A solution of commercial humic acid （80 mg/L, 28.5 mg－C/L） was subjected to a biodegradation test following ultrafine bubble ozonation. Semi-batch ozonation for 20 min （80 mg－O₃/L） removed 48% of the total organic carbon （TOC）, decreased the color unit from 950 to less than 50, and increased the ratio of biochemical oxygen demand （BOD₅） to TOC from 0.16 to 0.73 in the solution. Activated sludge microorganisms removed 30% of TOC from the untreated solution, but caused no marked decolorization. A 14－day biodegradation test following the 20－min ozonation revealed the TOC removal of more than 90%, but the color unit remained as 75, suggesting accumulation of colored metabolites. Three-dimensional excitation-emission matrix fluorescence spectral analysis revealed that ozonation shifted peaks at Ex200－300/Em450－600 and Ex450/Em540 in the humic acid solution, respectively, to peaks at Ex200－250/Em300－450 and Ex320/Em430. During biodegradation, those peaks decreased, but a peak at Ex230/Em450 remained, presumably representing colored metabolites.

Biological nitrification-denitrification process is cost-effective and energy-saving way to treat nitrogen wastewater. Many early studies have reported the effects of low temperatures on nitrogen removal performance, but not the effects of high temperatures. In Japan, it has been confirmed that the maximum temperature in summer exceeds 40℃. In the present study, we evaluated the effect of high temperature on nitrification performance in a continuous test system using two different types of carriers such as a polyvinyl alcohol sponge carrier （PVA carrier） and a polyethylene tubular carrier （PE carrier）. Consequently, no significant effect was observed when water temperatures was rapidly increased to 35, 38 and 40℃. However, when the water temperature was raised to 43℃, an increase in the nitrite concentration in the effluent was confirmed. Moreover, the nitrification activity decreased significantly when the water temperature was further raised to 45℃. As a result of the test of gradually raising the water temperature from 35℃ to 45℃ for about 4 months, the effluent nitrogen concentrations were not affected up to 43℃. However, effluent ammonium concentration was rapidly increased when the water temperature was raised to 45℃. Microbial community analysis revealed that the difference of microbial structure among two carriers, and response to the temperature changes.

Microplastics have received increasing attention as substances of potential risk due to their adverse effect on ecosystems and human health in recent year. Membrane bioreactors (MBRs) have excellent microplastic removal performance compared to conventional WWTPs. Meanwhile, there is a possibility that the membrane materials themselves become the source of microplastics when they deteriorate. Therefore, it is important to consider not only the antifouling performance for wastewater treatment but also the mechanical durability of the membranes to reduce microplastic production; thus, promoting application of MBRs. In this study, the mechanical durability and antifouling performance of three kinds of membranes, chlorinated polyvinyl chloride (CPVC), polytetrafluoroethylene (PTFE), and polyethersulfone (PES) used in a lab-scale submerged MBR for almost two months, was explored. The experiment was carried out in a lab-scale submerged MBR with effective working volume of 6.8 L. Synthetic wastewater was prepared with D-glucose, meat extract, polypeptone, and inorganic salts, and fed to the reactor. The mixed liquor suspended solids (MLSS) was constantly maintained within 11000-12500 mg/L. Significant breakage and rupture on the surface of the PES membrane and notable changes in the parameters such as pore size and surface roughness related to the membrane structure were observed through MBR operation. Contrarily, for the CPVC and PTFE membranes, only a slight change in the membrane structure and properties was observed. These results indicated that the PES membrane was more susceptible to damage by the shearing force with aeration for MBR than the other membranes. Therefore, the durability of the PES membrane was the lowest among the membranes studied, indicating high microplastic production risk, even though all three membranes have the same antifouling performance. This is the first report of changes in the membrane characteristics and morphology related to mechanical durability and the membrane fouling problem under MBR operation.

The characteristics of vegetative cell growth and akinete formation in the cyanobacterium Dolichospermum planctonicum were examined using three different media (WC, CB, and CT media), and two different methods for the recovery of akinetes, i.e. the lysozyme method and the sedimentation-separation method, were compared to evaluate which way was efficient. The equilibrium vegetative cell and akinete density were higher for the WC medium than those for the CB and CT media (p < 0.05), exhibiting ca. 1.23 × 10⁷ ± 1.58 × 10⁶ cells・mL^－1 and 1.60 × 10⁴ ± 3.46 × 10³ akinetes・mL^－1, respectively. These results suggest that the WC medium was appropriate for the cultivation of D. planctonicum. The lysozyme method and the sedimentation-separation method using a separatory funnel were compared to recover the akinetes of D. planctonicum. The results showed that the former method was found to be more successful in separating the akinetes from the vegetative cells, and the recovery rate was also higher (the lysozyme method: 66.7%, the sedimentation-separation method: 55.0%). The results obtained in the present study would be useful to elucidate the mechanisms of akinete germination and/or akinete recruitment from sediment, which could contribute to suppress the cyanobacterial bloom occurrence in the eutrophic lakes.