Responses of SNEDPR-AGS system under long-term exposure of polyethylene terephthalate microplastics for treating low C/N wastewater: granular effect and microbial structure
Dongyue Li, Jiarui Li, Yuhan Zhu, Yaodong Wu, Linzhu Du, Yanshuo Wu, Jun Li, Wei Guo
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引用次数: 0
Abstract
The removal of nutrients in wastewater treatment plants can be significantly impacted by carbon limitations, especially for treating low carbon to nitrogen ratio (C/N) wastewater, which can markedly increase operational costs. Simultaneous nitrification, endogenous denitrification, and phosphorus removal combined with aerobic granular sludge (SNEDPR-AGS) has emerged as one of the optimal processes for treating low C/N wastewater owing to its high carbon utilization efficiency; however, the long-term effect of microplastics (MPs) on this system remains unclear. This study investigated the granular effect and microbial response of an SNEDPR-AGS system for treating low C/N wastewater under long-term exposure (180 d) to polyethylene terephthalate microplastics (PET-MPs). The results showed that the integrity of the AGS structure was disrupted significantly as the PET-MP concentration increased, with clear AGS cracks appearing on days 180, 124, and 74 after exposure to 1, 10, and 100 mg/L of PET-MPs, respectively. Additionally, the addition of PET-MPs also inhibited denitrification and phosphorus removal due to a decrease in the relative abundance of functional genes (napAB, nirK/nirS, ppk1, ppk2, and ppx). Notably, both chemometric and high-throughput sequencing results indicated that the metabolic form of the system would shift from a polyphosphate-accumulating metabolism to a glycogen-accumulating metabolism. The reason may be that PET-MP stress inhibited the relative abundance of functional genes related to carbon, glycogen, phosphorus, and energy metabolism pathways in Candidatus Accumulibacter and Dechloromonas, but promoted their relative abundance of Candidatus Competibacter. Flow cytometry and molecular docking simulations have also demonstrated the direct toxic effects of PET-MPs on the SNEDPR-AGS system. The biological enhancement and functional recovery of damaged SNEDPR-AGS systems must be further investigated in future studies.
Environmental Implication
STPs are difficult to remove microplastics, and the vast majority of microplastics are trapped in the sludge system. It is necessary to evaluate the long-term effects on typical sludge systems. This study investigated the effects of long-term exposure (180 days) to PET-MPs on the SNEDPR-AGS system. Even in AGS systems with strong tolerance, the sludge structure will be destroyed, and the C, N, P metabolic processes of (D)PAOs will be inhibited. The metabolism of the system shifted from PAM to GAM, thereby impacting the stable operation of the SNEDPR-AGS system. This threat is more severe in traditional activated sludge processes.
期刊介绍:
The Journal of Hazardous Materials serves as a global platform for promoting cutting-edge research in the field of Environmental Science and Engineering. Our publication features a wide range of articles, including full-length research papers, review articles, and perspectives, with the aim of enhancing our understanding of the dangers and risks associated with various materials concerning public health and the environment. It is important to note that the term "environmental contaminants" refers specifically to substances that pose hazardous effects through contamination, while excluding those that do not have such impacts on the environment or human health. Moreover, we emphasize the distinction between wastes and hazardous materials in order to provide further clarity on the scope of the journal. We have a keen interest in exploring specific compounds and microbial agents that have adverse effects on the environment.