Multi-scale investigation of long-term performance of permeable reactive barrier systems subjected to (bio)passivation

This study investigated the microbial impact on the long-term reactivity and pore-structure changes of granular activated carbon (GAC)-based permeable reactive barriers (PRBs) for treating total petroleum hydrocarbons (TPH) through a series of column experiments. The erosion of superfine GAC particles, caused by rapid local pore flow, led to irregular TPH breakthrough from the columns. The coupled effect of transport and biodegradation demonstrated that microbial activity could potentially reduce the durability of the barrier. Micro X-ray computed tomography (Micro-CT) and tracer tests were used to identify changes in the pore structure and transport characteristics before and after column operation. Microbial activity markedly reduced mobile and effective porosity, increased non-effective pores, and intensified depth-dependent heterogeneity and connectivity loss. These findings provide important insights for predicting the lifespan of GAC-based PRBs and optimizing their design by accounting for biologically driven structural changes as well as physicochemical adsorption processes.