere, and associated microbial processes. The study highlights the potential of vegetated VSSFCWs as a decentralized treatment strategy for complex institutional wastewater and emphasizes the importance of species selection under site-specific operating conditions.

Arundo donax; Constructed wetlands; Microbial attenuation; Nutrient removal

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