The regulatory mechanism of humic acid on aerobic granular sludge under prolonged exposure to graphene and oxide grapheme
ZHANG Ming, FENG Xue-li, SHI Wen-xin, ZHANG Bing
Key Laboratory of Three Gorges Reservoir Region's Eco-Environment, Ministry of Education, College of Environment and Ecology, Chongqing University, Chongqing 400044, China
Abstract：This study aimed to investigate the mitigating effect and regulatory mechanism of humic acid (HA) on the physicochemical properties and pollutant treatment performance of aerobic granular sludge (AGS) under prolonged stress induced by graphene (G) and oxide graphene (GO). The results demonstrated that the optimal dosage of HA (10mg/L) significantly enhanced the physicochemical characteristics of AGS, and improved the pollutant treatment performance of the AGS reactor (R2 (1.0mg/L G) and R3 (1.0mg/L GO)). At the 75th day, in R3, there was an obviously increase in average particle size of AGS from 1224.1μm to 1407.5μm, while in R2it increased from 1313.0μm to 1461.3μm. Simultaneously, the enhancement of AGS physicochemical properties led to a respective increase of 2.3% and 7.6% in TN removal efficiency for R2 and R3. The introduction of HA resulted in a significant reduction in the levels of reactive oxygen species (ROS), lactate dehydrogenase activity, catalase activity, and superoxide dismutase activity in R2 and R3. This suggested that HA can effectively bind with accumulated ROS within cells to further mitigate oxidative stress levels induced by G and GO. The addition of HA also effectively alleviated the excessive secretion of extracellular polymeric substances (EPS) in AGS, resulting in a decrease in the content of aromatic proteins and tyrosine-like substances within EPS. Consequently, this led to a more compact and denser AGS particle structure in R2 and R3. Ultimately, the changes in Zeta potential of G and GO (before and after the addition of HA) indicate that the incorporation of HA can enhance the initial potential values of G and GO, thereby augmenting the repulsive effect between G/GO and microorganisms, reducing direct contact between microorganisms and G/GO, thus effectively mitigating the toxic effects exerted by G and GO on microorganisms.
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