Twenty activated sludge samples were collected from 15 wastewater treatment plants in 4 prefectures (Hokkaido, Saitama, Tokyo, and Okinawa) in each season throughout 1 year. They were analyzed by Fluorescence in situ Hybridization (FISH) technique with 6 oligonucleotide probes (targeted for Proteobacteria α-, β-, γ-subclasses, Gram positive high G+C content group, Cytophaga-Flavobacterium, and Eubacteria), and image analysis using confocal laser scanning microscope (CLSM). Experimental results showed that: In every season Proteobacteria was predominant in more than half samples and among Proteobacteria, α- and β-subclasses were predominant in almost all samples. Any clear relation between bacterial community and geographical condition or treatment method was not observed. Either, any clear correlation between water qualities and bacterial population was not observed. But some seasonal change was remarkable; increase of α-subclass from winter to summer and decrease from summer to winter, and the opposite tendency of HGC group.

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Phosphorus removal from small-scale domestic wastewater treatment systems by means of an electrolytic bath using of iron electrodes was examined.
We discovered, however, that an iron oxide layer forms on the surface of the iron electrodes, leading to a decreased phosphorus removal ratio.
To solve this problem, we discovered that specific electrolytic conditions can inhibit the formation of this iron oxide layer (FeOOH, Fe₃O₄) on the iron electrodes. One condition is the Fe:P ratio. An Fe/P ratio exceeding 1.5 inhibits the formation of this iron oxide layer. Another condition is the concentration of nitrate ions and nitrite ions. We have shown that the iron oxide layer forms when the nitrate nitrogen concentration is 60mg · l^-1 or the nitrite nitrogen concentration is 10mg · l^-1. However, a polarity reversal period of 24 hours inhibits the formation of the iron oxide layer when the nitrate nitrogen concentration is 60mg · l^-1 and the iron oxide produced by nitrate ions and nitrite ions is broken down by the chloride ion at a concentration exceeding 60mg · l^-1.

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Eutrophication proceeds in many lakes, marshes and ponds with an unusual growth of algae so that it became a serious problem in especially urban areas. Though many approaches were made to improve the eutrophicati on in the past, e.g., oxidation treatments represented by ultraviolet radiation and ozonation showed rather high effect to reduce algae. Also, an electric disinfection treatment represented by use of electrolysis to produce strongly acidic water is attracting more attention than before, because of strongly acidic and to produce a free chlorine.
The authors performed an experimental study focusing on the electrolytic oxidation treatment of algae in lake and marsh water, to examine its effect on the disinfection of algae using a batch- and circulation-type apparatus of laboratory scale.
As for the electrolytic oxidation treatment, it showed a great effect on the disinfection of algae. It was found also that there was a correlation between the effect and the quantity of electricity. It was found, further more, that a free chlorine produced by the electrolytic oxidation enhanced the disinfection of algae. On a continuous electrolytic oxidation treatment, the electrolytic cell used for the experiment made more than 24s · A in contact reaction time necessary.

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In order to reuse the advanced treatment water, the experiments of simultaneous removal of nitrogen (T-N) and suspended solids (SS) were carried out by using downflow process. The hydrogen donor used for denitrification reaction was methanol. The denitrification layer used in the experiments were the burned aggregate and anthracite. Also, the filtration layer used was usually sand on the marketed. The ability for both denitrification and filtration were examined, and then mass balance of SS and recovery of denitrification after backwashing operation were investigated. Furthermore, the accreted denitrification bacteria in denitrification layer was counted by most probable number (MPN) method.
The difference of performance for two kinds of denitrification packings was not observed. Under 0.1hr of HRT, 0.3 mg · l^-1 of SS and 1mg · l^-1 of T-N in effluent were attained. However, the increased biomass of denitrification bacteria was very much at above described HRT. Feed methanol for denitrification did not detect in effluent. In addition, in the cause of the flow of 2 times for packing volume, the denitrification after backwashing operation was recovered.

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Mass balances of nitrogen, phosphorus and organic carbon during irrigation period in a rice paddy in Shiga Prefecture, Japan, were determined in detail for three years. Size of the rice paddy is 100m×30m. Irrigation water is supplied from Lake Biwa through a pipeline irrigation system. Observation results are as follows :
1) Nitrogen and phosphorus outflows from a rice paddy were considerably influenced by the amount of precipitation.
2) Nitrogen and phosphorus outflows in May were the largest during irrigation period, i.e., those outflows in May occupied 45-55% of the total outflows during irrigation period. Net outflows of nitrogen and phosphorus in May occasionally exceeded the total net outflows during irrigation period because net outflows in some other months had negative values. Therefore, prevention of excessive nutrient outflows in May is important for achieving significant reduction in nutrient loading from rice paddies.
3) Saving the amount of intake water is important, especially in May, for reducing nutrient loading from rice paddies. Controlling the amount of applied fertilizer corresponding to the growth of rice is also important.

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To automate plankton examination, we have developed a plankton monitor that uses flow-type video imaging equipment and an image processor. This monitor was operated for 11 successive days (from 25 Aug. to 4 Sept. 1998) and had the following results. (1) Monitor counts agree well with microscopic examination counts of non-centrifuged samples (micro:monitor=1 : 1.4). (2) We also performed multiple regression analysis between the monitor line-particle counts and meteorological data (solar radiation, precipitation, temperature, wind speed). The line-particle counts had a high correlation with the level of solar radiation and precipitation measured two days previously (multiple correlation coefficient: 0.98).

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