Scale dependence of reaction rates in porous media

Meile, C
Tuncay, Kağan
Elemental turnover in porous media depends on substrate concentrations at the pore-scale. In this study, the effect of small scale variability in concentration fields on reaction rate estimates and the validity of the continuum approximation in reactive transport models are investigated via a pore-scale numerical model. Artificial porous media are generated using an identical overlapping sphere algorithm. By comparison between explicit pore-scale simulations and macroscopic continuum approximations, it is shown that inhomogeneous solute distribution within the pores can affect estimates of elemental turnover rates. The error associated with large scale rate estimates depends on the type of reaction, pore geometry, reaction kinetics and macroscopic concentration gradient. A correction term that involves a phenomenological parameter which can be evaluated numerically and macroscopic concentration gradients is introduced to improve the accuracy Of Upscaled homogeneous reaction rates. Implications for macroscopic descriptions of surface processes and surface attached microbial populations are discussed and it is shown that pore-scale heterogeneity can substantially affect estimates of heterogeneous reactions, while for homogeneous reactions, the error amounts to only a couple of percents.


Modeling biogeochemical processes in subterranean estuaries: Effect of flow dynamics and redox conditions on submarine groundwater discharge of nutrients
Spiteri, Claudette; Slomp, Caroline P.; Tuncay, Kağan; Meile, Christof (American Geophysical Union (AGU), 2008-02-22)
[1] A two-dimensional density-dependent reactive transport model, which couples groundwater flow and biogeochemical reactions, is used to investigate the fate of nutrients (NO(3)(-), NH(4)(+), and PO(4)) in idealized subterranean estuaries representing four end-members of oxic/anoxic aquifer and seawater redox conditions. Results from the simplified model representations show that the prevalent flow characteristics and redox conditions in the freshwater-seawater mixing zone determine the extent of nutrient ...
Periodic stationarity conditions for periodic autoregressive moving average processes as eigenvalue problems
Ula, TA; Smadi, AA (American Geophysical Union (AGU), 1997-08-01)
The determination of periodic stationarity conditions for periodic autoregressive moving average (PARMA) processes is a prerequisite to their analysis. Means of obtaining these conditions in analytically simple forms are sought. It is shown that periodic stationarity conditions for univariate and multivariate PARMA processes can always be reduced to eigenvalue problems, which are computationally and analytically easier to deal with. Two different lumpings of the periodic process are considered along this li...
Comparison of anaerobic acrylic acid biotransformation in single- and two-stage pH-stat completely stirred tank reactor systems
Demirer, Göksel Niyazi; Speece, RE (Wiley, 2000-01-01)
Performance of single- and two-stage pH-stat completely stirred tank reactor (CSTR) systems for anaerobic acrylic acid biotransformation was investigated and compared. In the experiments, acetate was added with acrylic acid. Acetate concentration in both single- and two-stage reactors was continuously maintained at a nonlimiting concentration of 2000 +/- 200 mg/L. using a computer-controlled pH-stat system to allow observation of the effect of acrylate biotransformation on the more sensitive methanogenic st...
Higher alkyl sulfatase activity required by microbial inhabitants to remove anionic surfactants in the contaminated surface waters
İçgen, Bülent; Goksu, Lale; Ulusoy, Huseyin; Yılmaz, Fadime (IWA Publishing, 2017-11-01)
Biodegradation of anionic surfactants, like sodium dodecyl sulfate (SDS) are challenged by some bacteria through the function of the enzyme alkyl sulfatases. Therefore, identifying and characterizing bacteria capable of degrading SDS with high alkyl sulfatase enzyme activity are pivotal. In this study, bacteria isolated from surfactant contaminated river water were screened for their potential to degrade SDS. Primary screening carried out by the conventional enrichment culture technique and assessment of SD...
Performance evaluation of satellite- and model-based precipitation products over varying climate and complex topography
Amjad, Muhammad; Yılmaz, Mustafa Tuğrul; Yücel, İsmail; Yılmaz, Koray Kamil (Elsevier BV, 2020-05-01)
Accuracy assessment of precipitation retrievals is a pre-requisite for many hydrological studies as it helps to understand the source and the magnitude of the uncertainty in hydrological response variables, particularly over regions with complex topography. This study evaluates GPM IMERGv05, TMPA 3B42V7, ERA-Interim, and ERA5 precipitation products using 256 ground-based gauge stations between 2014 and 2018 over Turkey known to have complex topography and varying climate. Error statistics, categorical perfo...
Citation Formats
C. Meile and K. Tuncay, “Scale dependence of reaction rates in porous media,” ADVANCES IN WATER RESOURCES, pp. 62–71, 2006, Accessed: 00, 2020. [Online]. Available: