Synchronous in-situ sludge reduction and enhanced denitrification through improving electron transfer during endogenous metabolisms with Fe(Ⅱ) addition

Yu Cheng; Chenghai Lu; Shujia Gao; Rashmi Koju; Haiyan Li; Zongqiang Zhu; Chengzhi Hu; Jiuhui Qu

doi:10.1016/j.watres.2024.121472

Synchronous in-situ sludge reduction and enhanced denitrification through improving electron transfer during endogenous metabolisms with Fe(Ⅱ) addition

Water Res. 2024 May 15:255:121472. doi: 10.1016/j.watres.2024.121472. Epub 2024 Mar 14.

Authors

Yu Cheng¹, Chenghai Lu², Shujia Gao³, Rashmi Koju², Haiyan Li⁴, Zongqiang Zhu⁵, Chengzhi Hu⁶, Jiuhui Qu²

Affiliations

¹ State Key Laboratory of Environmental Aquatic Chemistry, Research Center for Eco-Environmental Sciences, Chinese Academy of Sciences, Beijing 100085, China; School of Water Resources and Environment, China University of Geosciences (Beijing), Beijing 100083, China; Centre for Urban Environmental Remediation, Beijing University of Civil Engineering and Architecture, Beijing 102616, China.
² State Key Laboratory of Environmental Aquatic Chemistry, Research Center for Eco-Environmental Sciences, Chinese Academy of Sciences, Beijing 100085, China; University of Chinese Academy of Sciences, Beijing 100049, China.
³ State Key Laboratory of Environmental Aquatic Chemistry, Research Center for Eco-Environmental Sciences, Chinese Academy of Sciences, Beijing 100085, China; College of Environmental Science and Engineering, Guilin University of Technology, Jiangan Road 12, Guilin, Guangxi 541004, China.
⁴ Centre for Urban Environmental Remediation, Beijing University of Civil Engineering and Architecture, Beijing 102616, China.
⁵ College of Environmental Science and Engineering, Guilin University of Technology, Jiangan Road 12, Guilin, Guangxi 541004, China. Electronic address: zhuzongqiang@glut.edu.cn.
⁶ State Key Laboratory of Environmental Aquatic Chemistry, Research Center for Eco-Environmental Sciences, Chinese Academy of Sciences, Beijing 100085, China; University of Chinese Academy of Sciences, Beijing 100049, China. Electronic address: czhu@rcees.ac.cn.

PMID: 38552492
DOI: 10.1016/j.watres.2024.121472

Abstract

The creation of large amounts of excess sludge and residual nitrogen are critical issues in wastewater biotreatment. This study introduced Fe(II) into an oligotrophic anaerobic reactor (OAR_Fe) that was implemented to modify an anoxic-oxic process to motivate in-situ sludge reduction and enhance denitrification under an effective electron shuttle among organic matter, nitrogen, and Fe. The addition of 15 mg L^-1 Fe(II) resulted in a sludge reduction efficiency reached 32.0% with a decreased effluent nitrate concentration of 33.3%. This was mostly attributed to the electron transfer from Fe(II) to organic matters and nitrogen species in OAR_Fe. The participation of Fe(II) led to the upregulation of Geothrix and Terrimonas, which caused active organic matter hydrolysis and cell lysis to stimulate the release of extracellular polymeric substances (EPS) and substance transfer between each layer of EPS. The higher utilization of released bioavailable dissolved organic matter improved endogenous denitrification, which can be combined with iron autotrophic denitrification to realize multiple electron donor-based nitrogen removal pathways, resulting in an increased nitrate removal rate of 58.2% in the absence of external carbon sources. These functional bacteria associated with the transformation of nitrogen and carbon and cycling between ferrous and ferric ions were enriched in OAR_Fe, which contributed to efficient electron transport occurred both inside and outside the cell and increased 2,3,5-triphenyltetrazolium chloride electronic transport system activity by 46.9%. This contributed to the potential operational costs of chemical addition and sludge disposal of Fe-AO being 1.9 times lower than those of conventional A²O processes. These results imply that the addition of ferrous ions to an oligotrophic anaerobic zone for wastewater treatment has the potential for low-cost pollution control.

Keywords: EPS; Electron transfer; Endogenous denitrification; Ferrous ion; Sludge reduction.