An advanced type of constructed wetland (CW) called an engineered wetland (EW) has been developed which allows more efficient removals of contaminants from wastewaters and stormwaters at rates in many cases an order of magnitude higher than those achievable with ordinary CWs. In one type of advanced aerobic EW, the wastewater being treated flows sub-surface (SSF) beneath an aggregate substrate which is aerated mechanically from below. This ecotechnology allows very much higher removals (>95%) of those wastewater contaminants amenable to aerobic treatment (e.g., BOD, ammonia). A large 1.9 ha EW system treating glycol-contaminated water is now operating at Buffalo Niagara International Airport (BNIA) in upper New York State, USA. This system, which is successfully treating glycol-contaminated stormwater runoff and spent glycol from cold weather aircraft deicing activities, involves four very large aerated EW cells and is capable of treating up to 4,620 m³/d of glycol-contaminated water containing up to 4,535 kg/d of BOD (the BOD-equivalent of a city of 50,000 people), even in the coldest weather.

The occurrence of pharmaceutically active compounds (PhACs), nutrients, and an artificial sweetener acesulfame in wastewater, and subsequent removal in an engineered system comprising aerobic wetland, anaerobic wetland, and steel slag cells, were investigated. The PhACs evaluated in this study covered a range of octanol–water partition coefficients (log K_ow = 0.07–2.45) and acid dissociation constants (pK_a = 1.7–13.9) and included carbamazepine, caffeine, sulfamethoxazole, ibuprofen, and naproxen. The mean flow rate in the system was 0.89 m³ day⁻¹ (0.02 to 4.27 m³ day⁻¹), representing a hydraulic retention time of 5 days. The removal efficiencies of PO₄-P, NH₃-N, and cBOD₅ in the treatment system were >99, 82, and 98%. The removal efficiencies for the PhACs and acesulfame were classified into four groups, including those that were (a) efficiently removed (caffeine by >75%); (b) moderately removed (ibuprofen by 50–75%); (c) poorly removed (sulfamethoxazole and naproxen by 25–50%); and (d) recalcitrant (carbamazepine and acesulfame by <25%). Variability in concentrations and treatment efficiencies was observed in different sampling events, which may be due to variations in input concentrations or changes in the flow rate. The addition of a steel slag cell increased the overall removal efficiency of the studied compounds, except for carbamazepine.

A demonstration-scale outdoor constructed wetland (CW) wastewater treatment system was evaluated for about two years for its effectiveness in treating septic system effluents. The system included three treatment cells: an anaerobic cell, an aerated cell, and a basic oxygen furnace slag (BOFS)-based phosphorus (P) treatment cell. High removal efficiencies were achieved, with reductions of >99% for PO₄-P, >83% for NH₃-N, >99% for cBOD₅, and >76% for COD, with influent concentrations averaging 6, 48, 63, and 143 mg L⁻¹, respectively. Additionally, pathogens removal were high, with an over 99% decrease in E. coli and total coliform levels. The BOFS cell was critical, elevating effluent pH to 10.9 ± 1.5, which effectively inactivated pathogens. Environmental safety before discharge was ensured by CO_2(g) sparging to adjust the pH and a zero-valent iron layer in the BOFS cell to control dissolved metal concentrations. Analytical techniques (FESEM-EDX, FTIR, and XANES) confirmed the formation of Ca carbonate and Ca phosphate on spent BOFS, highlighting their role in the treatment process. This study highlights the potential of integrating complementary technologies in constructed wetlands for sustainable and efficient wastewater management.