An analytical model for chemical diffusion in layered contaminated sediment systems with bioreactive caps

Abstract

Summary An analytical model for contaminant transport in multilayered capped contaminated sediments including the degradation of organic contaminant is presented. The effect of benthic boundary layer was treated as a Robin‐type boundary condition. The results of the proposed analytical model agree well with experimental data. The biodegradation of contaminant in bioturbation layer shows a significant influence on the flux at the surface of system. The maximum flux for the case with t1/2,bio = 0.07 year can be 4.5 times less than that of the case without considering the effect of biodegradation. The thickness of bioturbation layer has a significant effect on the performance of the capped contaminated sediment. The maximum flux for the case with lbio = 15 cm can be 17 times larger than that of the case without bioturbation layer. This may be because the effective diffusion coefficient of sand cap can be 28 times lower than Dbio. The mass transfer coefficient should be considered for the design of the capping system as the contaminant concentration at the top of system for the case with kbl = 2.5 × 10−5 cm/s can be 13 times greater than that of the case with kbl = 10−4 cm/s. The proposed analytical model can be used for verification of complicated numerical methods, evaluation of experimental data, and design of the capping contaminated sediment systems with reactive cap layers.

Experimental investigations and numerical modelling of in-situ reactive caps for PAH contaminated marine sediments

“…Higher errors were instead collected for the remaining cases showing a lower accuracy of the numerical models compared to the experimental tests. This was possibly due to the competition and different PAH behavior occurring when more than two PAHs are present in a system, which has been shown to affect sorption of less hydrophobic PAHs (Wang et al, 2006;Khan et al, 2007), and to the necessity of a site-specific mass transfer coefficient (Yan et al, 2019 Finally, long term modelling was performed, in order to evaluate the transport of the three analyzed PAHs in the case of no cap and to guarantee the long-term efficiency of the ISC technologies tested.…”

“…As mentioned by Shen et al, (2018), sorption/desorption of some organic compounds could be slow and the local equilibrium assumption may be not sufficient to describe the rate of the sorption/desorption process, and mass transfer coefficients are required to represent the sorption kinetics. In addition, Minick and Anderson (2017) showed how the PAH dissolved concentration gradient and compound-specific distribution coefficient can determine the flux occurring across the sediment/water interface, while Yan et al (2019) highlighted the necessity to consider the effect of the mass transfer coefficient on contaminant transport through the contaminated sediment and the capping layer.…”

Discussion of “An analytical model for chemical diffusion in layered contaminated sediment systems with bioreactive caps” by Yan H, Wu J, Xie H, Thomas HR, Feng S, International Journal for Numerical and Analytical Methods in Geomechanics 2019;43:2471–2490

“…Yan et al presented an analytical model for contaminant transport in multilayered capped contaminated sediments considering the degradation of organic contaminant 1 . The analytical solution was obtained by the method of classic integral transform technique.…”

Reply to the discussion by Wu X. on “An analytical model for chemical diffusion in layered contaminated sediment”

“…It is noted that the trigonometric-trigonometric (T-T) eigenvectors, the "regular" eigenvectors which always arise in eigenvalue problems and contribute to most of the terms in the infinite solution series, 2 have already been studied and given in the original solution. 1 The hyperbolic-hyperbolic (H-H), hyperbolic-trigonometric (H-T), and trigonometrichyperbolic (T-H) eigenvectors, which were proposed by the discusser, were not considered in the original solution; and these eigenvectors only arise under some parameter conditions ( 2 < , Figure 1). Therefore, the readers are encouraged to check the eigenvalue of the concerned problem before using the original analytical solution as failure to consider hyperbolic eigenvectors in multilayered systems may lead to invalid results.…”

“…The authors wish to thank Dr. Wu for the discussion and providing the opportunity to submit additional information to clarify some issues. The discussion of Dr. Wu extended the analytical solution obtained by the classical integral transform technique 1 to consider the negative eigenvalue. The possible hyperbolic eigenfunctions corresponding to negative eigenvalue are presented.…”