The simulation model of water quality in a river is prepared for the purpose of analyzing the pollution load to the receiving water body such as a lake. Sedimentation of suspended solid, growth and respiration of attached biomass on the river bed and denitrification by attached biofilm are taken into account in the model. It describes the change of SS, DOC, NH₄ and NO₃ concentration in the flowing water.
The capacity of selfpurification is expressed using pollution load ratio of output to that of input in the river. The model also includes accumulation and degradation of pollutant on the river bed and its wash out by flash flood.
When the flow rate, river width, gradient and pollution load are given, the model can give the pollution load ratio of output to input.
By using the proposed model, the pollution load analysis to the lake Kasumi was performed. Regarding thirteen rivers flowing into the lake Kasumi, about 20% of organic carbon, and 5% of nitrogen to total amount of inflow are considered to be removed during the flow in the rivers.

View full abstract

Removal efficiency of a new equipment for treating gray water was analysed from the test results reported in the previous paper. Amounts of pollutants of the raw water, the pretreated water in the first tank and the treated water from the second tank were calculated by integration of the relationships between flow volume and water quality. The mean removal efficiency of the amounts of BOD, COD, SS, TOC and MBAS were 82, 74, 62, 64 and 83% respectively. Solid in the screening net and sediment in the first tank were also investigated in detail. The solid in the screening net increased about 1.8 wet-kg (0.2 dry-kg) in the first month but only 6 wet-kg at six monthes because of biodegradation. The volume of sediment in the first tank approached to the small constant values of 20-60 l.Wherefore, the sediment need to remove only once a year or two years. The typical carbon balance and microorganisms in the second tank were also discussed. From the above results, an improved equipment was designed and put into practical use.

View full abstract

The Water Quality data at 104 monitoring stations of 49 rivers in Chiba Prefecture from 1976 to 1982 were analyzed by the Principle Component Analysis (PCA) method.
Before the calculation of PCA, the outliers were examined carefully, and the missing data were replaced by estimate with regression equation.
The correlation matrix was little changed by the replacement. Annual changes of correlation coefficients between the 6 items were found to be fairly little throughout this period (1976-1982).
The first component (z₁), derived from the PCA based on the correlation matrix of six items (DO, BOD, COD, NH₄-N, PO₄-P, SS), indicated the water pollution levels caused by human activities. The z₁ score was defined as water quality index (WQI).
Most of the rivers which flow in the northern west part in Chiba Prefecture were found to be seriously polluted in the estimation using the WQI. The annual changes of the WQI indicated that the water quality was improved at 17, became deterionate at 14 and unchanged at 69 points throughout this period.

View full abstract

Laboratory tests of nitrified liquor recycle process by 30-litre capacity Sequencing Batch Reactors with three kinds of fludizing media have been carried out with the view to selecting the media for higher biomass (VSS) accumulations. Total operating time in a cycle was for 240 minutes and volumatic ratio of nitrified recycling liquor to influent was maintained 3 to 1. The results were summarized as follows ;
(1) Suspended VSS was usually superior to attached VSS in the 0.2mm glass beads reactor. The attached concentrations were less than 1g·l^-1 and more than 21mg·l^-1 of VSS was found in the effluent.
(2) Attached VSS was usually superior to suspended VSS in the 0.1mm glass beads reactor. When the total VSS concentrations were less than 5g·l^-1, attached concentrations were maintained more than 4g·l^-1. Average 13mg·l^-1 of VSS was found in the effluent without sludge drawing.
(3) Suspended VSS with remaining powders such as zeolite was usually superior to attached VSS in the 0.2mm fossil shell particles reactor. Less than 10mg·l^-1 of VSS was found in the effluent. Calciumion dissolved from the particles was utilized as pH adjustment at nitrification stage in the reactor.

View full abstract