Bacterial transport enhancement by colloidal gas aphrons in heterogeneous aquifers: Performance evaluation and mechanistic insights

Geological heterogeneity limits the transport and distribution of exogenous functional microbes in aquifers, thereby reducing the efficacy of bioaugmentation for groundwater remediation. This study introduced Tween80 colloidal gas aphrons (CGAs) as efficient carriers to enhance microbial delivery in heterogeneous aquifers. Red fluorescent protein (RFP)-tagging method was used for the real-time, non-invasive tracking of bacterial transport in two-dimensional (2-D) simulated aquifer systems. The results show that CGAs maintained robust bacterial viability, uniform cell dispersion, and synchronized co-transport with the model strain Pseudomonas veronii T1. Bacteria-laden CGAs achieved effective penetration and efficient bacterial transport in saturated sandy media, with migration distance increasing with larger media size and higher injection rates. In heterogeneous aquifers with permeability contrasts ranging from 10 to 10², CGAs boosted bacterial influx in low-permeability zones (fine or silt sand) by 2.71- to 4.99-fold. For small low-permeability lenses, the shear-thinning property of bacteria-laden CGAs enabled their direct penetration. For larger low-permeability layers, CGAs collapsed upon cross-layer entry, releasing bacterial suspensions that subsequently migrated into these challenging zones and markedly enhanced bacterial delivery within them. Additionally, CGAs substantially raised aquifer oxygen levels, potentially supporting aerobic biodegradation of pollutants in groundwater. These findings provide valuable theoretical insights and practical strategies for enhancing groundwater bioremediation.