Reduction of greenhouse gas emissions from closed activated sludge- to aerobic granular sludge-based biosystems via gas circulation

Jixiang Wang; Zejiao Li; Pengyu Xiong; Zhengwen Li; Hui Liu; Yili Zhang; Zhongfang Lei; Xiang Liu; Duu-Jong Lee; Xiaoyong Qian

doi:10.1016/j.biortech.2024.130748

Reduction of greenhouse gas emissions from closed activated sludge- to aerobic granular sludge-based biosystems via gas circulation

Bioresour Technol. 2024 Apr 26:401:130748. doi: 10.1016/j.biortech.2024.130748. Online ahead of print.

Authors

Jixiang Wang¹, Zejiao Li², Pengyu Xiong¹, Zhengwen Li¹, Hui Liu³, Yili Zhang³, Zhongfang Lei², Xiang Liu⁴, Duu-Jong Lee⁵, Xiaoyong Qian⁶

Affiliations

¹ Shanghai Academy of Environmental Sciences, Shanghai 200233, China; Department of Environmental Science and Engineering, Fudan University, Shanghai 200438, China.
² Faculty of Life and Environmental Sciences, University of Tsukuba, 1-1-1 Tennodai, Tsukuba, Ibaraki 305-8572, Japan.
³ Shanghai Academy of Environmental Sciences, Shanghai 200233, China.
⁴ Department of Environmental Science and Engineering, Fudan University, Shanghai 200438, China.
⁵ Department of Mechanical Engineering, City University of Hong Kong, Kowloon Tang, Hong Kong; Department of Chemical Engineering & Materials Science, Yuan-Ze University, Chungli 320, Taiwan.
⁶ Shanghai Academy of Environmental Sciences, Shanghai 200233, China. Electronic address: qianxy@saes.sh.cn.

PMID: 38677387
DOI: 10.1016/j.biortech.2024.130748

Abstract

Greenhouse gas (GHG) emissions from biological treatment units are challenging wastewater treatment plants (WWTPs) due to their wide applications and global warming. This study aimed to reduce GHG emissions (especially N₂O) using a gas circulation strategy in a closed sequencing-batch reactor when the biological unit varies from activated sludge (AS) to aerobic granular sludge (AGS). Results show that gas circulation lowers pH to 6.3 ± 0.2, facilitating regular granules but elevating total N₂O production. From AS to AGS, N₂O emission factor increased (0.07-0.86 %) due to decreasing ammonia-oxidizing rates while the emissions of CO₂ (0.3 ± 0.1 kg-CO₂/kg-chemical oxygen demand) and CH₄ remained in the closed biosystem. The gas circulation decreased N₂O emission factor by 63 ± 15 % after granulation higher than 44 ± 34 % before granulation, which is implemented by heterotrophic denitrification. This study provides a feasible strategy to enhance heterotrophic N₂O elimination in the biological WWTPs.

Keywords: Carbon dioxide; Granulation; Mitigation strategy; Nitrous oxide; Wastewater treatment.