Nature-based stormwater management for aquifer recharge: exploring bioclogging-induced challenges

Utilising excess urban stormwater to recharge groundwater can effectively mitigate the problems caused by the over-exploitation of subsurface environments while simultaneously making full use of valuable water resources. However, bioclogging can significantly reduce the efficiency of recharge projects in practical applications. This study is distinguished by its comprehensive consideration of unsaturated hydraulic conditions during stormwater recharge, which can influence microbial activities and the evolution of bioclogging, setting it apart from the predominant focus on saturated conditions in previous research. Microbial activity in the media became more vigorous under unsaturated conditions, and the cell volume decreased to 33–50 % of that under saturated conditions. Under unsaturated conditions, microbial EPS exhibited a curled morphology. At 60 % saturation, the contents of LB-EPS and polysaccharides increased by 141.23 and 187.47 μg/g sand, respectively, compared to saturated conditions. The reduction in saturation weakened microbial migration, promoted their deposition on the media surfaces, and reduced the non-uniformity of interlayer distribution. Simultaneously, unsaturated seepage conditions attenuated the effect of flow velocity (0.5–2 mL/min) changes on microbial migration and deposition. Bioclogging under unsaturated seepage conditions was governed by both EPS action and the EPS-bacterial interaction, with EPS secretion significantly influencing the degree of internal bioclogging development. This work contributes to a more comprehensive understanding of the bioclogging mechanisms under the unique hydrodynamic conditions of stormwater recharge, enabling more precise prevention and control of bioclogging during artificial stormwater recharge.