New ideas for enhancing the microbial reaction zone: Enhancing colloidal properties for the removal of benzene and naphthalene from groundwater

The uncontrolled release of aromatic hydrocarbons such as benzene and naphthalene from coal chemical sites poses significant threats to groundwater quality. In situ microbial reaction zone (IMRZ) technology offers a promising solution, but its effectiveness is often limited by poor microbial dispersion and colloid instability. This study presents a novel approach to enhancing IMRZ formation and performance by incorporating colloidal silica into the microbial inoculum of Achromobacter xylosoxidans BP1. Quartz sand column and flume experiments were conducted to assess microbial migration, aggregation, and biodegradation efficiency. Results showed that colloidal silica significantly improved microbial stability and diffusion, enabling the formation of clearly defined microbial reaction zones. The colloid-enhanced system achieved benzene and naphthalene degradation efficiencies of up to 57.47 % and 76.11 % in columns, and over 90 % in scaled-up flume systems. Whole-genome analysis and GC-MS metabolite profiling revealed that both primary degradation and co-metabolic pathways contributed to pollutant removal. This study demonstrates a scalable, efficient method to overcome key limitations in IMRZ technology, advancing the field of in situ bioremediation.