Nitrogen (N) is an input essential to agriculture which produces plant but also animal proteins. N cycle is a biological complex cycle, with biological fixation converting atmospheric unreactive di-nitrogen into many reactive nitrogen forms (Nr), essential for life. Nr forms are implicated in many transformations in air, water and soil, as well as within living organisms, until recovering to the N2 form through denitrification. These natural processes were amplified by the development of industrial husbandry and the massive use of N industrial fertilizers, making N expensive for forffarmers. Furthermore, its management in agriculture and its low efficiency in plant production and even more in animal production lead to losses to the environment. The most mediatized one is nitrate lixiviation with its impacts on water quality. N losses to atmosphere have become a matter of concern for the French public authorities since about twenty years, for their impacts on greenhouse balance (nitrous oxide N2 0), air quality and ecosystems and biodiversity (ammonia NH3 , and nitrogen oxides NOx). The costs of abatement strategies are more or less amortized thanks to the profits realized in economy (N expenses in agriculture) and for society (human health, global changes…). | L’azote (N) est un intrant indispensable à une agriculture productrice de protéines végétales mais surtout animales. Le cycle de l’azote est un cycle biogéochimique complexe, dont l’essentiel des entrées dans la biosphère est constitué par la fixation biologique. Toutes les formes d’azote chimiquement et biologiquement actives constituent l’azote dit réactif. Il l’eau et le sol, ainsi qu’au sein des êtres vivants, allant jusqu’au retour à sa forme diazote par la dénitrification. Ces processus naturels ont été amplifiés par le développement de l’élevage industriel et le recoursmassif aux engrais industriels azotés. Or l’azote coûte cher financièrement aux agriculteurs, et sa gestion en agriculture génère des rejets vers l’environnement liés aux faibles rendements d’utilisation de l’azote par les végétaux et surtout par les animaux. Les rejets les plus médiatisés sont les nitrates, avec les impacts sur la qualité des eaux. Les pertes vers l’atmosphèrepréoccupent les pouvoirs publics français depuis une vingtaine d’années, du fait de leurs impacts sur le réchauffement global de l’atmosphère (protoxyde d’azote, N2 0) mais aussi sur la qualité de l’air (ammoniac NH3 , et oxydes d’azote NOX). Les parades pour réduire les émissions de ces polluants et gaz à effet de serre ont également un coût, plus ou moins amorti selon lescomposés émis et/ou les postes émetteurs concernés grâce aux bénéfices économiques (poste azote en agriculture) et sociaux (santé humaine, changements globaux…) réalisés.

Gas emissions of Vertical Flow Constructed Wetlands (VFCW) treating raw wastewater have been poorly investigated. One of the main issue measuring gas emissions on such systems is related to their high heterogeneity of flow conditions (surface water distribution, feeding/resting periods etc). It is thus of importance to develop a specific methodology to be able first to determine representative gas emission fluxes and then to decide how filter‘s operation can affect these emissions. This study investigates greenhouse gas emissions from a full-scale VFCW for raw wastewater treatment. The plant designed for 800 population equivalents combines two stages of vertical subsurface flow filters planted with Phragmites. Australis. Gaseous emissions were continuously monitored during three weeks representing an overall feeding/resting period (1/3 weeks). Several automatic closed chambers connected to an infrared analyzer were placed at different strategic positions of the filters and allowed the measurement of tens of gaseous fluxes per day and per position. Dissolved N2O concentration was measured in the inlet and the outlet of each filtration stage using N2O micro-sensors. A combination of on-line sensors for NH4+ and NO3- and 24-h composite samples was used to characterize the process performances of each filtration stage. Finally, O2concentration was regularly measured in the air phase of the porous media in order to evaluate the aerobic conditions of the filters. Ammonium removal was on average of 94% during the monitoring period. The continuous measurement highlighted strong spatial and temporal variability of gaseous fluxes. This latter was observed at different time scales (day, week, feeding/resting cycle) and was linked to: (i) the intermittent feeding of the filters, (ii) oxygen content in the porous media and (iii) environmental conditions such as the ambient temperature. Dissolved N2O flux represented about 20% of the total flux (gas + liquid) which indicates the importance of accounting the dissolved flux in the N2O budget. The two filtration stages exhausted contrasted fluxes of methane and nitrous oxide in relation to carbon load and oxygen availability for carbon removal and nitrification. From a methodological point of view, this study indicates that: (i) continuous monitoring of greenhouse gas fluxes during at least an overall filtration cycle and (ii) appropriate spatial sampling strategy are decisive for a reliable determination of emission factors in VFCWs. The overall N2O emission factor estimated during the monitoring period was of 0.78% of the influent total nitrogen which is 28 times higher than the default IPCC factor (0.023% of the TN load). As N2O emissions were strongly correlated to the oxygen concentration within the porous media, it is suspected that nitrification was the main contributor to N2O production in the VFCW studied.

CWs for combined sewer overflow treatment (CSO CWs) are vertical flow filters with detention basin and fixed outflow rate. They receive stochastic loadsinduced by urban runoff and protect natural waters against pollutants and streambed erosion. Thefull-scale site at Marcy l‘Etoile was monitored to gain data about hydrology and to quantify NH4-N adsorption capacities and nitrification rate. The throttled outlet ensuresa uniformflow in the porous media, butonly aftersaturation. Until then,the percolation is focused to the inletzone. As only a partof the filteris water-contacted and detention times are shorter than normal, removal performances are lower. The phenomenon is referred to as shortcutting, a temporary state at commencing load, which might last at low inflow rates. Eighteen TDR probes weredug in the longitudinal section of the filter to follow changes in the water content. This enabled to createan animation of the expansion of saturated area until complete saturation. Furthermore, tracer tests were carried out to signify shortcutting at different stages in the filter (Fig. 1).The filter was fed at the inlet point at a fixed and lowrate until saturation and three fluorescein pulses were dosed withidenticaldelay.The basin was flooded after to follow tracer passage and washout. Results were used to parameterizethemodel-based design-support tool Orage [1]and to suggest an improvementof the outflow limitationstructureto minimize shortcutting.

This simulation study investigates the treatment performance of a French style single stage vertical flow constructed wetland using a zeolite layer in order to increase ammonia removal. For the modelling exercise, the CW"2D biokinetic model of the HYDRUS Wetland Module is used. The calibrated model is able to determine the effect of different depths of the zeolite layer on ammonia removal in order to optimize the design of the system. For calibration of the model, hydraulic effluent flow rates as well as influent and effluent concentrations of COD and NH4-N have been measured. To model the adsorption capacity of zeolite, Freundlich isotherms are used. The results present the simulated treatment performance within three different depths of the zeolite layer, 10 cm (default), 15 cm and 20 cm respectively. The increase of the zeolite layer depth leads to a decrease of the simulated NH4-N effluent concentration.

According to French standards, constructed wetlands treating combined sewer overflow (CSO CWs) are vertical flow filters with detention basin and outflow limitation. Their purpose is to treat rapid loads of wastewater with stochastic volumes, concentrations and periodicity. The first full-scale CSO CW at Marcy l‘Etoile was monitored to provide in-depth understanding of hydraulics and nitrogen dynamics. Monitoring lasted for three years incl. online equipment. The water content in the media was visualized along the longitudinal section of the filter to follow hydraulics in the fill stage. Tracer tests showed shortcutting at this stage weakening as the filter saturated which tallied with peaks of NH4-N concentrations diminishing at the outflow side. Adverse shortcutting effects can be diminished by minimizing fill time of the media. As for nitrogen dynamics, adsorption capacities showed no difference in the two filter sides, one with a sand-zeolite mixture and the other with pozzolana. An equation was fitted to temperature and adsorbed NH4-N mass measurements to calculate inter-event nitrification. The rate was found to double with every 5.7 °C. The results helped to calibrate the design-support software Orage. Finally, the washout dynamics of NO3-N were analysed to consider the possibility of a second filter stage for denitrification.

An ion exchange process was assessed to improve ammonium removal by vertical flow filters. Six columns, filled with gravel and zeolite (30cm and 10cm, respectively), were compared with a standard column with 40 cm of gravel. Columns were fed for 3.5 days with semi-synthetic wastewater then rested for 7 days. Each column, filled with zeolite, had different inlet characteristics in order to study the effects of operational parameters pointed out as affecting the ion exchange process. Two columns assessed the impact of concentration (100mgNH4-N.L-1 versus 2000mgNH4-N.L-1) on exchange capacity and performance. The effect of competition with another cation on efficiency and saturation rate was studied at three different concentrations of sodium (0 mg.L-1, 85 mg.L-1 and 300 mg.L-1, respectively). Finally, regeneration of exchange capacity by nitrification as well as its effects on treatment efficiency was studied. Although zeolite showed promising results in the early stages of operation (>80%), performances quickly declined, until reaching similar efficiency as the standard (60%), suggesting insufficient regeneration. Moreover the concentration strongly affected the exchange capacity, the latter one being quite low for the range of ammonium concentrations usually observed in domestic wastewater. The sodium supply did not result in performance reductions for the studied conditions.

Areas similar to free water surface constructed wetlands (FWS CWs) placed between wastewater treatment plants and receiving water bodies, under the perception that they increase water quality. More than 500 systems are in operation with a multitude of configurations and intended outcomes. In order to monitor these areas, research is being carried out to understand the fate of water and conventional pollutants in these systems. To this aim, a FWS CW located in southern France is monitored with traditional grab samples and 24-h flow composite samples. This site has also been instrumented with 6 Ion-Selective Electrodes (ISEs) probes recording continuously ammonium and nitrate concentrations. Because pollutant concentrations are usually low in treated wastewater, sometimes close to quantification limits of laboratory methods, we are developing appropriate methodologies for the management of the probes and the data processing. In this context, we propose a reliable methodology to increase the quality of data from ISE probes. This methodology is based on (i) laboratory experiments for sensor characterization and (ii) field tests. Laboratory experiments allowed characterizing the operating parameters like response time, linearity range, quantification limits, and interferences. Furthermore, for one-year, field tests are led every two weeks to (i) evaluate the required cleaning frequency and (ii) do grab samples analyses that help to validate data from the 6 ISEs. A drift in time appears to be significant for ammonium sensor. An additional experiment is currently monitoring this drift to correct this effect on measurement. This study has confirmed that it is fundamental to understand the technical limitations of the measuring equipment and set appropriate maintenance and calibration methodologies in order to have an accurate interpretation of data. The result is an operating protocol mainly concerning an acceptable cleaning frequency of two weeks, a stronger complementary calibration method using water from the experimental site, an evaluation of the drift and the determination of quantification limits of these ISEs (1 mg/L for ammonium and 0.5 m/L for nitrate). This protocol generates validated data that can be used to study nitrate and ammonium dynamics. In combination with the usual 24-h composite sampling method, it gives a good understanding of the fate of nitrogen within this FWS CW system. An example of data processing will be submitted.

The French Overseas Territories experience big sanitations problems and have to comply with both French and EU regulations. Vertical flow constructed wetland (VFCW) appear well adapted to the context of these regions, but their adaptation to tropical climate requires new guidelines to be defined (area needed, number of filters, species of plants, material to be used …). To this end ATTENTIVE project was build up in the French Antilles with local water offices and supported by the national water authorities. Three different VFCW fed with raw wastewater were built in Martinique and Guadeloupe and are now under monitoring. While the 3 plants are actually in operation, this paper will focus on Taupinière plant (Martinique), sized for 900 p.e., in operation since October 2014. The treatment plant is composed of aunsaturated/saturated vertical flow constructed wetland, receiving raw domestic wastewaters, followed by a simplified trickling filter.The first stage is 0,8m²/p.e. with two filters in parallel (360 m² each), with a 40 cm unsaturated first layer of 2/4 mm gravel, a 15 cm transition layer of 11/22 with intermediate passive aeration pipes and a 60 cm saturated layer at the bottom made of 20/40 pea gravel. The trickling filter(116 m²)is composed of 150 cm of pumice stones. The sludge accumulated at the bottom of the trickling filter is sent back to the first stage.A recirculation loop is implemented on the trickling filter. Before the outlet, effluent passes through UV. The regulationobjectives is to achieve 90% removal for COD, BOD5 and TSS, 80% for TKN, and less than 1000 unit per 100 mL for E.coli and intestinal streptococcus. Nevertheless, the monitoring look after optimal operation to increase TN removal rates as well as the maximum loads that can be treated. The monitoring consists on classical daily composite samples at each treatment stages (30 campaigns) as well as online measurements. The later aim at measuring flows, climatic conditions, and COD, BOD5, and Nitrate (UV/visible analysis) at each treatment stages. Three different loading phases has been implemented from 30 % of the nominal load to 150 %. The paper will present performances of this compact (less than 1 m²/p.e.) treatment system in both dry and rainy season and discuss the optimization of TN removal as well as the footprint reduction with the high loads that can be implemented.

CWs for combined sewer overflow treatment (CSO CWs) are vertical flow filters with detention basin and fixedoutflow rate. They receive stochastic loadsinduced by urban runoff and protect natural waters against pollutants and streambed erosion.However, due to the stochastic nature of flows, concentrations and periodicity, optimizing CSO CW design requires a dynamic approach.Computational tools are available but process-based models are difficult to handle [1].Moreover, the absence of user interface in design-oriented tools (e.g. RSF_Sim [2]) demands manual data handling and simulations of multiple designs. Therefore, a new tool called Orage was developed. Orage relies on a core model similar to RSF_Sim.Long-term hydraulics, COD and NH4-N were simulated with good accuracy. Filter material selection and scaling is based on inflow data series and a low number of inputs. The iterative shell calls for simulations repeatedly to (1) optimize hydraulics; (2) select the simplest material which isnecessary to satisfy emission requirements on NH4-N and (3) determine the minimalfilter area at which legislative thresholds can be met. A design is optimized if the maximum of moving average on simulated effluent concentrations (Peak_MA_cc) is at the legislative threshold (NH4N) or below (COD). Fig. 1 shows an example of the iteration process.

In recent years, unsaturated/saturated vertical flow constructed wetlands(VFCW) treating raw wastewateraregradually considered as apromising solution for their adaptation under various climatic conditions. These facilities provide surface optimization but alsobetter treatment efficiencies compare to classical French VFCW.The main performance improvements are: SS entrapment and carbon consumption for denitrification within saturated layer.When total nitrogen, by nitrification and denitrification,istargeted in the two successive zones, a design compromise has to be fund between nitrification efficiency and available carbon source for denitrification. As performance largely depends on unsaturated and saturated layers depths,a better understanding of their quantitative effects on treatment performance is essential for the adaptation of this system under various installation conditions. The aim of this study was to estimate the influence of these two linked design parameters onN efficiency with a focus onremoval limitations in regard to nitrogen loads. For this purpose, two different pilot-scale experimental configurations were designed: (i) 45 cm of unsaturated and 25 cm of saturated layers and (ii) 55 cm of unsaturated and 35 cm of saturated layers. The mature pilots were operated over 5 months using real wastewater with a feeding/resting period cycle of 3.5/3.5 days with a daily hydraulic load of 0.36 m d-1.In order to vary inlet nitrogen loads, ammonium nitrogen enrichments were added to vary loads from 10 to 40 g N m-2 d-1.24h flow composite samples at inlet and outlet of each pilot were semiweekly collected and analyzed for the following parameters: total suspended solids (TSS), total and dissolved chemical oxygen demand (COD), Kjeldahl nitrogen (TKN), ammonium, nitrate, phosphate and sulfate. Online measurement on a minute time step were done for inlet/outlet flows, oxygen content at three different depths, outlet ammonium and nitrate concentrationsby ion specific probes, and temperature. The paper will present the performance and limitations ofthe two configurations.Dynamics of nitrogen removal processes will be discussed in relation to physicochemical conditions (temperature, oxygen content, hydraulic retention time, carbon sources, etc.).