Bacterial community and molecular ecological network in response to Cr2O3 nanoparticles in activated sludge system.

The potential environmental risks of chromium oxide nanoparticles (Cr2O3 NPs) have caused great concerns. However, their possible impacts on activated sludge process are very limited. In this study, we carried out long-term exposure experiments to evaluate the influence of Cr2O3 NPs on wastewater nutrient removal, bacterial community and molecular ecological network (MEN) in the sequencing batch reactor (SBR). It was found that 1 mg/L Cr2O3 NPs increased the effluent concentrations of NO3--N and TP from 6.5 to 15.4 mg/L, and 0.6-2.7 mg/L, indicating the serious deterioration of denitrification and phosphorus removal. Cr2O3 NPs significantly decreased the bacterial richness in terms of the number of different OTUs (626 OTUs in Cr2O3 samples and 728 OTUs in controls). Detrended correspondence analysis (DCA) showed that the overall taxonomic structure of bacterial community was altered at Cr2O3 NPs in activated sludge systems. Further analysis revealed that three genera related to denitrification (Desulfovibrio, Pseudomonas and Hyphomicrobium) and two genera related to phosphorus removal (Accumulibacter and Rhodobacter) decreased significantly, which was consistent with the observed influences of Cr2O3 NPs on denitrification and phosphorus removal. MEN analysis showed that the overall architecture of the network under Cr2O3 NPs was substantially alerted. ß-Proteobacteria, playing an important role in nutrients removal, had less complex interactions in the presence of Cr2O3 NPs, which may be associated with the deterioration of denitrification and phosphorus removal. This study provides insights into our understanding of shifts in the bacteria community and their MEN under Cr2O3 NPs in activated sludge systems.

Impacts of multiwalled carbon nanotubes on nutrient removal from wastewater and bacterial community structure in activated sludge.

BACKGROUND: The increasing use of multiwalled carbon nanotubes (MWCNTs) will inevitably lead to the exposure of wastewater treatment facilities. However, knowledge of the impacts of MWCNTs on wastewater nutrient removal and bacterial community structure in the activated sludge process is sparse. AIMS: To investigate the effects of MWCNTs on wastewater nutrient removal, and bacterial community structure in activated sludge. METHODS: Three triplicate sequencing batch reactors (SBR) were exposed to wastewater which contained 0, 1, and 20 mg/L MWCNTs. MiSeq sequencing was used to investigate the bacterial community structures in activated sludge samples which were exposed to different concentrations of MWCNTs. RESULTS: Exposure to 1 and 20 mg/L MWCNTs had no acute (1 day) impact on nutrient removal from wastewater. After long-term (180 days) exposure to 1 mg/L MWCNTs, the average total nitrogen (TN) removal efficiency was not significantly affected. TN removal efficiency decreased from 84.0% to 71.9% after long-term effects of 20 mg/L MWCNTs. After long-term exposure to 1 and 20 mg/L MWCNTs, the total phosphorus removal efficiencies decreased from 96.8% to 52.3% and from 98.2% to 34.0% respectively. Further study revealed that long-term exposure to 20 mg/L MWCNTs inhibited activities of ammonia monooxygenase and nitrite oxidoreductase. Long-term exposure to 1 and 20 mg/L MWCNTs both inhibited activities of exopolyphosphatase and polyphosphate kinase. MiSeq sequencing data indicated that 20 mg/L MWCNTs significantly decreased the diversity of bacterial community in activated sludge. Long-term exposure to 1 and 20 mg/L MWCNTs differentially decreased the abundance of nitrifying bacteria, especially ammonia-oxidizing bacteria. The abundance of PAOs was decreased after long-term exposure to 20 mg/L MWCNTs. The abundance of glycogen accumulating organisms (GAOs) was increased after long-term exposure to 1 mg/L MWCNTs. CONCLUSION: MWCNTs have adverse effects on biological wastewater nutrient removal, and altered the diversity and structure of bacterial community in activated sludge.

[Phosphorus forms and its distribution characteristics in sediments and soils of water-level-fluctuating zone of the backwater reach from input river of Three Gorges Reservoir].

The contents of different phosphorus forms in surface sediments and the soils of water-level-fluctuating zone of the backwater reach from input river of Three Gorges Reservoirwere measured, using thestandard measurement and test (SMT) procedure of phosphorus forms in freshwater sediments. Correlation coefficients between phosphorus forms and sample geochemical characteristics, such as organic matter and major components were analyzed. The results indicated that the TP content in surface sediments varied from 483.4-848.4 mg/kg, and the average content was 569.0 mg/kg. The TP content in surface sediments placed in the mid-lower level, comparing with the TP content in surface sediment from the shallow lakes in the middle and lower reaches of Yangtze River. The TP content in soils of water-level-fluctuating zone varied from 488.9-1487.7 mg/kg, and the average content was 813.3 mg/kg. The average content of TP in soils of water-level-fluctuating zone whole exceeded the surface sediment, indicating of the influence of human's activity on phosphorus contents in soils of water-level-fluctuating zone. Distribution characteristics of phosphorus forms were different between the sediment and soils of water-level-fluctuating zone: (1) The ratio of IP/TP in the surface sediments (average value 55.7%) was higher than that in soils of water-level-fluctuating zone (average value 49.4%); (2) The domination phosphorus forms of IP in surface sediments was Ca-P (average ratio 83.5%), and the ratio of (Fe/Al-P)/IP was only 15%. The average ratio of Ca-P/IP in the soils of water-level-fluctuating zone was 73.9%, whereas the ratio of Fe/Al-P in IP raised to 22%; (3) The average content of active phosphorus (OP + Fe/Al-P) in surface sediment was 261.8 mg/kg, the average ratio of active phosphorus in TP was 49%, whereas the average content of active phosphorus (OP + Fe/Al-P) in soils of water-level-fluctuating zone was 405.7 mg/kg, the average ratio was 54%. The active phosphorus in soils of water-level-fluctuating zone would become potential pollution sources of water under correct environmental conditions,therefore, the potential impact of phosphorus on water eutrophication in soils of water-level-fluctuating zone couldn't be neglected.