Enhancing hydrological regulation and nitrogen removal capacity of bioretention cells using Portland cement-modified...

Using modified sludge as a filler to replace conventional soil and sand can effectively address issues of sewage sludge disposal and soil and sand resource overconsumption. In this study, a bioretention control column filled with conventional sand and soil (BC) and a modified column filled with Portland cement-modified sludge (BC@SS) were constructed to investigate the enhanced performance of BC@SS in hydrologic regulation and nitrogen removal capacity under varying rainfall intensities. The drainage cessation time for BC was dispersed (156-180 min), whereas that of BC@SS was more concentrated (147-155 min), demonstrating that BC@SS exhibited superior runoff reduction capacity. Under high rainfall intensity (P = 3 a), the ammonium nitrogen (NH₄⁺-N) removal efficiency of BC@SS (49.1%-61.8%) was significantly higher than that of BC (24.2%-42.6%). The denitrification capacity of BC@SS was not substantially compromised compared to BC and maintained stable performance. BC@SS facilitated a more stable pH and ORP, conducive to microbial growth and metabolism. In conclusion, the Portland cement-modified sludge filler demonstrated effective peak flow reduction and nitrogen removal performance, indicating it is an environmentally friendly alternative for stormwater treatment facilities.