Bacteria Transport in a Soil-Based Wastewater Treatment System under Simulated Operational and Climate Change Conditions

Abstract

Bacteria removal efficiencies in a conventional soil-based wastewater treatment system (OWTS) have been modeled to elucidate the fate and transport of bacteria under environmental and operational conditions that might be expected under changing climatic conditions. The HYDRUS 2D/3D software was used to model the impact of changing precipitation patterns, bacteria concentrations, hydraulic loading rates (HLRs), and higher subsurface temperatures at different depths and soil textures. Modeled effects of bacteria concentration shows that greater depth of treatment was required in coarser soils than in fine-textured ones to remove . The initial removal percentage was higher when HLR was lower, but it was greater when HLR was higher. When a biomat layer was included in the transport model, the performance of the system improved by up to 12.0%. Lower bacteria removal (<5%) was observed at all depths under the influence of precipitation rates ranging from 5 to 35 cm, and 35-cm rainfall combined with a 70% increase in HLR. Increased subsurface temperature (23°C) increased bacteria removal relative to a lower temperature range (5-20°C). Our results show that the model is able to effectively simulate bacteria removal and the effect of precipitation and temperature in different soil textures. It appears that the performance of OWTS may be impacted by changing climate.

Hell and High Water: Diminished Septic System Performance in Coastal Regions Due to Climate Change

“…coli in soil. Generally, bacterial pathogens in soil experience increased mortality with increased temperatures [18,34]. However, our results suggest that the combination of warmer and wetter soils may have enhanced the transport, survival and/or growth of FCB in all STA types.…”

“…coli transport in the STA at 20°C and 23°C found greater attenuation at the higher temperature, but predicted lower E . coli removal under simulated increases in rainfall leading to wetter soils [34]. These two effects were not coupled in the model; since we observed lower FCB attenuation in our experiment, this would suggest that the degree of soil moisture plays a larger role in bacterial removal than temperature.…”

Physiological characteristics, geochemical properties and hydrological variables influencing pathogen migration in subsurface system: What we know or not?

“…The heterogeneity of porous media can affect pathogen migration by altering the collision efficiencies and deposition capacities, because of the higher attachment at secondary minima at concave locations or detachment from primary minima at nanoscale convex asperities ( Shen et al, 2020 ). Fine-textured and poor-structured soils intercept bacteria through mechanical filtration for their small pore sizes and low hydraulic conductivity ( Morales et al, 2015 ). Accordingly, an increasing virus migration is observed with the standard deviations of hydraulic conductivity in heterogeneous aquifers in a migration model ( Torkzaban et al, 2019 ).…”

Fate and transport in environmental quality

“…Modeling was especially beneficial when more than one pathway was involved in F&T, as in the case of simultaneous transport of 1,3-dichloropropen in both liquid and gaseous phases (Wang et al, 2000). A modeling study with multiple scenarios was found to be a useful instrument to evaluate the effect of climate change on F&T in waste management systems (Morales et al, 2015). Kalin et al (2010) reported the first application of machine learning to estimate water quality across watersheds.…”