Non-equilibrium model for solute transport in differently designed biofilters targeting agricultural drainage water

Abstract

Biogeochemical processes in subsurface flow constructed wetlands are influenced by flow direction, degree of saturation and influent loading position. This study presents a simulation tool, which aims to predict the performance of the unit and improve the design. The model was developed using the HYDRUS program, calibrated and verified on previously measured bromide (Br) pulse tracer tests. Three different hydraulic designs (Horizontal (HF), Vertical upward (VF-up), Vertical downward (VF-down) and two different flow rates: Low (L), and High (H)) were investigated. The model simulated well the Br transport behaviour and the results underline the importance of the hydraulic design. Calibrated model parameters (longitudinal dispersivity, immobile liquid phase, mass transfer coefficient) showed a common trend for all the designs, for increasing flow rates within the investigated range. The VF-down performed best, i.e. had the highest hydraulic retention time.

Modeling the relationship of aeration, oxygen transfer and treatment performance in aerated horizontal flow treatment wetlands

“…For the fast flow field, hydraulic permeability k hk is twice as high and dispersion length a hk three times as high compared to k lk and a lk . Calibrated k are in range with reported values of medium gravel and materials with similar particle size (Judge, 2013); calibrated a are similar to results from conventional HF wetlands (Pugliese et al, 2017;Samsó and García, 2013). Cross-validation with the Control exhibited the models ability to simulate the main hydraulic behavior of a comparable wetland with sufficient accuracy (r = 0.83-0.98, E 1 = 0.33-0.77, Figure 3).…”

Nitrogen Removal in Woodchip‐based Biofilters of Variable Designs Treating Agricultural Drainage Discharges

“…Bruun et al (2016b) showed that the nominal HRT in this study did not differ between the CWs of similar volume, and solute transport modeling by Pugliese et al (2017) for the same six CWs demonstrated that the bromide (Br) tracer residence time differed among hydraulic designs due to differences in nonequilibrium solute transport. For the vertical upward flow CWs, nonequilibrium transport was more pronounced (Bruun et al, 2016b; Pugliese et al, 2017).…”

“…Bruun et al (2016b) showed that the nominal HRT in this study did not differ between the CWs of similar volume, and solute transport modeling by Pugliese et al (2017) for the same six CWs demonstrated that the bromide (Br) tracer residence time differed among hydraulic designs due to differences in nonequilibrium solute transport. For the vertical upward flow CWs, nonequilibrium transport was more pronounced (Bruun et al, 2016b; Pugliese et al, 2017). Based on the time of Br peak arrival and the nominal HRT, Bruun et al (2016b) demonstrated a higher hydraulic efficiency (λ) in CW1 and CW2 with horizontal flow design (λ = 0.52–0.62 h h −1 ) followed by CW5 and CW6 with vertical downward flow (λ = 0.49 h h −1 ), with markedly lower hydraulic efficiency for CW3 and CW4 with vertical upward flow (λ = 0.30–0.35 h h −1 ).…”

“…Although the effect of temperature on bioreactor performance is compelling (Christianson et al, 2012b; Addy et al, 2016; Hoover et al, 2016), there is a need for improving our understanding of the combined effects of temperature and HRT variations on the seasonal and annual variations in N reduction efficiency so that we can design and operate these systems better. In addition, HLR and hydraulic design (i.e., flow direction) may influence the solute transport and hydraulic efficiency of woodchip‐based biofilters (Bruun et al, 2016b; Pugliese et al, 2017), as well as the extent of greenhouse gas emissions (Bruun et al, 2017).…”