Hierarchical stringent response behaviors of activated sludge system to stressed conditions

Zhenyu Hang; Peipei Tong; Pian Zhao; Zhangwei He; Linjun Shao; Yanru Jia; Xiaochang C Wang; Zhihua Li

doi:10.1016/j.scitotenv.2023.161832

Hierarchical stringent response behaviors of activated sludge system to stressed conditions

Sci Total Environ. 2023 Apr 20:870:161832. doi: 10.1016/j.scitotenv.2023.161832. Epub 2023 Jan 28.

Authors

Zhenyu Hang¹, Peipei Tong¹, Pian Zhao¹, Zhangwei He¹, Linjun Shao¹, Yanru Jia¹, Xiaochang C Wang¹, Zhihua Li²

Affiliations

¹ Key Laboratory of Northwest Water Resource, Environment, and Ecology, MOE, School of Environmental and Municipal Engineering, Xi'an University of Architecture and Technology, Xi'an 710055, China.
² Key Laboratory of Northwest Water Resource, Environment, and Ecology, MOE, School of Environmental and Municipal Engineering, Xi'an University of Architecture and Technology, Xi'an 710055, China; Xi'an Key Laboratory of Intelligent Equipment Technology in Environmental Engineering, Xi'an University of Architecture and Technology, Xi'an 710055, China. Electronic address: lizhihua@xauat.edu.cn.

PMID: 36716870
DOI: 10.1016/j.scitotenv.2023.161832

Abstract

The stringent response of activated sludge systems to either stressed or harmful environments is important for the stable operation of activated sludge, which is examined by taking copper ion (Cu²⁺) as a stress model in this study. When weak stress was employed (Cu²⁺ ≤ 2.5 mg/L), the N-acyl-homoserine lactones (AHLs) of C6-, C8-, and C10-HSL increased by 30 %, 13 %, and 127 %, respectively, while the redox sensor green (RSG) intensity decreased by 28 %. Encountering the increased stress (2.5 mg/L < Cu²⁺ ≤ 5 mg/L), bacteria concentration in the supernatant increased by 87 %. However, the respiration rates of autotrophic and heterotrophic bacteria (SOUR_a and SOUR_h) and adenosine triphosphate decreased by 52 %, 18 %, and 27 %, respectively, and the flocs disintegrated with a diameter decreasing from 57 to 51 μm. When the stress became more serious (Cu²⁺ > 5 mg/L), the respiration rates continued to decline, but the quasi-endogenous respiration ratio (R_q/t) increased from 31 % to 47 %. Negligible changes occurred in the endogenous respiration rate (SOUR_e), adenosine diphosphate, and adenosine monophosphate. Based on these results, a hierarchical stringent response model of the activated sludge system to stressed conditions was proposed, and these responses were evaluated by respirogram. The initial response to weak stress was related to the most sensitive signals of quorum sensing and RSG intensity, well described by the quasi-endogenous respiration rate. The adaptive response to increased stress was the proactive migrations of low- and high-nucleic-acid bacteria to the supernatant, causing the looseness and even disintegration of sludge flocs, well described by SOUR_a, SOUR_h, and R_q/t. The lethal response to lethal stress was related to endogenous metabolic processes, well described by SOUR_e. This work provides new insights into understanding the stringent response of activated sludge systems to some stressed conditions. It helps to regulate the stability of activated sludge systems with respirogram technology.

Keywords: Activated sludge system; Bacteria migration; Environment shock; Hierarchical stringent response; Oxygen uptake rate.

MeSH terms

Acyl-Butyrolactones / metabolism
Adenosine Triphosphate / metabolism
Bacteria / metabolism
Bioreactors*
Quorum Sensing
Sewage* / microbiology

Substances

Sewage
Acyl-Butyrolactones
Adenosine Triphosphate