In the previous paper, R. filter GMDH correlation (coefficient was used as a criterion function for selection.) was presented to predict effluent quality from the sewage treatment plant in terms of influent quality and running condition.
In this paper, it was recognized that good effluent quality was attained under the condition in 80 SVI and 1700 mg/l MLSS as the result of investigating the influence of the input parameter to the effluent quality.
Frequency distribution curves of the input and output data were shown to investigate utility of prediction medel. For the similar influent quality, effluent quality observed under the conditions suggested by the prediction model is better than that under the other conditions.
Prediction model by R. filter GMDH with data in a limited period could not be well applied to period without revision. However, provided that the prediction model is remodeled by the method of least squares, it could be applicable to extended objective period for the prediction TRSe (transparency of effluent), SSe (suspended solid of effluent).

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Effects of mixing operations of jar test on the turbidity removal by polymeric flocculant were studied experimentaly. The significance of the operating conditions such as the duration of flocculant injection, the stirrer speed, the mixing time and the combination of rapid and slow mixing operations.
The conclusions are summarized as follows :
1. The condition of flocculant injection such as the injection position and the duration of injection should be clearly defined so as to secure the reproducibility of the test.
2. As the jar test is affected greatly by either the mixing intensity or the mixing time the results of the test should be interpreted in terms of not only the amount of energy input but also the scheme of mixing operation.
3. Under the condition of the equal amount of energy input the rapid and slow mixing operations should be in order.
4. Under the above condition there exists an optimal time distribution to the rapid and slow mixing operations.

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Operating characteristics of an air-lift type tubular wastewater treatment contactor were quantitatively investigated. First, the liquid circulation rate by the air-lift action was predicted by using the head balance equation and correlated with the air flow rate sparging into the inner tube. Then, dissolved oxygen concentrations in tank were predicted for two cases where the oxygen transfer in liquid phase to the microbial film was rate controlling and where the oxygen supply rate carried along with circulating liquid to the supporter part of the microbial film was rate controlling.
The power economy, which was defined as the amount of oxygen supply per unit power needed to air sparging into the inner tube were calculated and correlated with the oxygen demand per unit surface area of the microbial film and that per unit volume of the apparatus.
It was concluded from the view of the power economy characteristics that the tubuler contactor was not suited for the ordinary secondary treatment of wastewater and should be applied for the tertiary treatment.

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The nitrification and removals of NH₃-N, NO₂-N and NO₃-N by activated sludge were examined.
1) When NH₃-N was added, NO₃-N accumulated with correspondence to the decrease of NH₃-N. When glucose or sodium acetate was added simultaneously, NH₃-N and Inorganic-N (total amounts of NH₃-N, NO₂-N and NO₃-N) decreased rapidly. When xylose was added simultaneously, the decrease rate of these substances was not larger than those with glucose or acetate.
In alkaline range, NH₃-N decreased and NO₂-N accumulated. NO₃-N accumulated in neutral and alkaline range. Inorganic-N was removed around neutrality.
2) When NO₂-N was added, NO₂-N changed to NO₃-N, and the effect of carbon sources was small. In acidic range, NO₂-N decreased and NH₃-N increased. NO₃-N accumulated in neutral and alkaline range.
3) When NO₃-N was added, this substance decreased slowly. When glucose and sodium acetate was added simultaneously, the decrease rate of NO₃-N became larger, but the effect of xylose was not large. NO₃-N decreased rapidly in acidic range. NH₃-N increased in acidic range and NO₂-N did in acidic and alkaline ranges, especially in alkaline range accumulation of NO₂-N was large.

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Contents of heavy metals, ignition loss and clay were measured in sediment samples of the lower reach of the Nagara River and the data were subjected to multiple regression analysis. Heavy metal contents in sediments were correlated significantly with ignition loss and clay contents. Multiple regression coefficients were more than 0.92 among these three factors. Heavy metal concentration in sediments could be predicted with probability of over 85% by estimating ignition loss and clay using the multiple regression equations. The amounts of heavy metal accumulation on unit mass of ignition loss and clay were able to be separately calculated from the regression equations. Heavy metal accumulation on sediments was dependent more highly on ignition loss than clay. Constants in regression equations were good approximations to analytical results of heavy metals in sediments of unpolluted area in the river, therefore, they could be regarded as background values of heavy metals in sediments of the river.

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Pressure flotation experiments of metallic hydroxides were carried out without using any collectors in order to obtain fundamental data for elucidating the flotation mechanism.
When the solutions containing 1×10^-3 to 5×10^-3 mole/l of metallic ions, such as Cu²⁺, Zn²⁺ and Fe³⁺ ions, were used as sample solutions and the pH values were adjusted with NaOH or Ca (OH) ₂, metallic hydroxides precipitated were effectively floated. But, the flotation removal of metallic hydroxides decreased remarkably, as the initial concentration of metallic ions decreased to less than 1×10^-3 mole/l.
Ferric hydroxides precipitated with CaCO₃ from ferric sulfate solution could not be floated. These ferric hydroxides have good settling characteristics, the reason of which has been considered to be due to the cutting of their gelatiniform structure with gypsum formed on the surfaces of CaCO₃ particles. It was concluded, from the above experimental results, that the gelatiniform structure plays an important role which allows the trapping of gas bubbles in it in the pressure floatation of metallic hydroxides.
Cd²⁺ ions in waste waters are generally dilute in concentration and the solubility of cadmium hydroxides is large. However, the flotation removal of Cd²⁺ ions could be easily achieved by coprecipitating them with ferric hydroxides at comparatively low pH values.
Finally, the results of the pressure flotation of ferric hydroxides, which were precipitated by adding Ca (OH) ₂ to ferric sulfate solution, were compared with those of the settling. It was found that the pressure flotation could be operated in a shorter time than the settling. The residual ferric ion concentration and the sludge volume were the same in both methods.

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It was found that there was a good relation between the adsorbability of oils in water on molecular sieve 5A and BOD of water containing oils. The adsorbability of oils in water was determined by the method reported previously. This means that the biodegradability of oils in water can be determined with the use of molecular sieve 5A.

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