Impacts Of Multiwalled Carbon Nanotubes On Nutrient Removal From Wastewater And Bacterial Community Structure In Activated Sludge

Nanomaterials are widely used in different fields due to its unique chemical and physical properties; however, the production, use, and disposal of nanomaterials will inevitably lead to the eventual release to water environment. Although the risk and adverse impacts associated with nanomaterial for human health and the environment are increasingly gaining attention, investigations of the effects of nanomaterials on activated sludge in wastewater treatment system are still insufficient. This research thus focused on the impacts of multiwalled carbon nanotubes (MWCNTs), one of the most widely used carbon nanomaterials, on nutrient removal from wastewater and bacterial community structure in activated sludge.Short-(21days) and long-term (180days) effects of1and20mg·L-1MWCNTs on biological nutrient removal in activated sludge process were investigated, and it was found that short-term exposure to1and20mg·L-1MWCNTs had no significant influence on the performance of nutrient removal in activated sludge system. The average TN removal efficiency was not significantly affected after long-term exposure to1mg·L-1MWCNTs, but there was a period of (about70days) deterioration of the ammonia oxidation process during the long-term exposure. After long-term exposure (180days) to20mg·L-1, the average total nitrogen (TN) removal efficiency decreased from83.50%to71.97%, and the average effluent COD concentration slightly increased from22.30to42.85mg·L-1. Both1and20mg·L-1MWCNTs had inhibitory effects on biological phosphorus removal, and the average TP removal efficiencies were decreased from97.60%to51.40%and from98.04%to33.60%, respectively. Three hours activated sludge respiration inhibition test was conducted in order to investigate the effects of MWCNTs on the activity of activated sludge, besides, it was found that long-term exposure to20mg·L-1MWCNTs inhibited the relative activities of ammonia monooxygenase (AMO) and nitrite oxidoreductase (NOR), which are associated with biological nitrogen removal.1and20mg·L-1MWCNTs caused a decrease in the relative activities of exopolyphosphatase (PPX) and polyphosphate kinase (PPK), which are associated with biological phosphorus removal.Further study for the impacts of MWCNTs on the bacterial community structure was conducted by using MiSeq sequencing. The results indicated that1and20mg·L-1MWCNTs obviously decreased the diversity of bacterial community in activated sludge, and20mg·L-1showed more severe inhibitory effect than1mg·L-1. Changes of bacterial community structure also occurred after long-term exposure to1and20mg·L-1MWCNTs. Sequencing results indicated that MWCNTs differentially increased the abundance of α-Proteobacteria and γ-Proteobacteria, and decreased the abundance of Bacteroidetes. Long-term exposure to1mg·L-1MWCNTs decreased the abundance of Nitrosomonas which is a typical kind of ammonia oxidizing bacteria, and significantly increased the abundance of glycogen accumulating organisms (GAOs)(i.e. Defluviicoccus and Micropruina). By contrast,20mg·L-1had more severe inhibitory effect on the abundance of Nitrosomonas than1mg·L-1.20mg·L-1also inhibited the abundance of Nitrospira which is a typical kind of nitrite-oxidizing bacteria. The total abundance of phosphate accumulating organisms (PAOs) were also decreased by long-term exposure to20mg·L-1MWCNTs.