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Characterizing the performance of any treatment wetland (TW) system requires a fundamental understanding of the hydraulic behavior of the system. In aerated treatment, the air supply increases complexity, and the internal behavior of TWs can vary according to the adopted aeration strategy. Understanding these changes can provide insights into an optimized operation for aerated TWs. In this sense, the present work characterizes the hydraulics of a hybrid vertical and horizontal aerated TW through parallel tracer testing under different aeration strategies (varying aeration duration and aeration between the different compartments). The tracer test was conducted using amino-G acid and salt on a pilot scale system and measured at the outlet and inside the system. These results are subsequently compared to a full-scale system of a similar design to assess the validity of the results on a larger scale. The results allowed a characterization of actual retention time, the estimated number of tanks-in-series (NTIS), the volume of dead zones, and the identification of the hydraulic behavior under different aeration conditions. The results indicated that decreasing aeration duration led to more heterogeneity within the filter, the aeration on the primary filter plays an important role in mixing, and the pilot scale results can be upscaled for a larger scale. It also highlighted the impact of aeration in the different compartments of this hybrid aerated wetland system, which can contribute to an accurate characterization of specific pollutant removal kinetics. • The longer aeration duration prevents the formation of dead zones. • Aeration on the primary filter plays an important role in the mixing process. • Preferential pathways were identified with internal measurements. • Full scale results are in agreement with pilot scale system. [ABSTRACT FROM AUTHOR]

This study introduces a methodology for assessing the residence times of drinking water in distribution systems using a tracer. The injection of a tracer followed by an intensive sampling campaign was used to evaluate the residence times of water in Quebec City's main system, which is supplied by the St Charles River. Samples were also analysed to determine the hardness and conductivity of the water in order to identify interconnections with a neighbouring system supplied by the St Lawrence River, a source with different properties. To validate the assumptions of interconnectivity, a complementary conductivity campaign was carried out. The tracer campaign allowed us to obtain the mean residence times (MRTs) within the study area and to target areas with low and high MRTs between 6 and 33 h. The mixing zones between water from the various sources and with longer MRTs following a stay in a reservoir were also identified. Results of this study were used to develop strategies to minimise MRT in order to improve water quality. These strategies are presented in the 'companion paper' (Part II) in this issue. [ABSTRACT FROM AUTHOR]

The article presents a proposal of a method for computer-aided design and analysis of breeding reservoirs in zoos and aquariums. The method applied involves the use of computer simulations of water circulation in breeding pools. A mathematical model of a pool was developed, and a tracer study was carried out. A simplified model of two-dimensional flow in the form of a biharmonic equation for the stream function (converted into components of the velocity vector) was adopted to describe the flow field. This equation, supplemented by appropriate boundary conditions, was solved numerically by the finite difference method. Next, a tracer migration equation was solved, which was a two-dimensional advection-dispersion equation describing the unsteady transport of a non-active, permanent solute. In order to obtain a proper solution, a tracer study (with rhodamine WT as a tracer) was conducted in situ. The results of these measurements were compared with numerical solutions obtained. The results of numerical simulations made it possible to reconstruct water circulation in the breading pool and to identify still water zones, where water circulation was impeded. [ABSTRACT FROM AUTHOR]

Highlights: [•] Intermittent aeration improved TN (+30%) and NO3-N removal (+70%). [•] Intermittent aeration resulted in 78% TN mass removal at a loading of 8.5gTN/m2 d. [•] Hydraulics for the aerated vertical flow wetlands systems were similar to one CSTR. [Copyright &y& Elsevier]

Abstract: The advancement of experimental and computational resources has facilitated the use of computational fluid dynamics (CFD) models as a predictive tool for mixing behaviour in full-scale waste stabilization pond systems. However, in view of combining hydraulic behaviour with a biokinetic process model, the computational load is still too high for practical use. This contribution presents a method that uses a validated CFD model with tracer experiments as a platform for the development of a simpler compartmental model (CM) to describe the hydraulics in a full-scale maturation pond (7 ha) of a waste stabilization ponds complex in Cuenca (Ecuador). 3D CFD models were validated with experimental data from pulse tracer experiments, showing a sufficient agreement. Based on the CFD model results, a number of compartments were selected considering the turbulence characteristics of the flow, the residence time distribution (RTD) curves and the dominant velocity component at different pond locations. The arrangement of compartments based on the introduction of recirculation flow rate between adjacent compartments, which in turn is dependent on the turbulence diffusion coefficient, is illustrated. Simulated RTD’s from a systemic tanks-in-series (TIS) model and the developed CM were compared. The TIS was unable to capture the measured RTD, whereas the CM predicted convincingly the peaks and lags of the tracer experiment using only a minimal fraction of the computational demand of the CFD model. Finally, a biokinetic model was coupled to both approaches demonstrating the impact an insufficient hydraulic model can have on the outcome of a modelling exercise. TIS and CM showed drastic differences in the output loads implying that the CM approach is to be used when modelling the biological performance of the full-scale system. [Copyright &y& Elsevier]

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Five vertical-flow constructed wetland (VFCW) units planted with cattail (Typha augustifolia) were used to study the effects of feeding (continuous and batch), hydraulic loading rates (HLR) and drainage patterns (free drainage and percolate impounding) on hydraulic behaviour. The tracer studies were divided into two parts: (i) continuous feeding at an HLR of 0.005, 0.025, 0.05, 0.075, 0.1 and 0.3 m3 m-2 d-1 operating at different drainage patterns (i.e. free drainage and percolate impounding) and (ii) batch feeding at different water levels of percolate impounding (20, 30 and 40 cm). The results revealed that although the hydraulic behaviour of VFCW systems was strongly dependent on the operating pattern (feeding and drainage), it was not significantly affected by the hydraulic loading rate. The results of continuous feeding study concluded that (a) percolate impounding achieved an increase in HRT that was 1.6 times the HRT with free drainage, (b) the dispersion in both drainage patterns were moderate, and (c) the results from the tank-in-series (TIS) model correlated more closely with the data observed than with the dispersion plug flow (DPF) model. For batch feeding and percolate impounding, a uniform flow distribution of the tracer occurred in the water column after 2.1, 3.1 and 4.4 days for 20, 30 and 40 cm, respectively. [ABSTRACT FROM AUTHOR]

There are two main ways to obtain better knowledge of the hydraulics of ponds, namely measurements and simulations. In this study, the applicability of using three-dimensional simulations as an engineering tool in stormwater pond design was investigated. To do this, three-dimensional simulations were compared with measurements of flow pattern and residence time in a large physical model of a detention tank (13 × 9 × 1 m). The agreement between measurements and simulations concerning both flow pattern and residence time distribution curves was found to be good for high flow rates. [ABSTRACT FROM AUTHOR]

Abstract: The objective of this study was to evaluate the influence of the aspect ratio and granular medium size on the hydraulic behaviour of horizontal subsurface flow constructed wetlands (SSFs) by means of tracer tests. In addition, the accuracy of non-ideal flow models (plug flow (PF) with dispersion and complete stirred tanks (CSTs) in series with delay) in describing this hydraulic behaviour was assessed. Experiments were carried out in three pairs of lined beds that received an equal and controlled flow of primary effluent, and that had an almost equal surface area (54–56m2 each bed) with the following aspect ratios: 1:1, 1.5:1, and 2:1. The size of the granular medium of each bed within each pair also varied from coarse granitic gravel (D60 =10mm, Cu =1.6) to small granitic gravel (D60 =3.5mm, Cu =1.7). The water depth of all the beds was set to 0.5m. Tracer tests were conducted by a single-shot injection of a dissolution of KBr into the inlet tubes of the beds. During the experiment, the hydraulic loading rate was of approximately 36mm/day in all beds. The results indicate that one unit increase in the aspect ratio caused an increase of the normalized delay time of the tracer curve response by a factor of between 1.6 and 1.7, and a decrease in the dispersion number of approximately between 0.3 and 0.4 (depending on the size of the medium). The effect of the size of the medium on the hydraulic behaviour was not as clear as it was for the aspect ratio. This is because there was no clear relationship between the medium size and the normalized delay time, and because significant differences in the dispersion number were only found in two of the three pairs of beds. Of these two pairs, the beds with a fine medium showed a reduction in the dispersion number by a factor of 0.6 in comparison with the beds with a coarse medium. The CSTs in series with delay model represented the data more accurately than the PF with dispersion model (either when closed–closed or open–open boundary conditions were considered). This is because the former fits the asymmetry of the tracer response more accurately. The number of CSTs in series necessary for the model ranged approximately from 1 to 3. The main conclusion of this study is that the construction of a horizontal SSF with a higher aspect ratio and finer medium improves the hydraulic behaviour of the system by reducing internal dispersion. [Copyright &y& Elsevier]