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The use of treatment wetlands (TWs) presents particular challenges in regions with sub-zero winter temperatures, due to reduced biological activity and risk of pipe breakage or clogging due to freezing. We studied the vertical temperature distribution in four pilot-scale TWs exposed to winter temperatures in order to determine the impact of operational system parameters and the role of insulation on heat conservation inside the filtering bed. The overall temperature pattern was similar in all wetlands, with a trend of increasing temperature from the surface toward the bottom during the cold season. No freezing was detected in the wetlands despite average daily temperatures as low as -20 °C. Influent water temperature and hydraulic loading had a stronger influence on TW temperatures in winter than air temperature. The vertical distribution of temperatures in TWs is more sensitive to hydraulic loading variation in the percolating operating condition than in the saturated flow with forced aeration configuration. Our results suggest that TW systems can remain operational under cold winter conditions provided the surface is properly insulated by vegetation, mulch and/or snow.

The scope of this study was to investigate if using zeolite as a reactive material in a vertical-flow wetland under field conditions improves ammonium removal from domestic wastewater in the long term. The experimental setup consisted of two pilot-scale first stage French vertical flow treatment wetlands (2.3 m 2 surface area each), which were implemented under field scale conditions inside a wastewater treatment plant in the central region of France (L'Encloitre, 37360). The filters were operated during 27 months. A compact pilot containing Leca ® as a main filtration layer (Ø 1-5 mm) was compared to a similar one filled with natural zeolite (Ø 2-5 mm). The pilots were fed according to regular feeding/resting periods (3½/7 days) and the nominal loading rate was of 300 g COD m -2 d -1 and 33 g·N·m -2 ·d -1 during operation. In both pilots, results showed a removal efficiency of more than 90 and 85% for TSS and COD, respectively. They also showed an increased NH 4 -N removal of 9% on average (total removal efficiency of 84%) with the use of zeolite compared to Leca ® . The ion exchange capacity of zeolite seemed not to be affected after 27 months of experiments; however, the material was compacted and more friable after operation.

The objective of this study was to determine how macrophytes commonly used in treatment wetlands (TWs) respond to water with low pollutant concentration. We measured pollutant removal efficiency and compared growth and nutrient uptake of five macrophytes in demonstration scale units (volume >40 m 3 ) irrigated by water with pollutant concentrations representative of average urban stormwater quality. All species showed a strong productivity gradient along the beds, starting with high biomass - high density near the inlet, then decreasing progressively with distance. Cyperus was by far the most productive species. Phragmites and Thalia had higher biomass in the first few metres of the beds than Typha and Arundo. In terms of pollutant removal, decreasing plant growth may be interpreted as indicative of high efficiency when caused by nutrient depletion. Differences in aboveground biomass between species did not translate into measurable differences in removal efficiency at the outlet. Although Phragmites australis is the species most commonly used in TWs, under the low nutrient load, Cyperus had twice its biomass, and higher N and P uptake. These results highlight the importance of considering wastewater characteristics when selecting macrophyte species for TWs.

This simulation study investigates the treatment performance of a compact French vertical flow wetland using a zeolite layer in order to increase ammonium nitrogen removal. For the modelling exercise, the biokinetic model CW2D of the HYDRUS Wetland Module is used. The calibrated model is able to predict the effect of different depths of the zeolite layer on ammonium nitrogen removal in order to optimize the design of the system. For the model calibration, the hydraulic effluent flow rates as well as influent and effluent concentrations of chemical oxygen demand (COD) and NH 4 -N have been measured. To model the adsorption capacity of zeolite, Freundlich isotherms have been used. The results present the simulated treatment performance with three different depths of the zeolite layer, 10 cm (default), 15 cm and 20 cm, respectively. The increase of the zeolite layer leads to a significant decrease of the simulated NH 4 -N effluent concentration.