Effect of biofilms on the clogging mechanisms of suspended particles in porous media during artificial recharge

Artificial recharge of groundwater is an effective technology for solving the shortage of water resources. The clogging of porous media is a bottleneck that limits the application of this technology. In this study, percolation experiments in sand columns were conducted to investigate the influence of different types of biofilms on the deposition of suspended particles and clogging evolution during artificial recharge. A unique aspect of this study is the consideration of biofilms coated on porous media when the clogging mechanisms of suspended particles in porous media are explored. At the end of the recharge process, the relative hydraulic conductivity (K’) of the porous media in descending order was Pseudomonas aeruginosa experimental group (PA) > Bacillus subtilis experimental group (BS) > mixed microbial consortium experimental group (MC) > suspended particle only group (SP). The suspended particles in SP- moved more deeply into the sand column than those in BS, PA, and MC. Electron microscopy, high-throughput sequencing, and confocal laser scanning microscopy were used to identify the mechanisms governing clogging evolution under the influence of biofilm existence. The presence of a biofilm not only alters the surface charge and physical roughness of the porous media, but also affects the electrostatic interaction between the porous media and suspended particles. Biofilms combine tightly with suspended particles by binding and adhesion, which can form tight biofilm-particle aggregations. Compared with deposition of particle-only in SP, the biofilm-particle aggregations on the surface of the porous media are more firm. The biofilm coated on the surface of porous media occupied the pore vacancy and narrowed the void space compared with that in clean sand, which induced physical straining. As the thickness of biofilm coated on the sand surface increased, the more suspended particles were deposited on the sand surface in PA. These findings provide insights into clogging under the influence of biofilms and have implications for future field-based artificial recharge.