Yang Xiangyu, He Qiang, Liu Tao, Zheng Feifei, Mei Han, Chen Mengli, Liu Gang, Vymazal Jan, Chen Yi
Key Laboratory of the Three Gorges Region's Eco-Environment, Ministry of Education, College of Environment and Ecology, Chongqing University, Campus B 83 Shabeijie, Shapingba, Chongqing 400044, China; National Centre for International Research of Low-carbon and Green Buildings, Chongqing University, Chongqing, 400044, China; State Key Laboratory of Environmental Aquatic Chemistry, Research Center for Eco-Environmental Sciences, Chinese Academy of Sciences, Beijing 100085, China; University of Chinese Academy of Sciences, Beijing 100049, China.
Key Laboratory of the Three Gorges Region's Eco-Environment, Ministry of Education, College of Environment and Ecology, Chongqing University, Campus B 83 Shabeijie, Shapingba, Chongqing 400044, China; National Centre for International Research of Low-carbon and Green Buildings, Chongqing University, Chongqing, 400044, China.
Water Res. 2022 Jun 15;217:118430. doi: 10.1016/j.watres.2022.118430. Epub 2022 Apr 8.
Presence of microplastics (MPs) in wastewater has posed a huge ecosystem risk. Constructed wetlands (CWs) can effectively intercept MPs, while with MPs accumulation the response of CWs' performance is still unclear. In order to evaluate those effects, we conducted a 370-day experiment using CW microcosms fed with different levels (0, 10, 100, and 1000 μg/L) of polystyrene (PS) MPs (diameter: 50-100 μm). Results showed that nitrogen removal efficiency was increased (by 3.9%-24.7%) during the first 60 days and then decreased (by 7.1%-41.3%) with MPs accumulating, but no obvious change in COD and TP removal was observed. From further analysis, MPs accumulation changed the biofilm composition (TOC content increased from 41.4% to 52.7%), substrate porosity (electrical resistivity increased by 1.2-2.4 folds), and oxygen mass transfer (|K| increased from 3.5% to 18.6%). Moreover, the microbial dynamics presented a higher abundance of nitrifiers (Nitrospira and Nitrosomonas) during the 60-day experiment and a lower abundance in the last days, while denitrifiers (Thauera, Thiobacillus, and Anaerolinea) had a high relative abundance throughout the experiment, being consistent with the variation of nitrification and denitrification rates. Finally, structural equation model analysis proved that due to the changes of substrate characteristics and microbial compositions and activities, the obvious decrease in nitrification efficiency was a direct reason for the decline of nitrogen removal during 370-day MPs accumulation. Overall, our study first prove that MPs accumulation can cause a series of changes in physicochemical and microbial characteristics of substrate, and ultimately affect the nitrogen-transforming process in CWs. Although our conclusions were based on the lab-scale CWs being different from the real wetlands, we hope that the conclusions can provide the effective regulatory strategies to guide the control of MPs in the actual wetlands.
废水中微塑料（MPs）的存在已构成巨大的生态系统风险。人工湿地（CWs）能够有效拦截微塑料，然而随着微塑料的积累，人工湿地性能的响应仍不明确。为了评估这些影响，我们进行了一项为期370天的实验，使用人工湿地微型生态系统，投喂不同水平（0、10、100和1000μg/L）的聚苯乙烯（PS）微塑料（直径：50 - 100μm）。结果表明，在前60天，氮去除效率提高了（3.9% - 24.7%），随后随着微塑料的积累而下降（7.1% - 41.3%），但未观察到化学需氧量（COD）和总磷（TP）去除有明显变化。通过进一步分析，微塑料的积累改变了生物膜组成（总有机碳（TOC）含量从41.4%增加到52.7%）、基质孔隙率（电阻率增加了1.2 - 2.4倍）和氧气传质（|K|从3.5%增加到18.6%）。此外，微生物动态显示，在为期60天的实验期间硝化细菌（硝化螺菌属和亚硝化单胞菌属）丰度较高，而在后期丰度较低，反硝化细菌（陶厄氏菌属、硫杆菌属和厌氧绳菌属）在整个实验过程中相对丰度较高，这与硝化和反硝化速率的变化一致。最后，结构方程模型分析证明，由于基质特性以及微生物组成和活性的变化，硝化效率的明显降低是370天微塑料积累过程中氮去除下降的直接原因。总体而言，我们的研究首次证明微塑料积累会导致基质的一系列物理化学和微生物特性变化，并最终影响人工湿地中的氮转化过程。尽管我们的结论基于与实际湿地不同的实验室规模人工湿地，但我们希望这些结论能提供有效的调控策略，以指导实际湿地中微塑料的控制。
