The River Godani, a tributary of the River Kakehashi which joins with main stream of the River Kakehashi about 5km downstream, is known for its pollution due to the mining water. Typhoon No.7 passed through Ishikawa Prefecture on September 22 in 1998 with locallized torrential down pour.
In this study, Vie examined the effect of the Typhoon No.7 on those Rivers from the viewpoint environmental factors of the river water and the ecological viewpoint based on the change of the epilithic diatom assemblages on the river bed.
Each of the four surveys <1998-1999> showed a tendency, in its measurement of EC values decreasing from upperstream to downstream in order.
The concentration of heavy metals increased in all sites after 6 months. At each sampling site 6 months after flood, the concentration of Cu was 1.3-2.0 higher, and that of Zn was 1.3-3.3 times greater than those obtained before flood, while the concentration of Cd showed no district difference from those obtained before flood.
The concentration of heavy metals in attached materials was far higher than that of heavy metals in the mud of river bed. This may be due to the fact that the greatest part of attached material consist of epilithic algae (organic materia1) and the rest is silt (inorganic material), while in the case of mud the volume of silt is much greater, than that of residue of epilithic algae. After all weight of epilithic algae per unit volume is small compared with silt, but they absorbs heavy metals. On the other hand, inorganicsilt only absorbs heavy metals but no process of concentration occurs.
Three surveys, B (November 2, 1988), C (December 21, 1988) and D (March 24, 1999) were after flood.
In the survey B, Achnanthes minutissima which has strong tolerance to heavy metals was the most abundant taxon in almost all sampling sites.
It is noticeable that in all sites of D (150 days after flood), the most abundant taxon was A. minutissima. The tempomry change of the most abundant taxon at Sites 3, 4 (cf. Fig.2) is considered to be due to the fact that materials on the river bed easily came off and were carried downstream and pilled up there temporarily.

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Technology to remove nitrogen from wastewater by carrying out a new automatic control of aeration time to an intermittent aeration activated sludge process has been developed by the author. The control system is to measure DO concentration of an aeration tank and to calculate respiration rates of activated sludge. To integrate the respiration rates in one intermittent aeration period, required oxygen demand is calculated. The system controls the aeration times in intermittent aeration activated sludge process to meet required oxygen demand. The control system was installed in g full-scale wastewater treatment plants, which had 54-3, 100 m³/day design flow rate.
This new process made it possible to achieve not only stable and heightened nitrogen removal but also reduced the electric power costs of the blowers.

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Severe outbreaks of cyanobacteria cause serious problems with regard to effective utilization of water-resources. As a means of controlling undesired cyanobacterial growth, reed that lives worldwide could be used. Although a feasibility of controlling cyanobacterial growth using reed exists, the causes of growth inhibition and how the effect of inhibition change are still unknown. In this experiment, extraction solution from reed (ESR) sampled every each season were used in laboratory to confirm allelopathic effects of reed on cyanobacterial growth and were analysed in GC/MS to identify anti-cyanobatcterial allelochemicals. The result showed that the cyanobacterial (Phormidium tenue) growth was significantly inhibited by extracted solution. The correlation between the level of inhibition for P. tenue's growth and the DOC concentration was observed. The seasonal changes of DOC concentration in extracted solution from reed was confirmed, too. It was suggested that fatty acids such as Pelargon acid and Myristic acid in extracted solution from reed contribute to allelopathic effects on the growth of P. tenue probably.

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Simultaneous nitrification-denitrification under fixed constant dissolved oxygen (DO) condition in a single reactor was examined by using two different carriers, polyacrylamide-gel carrier and cellulose carrier immobilizing nitrifiers and denitrifiers, respectively. The DO condition enabling the highest simultaneous nitrification-denitrification rate was found between 0.5 and 0.75 mg/l. When DO concentration of culture broth was maintained at 0.5 mg/l, the simultaneous nitrification-denitrification was successfully realized in a single reactor as designed, resulting in the apparent nitrogen removal rate corresponding to 83% of the theoretical value.

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