Nitrogen compounds, represented by ammonia, are one of the most critical pollutants in water bodies because of their role in eutrophication and their toxicity to aquatic organisms. Recently, the biological treatment of ammonia in water resources has been rapidly improved and being applied to numerous water treatment plants, as more and more knowledge has been accumulating on microbial participation of ammonia-utilizing organisms. However, most of the researches on biological removal of ammonia focused on waste water treatment plants (WWTPs) or pilot/laboratory water treatment reactors, where ammonia concentration in the influent waters is usually from 4 to several hundreds even thousands of mg N/L. By far, knowledge of ammonia removal performance with low ammonia load (especially when less than 2.0 mg N/L), such as in drinking water treatment plants (DWTPs), is still limited. Thus in this research, we sampled biofilm from a practical biological DWTP and carried out ammonia removal tests in lab with low ammonia inflow (1.0 mg/L) under dark condition. Our results showed that ammonia can be effectively removed within 2-day incubation when temperature was as low as 11℃, while no significant ammonia removal could be confirmed at 7℃. Molecular analysis showed that canonical ammonia oxidizers (AOA and beta-AOB) may not be responsible for the observed ammonia abatement in the sampled DWTP as well as in laboratory incubation vials. Instead, microbial ammonia assimilation or comammox process may be the probable ammonia removal pathway in low ammonia conditions such as DWTPs.

 Membrane bioreactors (MBRs) are promising treatment techniques, especially for wastewater, including dense suspension and high salinity. However, membrane fouling is still a critical problem for continuous application. The hydrophilicity of a membrane has so far been considered as one of the important factors contributing to the fouling phenomena. In general, a hydrophobic membrane has a higher development on the fouling than hydrophobic one, however, there is no conclusion in this matter because many contradictory results have also been reported. In addition, there have been only a few studies to reveal the influence of the only membrane hydrophilicity on fouling development in an MBR for a long operation period. In this study, therefore the influence of the only surface hydrophilicity of the membrane on fouling development was investigated using a lab-scale MBR with polytetrafluoroethylene (PTFE) flat-sheet membranes to confirm the influence of membrane hydrophilicity on the fouling development. No remarkable difference in the change of trans-membrane pressure was observed between hydrophilic and hydrophobic PTFE membranes, indicating that the hydrophilicity of the membrane has little influence on the fouling phenomena. The relationship between hydrophilicity and pore fouling resistance were slightly suggested; however, the dominant factor in membrane fouling was cake layer resistance. It was indicated that the adsorption of protein-like compounds, which were present in the suspension liquid, inside the membrane contributed to the pore fouling resistance from the results of extracellular polymeric substances measurement and three-dimensional excitation-emission matrix analysis.

 This research focused on the impacts of environmental policies on the conservation and improvement of urban river water quality in Mongolia. Wastewater contaminated by heavy metal (chromium) from the thriving tanning industry has been recognized as a problem in Ulaanbaatar, the capital of Mongolia, and a facility for pretreatment of chromium-contaminated wastewater was introduced in 2016. To verify the impact of this facility on the water quality of the urban area surrounding the Tuul River, and to assess the current status of potential water pollution, a long-term survey (2014－2018) was conducted using data from 10 monitoring points located upstream and downstream of the wastewater discharge point. Results showed that the concentrations of inorganic nitrogen, phosphorus, and organic matter (biochemical oxygen demand and chemical oxygen demand) were extremely low at points upstream of the point of wastewater discharge from the treatment plant in Ulaanbaatar. Downstream of the point of wastewater discharge, the chromium concentration decreased following commissioning of the pretreatment facility, indicating that the facility is effective. However, concentrations of organic matter, inorganic nitrogen, and phosphorus increased rapidly, indicating inadequate treatment at the plant, especially in winter. Therefore, new treatment measures are necessary and the formulation of appropriate environmental effluent discharge standards and safety standards are required for proper operation of wastewater treatment plants in extremely cold regions.