Bioretention cell incorporating Fe-biochar and saturated zones for enhanced stormwater runoff treatment

• Published in: Chemosphere (Oxford) 2019-12, Vol.237, p.124424, Article 124424
• Main Authors: Xiong, Jiaqing, Ren, Sihui, He, Yifan, Wang, Xiaochang C., Bai, Xuechen, Wang, Jiaxuan, Dzakpasu, Mawuli
• Format: Article
• Language: English
• Subjects: Amended media; Bioretention; Charcoal - chemistry; Denitrification; Iron; Iron-modified biochar; Nitrates; Nitrogen - isolation & purification; Nutrients; Phosphorus - isolation & purification; Rain; Runoff pollution; Soil - chemistry; Water Purification - methods
• ISSN: 0045-6535; 1879-1298
• DOI: 10.1016/j.chemosphere.2019.124424

Nitrogen (N) and phosphorus (P) removal in conventional bioretention systems is highly variable. Therefore, five novel experimental columns with different media configurations and constituents, and incorporating a saturated zone were developed and assessed to optimize the removal of N, P and other nutrients. Three types of media composed of the conventional mixed sand and soil media (T1), biochar-amended media (T2), and iron-coated biochar (ICB)-amended media (T3) were evaluated. Two of the experimental columns were designed with double-layer configurations, while the other three were of a single-layer structure. Removal efficiencies of nutrients in the experimental columns were evaluated and compared using simulated runoff. Also, the effect of media depth on the retention of P and denitrifying enzyme activity (DEA) in the bioretention columns were evaluated. The experimental column only filled with T3 showed the best performance for COD, ammonia (NH4+-N) and total phosphorus (TP) removal (94.6%, 98.3% and 93.70%, respectively), whereas columns filled with T2 performed poorly for TP removal (57.36%). For the removal of nitrate (NO3−-N) and total nitrogen (TN), the columns using a single-layer and only filled with either T3 or T2 exhibited the best performance (93% and 97% TN removal, respectively). Overall, this study demonstrates that our proposed single-layered bioretention cell only filled with T3 and incorporating a saturated zone effectively improves the runoff quality, and can provide a new bioretention cell configuration for efficient stormwater treatment. •Iron-coated biochar (ICB) increased the adsorption of the media to phosphorus.•ICB supplied the carbon source for the denitrification reaction.•Single-layered experimental columns were more conducive to the removal of nitrate.•Denitrifying enzyme activity of media is higher at the media boundary.