Recycling silage leachate and biochar for improving nitrate removal by woodchip bioreactor

Yuchuan Fan; Michael Essington; Jie Zhuang; Xi Zhang; Sindhu Jagadamma; John Schwartz; Jinsheng Huang; Jehangir Bhadha; Jaehoon Lee

doi:10.1016/j.jenvman.2023.118735

Recycling silage leachate and biochar for improving nitrate removal by woodchip bioreactor

J Environ Manage. 2023 Nov 1:345:118735. doi: 10.1016/j.jenvman.2023.118735. Epub 2023 Aug 2.

Authors

Yuchuan Fan¹, Michael Essington², Jie Zhuang³, Xi Zhang⁴, Sindhu Jagadamma², John Schwartz⁵, Jinsheng Huang⁶, Jehangir Bhadha⁷, Jaehoon Lee⁸

Affiliations

¹ Everglades Research and Education Center, University of Florida, Belle Glade, FL, 33430, USA; Department of Soil, Water, and Ecosystem Sciences, University of Florida, Gainesville, FL, 32611, USA; Biosystems Engineering and Soil Science Department, University of Tennessee, Knoxville, TN, 37996, USA.
² Biosystems Engineering and Soil Science Department, University of Tennessee, Knoxville, TN, 37996, USA.
³ Biosystems Engineering and Soil Science Department, University of Tennessee, Knoxville, TN, 37996, USA; Center for Environmental Biotechnology, University of Tennessee, Knoxville, TN, 37996, USA.
⁴ Red River Research Station and School of Plant, Environmental and Soil Sciences, Louisiana State University-Agricultural Center 262 Research Station Drive, Bossier City, LA, 71112, USA.
⁵ Civil and Environmental Engineering Department, University of Tennessee, Knoxville, TN, 37996, USA.
⁶ Department of Agricultural and Biological Engineering, University of Florida, Gainesville, FL, 32611, USA.
⁷ Everglades Research and Education Center, University of Florida, Belle Glade, FL, 33430, USA; Department of Soil, Water, and Ecosystem Sciences, University of Florida, Gainesville, FL, 32611, USA.
⁸ Biosystems Engineering and Soil Science Department, University of Tennessee, Knoxville, TN, 37996, USA. Electronic address: jhlee@utk.edu.

PMID: 37540981
DOI: 10.1016/j.jenvman.2023.118735

Abstract

Woodchip bioreactor (WBR) is commonly used to remove nitrate from drainage and runoff. However, the efficiency of nitrate removal in WBR is highly variable due to the properties of filling materials. In this study, we investigated the potential of recycling two waste materials, biochar (B) and silage leachate (SL), to enhance nitrate removal by providing a better living habitat and extra available carbon for denitrification. We constructed twelve lab-scale bioreactors with different filling materials (WBR, WBR + B, WBR + SL, WBR + B + SL), hydraulic retention times (HRT: 0.5-24 h), and nitrate concentrations (5.4-33 mg L^-1) to test nitrate removal efficiency (NRE) and nitrate removal rate (NRR). Our results showed that the combination of biochar and silage leachate led to the highest NRE and NRR, with improvements of 23% and 48%, respectively, compared to WBR alone. However, the benefits of adding biochar and silage leachate were less apparent at longer HRTs. According to the results of our structural equation modeling (SEM), we have attributed the improved denitrification to several factors. These factors include the decrease in dissolved oxygen, saturated hydraulic conductivity, and pH value, as well as an increase in dissolved organic carbon after the addition of silage leachate. Therefore, our study provides evidence that recycling biochar and silage leachate as an additive to WBR could be a beneficial strategy for enhancing nitrate removal. Overall, this study highlights the potential of a win-win solution to improve the efficiency of nitrate removal in water treatment processes.

Keywords: Crop-livestock-industry system; Denitrifying; Structural equation model; Water quality; Woodchip bioreactor.

MeSH terms

Bioreactors
Denitrification*
Nitrates*
Nitrogen
Silage

Substances

Nitrates
biochar
Nitrogen