Microbiota and genetic potential for reducing nitrous oxide emissions by biochar in constructed wetlands

Jun-Feng Wang; Ze-Xiang Cai; Yi-Hao Li; Yun-Yun Sun; Hai-Ming Wu; Xin-Shan Song; Hui Zhu

doi:10.1016/j.scitotenv.2023.166489

Microbiota and genetic potential for reducing nitrous oxide emissions by biochar in constructed wetlands

Sci Total Environ. 2023 Dec 10:903:166489. doi: 10.1016/j.scitotenv.2023.166489. Epub 2023 Aug 22.

Authors

Jun-Feng Wang¹, Ze-Xiang Cai¹, Yi-Hao Li², Yun-Yun Sun¹, Hai-Ming Wu³, Xin-Shan Song⁴, Hui Zhu⁵

Affiliations

¹ Guangdong Key Laboratory of Environmental Pollution and Health, School of Environment, Jinan University, Guangzhou 510632, PR China.
² South China Institute of Environmental Sciences, Ministry of Ecology and Environment (MEE), Guangzhou 510655, PR China.
³ Shandong Key Laboratory of Water Pollution Control and Resource Reuse, School of Environmental Science and Engineering, Shandong University, Qingdao 266237, PR China.
⁴ State Environmental Protection Engineering Center for Pollution Treatment and Control in Textile Industry, College of Environmental Science and Engineering, Donghua University, Shanghai 201600, PR China.
⁵ Key Laboratory of Wetland Ecology and Environment, Northeast Institute of Geography and Agroecology, Chinese Academy of Sciences, Changchun 130102, PR China. Electronic address: zhuhui@iga.ac.cn.

PMID: 37611707
DOI: 10.1016/j.scitotenv.2023.166489

Abstract

The denitrification process in constructed wetlands (CWs) is responsible for most of the nitrous oxide (N₂O) emissions, which is an undesired impact on the ecology of sewage treatment systems. This study compared three types of CWs filled with gravel (CW-B), gravel mixed with natural pyrite (CW-BF), or biochar (CW-BC) to investigate their impact on microbiota and genetic potential for N₂O generation during denitrification under varying chemical oxygen demand (COD) to nitrate (NO₃^--N) ratios. The results showed that natural pyrite and biochar were superior in enhancing COD (90.6-91.2 %) and NO₃^--N removal (90.0-93.5 %) in CWs with a COD/NO₃^--N ratio of 9. The accumulation of NO₂^--N during the denitrification process was the primary cause of N₂O emission, with the fluxes ranging from 95.6-472.0 μg/(m²·h) in CW-B, 92.9-400 μg/(m²·h) in CW-BF, and 54.0-293.3 μg/(m²·h) in CW-BC. The addition of biochar significantly reduced N₂O emissions during denitrification, while natural pyrite had a lesser inhibitory effect on N₂O emissions. The three types of substrates also influenced the structure of microbiota in the biofilm, with natural pyrite enriched nitrogen transformation microorganisms, especially for denitrifiers. Notably, biochar significantly enhanced the abundance of nosZ and the ratio of nosZ/(norB + norC), which are critical factors in reducing N₂O emissions from CWs. Overall, the results suggest that the biochar-induced changes in microbiota and genetic potential during denitrification play a significant role in preventing N₂O production in CWs, especially when treating sewage with a relatively high COD/NO₃^--N ratio.

Keywords: Constructed wetlands; Denitrification; Microbiota and genes; Nitrous oxide; Substrates.