A Mathematical Model for Transport and Growth of Microbes in Unsaturated Porous Soil

In this work, we develop a mathematical model for transport and growth of microbes by natural (rain) water infiltration and flow through unsaturated porous soil along the vertical direction under gravity and capillarity by coupling a system of advection diffusion equations (for concentration of microbes and their growth-limiting substrate) with the Richards equation. The model takes into consideration several major physical, chemical, and biological mechanisms. The resulting coupled system of PDEs together with their boundary conditions is highly nonlinear and complicated to solve analytically. We present both a partial analytic approach towards solving the nonlinear system and finding the main type of dynamics of microbes, and a full-scale numerical simulation. Following the auxiliary equation method for nonlinear reaction-diffusion equations, we obtain a closed form traveling wave solution for the Richards equation. Using the propagating front solution for the pressure head, we reduce the transport equation to an ODE along the moving frame and obtain an analytic solution for the history of bacteria concentration for a specific test case. To solve the system numerically, we employ upwind finite volume method for the transport equations and stabilized explicit Runge–Kutta–Legendre super-time-stepping scheme for the Richards equation. Finally, some numerical simulation results of an infiltration experiment are presented, providing a validation and backup to the analytic partial solutions for the transport and growth of bacteria in the soil, stressing the occurrence of front moving solitons in the nonlinear dynamics.

Analysis of Conveyance Losses from Tertiary Irrigation Network

Irrigation canals are generally made through porous soil formations, since the soil is loose porous media – a huge amount of canal water is lost to conveyance losses. The situation becomes direr when these losses result in non-beneficial losses. The Sindh province of Pakistan has more than 70% saline groundwater, conveyance losses to such areas in the province not only become unusable but also creates water management problems. Perhaps the only cost-effective way to address these losses is canal lining. The present study was conducted in the command area of Belharo distributary, Sindh, Pakistan with an aim to determine the extent of losses from the tertiary irrigated network as these water channels are less considered in the literature with regards of conveyance losses. Using water balance method, conveyance efficiency and conveyance losses at 30% lined and 50 and 75% unlined length of the watercourses was observed. The results revealed that the tertiary irrigation channels face an average of 43% conveyance losses and major proportion of these losses is lost to non-beneficial losses from the study area. The study further suggests 75% lining of watercourses in order to minimize non-beneficial losses. This study also infers that with the use of geo-membrane lining, sizeable amount of fresh water can be saved. Doi: 10.28991/cej-2021-03091756 Full Text: PDF

Open-Source Script for Design and 3D Printing of Porous Structures for Soil Science

Three-dimensional (3D) printing in soil science is relatively rare but offers promising directions for research. Having 3D-printed soil samples will help academics and researchers conduct experiments in a reproducible and participatory research network and gain a better understanding of the studied soil parameters. One of the most important challenges in utilizing 3D printing techniques for soil modeling is the manufacturing of a soil structure. Until now, the most widespread method for printing porous soil structures is based on scanning a real sample via X-ray tomography. The aim of this paper is to design a porous soil structure based on mathematical models rather than on samples themselves. This can allow soil scientists to design and parameterize their samples according to their desired experiments. An open-source toolchain is developed using a Lua script, in the IceSL slicer, with graphical user interface to enable researchers to create and configure their digital soil models, called monoliths, without using meshing algorithms or STL files which reduce the resolution of the model. Examples of monoliths are 3D-printed in polylactic acid using fused filament fabrication technology with a layer thickness of 0.20, 0.12, and 0.08 mm. The images generated from the digital model slicing are analyzed using open-source ImageJ software to obtain information about internal geometrical shape, porosity, tortuosity, grain size distribution, and hydraulic conductivities. The results show that the developed script enables designing reproducible numerical models that imitate soil structures with defined pore and grain sizes in a range between coarse sand (from 1 mm diameter) to fine gravel (up to 12 mm diameter).

Transmission of SARS-Cov-2 and other enveloped viruses to the environment through protective gear: a brief review

Over the past two decades, several deadly viral epidemics have emerged, which have placed humanity in danger. Previous investigations have suggested that viral diseases can spread through contaminants or contaminated surfaces. The transmission of viruses via polluted surfaces relies upon their capacity to maintain their infectivity while they are in the environment. Here, a range of materials that are widely used to manufacture personal protective equipment (PPE) are summarized, as these offer effective disinfection solutions and are the environmental variables that influence virus survival. Infection modes and prevention as well as disinfection and PPE disposal strategies are discussed. A coronavirus-like enveloped virus can live in the environment after being discharged from a host organism until it infects another healthy individual. Transmission of enveloped viruses such as SARS-CoV-2 can occur even without direct contact, although detailed knowledge of airborne routes and other indirect transmission paths is still lacking. Ground transmission of viruses is also possible via wastewater discharges. While enveloped viruses can contaminate potable water and wastewater through human excretions such as feces and droplets, careless PPE disposal can also lead to their transmission into our environment. This paper also highlights the possibility that viruses can be transmitted into the environment from PPE kits used by healthcare and emergency service personnel. A simulation-based approach was developed to understand the transport mechanism for coronavirus and similar enveloped viruses in the environment through porous media, and preliminary results from this model are presented here. Those results indicate that viruses can move through porous soil and eventually contaminate groundwater. This paper therefore underlines the importance of proper PPE disposal by healthcare workers in the Mediterranean region and around the world.

Modeling of pollutant degradation inside 3D reconstructed porous soil structures using plasma technology

<p>A Dielectric Barrier Discharge (DBD) plasma reactor is modelled during soil remediation process. In this study we investigate the antibiotic degradation by highly reactive species that are created, when a nanosecond pulse is applied. Antibiotics are lately drawing much attention due to their highly concentration and persistency in soil ground. In addition, antibiotics transport enhances the need for immediate soil remediation. In this study, different soils are computationally reconstructed based on either random stochastic (such as Monte Carlo technique) or grid arrangement algorithms. Monte Carlo technique that is currently used is for randomly generated spheres with the constrain of non-overlapping spheres. On the other hand, structures based on grid arrangements are developed using equally sized spheres, creating structures according to FCC (face center cubic) packing and for the denser structures non-equally sized spheres are used according to HCP (hexagonal close packed). The structures that are regenerated through this process offer 3D computer representations, where plasma physics and mass transport models, using COMSOL Multiphysics® are applied. Emphasis is placed on plasma generation inside porous structures. Parameters such as soil porosity (dense or sparse medium) and electric mobility (characteristic parameter for ionized species transport) are estimated inside multiple soil structures. The models show that soil porosity and mobility do affect the plasma generation inside pores. In addition, during plasma generation (i.e. ionized species creation) the oxidized species that are responsible for antibiotic degradation (for instance Ozon, Nox etc.) are estimated and introduced in a macroscopic model for solving the mass and reaction problem. Pollutant degradation curve is estimated for the case of Ozone, where Ozone species (from plasma model inside porous soil) react with the antibiotic molecules. According to these calculations, antibiotic degradation caused by Ozone species inside the porous soil is estimated at one fifth of the total degradation.</p>

Hydrothermal Enhancement of Horizontal Ground Source Heat Pump

This study investigates a novel method for controlling the thermal conductivity of soil to enhance the performance of a horizontal ground source heat pump (GSHP). The method calls for irrigation lines to be buried in parallel with the ground pipes for the distribution of water in the area around the pipes thereby contributing to and controlling the soil’s moisture content. The controlled distribution of water within the porous soil promotes heat paths improving the performance of the GSHP system based on the transient seasonal spatial-temporal conditions. A computational fluid dynamics model of the porous soil is developed to simulate the hydro-thermal phenomenon over a short duration (40 hours) during winter conditions. The model is employed to investigate the heat transfer rate between the ground and pipes when the soil’s moisture content is modified and how this affects performance.

3D soil void space lacunarity as an index of degradation after land use change

In this work, lacunarity analysis is performed on soil pores segmented by the pure voxel extraction method from soil tomography images. The conversion of forest to sugarcane plantation was found to result in higher sugarcane soil pore lacunarity than that of native forest soil, while the porosity was found to be lower. More precisely, this study shows that native forest has more porous soil with a more uniform spatial distribution of pores, while sugarcane soil has lower porosity and a more heterogeneous pore distribution. Moreover, validation through multivariate statistics demonstrates that lacunarity can be considered a relevant index of clustering and can explain the variability among soils under different land use systems. While porosity by itself represents a fundamental concept for quantification of the impact of land use change, the current findings demonstrate that the spatial distribution of pores also plays an important role and that pore lacunarity can be adopted as a complementary tool in studies directed at quantifying the effect of human intervention on soils.