Processes of nitrogen removal from rainwater runoff in bioretention filters modified with ceramsite and activated carbon
Creators: name: Cheng, Junrui
name: Bi, Junpeng
name: Gong, Yuemin
name: Cheng, Xin
name: Yu, Jie
name: Gan, Huihui
name: Wang, Rong
name: Wang, Kan
Publisher: name: Taylor & Francis
Year: 2022
Subjects: subject: Space Science
subject: Microbiology
subject: FOS: Biological sciences
subject: Sociology
subject: FOS: Sociology
subject: Environmental Sciences not elsewhere classified
subject: Ecology
subject: Biological Sciences not elsewhere classified
subject: Marine Biology
subject: Science Policy
subject: Plant Biology

description: Conventional bioretention filters lack satisfactory performance in nitrogen removal. In this study, we used a mixture of cultivated soil and river sand as the bioretention filter to remove nitrogen pollutants from simulated rainwater runoff. To improve its permeability and nitrogen removal performance, both activated carbon and ceramsite were used as additives. The nitrogen removal processes and its mass accumulation in the modified bioretention filters were studied. The contribution of adsorption and biotransformation processes, together with the effects of percolate rate on nitrogen removal performance was explored. The results showed that an activated carbon layer in the bioretention filters could obviously improve nitrogen removal efficiencies, but its location made no significant difference in nitrogen removal performance. Bioretention filters modified with 20% of ceramsite could achieve the optimal percolate rate and nitrogen removal efficiencies. At given conditions, the average removal efficiencies of ammonium nitrogen (NH<sub>3</sub>–N), nitrate-nitrogen (NO<sub>3</sub>–N), and total nitrogen (TN) by the modified bioretention filter reached 80.27%, 41.48%, and 59.45%, respectively. During the leaching processes, organic nitrogen originated in the filter materials can be mineralised into NH<sub>3</sub>–N, then be denitrified and completely removed in the anaerobic environment under flooding conditions. Biotransformation in the modified bioretention filters caused a reduction of NH<sub>3</sub>–N removal efficiency by 15.41% and an increase of NO<sub>3</sub>–N removal efficiency by 31.03%. The modified bioretention filter can withstand a long-term operation. Compared with NO<sub>3</sub>–N and TN, the pollutant of NH<sub>3</sub>–N in rainwater runoff is not easy to form a mass accumulation in the modified bioretention filter. <b>Highlights</b>The modified bioretention filter showed high percolation rate and nitrogen removal.Hydraulic residence time is a critical design parameter to achieve nitrogen removal.NH<sub>3</sub>–N is not easy to form a mass accumulation in the filler media as NO<sub>3</sub>–N.Biodegradation increased NO<sub>3</sub>–N removal efficiency by 31.03% at given conditions. The modified bioretention filter showed high percolation rate and nitrogen removal. Hydraulic residence time is a critical design parameter to achieve nitrogen removal. NH<sub>3</sub>–N is not easy to form a mass accumulation in the filler media as NO<sub>3</sub>–N. Biodegradation increased NO<sub>3</sub>–N removal efficiency by 31.03% at given conditions.