Bioclogging in porous media: Model development and sensitivity to initial conditions

This work presents a numerical model able to simulate the effect of biomass growth on the hydraulic properties of saturated porous media, i.e., bioclogging. A new module for an existing coupled flow and reactive-transport code -- PHWAT -- was implemented. Laboratory experiments were used to validate the model. Good agreement with the experimental data was found. Model behavior was satisfactory in terms of numerical discretization errors and parameter calibration, although-grid independent results were difficult to achieve. The new code was applied to investigate the effect of the initial conditions on clogging development. A set of simulations was conducted considering 1D and 2D flow conditions, for both uniform and heterogeneous initial biomass concentrations. The simulation results demonstrated that the rate and patterns of bioclogging development are sensitive to the initial biomass distribution. Thus, the common assumption of an initially uniform biomass distribution may not be appropriate and may introduce a significant error in the modeling results

Three-dimensional modeling of permeability and porosity reductions in saturated porous media

Changes in hydraulic properties of soils and aquifers as a result of biogeochemical transformations, such as bacteria growth and mineral phase precipitation/dissolution, may lead to significant modifications of the groundwater flow field. This affects in turn the migration pathways and transport rates of solutes, and consequently their spatial distribution. The aim of this work is to investigate different aspects of the field-scale evolution of porosity and hydraulic conductivity in saturated porous media due to bacteria development in the pore space. As a part of this study, a new module was developed for PHWAT to add the capability of modeling clogging. PHWAT is a general flow and multi-component reactive transport computer code based on SEAWAT and PHREEQC-2. The new model incorporates several constitutive equations to convert porosity changes to hydraulic conductivity, as well as biomass attachment/detachment dependent on pore water velocity. Spatial distributions of simulated porosity and hydraulic conductivity changes were compared both against published laboratory data and previous modeling results. We concluded that the model is able to reproduce the clogging process in a reasonably accurate way. Nevertheless, the choice of the constitutive equations and selection of their parameters is problematic. We observed that a single relationship may not be suitable to capture the observed behavior as the hydraulic conductivity decreases. Further research needs to be devoted to understand the pore-scale processes contributing to permeability changes. Following model validation, a synthetic yet realistic contamination scenario was set up to study how porosity and permeability reductions induced by microbial oxidation of contaminants interact with existing geological heterogeneities. We observed strongly nonlinear behavior, resulting in the development of complex spatial contaminant distributions. The original heterogeneous distribution of hydraulic conductivity is modified by the clogging, with the creation of preferential paths that may enhance contaminant spread

The Decent Work Questionnaire: Psychometric properties of the Italian version

Decent work is an integrative concept that may account for several labor-related issues. It represents the defence and promotion of human rights at work and business and the fulfilling and productive work maintained with social dialogue. Previous studies developed the Decent Work Questionnaire (Ferraro, Pais, dos Santos, et al., 2018) based on International Labor Organization propositions and workers' perceptions. The paper reports the adaptation and validation of its Italian version in a high-skilled workers sample (N = 1,465). Confirmatory factor analysis confirmed the original version's structural dimensions and good internal consistency reliability. Convergent and discriminant validity, tested using work engagement and personal burnout scales, were supported by the data. Therefore, the DWQ Italian version appears to yield reliable and valid data as a Decent Work measure in Italian workplaces