Aso-Kai is a brackish lagoon separated by sand bar of Amanohashidate, one of the three noted views of Japan, from Miyazu Bay, having an area of 5 km² and an average depth of 8.4m. COD data of the surface water have often exceeded 3 mg·l^-1 and transparencies have been less than 2m, following the progress of water pollution since about 1970. Investigation of standing mass of COD, nitrogen and phosphorus and the factors determining them is quite important in explaining the mechanism of Aso-Kai's water pollution.
In this research, the authors studied the tidal exchange ratio of Aso-Kai's water with the open-sea water of Miyazu Bay through two channels which is considered one of the factors controlling them.
The results are as follows :
1) According to the survey in October, 1980, the tidal exchange ratios at flood tide and ebb tide were about 0.84 and 0.55 respectively, and the tidal exchange ratio (r_G) that Aso-Kai's water exchange directly with Miyazu Bay's in one tidal cycle was about 0.49;
2) It was estimated that r_G changed seasonally and it was generally high from winter to spring and low from summer to autumn. The median of estimated r_G of each month varied between 0.29 and 0.61.

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Adsorption method of orthophosphate on activated alumina was examined as a tertiary treatment to remove it from the wastewater also containing calcium ions.
Activated alumina of 0.2g was added to the 100ml solution being adjusted at pH of 7 and containing phosphate of 5.0 mg·l^-1, total alkali of 100 mg·l^-1 and calcium of 23.2 mg·l^-1. After shaking the solution for 12h, 90% removal ratio of phosphate was observed, while in the absence of calcium ions the ratios lay between 60-64%. The amount of phosphate removed was significantly influenced by the pH of the solution, it increased at lower pH but decreased at higher pH. The existence of calcium ions participated in relaxation of the strong pH-dependence.
The solution containing phosphate of 5.0 mg·l^-1, total alkali of 100 mg·l^-1, calcium of 23.2 mg·l^-1 and being adjusted at pH of 7.0 was passed through the column at SV=10 h^-1 packed with activated alumina of 2.0g. The sum volume of the effluent passed was 12 times as large as that without the calcium ions until the concentration of phosphate in the effluent reached 1.5 mg·l^-1. In the same experimental condition the molar ratio of calcium to orthophosphate removed was about 2.1 immediately after the effluent of 28l had passed.

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The inhibition of algal growth is considered to be affected by such factors as algal species, medium composition, culture methods etc.. In this study, the effect of culture conditions on algal growth characteristics and the toxicity of heavy metals to the growth of Chlorella ellipsoidea were evaluated. The algal growth was dependent on the medium composition, the strength of medium (the reciprocal of the dilution rate in the original medium), and the culture methods.
The lower the strength of the medium became, the higher the inhibition rate of cadmium for the algal growth became. Six kinds of heavy metals used in these experiments influenced the growth and the cell volume of C. ellipsoidea and they gave different modes in concentration-effect curves. These curves were well depicted with both the Weibull and the Probit models.
The toxic intensity of heavy metals evaluated from EC₅₀ was in the following order, silver, copper, cadmium, chromium, nickel, and cobalt. The EC₁₀ values obtained from the Weibull model were, however, lower than those obtained from the Probit model.

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Recently, some attempts have been made to apply Knowledge Engineering (KE) techniques in many fields, also in the field of wastewater treatment. In this study, KE techniques were applied to a typical problem of this field, particularly the operation of the process of activated sludge method. The main purposes were to give careful considerations to the availability or limitations of the KE approach, and then to develop the applicable method.
An intelligent support system for wastewater treatment plant was developed, and the prototype system described here demonstrated intelligent support.
The KE techniques were found to be useful and promising for the support of the plant operation on a higher level.

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