Characteristics Of TiO₂Nanoparticle In Water And Effects On The Satability Of SBR Activated Sludge System

Nanotechnology was of priority in the developed countries, and has been applied inthe areas of industry, farming and science and technology. In the meantime, it willinevitable cause the release of nanoparticles to the environment by direct or indirectways. Thus the corresponding environmental implications arise great concerns. Aquaticenvironment was the main receptor of nanoparticles, and the behavior and stability ofnanoparticles would change under the complicated water conditions. Also the inhibitionof wastewater treatment efficiency and organism’ property may also be inhibited for thereason of the interaction of activated sludge and nanoparticles, which will threaten thewater safety eventually. For these reasons, the nano TiO₂, one of the most commonnanomaterials was selected for the study of the surface characteristic in aquatic system.And the diameter distribution, stability and the effect factors of nano TiO₂in surfacewater and wastewater were analyzed. On the other hand, effects of nano TiO₂on thefloc stability and surface characteristic in biological wastewater treatment plant（WWTP）were studied to confirm the physical and chemical mechanism. Additional, the newpyrosequencing was employed to investigate the effects of nano TiO₂on the biologicalstability. The response of physiological/biochemical characteristics and microbialcommunity structures to nano TiO₂was evaluated. This research will provide theorybasis for the study of potential risks of nanoparticles to aquatic environment.The distribution of nano TiO₂was even and the differences of diamater wasneglectable, which resulted in acceptable distribution degree. The zero potential pointlocation was between the pH6and7, and the absolute value of potential increased asthe pH deviated from the isoelectric point. The results of the fourier transform infraredspectroscopy and three-dimensional fluorescence spectrum showed that the interactionof nano TiO₂and dissolved organic matters was the electrostatic repulsion and ligandexchange, in which the ligand exchange was dominated by the interaction of thefunctional group of carboxyl and phenol hydroxyl groups. The stronger reaction wasdrived by ligand exchange in the situation of smaller molecular weight of dissolvedorganic matters as the pH was7. However, the electrostatic repulsion dominated theinteraction of high molecular weight dissolved organic matters and nano TiO₂, whichresulted in more stability of particles’aggregators. On the contrary, at pH was5, theadsorption of nano TiO₂and dissolved organic matters was accompliced by both thesetwo effects, and the adsorption was greater in smaller molecular weight of dissolvedorganic matters and nano TiO₂. In consistent with the situation of natural aquaticenvironment, the dominated effect of nano TiO₂and dissolved organic carbon waselectrostatic repulsion and ligand exchange for bigger and smaller molecular weight of dissolved organic carbon respectively in wastewater environment, and the interactionwas principally achieved by smaller molecular weight of dissolved organic matters.These results would be a theory basis for the removal of nanoparticles in WWTP.The wide application of nanosized titanium dioxide （nano TiO₂） will result in highconcentrations of the molecule in the aquatic environment, especially in the influent ofWWTP. The present study focuses on the potential effect of nano TiO₂on thephysicochemical stability of activated sludge flocs after long-term exposure, on whichlimited information is currently available. Kelvin probe force microscopy （KPFM） wasinnovatively applied to assess the surface potential of the activated sludge in situ. Thephysicochemical characteristics of the bioflocs with and without long-term exposure tonano TiO₂were well elucidated by the thermodynamic approach. The results showedthat the repulsive force predominated the bioflocs system as the concentration of nanoTiO₂increased, owing to the corresponding increase in the density of the negativecharge. The bioflocs exposed to100ppm nano TiO₂presented the strongest stabilitycompared to the other two samples with low concentrations of nano TiO₂, which alsoindicated that the bioflocs with long-term exposure to nano TiO₂had a low settlementefficiency of the corresponding activated sludge. Further, the extended Derjaugin,Landau, Verwey, and Overbeek （XDLVO） theory was used to explore the flocculationstability of the bioflocs system. As the concentration of nano TiO₂increased, the van derWaals interaction and the effective Hamaker constant decreased, the electrostaticdouble-layers interaction increasingly contributed to the interfacial repulsion, the Lewisacid–base interaction also exhibited a repulsive contribution to the total interactionenergy and the total free energy of interaction exhibited a repulsive contribution. Theseresults are the keys for interpreting the adverse effects of nano TiO₂on the activatedsludge flocs of WWTP.The effects of long-term exposure of nano TiO₂at different concentration on thepollutions removal, physiological/biochemical characteristics and microbial communitystructures were evaluated in sequencing batch reactor. The results suggested that, theNH3-N and TOC removal was remarkable inhibited by nano TiO₂, and the inhibitionwas enhanced along with the increase dosage of nano TiO₂, whereas the biologicalphosphorus removal was unaffected. In accordance with the removal efficiency, theMLVSS and activities of microorganism were effected directly by the nanoTiO₂in theinfluent. For the reason of the ligand exchange, the MLVSS decreased to18.4%and22.9%, and the TTC-ETS decreased19.95%and44.77%as the dosage was25and100mg/L respectively, also the protein and carbohydrate in extracellular polymericsubstances were inhibited.The response of physiological/biochemical characteristics and microbial community structures to nano TiO₂were analyzed by pyrosequencing. The resultsillustrated that nano TiO₂obviously reduced the diversity of microbial community inactivated sludge. The Shannon index was highly decreased after long-term exposure tonano TiO₂, which resulted in the deterioration of activated sludge floc stability. Furtherstudy revealed that the predominance microbial community was changed afterlong-term exposure to nano TiO₂. The response of predominance microbial communitywere consistent with the observed influences of nano TiO₂on biological nitrogen andphosphorus removal, and the differences were found in cluster relation. The effects werefound on the levels at phylum, class and genus, especially on Actinobacteria andActinobacteria which were in charge of nitration and heterotrophism, and the proportionof Proteobacteria was increased.