A simple simulation of the degradation of natural organic matter in homogeneous and heterogeneous advanced oxidation processes

The degradation of natural organic matter (NOM) in homogeneous and heterogeneous advanced oxidation processes (AOP) was simulated using a simple underlying physical model. By treating the NOM molecules as linear chains and allowing them to be cleaved at any point selected at random, it is possible to reproduce well the results for homogeneous AOP experiments. To simulate a heterogeneous process, a bias was introduced (in the form of different weights for different chain lengths) according to literature data on the adsorption of NOM onto TiO2 nanoparticle agglomerates. After introduction of the (adsorption) bias, the simulation closely followed the degradation sequence observed in heterogeneous photocatalysis with TiO2 suspensions. Thus, the experimental results for homogeneous AOP may well be explained by a random breakdown of the NOM molecules; that is, we find no evidence for a selective degradation of the large molecular size material. However, a selectivity is present in the heterogeneous system due to the differential adsorption of NOM onto the reactive surface. (C) 2009 Elsevier Ltd. All rights reserved.