This research was carried out to appreciate a slow sand filtration treatment by an investigation of suspended matter distribution in sand beds of Ishifune and Someya slow sand filters. The core-sampler was inserted to take suspended matter in slow sand filter beds during the filter operation when the filters were easy to clog in winter. The following results were obtained.
From the depth distribution of the Total Organic Carbon, Someya slow sand filter detained larger amount of suspended matter than Ishifune slow sand filter. And suspended matter was detained until deeper layer of the sand column at Someya water works.
The depth distribution of the Chl/SAND indicated the nearly same profile as TOC distribution.Pheophytin content in the sand column at Someya water works was several times larger at the deeper layer in the sand columns than Ishifune slow sand filter. From the depth distribution of the Chl/TOC ratio, Someya slow sand filter suggested that algae which had brought by inflow water at early times of filter run detained at the upper sand layer. Total cells number of the algae in the sand columns at Someya slow sand filter were from sevral to ten times higher than Ishifune slow sand filter.

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The differences of algal mat development on the slow sand filter beds in shallow ponds (110 cm depth) and in deep ponds (171 cm depth) were studied at Wakata water works, Takasaki city. The algal mat development in shallow ponds was high growth rate and marked a high standing mass. This was remarkable in summer. Decrease of algal biomass was observed after the peak biomass on 10 days in shallow ponds. It was estimated that this decrease was caused by the grazing of Chironomidae larvae. Colony size of the length of filamentous diatom of Melosira was measured to evaluate the health condition of diatom. Empty shells and small numbers of cology were abundant in deep filter beds. And chlorophyll a content to total pigments of algal mat in shallow ponds was higher than that in deep ponds. It seems that active growth of filamentous diatom in a shallow filter pond keeps an aerobic condition in the filter bed.

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Ten strains of myxobacteria were isolated from eutrophic lakes, which were identified as Myxococcus. They contained geosmin in the cell and excreted it in the growth medium. These observations suggest that myxobacteria are the cause of the earthy odour of the eutrophic lakes.

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We studied microbial population shifts in laboratory-scale synthetic-waste activated sludge from plant-scale sewage sludge on the basis of respiratory quinone profiles. The laboratory sludge reactors were seeded with the sewage sludge and operated on a fill-and-draw basis in a 24 h batch cycle with either raw domestic sewage or each of three different synthetic wastewaters containing acetate, glucose, skim milk, and/or peptone as a primary component. After two months of acclimation, the quinone compositions of the laboratory sludges were analyzed compared with the seed sludge. Numerical analysis of quinone profiles showed that there was no significant difference in population structures between the seed sludge and the laboratory sludge loaded with raw sewage, while significant population shifts occurred in the three synthetic-waste laboratory sludges. These results suggest that laboratory activated sludge loaded with synthetic wastewater can not be regarded as a model of plant-scale sewage sludge in their microbiological aspects.

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The predominant methanogens in an anaerobic wstewater treatment plant were studied by using a molecular technique without isolation and cultivation. The 16S rRNA genes from the bulk DNA of the anaerobic sludge were amplified by PCR, cloned, and reamplified. Of 30 clones isolated and tested, 24 clones contained a 16S rDNA insert. These positive clones were divided into four ribotypes on the basis of restriction fragment length polymorphism (RFLP) patterns with Hae III. The RFLP pattern of the most abundant ribotype (designated ribotype 1) was almost the same as that of Methanosaeta soehngenii which was computer-predicted and/or experimentally obtained. This was also supported by the results of RFLP analyses with HhaI and SmaI. Phylogenetic trees for methanogens was constructed on the basis of 16S rDNA sequences and 16S rDNA-RFLP patterns. Although there were some differences in branching patterns between the two trees, the RFLP-based tree was suggested to be used roughly as a model showing natural phylogenetic relationships among methanogens. The results of this studyshow that 16S rDNA-KELP analysis with PCR cloning has a promise to identify the predominant methanogens in anaerobic wastewater treatment systems.

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For the purification of urban river water polluted with grey water, a new method applying various kinds of contact materials and aquatic plant as nutrient absorber was invented and its purification capabilities were experimentally made clear. Actual purification plant, whose working volume was 26.4m³, was consisted of contact oxidation tanks and aquatic plant cultivation tank. Oxidation tanks were composed of wavy contact material and porous concrete block. Water lettuce (Pistia stratiotes) was cultivated in an aquatic plant cultivation tank. This purification plant was continuously operated under TOC loading rate of 50-170g/m³/d. TOC was removed at the efficiencies of about 40% and SS and anionic surfactants were effectively removed. Cultivation of water lettuce was succeeded by using the effluent from contact oxidation tank. 30kg (wet weight) of water lettuce were harvested from aquatic plant cultivation tank whose cultivation area was only 2.16m². Purification of polluted river water using contact materials and aquatic plant was experimentally proved to have a high application potential.

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In the River Yoshino and its tributaries, 30 samples of attached diatom assemblage on the river bed were collected and some physicochemical values of river water in each sampling site were measured in September and October 1996 and February 1997.In this study, the following results were obtained.
1. The DAIpo values ranged from 55 to 91 in this river system, indicating that the degree of water pollution at almost all sites corresponds to α-oligosaprobic in the former saprobic level.
2. From the numerical water pollution chart for this river using the DAIpo value of each sampling site, the main course of this river was classified into next three course.
(1) Clean upper course from site 1 to site 7, DAIpo values over 80.
(2) Clean middle course from site 8 to site 17, DAIpo values from 70 to 79.
(3) Polluted lower course from site 18 to site 20, DAIpo values bellow 70.

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