Konstantinos Liolios

Comparative Modeling of HSF Constructed Wetland Performance With and Without Evapotranspiration and Rainfall

The effects of meteorological parameters, i.e., evapotranspiration (ET) and rainfall (P), on the flow and BOD fate in horizontal subsurface flow constructed wetlands (HSF CW) are presented based on numerical simulation, using the Visual MODFLOW-MT3DMS code, which is based on the finite difference method. This model was used to simulate five HSF CW pilot-scale units, which were constructed and operated in the Laboratory of Ecological Engineering and Technology. Experimental data from these facilities were used to calibrate and verify the numerical procedure. ET was estimated based on a previous study proposing the use of the Blaney-Criddle method, and was introduced in the model. For a characteristic time period, rainfall values from observed events were also entered in the model. The model was then used to test effects of ET and rainfall on effluent concentration under various conditions, showing a more intense effect of ET and a less significant effect of rainfall. It was also used in test runs comparing the performance, without and with ET, under various vegetation, porous media size, HRT and temperature conditions.

A computational approach for the earthquake response of cable-braced reinforced concrete structures under environmental actions

A numerical treatment for the seismic response of reinforced concrete structures containing cable elements is presented. The cable behaviour is considered as nonconvex and nonmonotone one and is described by generalized subdifferential relations including loosening, elastoplastic - fracturing etc. effects. The problem is treated incrementally by double discretization: in space by finite elements and piece-wise linearization of cable - behaviour, and in time by the Newmark method. Thus, in each time - step an incremental linear complementarity problem is solved with a reduced number of problem unknowns.

Numerical simulation of phosphorus removal in horizontal subsurface flow constructed wetlands

AbstractThe removal of total phosphorus (TP) in horizontal subsurface flow constructed wetlands (HSF CW) is numerically investigated using the Freundlich linear isotherm for adsorption. For the numerical simulation, the Visual MODFLOW code family, based on the finite difference method, was used. This model is applied in the simulation of five pilot-scale HSF CWs. Influent–effluent TP concentration experimental data from these facilities were used to first calibrate this model and derive appropriate values of the distribution coefficient Kd and the first-order removal coefficient λ. Then, the model was verified using the values of λ and Kd from calibration and independent experimental data from these facilities. The calibrated model was applied to comparatively simulate differences in removal efficiency under various design and operational parameters.

A computational approach for remediation procedures in horizontal subsurface flow constructed wetlands

A large-scale computational approach for groundwater flow and contaminant transport and removal in porous media is presented. Emphasis is given to remediation procedures in horizontal subsurface flow constructed wetlands. For the numerical procedure, the MODFLOW computer code family is used. Application is made for the simulation of horizontal subsurface flow wetlands pilot-scale units, constructed and operated in Democritus University of Thrace, Xanthi, Greece. The effects of the inlet and outlet recharge positions to the optimum contaminant removal are also numerically investigated.

Modelling Alternative Feeding Techniques in HSF Constructed Wetlands

The effects of two alternative operational techniques, i.e., effluent recirculation and step-feeding, on the removal of Biochemical Oxygen Demand (BOD) in Horizontal Subsurface Flow Constructed Wetlands (HSF CWs) are evaluated numerically. These include two feeding techniques: under the first technique, a percentage of the effluent is re-introduced to the wetland inlet; while under the second, wastewater is introduced to the HSF CW at several points along the flow path. For the numerical simulation, the Visual MODFLOW family code was used. This model has been calibrated using experimental data collected in five HSF CW pilot-scale units. Application of the model to study effluent recirculation showed that this operation mode does not improve the performance of the Constructed Wetlands (CWs), which seems to decrease as the effluent recirculating quantity increases. Although recirculation dilutes the influent pollutant concentration, the decrease in Hydraulic Residence Time (HRT), due to the additional flow entering the system, seems to act negatively on CW performance. For the step-feeding case, various values of the step-feeding percentage factors have been investigated at three inflow points along the CW. Again, the results showed no performance improvement. Thus, both operation modes are not recommended for HSF CWs.

Geothermal Effects for BOD Removal in Horizontal Subsurface Flow Constructed Wetlands: A Numerical Approach

A simplified numerical approach is presented for the simultaneous groundwater flow, geothermal energy (heat) transport and contaminant transport and removal in shallow unconfined aquifers. Emphasis is given to Biochemical Oxygen Demand (BOD) removal in Horizontal Subsurface Flow Constructed Wetlands (HSF CW), under non-isothermal conditions. The system of the governing non-linear partial differential equations is treated numerically by using the family computer code Visual MODFLOW. In a numerical example, where BOD is injected in entering geothermal water, the so-resulted computational results are compared with available experimental data.

A Computational Investigation of the Optimal Reaction Type Concerning BOD Removal in Horizontal Subsurface Flow Constructed Wetlands

A numerical simulation of Biochemical Oxygen Demand (BOD) removal in Horizontal Subsurface Flow Constructed Wetlands (HSF CW) is presented. Emphasis is given to select the optimal type of the reaction concerning the BOD removal. For this purpose, a computational investigation is realized by comparing the most usual reaction type, the first-order one, and the recently proposed Monod type, with simulated experimental data obtained from five pilot-scale HSF CW units. These units were operated for 2 years in the facilities of the Laboratory of Ecological Engineering and Technology (LEET), Democritus University of Thrace (DUTh), Xanthi, Greece. For the numerical simulation the Visual MODFLOW family computer code is used, and especially the RT3D code.

A Numerical Approach to the Non-convex Dynamic Problem of Steel Pile-Soil Interaction under Environmental and Second-Order Geometric Effects

The paper deals with a numerical approach for the dynamic soil-pile interaction, considered as an inequality problem of structural engineering. So, the unilateral contact conditions due to tensionless and elastoplastic softening/fracturing behaviour of the soil as well as due to gapping caused by earthquake excitations are taken into account. Moreover, soil-capacity degradation due to environmental effects and second-order geometric effects for the pile behaviour due to preexisting compressive loads are taken into account. The numerical approach is based on a double discretization and on mathematical programming. First, in space the finite element method (FEM) is used for the simulation of the pile and the unilateral contact interface, in combination with the boundary element method (BEM) for the soil simulation. Next, with the aid of Laplace transform, the equality problem conditions are transformed to convolutional ones involving as unknowns the unilateral quantities only. So the number of unknowns is significantly reduced. Then a marching-time approach is applied and finally a nonconvex linear complementarity problem is solved in each time-step.

A numerical investigation for the optimal contaminant inlet positions in horizontal subsurface flow wetlands

The paper presents a numerical treatment of flow and contaminant removal in porous media with emphasis to horizontal subsurface flow constructed wetlands. The purpose here is to find their optimal design characteristics as concerns the contaminant inlet positions, in order to maximize the removal efficiency.

Total Phosphorus Removal in Horizontal Subsurface Flow Constructed Wetlands: A Computational Investigation for the Optimal Adsorption Model

A numerical simulation concerning Total Phosphorus (TP) removal in Horizontal Subsurface Flow Constructed Wetlands (HSF CWs) is presented. For the phenomenon of absorption, a comparison between the results of a linear and a non-linear model is realized. The purpose is to investigate which one of these two adsorption models is the optimal one for the computational simulation of TP removal. The simulations concern five pilot-scale HSF CWs units, which were constructed and operated in the facilities of the Laboratory of Ecological Engineering and Technology (LEET), Department of Environmental Engineering, Democritus University of Thrace (DUTh), Xanthi, Greece. Concerning the numerical simulation, the Visual MODFLOW computer code is used, which is based on the finite difference method. Finally, a comparison between computational and available experimental results is given.