Impact and microbial mechanism of continuous nanoplastics exposure on the urban wastewater treatment process. (1st September 2022)

• Record Type: Journal Article
• Authors: Song, Kang; Xue, Yunpeng; Li, Lu; Deng, Min; Zhao, Xiaoli
• Is Part Of: Water research. Volume 223(2022)
• Publication Date: 2022-09-01
• Subjects: Nanoplastics -- Urban wastewater -- Nitrification -- Denitrification -- Nitrous oxide -- Microbial mechanism; Water -- Pollution -- Research -- Periodicals; 363.7394
• DOI: 10.1016/j.watres.2022.119017
• Languages: English
• ISSNs: 0043-1354

Abstract

Highlights: Long term exposure of nanoplastics 1000 μg/L did not affect total nitrogen removal. Ammonia oxidation and nitrate reduction inhibited with exposure to nanoplastics. Long term exposure of 100 μg/L nanoplastics demonstrated highest N2 O reduction rate. Microbes were selectively cultured with the long term exposure of nanoplastics. Lipid metabolism function was suppressed at reactor with nanoplastics 1000 μg/L. Abstract: Contamination by nanoplastics in urban water has aroused increasing concern. The impact of nanoplastic exposure on the wastewater treatment process in the long term is still unclear. This study investigated the effect of continuous nanoplastic exposure (R1:0, R2:10, R3:100, and R4:1000 μg/L) on the nitrification and denitrification processes for over 200 days in a sequencing batch reactor (SBR). The results revealed that nanoplastic exposure does not demonstrate significant inhibition of total nitrogen removal. The ammonia oxidation rate (19.24 ± 0.01 mgN/gMLVSS/h, p < 0.05) and denitrification rate (11.78 ± 0.11 mgN/ gMLVSS/h, p < 0.05) in R4 was significantly lower than the control (R1: 0 μg/L). The maximal reaction velocities of N2 O reduction ( V max) were improved after long-term exposure to nanoplastics in high concentrations. The R3 demonstrated the highest V max value—six times higher than R4 and approximately 20 times higher than R1 and R2. The microbial structure largely varied with the exposure to nanoplastics, where the exposure to a high concentration largely suppressed the nitrifier and selectively enriched the denitrifier. The percentage of the top 20 genera of denitrifiers increased from 31.76% to 63.42%, and the nitrifiers decreased from an initial 12.40% to 2.83% for R4. The predominant genera were found to be Thauera, Azoarcus, and Defluviicoccus in R4 and R3 which indicated their tolerance to nanoplastics. The function prediction results indicated that the membrane transport function was significantly enhanced and the lipid metabolism function was significantly reduced in R4 as compared with the control (R1, p <0.05). This may be attributed to the adsorption of nanoplastics on bacteria. Observation under a scan electronic microscope demonstrated that the nanoplastics were firmly attached to the microbe surface and aggregated in activated sludge at high nanoplastics dosed reactor. These results deepen the understanding of the effect of nanoplastics on the urban wastewater treatment process and provide valuable information for the management of nanoplastic contamination in urban wastewater.