Unified model for sorption, sequestration and degradation in soils and sediments

The objective of this study is to combine ad/desorption models for organic compounds with the growth and degradation kinetics of microbes in a mathematical simulation model. The goal is to interpret and predict observed effects, such as increasing persistence with time, decreasing degradation rates with concentration, and effects of amendments on sorption and degradation. A second objective is the mathematical definition of the terms “persistence”, “bioavailability”and “bioaccessibility”. A numerical model was set up that combines ad/desorption, microbial metabolism and the formation of non-extractable residues (NER). It contains the compartments non-aqueous phase liquids or solids (N), dissolved compound (D), adsorbed (A) and sequestered (S) compound, bacterial mass (X) and biotic as well as abiotic NER. The exchange between these compartments is expressed by rates. Bacterial growth follows Monod kinetics minus decay (maintenance) rate, degradation is due to bacterial maintenance or growth. The evolving non-linear differential equations are solved numerically. The model is formulated in activity notation and implemented in Matlab. Comparison to the analytical Best equation gave (for suitable scenarios) full agreement, which is a verification of the model structure, mathematics and implementation of the numerical model. Validation by comparison to experimental studies is underway (see Rein et al., this session). The unified model allows the simulation of sorption, sequestration, bacterial growth and degradation processes simultaneously and coupled together. By this, we hope to get a better understanding of aging and persistence in soil and of the formation of bound residues (better: non-extractable residues), but the goal is also the optimization of amendments, such as DOC, compost or charcoal. Acknowledgement - The authors thank the European Commission for funding by the FP 7 grant No. 245226 MAGICPAH”’Molecular Approaches and MetaGenomic Investigations for optimizing Clean-up of PAH contaminated sites, and the Research School of Environmental Chemistry, Microbiology and Toxicology (RECETO) for funding the project PUB - Prediction of persistence of soil pollutants under various conditions of bioavailability.