A pilot-scale, bi-layer bioretention system with biochar and zero-valent iron for enhanced nitrate removal from stormwater

Jing Tian; Jing Jin; Pei C Chiu; Daniel K Cha; Mingxin Guo; Paul T Imhoff

doi:10.1016/j.watres.2018.10.030

A pilot-scale, bi-layer bioretention system with biochar and zero-valent iron for enhanced nitrate removal from stormwater

Water Res. 2019 Jan 1:148:378-387. doi: 10.1016/j.watres.2018.10.030. Epub 2018 Oct 17.

Authors

Jing Tian¹, Jing Jin², Pei C Chiu³, Daniel K Cha⁴, Mingxin Guo⁵, Paul T Imhoff⁶

Affiliations

¹ College of Chemistry and Materials Science, Sichuan Normal University, Chengdu, Sichuan, 610066, PR China; Department of Civil and Environmental Engineering, University of Delaware, Newark, DE, 19716, USA. Electronic address: wltian@sicnu.edu.cn.
² Department of Civil and Environmental Engineering, University of Delaware, Newark, DE, 19716, USA.
³ Department of Civil and Environmental Engineering, University of Delaware, Newark, DE, 19716, USA. Electronic address: pei@udel.edu.
⁴ Department of Civil and Environmental Engineering, University of Delaware, Newark, DE, 19716, USA. Electronic address: cha@udel.edu.
⁵ Department of Agriculture and Natural Resources, Delaware State University, Dover, DE, 19901, USA. Electronic address: mguo@desu.edu.
⁶ Department of Civil and Environmental Engineering, University of Delaware, Newark, DE, 19716, USA. Electronic address: imhoff@udel.edu.

PMID: 30396103
DOI: 10.1016/j.watres.2018.10.030

Abstract

Nitrogen (N) removal in conventional bioretention systems is highly variable owing to the low nitrate (NO₃^-) elimination efficiency. We hypothesized that amending bioretention cells with biochar and zero-valent iron (ZVI) could improve the NO₃^- removal performance. A well-instrumented, bi-layer pilot-scale bioretention cell was developed to test the hypothesis by investigating its hydrologic performance and NO₃^- removal efficacy as affected by biochar and ZVI amendments. The cell containing 18% (v/v) wood biochar in the vadose zone and 10% (v/v) ZVI in the saturation zone was monitored for 18 months of field infiltration tests using synthetic stormwater amended with bromide (tracer) and NO₃^-. Compared to the Control cell without amendments, the Biochar/ZVI cell increased water retention by 11-27% and mean residence time by 0.7-3.8 h. The vadose zone of the Biochar/ZVI cell removed 30.6-95.7% (0.6-12.7 g) of NO₃-N from the influent, as compared with -6.1-89.6% (-0.1-2.9 g) by that of the Control cell. While the performance varied with synthetic storm events and seasons, in all cases the Biochar/ZVI cell resulted in greater NO₃^- removal than the Control cell. This improvement was presumably due to biochar's ability to improve water retention, facilitate anoxic conditions, increase residence time, and provide electrons for microbial denitrification. The saturation zone with ZVI amendment further promoted NO₃^- removal: removal was 1.8 times greater relative to the control in the first infiltration test, but was minimal in following tests. The reduction in performance of the ZVI amendment in subsequent tests might be due to diminished NO₃-N input to the saturation zone after treatment by the biochar-amended vadose zone. The redox potential and dissolved oxygen content at the vadose/saturation zone interface also indicated more favorable denitrification conditions in the Biochar/ZVI cell. Biochar amendment demonstrated significant promise for increasing nitrate removal in bioretention systems.

Keywords: Internal water storage; Nitrate removal; Redox potential; Tracer test; Water retention.

Publication types

Research Support, Non-U.S. Gov't

MeSH terms

Charcoal*
Denitrification
Iron
Nitrates*

Substances

Nitrates
biochar
Charcoal
Iron