Structure and mass transportation model of slow-release organic carbon-source material for groundwater in situ denitrification

Abstract

Based on the theories of organic polymer and chemical kinetics, the structure and mass transportation model of slow-release organic carbon-source (SOC) material was developed in this study to reveal and predict the carbon release mechanisms of polymer carbon source, which was feasible for in situ denitrification in nitrate-contaminated groundwater. Composed of polyvinyl alcohol (PVA) and starch, the SOC material formed the interlocking/disperse-phase structure. PVA performed as continuous phase and skeleton, whereas the starch or cellulose behaved as release component. Carbon release process was identified in two stages: solid-phase (inner) and interface (gel layer) diffusion. Solid-phase diffusion was affected by material porous medium parameters, for example, distance between the crosslinking points and starch free energy. The interface diffusion depended mostly on the groundwater dynamics and interface energy distribution. The interface diffusion was found as the limiting step of carbon release process, and the carbon release coefficient corresponded to k_D,I as static coefficient and k_C,I as dynamic coefficient. As the key indicator to evaluate carbon release capacity, k_D,I and k_C,I represented appropriate boundary conditions and interface properties. Sensitivity analysis showed that the key parameters of the carbon release model were the distance between the crosslinking points and the free energy of polymer, influenced by regulation of preparation technique, raw material composition and additive dosage.

Keywords:

• slow-release organic carbon-source (SOC)
• slow release
• model
• Fickian diffusion
• denitrification

Acknowledgements

This project was funded by National Science Foundation of China (NSFC, 40372107) and Royal Society Joint Project (2005/R1-JP).

Funding

The authors declare no competing financial interest.

Supplemental data

Supplemental data for this article can be accessed at http://dx.doi.org/10.1080/09593330.2014.979249.