Titanium dioxide (TiO2) nanopowders at different concentrations (0–50 mg L−1) were injected into an aerobic-sequencing batch reactor (SBR) to investigate the effects of long-term exposure to nanoparticles on bacterial and protozoan communities. The detection of nanoparticles in the bioflocs was analyzed by scanning electron microscopy, transmission electron microscopy, and energy-dispersive x-ray spectroscopy. The SBR wastewater experiments were conducted under the influence of ultraviolet light with photocatalytic TiO2. The intrusion of TiO2 nanoparticles was found both on the surface and inside of the bioflocs. The change of microbial population in terms of mixed liquor-suspended solids and the sludge volume index was monitored. The TiO2 nanoparticles tentatively exerted an adverse effect on the microbial population, causing the reduction of microorganisms (both bacteria and protozoa) in the SBR. The respiration inhibition rate of the bacteria was increased, and the viability of the microbial population was reduced at the high concentration (50 mg L−1) of TiO2. The decreasing number of protozoa in the presence of TiO2 nanoparticles during 20 days of treatment with 0.5 and 1.0 mg L−1 TiO2 is clearly demonstrated. The measured chemical oxygen demand (COD) in the effluent tends to increase with a long-term operation. The increase of COD in the system suggests a decrease in the efficiency of the wastewater treatment plant. However, the SBR can effectively remove the TiO2 nanoparticles (up to 50 mg L−1) from the effluent.

No abstract

The biodegradation of paraquat was investigated using immobilized microbial cells on nanoceramics fabricated from nanoscale kaolinite. Pseudomonas putida and Bacillus subtilis, which degrade paraquat, were immobilized separately on nanoceramics (respectively called ICnc−P and ICnc−B). The attachment of bacteria to nanoceramics resulted from electrostatic force interactions, hydrogen bonding, and covalent bonding (between the cells and the support materials). The initial 10 mg L−1 concentration of paraquat in water was removed by the adsorption process using nanoceramics at 68% and ceramics at 52%, respectively. The immobilized cells on the nanoceramics were able to remove approximately 92% of the paraquat within 10 h, whereas the free cells could only remove 4%. When the paraquat was removed, the cell−immobilized nanoceramics exhibited a significant decrease in dissolved organic nitrogen (DON). ICnc−B was responsible for 34% of DON biodegradation, while ICnc−P was responsible for 22%. Ammonia was identified as the end product of ammonification resulting from paraquat mineralization.

No abstract