Impacts Of Cerium Oxide Nanoparticles On Activated Sludge System

Nanomaterials (NMs) with specific physicochemical characteristics are widely applied to various fields of production and people’s life. The large production and utilization of NMs will cause their release into the water environment. Potential influences of NMs on human and other living creatures have been attracting more and more scholarly attention, but it has limited understanding whether NMs also show the negative impacts on the biological wastewater treatment system. This research focused on the acute and chronic effects of cerium oxide nanoparticles (CeO2 NPs), one of the most highly potential and market prospective NMs, on wastewater treatment efficiency and the changes of microbial community structure in activated sludge system. The conclusions are as follows:1. Three hours contact with aerobic microorganisms in activated sludge system test confirmed that the toxicity effcct of CeO2 NPs on microbial was weak when the concentration was less than 100 mg·L-1. Respiratory inhibition rate increased rapidly along with the increase of concentration when CeO2 NPs was over 100 mg·L-1. The half effective concentration of CeO2NPs on activated sludge was 527.39 mg·L-1.2. Acute influences of CeO2NPs (1 and 10 mg·L-1) on wastewater biological treatment effect:After one circle exposured to CeO2NPs, the performance of organic pollutants, nitrogen and phosphorus removal in experiment groups S1 (1mg·L-1 CeO2NPs) and S2 (10 mg·L-1 CeO2NPs) was consistent with that in control group SO (0 mg·L-1 CeO2 NPs) in the next circle. After one sludge age (20 days) exposure, there had no adverse effects on effluent quality and sludge sedimentation performance of S1 and S2 compared with SO.3. Chronic impacts of CeO2 NPs on wastewater biological treatment effect:After 150 days running, the effluent COD, NO2--N of S1 and S2 did not show obvious distinction compared with SO. The mean concentrations of effluent NH4+-N of S1 and S2 were 4.33 mg·L-1 and 6.26 mg·L-1, which were higher than SO with 1.63 mg·L-1. The effluent NO3--N of S1 (4.55 mg·L-1) and S2 (3.91 mg·L-1) were lower than that of SO (5.39 mg·L-1). The total nitrogen (TN) removal efficiency of S1 and S2 from 78.6% and 78.3% reduced to 71.3% and 67.5%. The total phosphorus (TP) of S1 and S2 from 0.23 mg·L-1 and 0.29 mg·L-1 increased to 0.47 mg·L-1 and 0.58 mg-L"1, and removal rate reduced by 4.8% and 6%. Meanwhile, the sludge volume index (SVI) of S1 (94 mL·g-1) and S2 (109 mL·g-1) were higher than that of SO (82 mL·g-1), and sedimentation performance of activated sludge got worse in S1 and S2.4. Through analysis of microbial community structure in activated sludge indicated that chronic exposure of CeO2 NPs on activated sludge system caused insignificant impacts on community diversity, but showed inhibitory effect on Proteobacteria. Conversely, it increased the abundance of Actinobacteria, and the extent of the increase had right correlation with the concentration of CeO2 NPs. CeO2 NPs caused the abundance of denitrification bacteria increasing, but it reduced the abundance of nitrification bacterial (Nitrosomonas and Nitrospire) and Zoogloea which is relate to sludge settling performance, and high concentration showed more severe inhibitory influences than low concentration. Chronic exposure to different concentrations of CeO2 NPs inhibited the growth of phosphorus accumulating organisms, but increased abundance of Defluviicoccus, which is a category of glycogen accumulating organisms.