A field investigation was carried out to examine the seasonal changes and vertical distribution of picophytoplankton in 15 water resource reservoirs in Japan. From the results obtained, the maximum abundance of picophytoplankton was above 10⁵ cells·ml^-1 in all reservoirs where their trophic states were varied from oligotrophic types to eutrophic ones. Picophytoplankton abundance reached maximum in the summer season, and the dominant types were found to be two types of cyanobacterial plankton which contained phycoerthrin (PE) or phycocyanin (PC) as a main photosynthetic pigment. Cyanobacterial picophytoplankton dominancy was related to the T-P concentration of reservoirs water. PE-rich type was dominant in the reservoirs where T-P concentration was relatively low, whereas PC-rich type was dominant in the reservoirs where T-P was relatively high.
Vertical profile of picophytoplankton in reservoirs showed that almost cells were distributed in the surface layers. This observation was different from natural lakes which commonly show abundance peak in more deep layers.
As the abundance of picophytoplankton slightly increase with the increase of T-P concentration, the proportion of picophytoplankton to the total phytoplankton by Chlorophyll-a was varied widely, and showed large values (30-45%) in the oligotrophic reservoirs as comparing with those in eutrophic ones.

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Effect of activated carbon (AC) was examined on biodegradation of organic micropollutants such as fenitrothion, phenol and aniline in water. Degradation curves of organic micropollutants were determined in the presence of AC. Biodegraded quantity in the presence of AC was generally larger than that without AC on each micropollutant, so biodegradation was found to be promoted by AC. Abiotic degradation of fenitrothion was also promoted by the presence of AC. On biodegradation of phenol, maximum consumption rate of oxygen became larger and the induction time became shorter in the presence of AC. The increased oxygen consumption approximately corresponded to the increased biodegraded quantity.

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Biological filter treatment process with contact media such as plastic resins, ceramics etc. were used in water and wastewater treatment. However, there have been few reports on its application to environment restoration.
The purpose of this study was to evaluate the removal efficiency of algae in a polluted pond using biological filter treatment process. Two experimental systems were conducted to remove algae for promoting tansparency of polluted water in Oozutsumi pond, locating at south of Sendai city. One is called as horizontal flow system packed with ringlace as a contact medium, the other is upflow filtration system packed with nonwoven fabric.
It was observed that partial of Chlorophyll-a removed in the system was degraded and preyed by Protozoa and Metazoa attached on the biofilm in both systems. 50% of attached Chlorophyll-a was removed due to back-washing. It was also found that the removal efficiency of diatoms was much higher than that of green algae because of the difference of adhesion potential to biofilm of the two species of algae. In addition, horizontal flow system showed effective to remove green algae.

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We have developed a double tank type intermittent aeration process as a system to perform biological simultaneous removal of nitrogen and phosphorus. This process adopts a time-shared system to freely set anaerobic, anoxic or aerobic condition in the aeration tanks, and specializes the functions of the two aeration tanks perform stable removal of nitrogen and phosphorus.
This system was applied to a pilot plant with a treatment volume of 21.3m³·d^-1, and continuous experiment has been conducted using actual sewage for one year. From the result of this experiment, we obtained the following removal ratios : 97.9% for BOD, 94.1% for SS, 91.0% for T-N, and 85.0% for T-P. Research on one cycle of the experiment proved that ORP bending point is useful as an index of the end of denitrification and the beginning of phosphorus release. The change in time ratios in each biological reaction and Kr value in each reaction tank revealed that high loading operation in the 1st aeration tank allows maximum removal of pollutant components and accomodation of fluctuating inflow loading to some extent, which enables the 2nd aeration tank to be operated with sufficient time to remove these pollutants.

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Industrial wastewaters containing high concentrations of organic substances and ammonia nitrogen, such as leather industry wastewater, are sometimes treated by an activated sludge process in a sewage treatment plant. Such wastewaters tend to raise COD and color in the effluent of an activated sludge process. Refractory organic substance and nitrite build-up are the main causes of COD. It is difficult to reduce COD and color efficiently by the conventional activated sludge process.
We studied a two-stage biological process combined an activated sludge process and a fixed-bed reactor to treat leather industry wastewater efficiently. And the use of ozone was studied to reduce COD and color.
A two-stage biological process could promote nitrification reaction producing nitrate. COD originated from nitrite build-up was not observed. However, the two-stage biological process could not remove color.
Ozone could reduce both COD and color in the effluent of an activated sludge process. However, nitrite build-up worsened the efficiency of ozone oxidation. In view of the economical point, it is important to prevent nitrite build-up in a biological process.

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