Modelling the transport of antibiotics, antibiotic resistant bacteria and antibiotic resistant genes in the subsurface- Reuse of treated waste water applications

Aparna Chandrasekar1, Rudolf Liedl1, David Kneis2
1 Institut für Grundwasserwirtschaft, Technische Universität Dresden
2 Institut für Hydrobiologie,Technische Universität Dresden

P 19.10 in Young Hydrogeologists forum

Reuse of Treated Wastewater (TWW) for irrigation, and aquifer recharge is an approach to overcome increasing water scarcity in many regions of the world. However, TWW reuse can be associated with an underlying risk in spreading contaminants like antibiotics- that are not readily removed by waste water treatment plants. The focus of this study, is to model the transport of sub-inhibitory concentrations of antibiotics, antibiotic resistant bacteria (ARB) and antibiotic resistant genes (ARG), in surface/ground water. A process-based modelling approach is used to understand the most important processes affecting bacterial abundances and antibiotic concentrations during soil passage.

The model can be broadly divided to include hydrodynamic and biological processes that possibly undergo when the bacteria moves through the subsurface. The model is implemented in R/Fortran using the 'rodeo' package [1]. The governing 1-dimensional Partial Differential Equations (PDE) are solved by the Method-of-Lines approach.

Due to the high number of parameters present in the model, the model is non-dimensionalized, thus enabling, a small reduction in the number of parameters. Further information about the parameters is obtained by conducting column experiments which are then fitted in the model by employing optimization algorithms from FME [2]. Knowledge of the parameters and the dimensionless numbers give insights into the relative importance of the process in the model. Based on this information the model is further simplified to include only the important (rate limiting) processes that occur during bacterial and antibiotic transport in the subsurface.  

 Furthermore, a global sensitivity analysis is conducted on the model to understand the effect of changing parameter values on the variables. This study enables us to understand the effect of changing parameter values on the concentrations of the various species.

 Further scope of the study is aimed at conducting the parameter estimation studies and sensitivity analysis to develop models that can simulate the natural conditions under which bacteria are transported in the subsurface. Validation of the model, and estimation of the relevant parameters will be done at each stage of the model construction. This will enable quantitative and qualitative risk assessment of reusing treated waste water to surface and groundwater systems.

[1] Kneis. D, Petzoldt. T, Berendonk. T. (2017). An R-package to boost fitness and life expectancy of environmental models. Environmental Modelling & Software, 96, 123-127.

[2] Soetaert, K., & Petzoldt, T. (2010). Inverse Modelling, Sensitivity and Monte Carlo Analysis in R Using Package FME. Journal of Statistical Software, 33(3), 1 – 28.