Aerobic granular sludge for complex heavy metal-containing wastewater treatment: characterization, performance, and mechanisms analysis

Chong Liu; Yao Shen; Yuguang Li; Fengguang Huang; Shuo Wang; Ji Li

doi:10.3389/fmicb.2024.1356386

Aerobic granular sludge for complex heavy metal-containing wastewater treatment: characterization, performance, and mechanisms analysis

Front Microbiol. 2024 Jan 31:15:1356386. doi: 10.3389/fmicb.2024.1356386. eCollection 2024.

Authors

Chong Liu¹, Yao Shen², Yuguang Li¹, Fengguang Huang¹, Shuo Wang^{2

3}, Ji Li^{2

3}

Affiliations

¹ Key Laboratory of Embalming Methodology and Cosmetology of Cadavers of the Ministry of Civil Affairs, 101 Institute of the Ministry of Civil Affairs, Beijing, China.
² Jiangsu Key Laboratory of Anaerobic Biotechnology, School of Environment and Ecology, Jiangnan University, Wuxi, China.
³ Jiangsu College of Water Treatment Technology and Material Collaborative Innovation Center, Suzhou, China.

Abstract

Complex heavy metal (HM)-containing wastewater discharges pose substantial risks to global water ecosystems and human health. Aerobic granular sludge (AGS) has attracted increased attention as an efficient and low-cost adsorbent in HM-containing wastewater treatment. Therefore, this study systematically evaluates the effect of Cu(II), Ni(II), and Cr(III) addition on the characteristics, performance and mechanism of AGS in complex HM-containing wastewater treatment process by means of fourier transform infrared spectroscopy, inductively coupled plasma spectrocopcy, confocal laser scanning microscopy, extracellular polymeric substances (EPS) fractions detection and scanning electron microscope-energy dispersive X-ray. The results showed that AGS efficiently eliminated Cu(II), Ni(II), and Cr(III) by the orchestrated mechanisms of ion exchange, three-layer EPS adsorption [soluble microbial products EPS (SMP-EPS), loosely bound EPS (LB-EPS), tightly bound EPS (TB-EPS)], and inner-sphere adsorption; notably, almost 100% of Ni(II) was removed. Three-layer EPS adsorption was the dominant mechanism through which the HM were removed, followed by ion exchange and inner-sphere adsorption. SMP-EPS and TB-EPS were identified as the key EPS fractions for adsorbing Cr(III) and Cu(II), respectively, while Ni(II) was adsorbed evenly on SMP-EPS, TB-EPS, and LB-EPS. Moreover, the rates at which the complex HM penetrated into the granule interior and their affinity for EPS followed the order Cu(II) > Ni(II) > Cr(III). Ultimately, addition of complex HM stimulated microorganisms to excrete massive phosphodiesterases (PDEs), leading to a pronounced decrease in cyclic diguanylate (c-di-GMP) levels, which subsequently suppressed EPS secretion due to the direct linkage between c-di-GMP and EPS. This study unveils the adaptability and removal mechanism of AGS in the treatment of complex HM-containing wastewater, which is expected to provide novel insights for addressing the challenges posed by intricate real wastewater scenarios.

Keywords: aerobic granular sludge; complex heavy metals; cyclic diguanylate; extracellular polymeric substances fractions; phosphodiesterases; removal mechanisms.

Grants and funding

The author(s) declare financial support was received for the research, authorship, and/or publication of this article. The authors gratefully acknowledge the financial support provided by Special Funding for Basic Scientific Research Operations of Central-level Public Welfare Scientific Research Institutes (102118220110000009024), Laboratory operation maintenance and funeral equipment supply monitoring program (102118220110000009025), National Key Research and Development Program of China (2023YFC3207601), Jiangsu Policy Guidance Program (International Science and Technology Collaboration) (BZ2021030), and the Pre-research Fund of Jiangsu Collaborative Innovation Center of Technology and Material of Water Treatment (XTCXSZ2020-2).