The bottom sediments from the Suimon River polluted by the effluent of a chemical plant were analyzed for mercury and other heavy metals, and the surface areas of sediments were measured. The relationship between mercury concentrations and specific surface areas of sediments in each sampling station could be represented by the following equation.
M = C exp (kS)
where M is mercury concentration, S is specific surface area, and C and k are the constants. Concentrations of cadmium, lead and copper also correlated significantly to specific surface areas of sediments. The C -value became larger with increase of ignition loss, and it was in the order copper > lead > mercury> cadmium for sediments rich in ignition loss. The k-value decreased with increase of ignition loss, and it was in the order mercury > cadmium≥lead > copper for sediments poor in ignition loss. But there were little differences of k-value among the metals in sediments rich in ignition loss.

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The physical characteristics of activated sludge flocs cultured under various operational conditions were investigated using the structure model previously proposed.
Experimental results are summarized as follows :
1) Nitrogen deficiency in fill and draw culture resulted in the increase of loosely microorganisms-occupied flocs and the increase of Sludge Volume Index (SVI). However, the continuance of the fill and draw culture changed the floc structure into densely microorganisms-occupied one and lowered SVI.
2) Phosphorus deficiency in fill and draw culture resulted in the decrease of floc size and floc density, but the remarkable increase of SVI was not observed. The flocs had loosely microorganisms-occupied structure.
3) As substrate loading was increased in fed batch culture, floc size increased by the extreme growth of filamentous microorganisms. The SVI value exceeded 300.
4) As substrate loading was increased in fill and draw culture, flocs were disrupted into small particles. Although the SVI value increased, filamentous microorganisms were not observed.

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Organic carbon balance model was utilized to describe the variations of SS, DOC and sediment in urban polluted rivers. This model incorporates dispersion, convection, sedimentation, aerobic decomposition, anaerobic decomposition and growth of benthic biomass.
The calculation based on this model is compared with the observed values in the Nogawa River - one of the tributaries of the Tama River - a shallow and polluted river with approximate flow rate of 0.46 m³/sec at midreaches.
The model shows that considerable fraction of suspended solid is accumulated in sediment of the river. This is the reason why apparent high selfpurification constants are observed in midreaches. The sediment is flushed out during showers and heavy rains. Run off of organic carbon (3.3 ton) was observed during a shower on July 13, 1981. The estimated value from the model reasonably explains this result which assures the plausibility of the model proposed.

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Deterioration of water quality in a shallow and eutrophicated river is caused by respiration and detachment of attached algae on river bed (which is refered to as Selfpollution). A model based on longitudinal inorganic carbon balance is proposed to account for selfpollution rate in such urban polluted rivers. By applying this model to the Nogawa River (a branch of the Tama River), it is found that the alkalinity in polluted rivers is not constant because of the diurnal and longitudinal fluctuations of NH⁺₄·N, NO^-₂·N and NO^-₃·N concetration.
The material balance reveals that about 347 kg/ day (in summer) or 163 kg/ day (in winter) of inorganic carbon is fixed by benthic algae in the midreaches (10 km) of the Nogawa River. If all of the fixed carbon becomes an organic carbon represented by glucouse (C₆H₁₂O₆), this amount corresponds to 925 kg BOD per day which is equal to BOD discharge of as much as 23000 peoples.
Thus it is of importance to control benthic algal growth for the purpose of reclamation of water quality in shallow urban rivers.

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Developement of phosphorus removal process to prevent water area from eutrophication has been carried out by many workers.
Among conventional methods, flocculation and sedimentation process has been employed widely. This process, however, produces large amounts of sludge and has many problems in the treatment of sludge.
Therefore we have investigated and developed the phosphorus removal process employing crystallization, which can minimize the amounts of sludge.
Application of this process to various wastewaters were studied by using laboratory and pilot scale plants.
The results are summarized as followed.
In case of application to sewage and night soil with pilot plants, this process demonstrated excellent performance and sludge production was less than one fifth compared with flocculation and sedimentation process by alum.

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This report describes the experimental procedure and the measurement of oxygen solubility (dissolved oxygen concentration with air) in pure water, which is used for the calibration of dissolved oxygen meters. The solubility in the region of 0-40°C C was measured by means of modified Winkler titrimetric technique in which the iodine volatilization was controlled.
Experimental result showed that the solubility c₅ (mg/l) at temperature t (°C) was expressed with following polynominal equation and its accuracy was better than ±0.4 %.
c₅ = 14.536- 0.4049t+ 8.520×10^-3t²-1.123×10^-4t³ + 6.34×10^-7t⁴.
The influences, of the iodine volatilization, the atmospheric pressure, and dissolved oxygen in reagents on the measured value were discussed and the result was compared with the previous works.

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