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Published on: August 14, 2020
Effects of dissolved oxygen and carbon source forms on carbon source capture efficiency in activated sludge system:
Peng Zhang1, Jie-Yuan Wang1, Shao-Yang Liu2
1Key Laboratory of the Three Gorges Reservoir Region's Eco-Environment, Ministry of Education, Chongqing University, Chongqing 400045, China; College of Environment and Ecology, Chongqing University, Chongqing 400045, China.
None:
Efficient carbon capture by activated sludge is essential for energy recovery and carbon neutralization in wastewater treatment plants, but the mechanisms by which dissolved oxygen (DO) affects carbon source capture efficiency remain unclear. In this study, the capture efficiencies and mechanisms of activated sludge exposed to different DO levels (aerobic, anoxic, and anaerobic states) toward particulate, colloidal, and soluble carbon sources were systematically investigated. Results showed that the particulate and colloidal COD (pCOD + cCOD) is converted faster than soluble COD (sCOD) under all DO conditions. At a DO concentration of 2 mg L-1, activated sludge exhibits the highest carbon source capture efficiency of 51.7%. Adsorption and storage dominated carbon capture compared with assimilation. Compared with anaerobic (DO = 0.1 mg L-1) and anoxic (DO = 0.8 mg L-1) activated sludge, aerobic activated sludge (DO = 2 mg L-1) exhibited higher metabolic activity and EPS production, with a greater hydrophobic/hydrophilic amino acid ratio and a looser structure in protein, thereby enhancing surface hydrophobicity. The surface plasmon resonance results show that the carbon source molecules preferentially adhere to the hydrophobic surface. Moreover, under aerobic conditions, genes associated with carbon metabolism (e.g. pycA, ACLY), glycogen metabolism (e.g. GYS, K16153), energy metabolism (e.g. Ndufs7, CoxAC), and hydrophobic amino acid metabolism (e.g. SDS, aroA, CCBL) were more abundant, potentially altering the composition and surface properties of EPS. These findings elucidate the mechanistic roles of DO levels in regulating carbon capture efficiency in wastewater treatment systems.
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