Gravity Driven Membrane Bioreactor Simulates the Effect of Permeable Brick on Pollution Reduction of Rainwater Runoff in Low Impact Development (LID)

As urbanization progresses, green spaces and water bodies are reducing continuously while impervious hard pavements are expanding, leading to a significant decline in rainfall absorption and the increased flooding risk. The presence of dissolved organic pollutants and soluble heavy metal ions in rainfall runoff significantly influences environmental behavior, making the improvement of runoff pollution crucial for enhancing water quality. Permeable bricks, a commonly utilized material in sponge cities, effectively mitigate rainwater runoff and pollutant discharge. The humus coating facilitates the effective interaction between metal ions and internal binding sites of humic acid particles, resulting in strong binding and limited release. In this study, a gravity-driven coupled membrane bioreactor (GDMBR) was employed to analogy permeable bricks with its upper surface coated with humus to investigate the mitigation effect on runoff pollution. And during 66-days operation, the removal rate of NH3-N was exceeding 80 %, while UV254 and CODMn decreased significantly, indicating that organic matter may be degraded by microorganisms and humus on the membrane surface. The membrane surface was found to harbor a substantial population of active bacteria based on scanning electron microscopy (SEM), laser scanning confocal microscopy (CLSM), and ATP content analysis. Besides, nitrifying bacteria existed in both humus layer and underside layer, which formed biofilms and improved the removal rate of NH3-N. The feasibility report shows that permeable brick is more promising to apply in stormwater runoff pollution control.