Aquatic humic substances (AHSs) from the eutrophic Lake Kasumigaura were isolated using XAD-8 resin. The effects of these isolated AHSs on the growth of Microcystis aeruginosa cultures were evaluated. M. aeruginosa was isolated from algal blooms in Lake Kasumigaura and grown in a chmically defined medium under iron limitation. The production of siderophores, iron-specific complexing agents, by M. aeruginosa was also examined.
Under iron limitation, M. aeruginosa was confirmed to produce hydroxamate-type siderophores; however, they were not effective to enable substantial recovery of the growth rate. The fulvic acid (lower molecular-size fraction of AHSs) isolated from Lake Kasumigaura was found to significantly inhibit the growth of M. aeruginosa. The fulvic acid at 2 mg dry weight l^-1, the same level as in the lake, significantely inhibited the growth of M. aeruginosa even though siderophores were produced. This inhibition was probably due to a deficiency of iron caused by iron complexation with the fulvic acid. These results suggest that AHSs, through their iron complexation reactions, may play an important role in formation of M. aeruginosa algal blooms.

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Road runoff in rainy days is assumed to include sediment having organic compounds originated from mobile exhaust. We evaluated genotoxicity and ecotoxicity of these compounds by using bacterial assay umu-test, growth inhibition test with algae and acute toxicity test with Thamnocephalus.
The effluent from a sewage treatment plant receiving runoff water and runoff from a road in the rainy days were collected. The elute of their particulate and dissolved portions were found to have geno- and ecotoxicity. These toxicities were also found in dust in a collector of tunnel and on the road sediment.

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Testacealobosia, Arcella vulgaris is well known as the typical protozoa found in the activated sludge and biofilm when nitrification is in progress. The effects of good source, water temperature, pH and phosphate buffer concentration on specific growth rate of A. vulgaris isolated from activated sludge were examined. A. vulgaris was successfully cultured when Chlorella powder suspension media and sludge bacteria were used as food sources. The growth parameters wwere determined using Chlorella powder suspension media. The specific maximum growth rate and half-saturation constant were 1.05d^-1 and 1.4TOCmg·l^-1, respectively. The growth of A. vulgaris was observed from 10°C to 36°C with optimal growth at 32°C. A. vulgaris was able to grow when the concentration of phosphate buffer was higher than 2/75M and pH value ranged from 4.2 to 9.0. The results show that food concentration and water temperature are the important parameters for the growth of A. vulgaris.

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Characteristics of soluble organic compounds which were accumulated in the activated sludge process with ultrafiltration for solid-liquid separation were evaluated through bench-scale experiments of artificial wastewater treatment. In one experiment (Run I), a sheet of ultrafiltration membrane was used during the whole experiment. However, in the other experiment (Run II), frequent replacement of ultrafiltration membrane was performed to control the accumulation of the compounds in the second stage of the experiment after around one month.
In the both cases with and without replacement of the membrane, TOC concentration and E²⁶⁰ value of the filtrate increased to each maximum value. However, in Run II with frequent replacement of the membrane, TOC concentration and E²⁶⁰ value decreased, and oxygen uptake rate for substarate metabolism was recovered to a certain level.
In Run I without replacement of the membrane, effects of the organic compounds on the growth of E. coli was examined to evaluate the potential effects of membrane separation on the growth of enteric bacteria. Those compounds had the actions to shorten a lag time and to suppress maximum biomass. As for the actions to maximum growth rate, there were two groups of compounds which accelerate and suppress. And the membrane blocked the compounds to suppress maximum growth rate and maximum biomass, but a portion of the compounds to shorten lag time passed through the membrane.

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People usually evaluate the amenity of water environment by transparence to look at water. Water transparence is measured by transparency or transparency by cylinder test. However, these methods have some defects such as difficulties in measuring at shallow and clean waters, because transparency is limited by water depth and transparency by cylinder test is limited by length of a cylinder. Moreover, the lack of objectivity is pointed out, since transparency measuring is due to personal sensitivity. To conquer these problems, we designed a measuring method of horizontal transparency, and developed a measuring equipment by using an eye-test chart and a waterproof camera. We applied this method to water quality investigation of Matsushima Bay, Miyagi prefecture, and studied the characteristics of horizontal transparency comparing with transparency, transparency by cylinder test and so on. The results obtained were as follows; (1)Horizontal transparevcy has superior objectivity, because evaluation by plural number of people diminish personal errors. (2)Horizontal transparency is possible to express water transparence quantitatively without any limits, though conventional methods cannot apply to relatively clear and shallow waters. (3)Horizontal transparency has a very good correlation between not only transparency but also turbidity and suspended solids that are mainly affect to transparency. (4)The sense of visitors and fishermen about the water quality of Matsuhima Bay can be represented by horizontal transparency.

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A questionnaire survey was conducted in Kobe and Ashiya to find out the situation of water acquirement during a water supply suspension period following the Great Hanshin-Awaji Earthquake. The main results obtained from 406 respondents are as follows : (1) Personal water acquirement quantity in the stricken area was 1-30, 5-50 and 10-60l·d^-1·ca^-1, respectivery for the phase immediately after the disaster, for the intermediate and for that just before the restoration of water supply. (2) Tha variety of water sources is quite important for the water quantity obtained in such extraordinary situations, and the sources of wells and storage tanks especially well contributed to the increase of the amount. (3) Family size had an effect to increase the water acquirement quantity in each family, but the quantity based on each person tended to decrease with the increase of family size. (4) Residential location, type of house and kind of water source were also factors affecting the personal water quantity.

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The purpose of this study was to idntify the controlling factors to construct tidal flat ecosystems having similar characteristics as natural ones. We transplanted the soil in a constructed tidal flat to a natural one and vice versa. Parameters monitored after these transplantations were silt content, organic matter, bacterial population and oxidation-reduction potential. Moreover, the relationship among silt content, organic matter and bacterial population was investigated by laboratory column experiment.
The silt content, organic matter, bacterial population and vertical profile of oxidation-reduction potential in the soil transplanted from the constructed tidal flat to the natural one changed to similar values to those in the natural one. On the contrary, all the parameters for the soil transplanted from the natural tidal flat to the constructed one changed to similar values as those in the constructed one. The silt contents in these two transplanted soils were in proportion to the organic carbon contents and bacterial population. Similary, the bacterial population in laboratory column experiment increased with the increase in silt and organic matter contents.
It seemed to be important to select a place to enhance accumulative of silt and/or to maintain the silt content by hydrodynamical control of seawater in order to construct a tidal flat having similar characteristics as natural one.

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Dynamic behavior of Nitrosomonas cells immobilized in PVA gel pellets was investigated by fluorescent in situ hybridization (FISH) of oligonucleotide probes. Two laboratory-scale reactors were seeded with PVA-immmobilized Nitrosomonas cells, and then operated for 160 days by feeding with either a synthetic wastewater containing ammonium solely or a synthetic wastewater composed of ammonium and organic source (acetate). The nitrogen loading on the first reactor (organic-free) was varied from 0.2 up to 0.6kgN·m^-3·d^-1 by stepwise reducing hydraulic retention time, while the second reactor was operated by varying the C/N ratio of the feed from 0 to 0.8.
The first reactor (organic-free) achieved 99% of ammonia removal at 300mg-N·l^-1·d^-1, and ammonia-oxidation activity per unit pellet volume remained unchanged above 4.5 mg-N·ml^-1·d^-1 throughout 160 days operation. On the other hand, a severe deterioration in ammmonia oxidation was observed in the second reactor (organic-fed) when the feed C/N ratio was increased to 0.8. For the both reactors, the presence ratio of Nitrososnonas cells to DAPI-stained total cells decreased to below 2% within the initial 90 days operation, regardless of the pressence of organic source in the feed.
Nitrosomonas cells were present only up to 50μm-depth of the pellets in the form of large cell clusters. The cluster-forming growth of Nitrosomonas tended to break the lattice-structure of PVA gel material, causing the disappearance of these bacteria from the pellets.

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The number of fecal coliforms in several spots of the Umeda and Nanakita rivers in Sendai City wwere estimated by inoculating the sample onto MacConkey agar medium, incubating them at 44.5°C for 24hr and counting the number of the red colonies formed. The numbers of fecal coliform varied depending on the sampling spot and date in both rivers. Greater numbers of fecal coliforms were found in the middle sections of both rivers compared to the upper and lower paarts of both rivers. Quite a high percentage of drug resistant strains of E.coli (15-35% of the isolated strains of E.coli) were detected in both rivers and some of the drug resistant E.coli were multiple drug resistant.

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